Highly-effective removal of Pb by co-pyrolysis biochar derived from rape straw and orthophosphate

Functionality of wheat straw-derived biochar enhanced its efficiency for actively capping Cd and Pb in contaminated water and soil matrices: Insights through batch adsorption and flow-through experiments

The impact of functionality of biochar on pressing environmental issue of cadmium (Cd) and lead (Pb) co-contamination in simultaneous soil and water systems has not sufficiently reported. This study investigated the impact of Fe- and Mg-functionalized wheat straw biochar (Fe-WSBC and Mg-WSBC) on Cd and Pb adsorption/immobilization through batch sorption and column leaching trials. Importantly, Fe-WSBC was more effective in adsorbing Cd and Pb (82.84 and 111.24 mg g-1), regeneration ability (removal efficiency 94.32 and 92.365), and competitive ability under competing cations (83.15 and 84.36%) compared to other materials (WSBC and Mg-WSBC). The practical feasibility of Fe-WSBC for spiked river water verified the 92.57% removal of Cd and 85.73% for Pb in 50 mg L-1 and 100 mg L-1 contamination, respectively. Besides, the leaching of Cd and Pb with Fe-WSBC under flow-through conditions was lowered to (0.326 and 17.62 mg L-1), respectively as compared to control (CK) (0.836 and 40.40 mg L-1). In short, this study presents the applicable approach for simultaneous remediation of contaminated water and soil matrices, offering insights into environmentally friendly green remediation strategies for heavy metals co-contaminated matrices.

Novel chitosan-modified biochar prepared from a Chinese herb residue for multiple heavy metals removal: Characterization, performance and mechanism

In this study, the sorption properties of Cr(VI), As(III), and Pb(II) on chitosan-modified magnetic biochar (CMBC) derived from residues of Ligusticum chuanxiong Hort. were investigated. CMBC was found to be a valuable material for removing three heavy metals from water simultaneously. Kinetic analysis suggested Cr(VI), As(III), and Pb(II) were chemisorbed onto CMBC, while isotherm data conformed well to Langmuir model, the maximum adsorption capacity of CMBC was found to be 65.74 mg/g for Cr(VI), 49.32 mg/g for As(III), and 69.45 mg/g for Pb(II). Experiments, characterization, and density functional theory (DFT) calculations were employed to explore the mechanisms. Furthermore, CMBC demonstrated excellent removal rates of over 95% for Cr(VI), 99% for As(III) and Pb(II) from contaminated water bodies. This work shows that CMBC holds significant potential for wastewater treatment of heavy metals and provides an effective solution for the utilization of Chinese herb residues in environmental remediation.

Cadmium immobilization in soil using phosphate modified biochar derived from wheat straw

The phosphate-modified biochar (BC) immobilizes cadmium (Cd), yet little is known about how phosphate species affect Cd detoxification in contaminated soils. We developed phosphate-modified biochar through the pyrolysis of wheat straw impregnated with three types of phosphate: mono‑potassium phosphate (MKP), dipotassium hydrogen phosphate (DKP), and tripotassium phosphate (TKP). The Cd adsorption mechanism of modified biochar was investigated by biochar characterization, adsorption performance evaluation, and soil incubation tests. The results demonstrated that the efficiency of biochar in immobilizing Cd2+ followed the order: TKP-BC > DKP-BC > MKP-BC. The TKP-BC had the highest orthophosphate content, the fastest adsorption rate, and the largest adsorption capacity (Langmuir) of 257.28 mg/g, which is 6.31 times higher than that of the unmodified BC (CK). In contrast, pyrophosphate was predominant in MKP-BC and DKP-BC. The primary adsorption mechanism for Cd2+ was precipitation, followed by cation exchange, as evidenced by the formation of CdP minerals on the BC surface, and an increase of K+ in solution (compared to water-soluble K+) and a decrease of K+ in the biochar during adsorption. Desorption of Cd from the TKP-BC after adsorption was 9.77 %-12.39 % at a pH of 5-9, much lower than that of CK. The soil incubation test showed the diethylenetriaminepentaacetic acid extracted Cd of TKP-BC, MKP-BC, and DKP-BC was reduced by 67.93 %, 18.41 % and 31.30 % over CK, respectively. Using the planar optodes technique, we also found that TKP-BC had the longest effect enhancing in situ soil pH. This study provides a theoretical basis for developing heavy metal pollution control technology using green remediation materials and offers insights into the remediation mechanisms.

Simultaneous removal of ammonia nitrogen, calcium and cadmium in a biofilm reactor based on microbial-induced calcium precipitation: Optimization of conditions, mechanism and community biological response

With the enhancement of environmental governance regulations, the discharge requirements for reverse osmosis wastewater have become increasingly stringent. This study proposes an innovative approach utilizing heterotrophic nitrification and aerobic denitrification (HNAD)-based biomineralization technology, combined with coconut palm silk loaded biochar, to offer a novel solution for resource-efficient and eco-friendly treatment of reverse osmosis wastewater. Zobellella denitrificans sp. LX16 were loaded onto modified coir silk and showed removal efficiencies of up to 97.38, 94.58, 86.24, and 100% for NH4+-N (65 mg L-1), COD (900 mg L-1), Ca2+ (180 mg L-1), and Cd2+ (25 mg L-1). Analysis of the metabolites of microorganisms reveals that coconut palm silk loaded with deciduous biochar (BCPS) not only exerts a protective effect on microorganisms, but also enhances their growth, metabolism, and electron transfer capabilities. Characterization of precipitation phenomena elucidated the mechanism of Cd2+ removal via ion exchange, precipitation, and adsorption. Employing high-throughput and KEGG functional analyses has confirmed the biota environmental response strategies and the identification of key genes like HNAD.

The application of P-modified biochar in wastewater remediation: A state-of-the-art review

Phosphorus modified biochar (P-BC) is an effective adsorbent for wastewater remediation, which has attracted widespread attention due to its low cost, vast source, unique surface structure, and abundant functional groups. However, there is currently no comprehensive analysis and review of P-BC in wastewater remediation. In this study, a detailed introduction is given to the synthesis method of P-BC, as well as the effects of pyrolysis temperature and residence time on physical and chemical properties and adsorption performance of the material. Meanwhile, a comprehensive investigation and evaluation were conducted on the different biomass types and phosphorus sources used to synthesize P-BC. This article also systematically compared the adsorption efficiency differences between P-BC and raw biochar, and summarized the adsorption mechanism of P-BC in removing pollutants from wastewater. In addition, the effects of P-BC composite with other materials (element co-doping, polysaccharide stabilizers, microbial loading, etc.) on physical and chemical properties and pollutant adsorption capacity of the materials were investigated. Some emerging applications of P-BC were also introduced, including supercapacitors, CO2 adsorbents, carbon sequestration, soil heavy metal remediation, and soil fertility improvement. Finally, some valuable suggestions and prospects were proposed for the future research direction of P-BC to achieve the goal of multiple utilization.

Petroleum-contaminated soil bioremediation and microbial community succession induced by application of co-pyrolysis biochar amendment: An investigation of performances and mechanisms

This study aimed to remediate petroleum-contaminated soil using co-pyrolysis biochar derived from rice husk and cellulose. Rice husk and cellulose were mixed in various weight ratios (0:1, 1:0, 1:1, 1:3 and 3:1) and pyrolyzed under 500 °C. These biochar variants were labeled as R0C1, R1C0, R1C1, R1C3 and R3C1, respectively. Notably, the specific surface area and carbon content of the co- pyrolysis biochar increased, potentially promoting the growth and colonization of soil microorganisms. On the 60th day, the microbial control group achieved a 46.69% removal of pollutants, while the addition of R0C1, R1C0, R1C3, R1C1 and R3C1 resulted in removals of 70.56%, 67.01%, 67.62%, 68.74% and 67.30%, respectively. In contrast, the highest efficiency observed in the abiotic treatment group was only 24.12%. This suggested that the removal of petroleum pollutants was an outcome of the collaborative influence of co-pyrolysis biochar and soil microorganisms. Furthermore, the abundance of Proteobacteria, renowned for its petroleum degradation capability, obviously increased in the treatment group with the addition of co-pyrolysis biochar. This demonstrated that co-pyrolysis biochar could notably stimulate the growth of functionally associated microorganisms. This research confirmed the promising application of co-pyrolysis biochar in the remediation of petroleum-contaminated soil.

Adsorption effect and mechanism of Cd(II) by different phosphorus-enriched biochars

The resource utilization of agricultural and forestry waste, especially the high-value transformation of low-grade phosphate rock and derivatives, is an important way to achieve sustainable development. This study focuses on the impregnation and co-pyrolysis of rice straw (RS) with fused calcium magnesium phosphate (FMP), FMP modified with citric acid (CA-FMP), and calcium dihydrogen phosphate (MCP) to produce three phosphorous-enriched biochars (PBC). The Cd(II) removal efficiency of biochars before and after phosphorus modification was investigated, along with the adsorption mechanism and contribution of biochars modified with different phosphorus sources to Cd(II) adsorption. The result indicated that CA-FMP and MCP could be more uniformly loaded onto biochar, effectively increasing the specific surface area (SSA) and total pore volume. The adsorption of Cd(II) onto PBC followed a mono-layer chemisorption process accompanied by intraparticle diffusion. The adsorption of Cd(II) by PBC involved ion exchange, mineral precipitation, complexation with oxygen-containing functional groups (OFGs), cation-π interaction, electrostatic interaction, and physical adsorption. Ion exchange was identified as the primary adsorption mechanism for Cd(II) by BC and FBC (51.53% and 53.15% respectively), while mineral precipitation played a major role in the adsorption of Cd(II) by CBC and MBC (51.10% and 47.98% respectively). Moreover, CBC and MBC significantly enhanced the adsorption capacity of Cd(II), with maximum adsorption amounts of 128.1 and 111.5 mg g-1 respectively.

Facet-Controlled Growth of Hydroxyapatite for Effectively Removing Pb from Aqueous Solutions

To address the growing concerns regarding severe water pollution, effective and environmentally friendly adsorbents must be identified. In this study, we prepared hydroxyapatite (HAp, Ca10(PO4)6(OH)2) as an eco-friendly absorbent via simple precipitation and obtained rod- (r-HAp) and plate-shaped HAp (p-HAp). The approach to obtaining p-HAp involved a low pH titration rate, promoting growth along the c-axis due to the adsorption of OH- on the (110) facet. Conversely, r-HAp was obtained by maintaining a high concentration of OH- during the initial stage through rapid pH titration, leading to a stronger restrictive effect on the growth of positively charged a(b)-planes. p-HAp demonstrated superior adsorption capacity, removing Pb through dissolution and recrystallization, achieving an impressive 625 mg/g within a 60 min reaction time compared to r-HAp. Our findings afford insights into the Pb removal mechanisms of HAp with different morphologies and can aid in the development of water purification strategies against heavy metal contamination.

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Effective Removal of Cd from Aqueous Solutions Using P-Loaded Ca-Mn-Impregnated Biochar

Cadmium (Cd) pollution in wastewater has become an increasingly widespread concern worldwide. Studies on Cd (II) removal using phosphate-adsorbed sorbents are limited. This study aimed to elucidate the behaviors and mechanisms of Cd (II) sorption on phosphate-loaded Ca-Mn-impregnated biochar (Ps-CMBC). The Cd (II) sorption on Ps-CMBC reached equilibrium within 2 h and exhibited a higher sorption efficiency than biochar and CMBC. Additionally, the Langmuir isotherm could better describe the Cd (II) adsorption on the sorbents. P75-CMBC had a maximum Cd (II) sorption capability of 70.13 mg·g-1 when fitted by the Langmuir isotherm model, which was approximately 3.18 and 2.86 times greater than those of biochar and CMBC, respectively. Higher pH (5-7) had minimal effect on Cd (II) sorption capacity. The results of characterization analyses, such as SEM-EDS, FTIR, and XPS, suggested that there was a considerable difference in the sorption mechanisms of Cd (II) among the sorbents. The primary sorption mechanisms for biochar, CMBC, and Ps-CMBC included electrostatic attraction and surface complexation; additionally, for Ps-CMBC, Cd (II)-π interactions and coordination of Cd (II) with P=O were critical mechanisms for Cd (II) removal. The results of this study demonstrate that phosphate-loaded CMBC can be used as an effective treatment for heavy metal pollution in aqueous media.

The role of phosphorus speciation of biochar in reducing available Cd and phytoavailability in mining area soil: Effect and mechanism

The effect of phosphorus (P) speciation in biochar on soil available Cd and its mechanism to alleviate plant Cd stress remain largely unknown. Here, ammonium polyphosphate (PABC)-, phosphoric acid (PHBC)-, potassium dihydrogen phosphate (PKBC)-, and ammonium dihydrogen phosphate (PNBC)-modified biochar were used to investigate P speciation. The Cd immobilization mechanism of biochar was analyzed by XPS and ³¹P NMR, and the soil quality and the mechanism for the biochar to alleviate Cd stress were also determined. The results demonstrated that PBC (pristine biochar), PABC, PHBC, PKBC, and PNBC reduced the content of soil DTPA-Cd by 14.96 % - 32.19 %, 40.44 % - 47.26 %, 17.52 % - 41.78 %, and 21.90 % - 36.64 %, respectively. The XPS and ³¹P NMR results demonstrated that the orthophosphate on the surface of PABC, PHBC, PKBC, and PNBC accounted for 82.06 %, 62.77 %, 33.1 %, and 54.46 %, respectively, indicating that PABC has the highest passivation efficiency on soil Cd, which was ascribed to the highest orthophosphate content on the biochar surface. Pot experiments revealed that PABC could reduce the Cd content by 4.18, 4.41, 4.43, 2.94, and 2.57 folds in roots, stems, leaves, pods, and grains, respectively, and at the same time increase the dry and fresh weight of soybean and decrease Cd toxicity to soybean by improving the antioxidant system. In addition, application of the P-modified biochars improved the enzyme activity and physicochemical properties of the soil. This study provides a new perspective for studying the effect of P-modified biochars on soil Cd immobilization.

Synthesizing sulfhydryl-functionalized biochar for effectively removing mercury ions from contaminated water

Biochar is regarded as an effective adsorbent for heavy metal pollution treatment, and functional optimization is still needed to improve its performance. We created raw biochar (BC and BP) from corn straw and pine sawdust, which were modified to produce sulfhydryl-modified biochar (MBC and MBP). Isothermal adsorption experiments and adsorption kinetics experiments as well as the related model fitting were performed to evaluate the adsorption performance of biochar on Hg(II). According to the results of the Langmuir model fitting, the maximum adsorption capacities of sulfhydryl-modified biochar were 193.05 mg/g (MBC) and 178.04 mg/g (MBP), respectively, which were approximately 1.6 times higher than the raw biochar. The results showed that adding sulfhydryl groups to biochar can improve its adsorption performance. The prompt effect resulted from the sulfhydryl modification providing additional functional groups and enhanced chemisorption and physical adsorption properties.

Biochar enhanced organic matter transformation during pig manure composting: Roles of the cellulase activity and fungal community

Fungal degradation of cellulose is a key step in the conversion of organic matter in composting. This study investigated the effects of adding 10% biochar (including, prepared from corn stalk and rape stalk corresponding to CSB and RSB) on organic matter transformation in composting and determined the role of cellulase and fungal communities in the conversion of organic matter. The results showed that biochar could enhance the conversion of organic matter, especially in RSB treatment. Biochar could increase cellulase activity, and RSB could enhance 33.78% and 30.70% the average activity of cellulase compared with the control and CSB treatments in the mesophilic to thermophilic phase, respectively. The results of high throughput sequencing demonstrated that Basidiomycota dominant in mesophilic phase, and Ascomycota dominant in other phases of composting. The redundancy analysis showed that Alternaria, Thermomycees, Aspergillus, Wallemia, and Melanocarpus might be the key fungi for the degradation of organic matter, and Fusarium, Penicillium, and Scopulariopsis may promote the conversion of organic matter. Network showed that the addition of RSB changed the interactions between fungal communities and organic matter transformation, and RSB treatment enriched members of Ascomycota related to organic matter transformation and cellulase activity. These results indicated that RSB improved organic matter conversion by enhancing the role of cellulase and fungal communities.

Customized oxygen-rich biochar with ultrahigh microporosity for ideal solid phase microextraction of substituted benzenes

The synergistic effect of high microporosity and abundant heteroatoms is important for improving the performance of biochar in various fields. However, it is still challenging to create enough micropores for biochar, while simultaneously retaining the heteroatoms from biomass. A series of biochar with variable microstructures was successfully prepared by carbonization and following ball milling on lotus pedicel (LP), watermelon rind (WR), and litchi rind (LR). The pore structures and heteroatoms of biochar were characterized in detail. Notably, high microporosity could be realized by the carbonization of LR, and further ball milling resulted in a higher microporous surface area (1323.4 m²·g^-1) and richer oxygen. Furthermore, the obtained biochar was fabricated as solid phase microextraction (SPME) coatings with uniform morphologies and similar thicknesses to deeply investigate the relationships between the microstructures and extraction performance. The best performance was demonstrated by the LR800BM, with enrichment factors from 1780 to 155,217. Finally, it was coupled with gas chromatography-mass spectrometry (GC-MS) to develop an analytical method with a wide linear range (1-50,000 ng·L^-1), low limits of detection (0.10-1.4 ng·L^-1), good repeatability (0.83 %-7.5 %) and reproducibility (4.2 %-8.9 %). This work provides valuable insights into the structure-performance relationship of biochar, which is important for the design of high-performance biochar-based adsorbents and their applications in the environment.

Manganese-doped hydroxyapatite as an effective adsorbent for the removal of Pb(II) and Cd(II)

The water polluted by lead(Pb(II)) and cadmium(Cd(II)) seriously endangers ecological safety and needs to be solved urgently. Because of the relatively low adsorption rate of pure hydroxyapatite for heavy metals, a series of manganese-doped hydroxyapatites (MnHAPs) were prepared by using manganese, a common impurity in hydroxyapatite, as a doping element to improve the adsorption performance. The structural and functional groups of the materials with different Mn/(Ca +Mn) molar ratios (0%, 5%, 10%, 20%, and 30%) were investigated by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD), Raman spectrometer and Fourier transform infrared spectroscopy (FTIR) characterization. The presence of manganese influenced the formation and growth of hydroxyapatite crystals, resulting in lattice distortion and a large number of lattice defects in materials. Among them, manganese-doped hydroxyapatite with a Mn/(Ca +Mn) molar ratio of 10% (MnHAP-10) could most effectively remove Pb(II) and Cd(II), with the adsorption capacity of 1806.09 mg g^-1 for Pb(II) at pH = 5 and 176.88 mg g^-1 for Cd(II) at pH = 5.5. Then the adsorption behavior and mechanism were further researched systemically. It was concluded that the immobilization of Pb(II) by MnHAP-10 was mainly through dissolution precipitation and ion exchange, while Cd(II) was adsorbed by ion exchange and electrostatic interaction. In conclusion, MnHAP-10 has the potential to be applied as an effective adsorbent for the removal of Pb(II) and Cd(II) pollution.

Enhanced Cr (VI) reduction and removal by Fe/Mn oxide biochar composites under acidic simulated wastewater

Chromium (Cr (VI)) can cause severe damage to the ecosystem and humans because of its toxicity. In this paper, the adsorbed Fe/Mn ions Bacillus cereus ZNT-03, lotus seeds, and graphene oxide were co-cultured as the raw materials. Fe/Mn oxide biochar composite (FMBC) was prepared to treat Cr (VI) by one-step pyrolysis. FMBC has high-density micropores, and the average pore size is about 0.82 nm. Fe (II), Mn (II), and N-containing functional groups could serve as electron donors for Cr (VI) reduction. The removal of Cr (VI) is monolayer chemisorption and pH-dependent. The maximum adsorption capacity of FMBC is 21.25 mg g^-1. Cr (VI) is reduced and adsorbed on FMBC by physical adsorption, reduction, complexation, electrostatic attraction, and coprecipitation. The contribution ratio of the reduction mechanism to Cr (VI) is 72.25%. The packed column and regeneration experiments indicated that FMBC had excellent adsorption stability even after soaking in acidic simulated wastewater after 180 days (pH 1.5). These results indicate that FMBC can provide rapid reduction and efficient adsorption for Cr (VI), making it possible to apply in water treatment.

Magnetic seeds promoted high-density sulfonic acid-based hydrochar derived from sugar-rich wastewater for removal of methylene blue

Methylene blue (MB) removal from dyeing wastewater using low-cost bio-derived adsorbent is a significant and challenging field. Herein, magnetic sugar hydrochar (MGHC) precursors derived from sugar-rich wastewater with small particle size and rich oxygen-containing functional groups (OCFGs) are prepared from sugar-rich aqueous solution via Fe salt-modified hydrothermal procedure. The role of Fe₃O₄ nanoparticles formed during the sugar carbonization is to provide numerous magnetic seeds to generate MGHC with core-shell structure, which reduces the particle size of hydrochar. This increases the amount of OCFGs on the surface of MGHC for bonding the sulfonic acid groups. Therefore, sulfonic acid-modified MGHC-SA shows the rapid MB adsorption rate and excellent adsorption capacity. The highest MB capacity is 869.6 mg/g at pH = 11.0 and 298 K. Additionally, the MGHC-SA can be easily recovery by magnet. And the stability of MGHC-SA was also evaluated, no degradation of adsorption performance was observed, even the adsorbent was regenerated 10 times. This study puts forward a promising way to acquire functional groups rich and easy recovery hydrochar from sugar wastewater for MB removal.

Co-pyrolysis of biomass and phosphate tailing to produce potential phosphorus-rich biochar: efficient removal of heavy metals and the underlying mechanisms

Application of biochar to treat heavy metal polluted wastewater has received increasing attention; however, the immobilization ability of pristine biochar for metal ions is still limited. In this study, phosphate tailing was co-pyrolyzed with sawdust and peanut shell to acquire phosphorus-rich biochars with high removal rates for Cd, Zn, Pb, and Cu. Meanwhile, the improvement mechanisms by phosphate tailing were clarified by XRD, FTIR, SEM-EDS, BET-N₂, and model fitting. Results showed that after phosphate tailing impregnation, surface area of sawdust, and peanut shell biochars increased from to 11.6 m² g^-1, and from 43.5 to 53.4 m² g^-1, respectively. Functional groups of -COOH and CO₃^2- on biochar increased and the P₂O₇^4- newly generated. Besides, large amounts of Ca(PO₃)₂ and Ca₂P₂O₇ crystals were detected in biochar ash. As for sawdust biochar, loading of phosphate tailing raised the sorption rates of Cd, Zn, Pb, and Cu by 0.35, 0.61, 1.10, and 2.64 times, respectively, as for peanut shell biochar, it was raised by 0.12, 0.47, 0.11, and 1.98 times, respectively. The sorption isotherms by phosphate tailing-loaded biochars were better fitted to Langmuir (R² = 0.85-1.00) than Freundlich model (R² = 0.58-0.91). Heavy metals could bind with -OH and -COOH on phosphate tailing-loaded biochars, meanwhile generated phosphorus-rich precipitation with PO₃^- and P₂O₇⁴⁺, including Cd₂P₂O₇, Cd(PO₃)₂, Zn (PO₃)₂, Pb (PO₃)₂, Pb₂P₂O₇, Cu(PO₃)₂, and Cu₂P₂O₇. This study proposed an innovative method to produce phosphorus-rich biochars by loading phosphate tailing for highly efficient removal of heavy metals from water bodies, and also realized the resource utilization of phosphate tailing, which was of great significance to reduce environmental pollution.

Preparation of phosphorus-modified biochar for the immobilization of heavy metals in typical lead-zinc contaminated mining soil: Performance, mechanism and microbial community

The use of modified biochar for the remediation of heavy metal (HM) has received much attention. However, the immobilization mechanism of biochar to multiple HMs and the interaction of different forms of HMs with microorganisms are still unclear. K₂HPO₄-modified biochar (PBC) was produced and used in a 90-days immobilization experiment with soil collected from a typic lead-zinc (Pb-Zn) mining soil. Incubation experiments showed that PBC enhanced the transformation of Cd, Pb, Zn and Cu from exchangeable (Ex-) and/or carbonate-bound forms (Car-) to organic matter-bound (Or-) and/or residual forms (Re-). After scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS), X-ray diffractometry (XRD), fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) analysis, the mechanisms of HM immobilization by PBC were proposed as precipitation (PO₄^3-, HPO₄^2-, OH^- and CO₃^2-), electrostatic attraction, complexation (-COOH, -OH and R-O-H) and the indirect roles of soil parameter variations (pH, moisture and microbial community). Microbial community analysis through high-throughput sequencing showed that PBC reduced bacterial and fungal abundance. However, addition of PBC increased the relative proportions of Proteobacteria by 15.04%-42.99%, Actinobacteria by 4.74%-22.04%, Firmicutes by 0.76%-23.35%, Bacteroidota by 0.16%-12.34%, Mortierellomycota by 4.00%-9.66% and Chytridiomycota by 0.10%-13.7%. Ex-Cd/Pb/Zn, Car-Cd/Zn and Re-Cd/Pb/As were significantly positively (0.001<P≤0.05) correlated with bacterial phyla of Crenarchaeota and Methylomirabilota, and Re-Cu and Ex-/Car-/Fe-Mn oxide-bound (Fe-Mn-)/Or-As were significantly positively correlated (0.001<P≤0.05) with the bacterial phyla of Proteobacteria and Bacteroidota. While Car-Cd/Zn and Re-Pb/As were positively correlated (0.01<P≤0.05) with fungal phyla of Ascomycota, Glomeromycota, Kickxellomycota, Basidiomycota and Mucoromycota. The bacterial network contained more complex interactions than the fungal network, suggesting that bacteria play a larger role in HMs transformation processes. The results indicate that PBC is an effective agent for the remediation of HMs polluted soil in Pb-Zn mining areas.

Synergistic removal of nitrate by a cellulose-degrading and denitrifying strain through iron loaded corn cobs filled biofilm reactor at low C/N ratio: Capability, enhancement and microbiome analysis

Optimization of nitrate removal rate under low carbon-to-nitrogen ratio has always been one of the research hotspots. Biofilm reactor based on functional carrier and using interspecific synergic effect of strains provides an insight. In this study, iron-loaded corn cob was used as a functional carrier that can contribute to the cellulose degradation, iron cycling, and collaborative denitrification process of microorganisms. During biofilm reactor operation, the maximum nitrate removal efficiency was 99.30% and could reach 81.73% at no carbon source. Dissolved organic carbon and carrier characterization showed that strain ZY7 promoted the release of carbon source. The crystallinity of cellulose I and II in carrier of experimental group increased by 31.26% and decreased by 21.83%, respectively, in comparison to the control group. Microbial community showed the synergistic effect among different strains. The vitality and metabolic activity of the target microorganisms in bioreactor were increased through interspecific bacterial cooperation.

Highly Efficient Removal of Lead/Cadmium by Phosphoric Acid-Modified Hydrochar Prepared from Fresh Banana Peels: Adsorption Mechanisms and Environmental Application

In this work, a phosphoric acid (H₃PO₄)-modified hydrochar (BPH200) was prepared at a low temperature (200 °C) in an air atmosphere with fresh banana peels as the raw material. The Cd²⁺ and Pb²⁺ adsorption behaviors and mechanisms of BPH200 were explored. As the temperature rose, co-hydrothermal carbonization of the banana peels and H₃PO₄ enhanced the transformation of phosphorus (P) species. More orthophosphate and metaphosphate were found in BPH200 than in banana peel hydrochar (BP) without modification. The adsorption kinetics for Cd²⁺ and Pb²⁺ followed the pseudo-second-order model. The Redlich-Peterson model best fit the experimental results of the adsorption isotherm, with maximum adsorption capacities of 84.25 and 237.90 mg·g^-1 for Cd²⁺ and Pb²⁺, respectively. H₃PO₄ promoted Cd²⁺ and Pb²⁺ adsorption by forming precipitates, which, respectively, accounted for 32.75 and 41.12% of the total adsorption onto BPH200. In addition, the cation-exchange capacities of BPH200 with Cd²⁺ and Pb²⁺ were weakened compared with those of BP. However, complexation with these two ions strengthened, accounting for 26.68 and 32.81%, respectively, of the total adsorption capacity. This indicated that the adsorption of Cd²⁺ and Pb²⁺ onto BPH200 was dominated by precipitation with minerals and complexation with oxygen-containing functional groups. The removal rates of Cd²⁺ and Pb²⁺ by BPH200 from different water bodies were more than 99.95 and 99.97%, respectively. The addition of BPH200 also decreased the amounts of bioavailable Cd²⁺ and Pb²⁺ in the soil, resulting in relatively high immobilization rates of Cd²⁺ (67.13%) and Pb²⁺ (70.07%).

Effective and stable adsorptive removal of Cadmium(II) and Lead(II) using selenium nanoparticles modified by microbial SmtA metallothionein

Metallothionein SmtA-modified selenium nanoparticles (SmtA-SeNPs), efficient adsorbents for Cd(II) and Pb(II), were synthesized in the present work. The ligand, microbial SmtA protein, was synthesized using an engineered strain Escherichia coli, posing the benefits of simplicity, safety, and high production. SmtA-SeNPs were spheres with diameters between 68.1 and 122.4 nm, containing amino, hydroxyl, and sulfhydryl functional groups with negatively charged (pH > 5). SmtA-SeNPs displayed better adsorption performance than dissociative SmtA and SeNPs. The adsorption of Cd(II) and Pb(II) mainly depends on the electrostatic attractions and the metal chelation of abundant functional groups. The maximum adsorption capacity was 506.3 mg/g for Cd(II) and 346.7 mg/g for Pb(II), which were higher than the values of most nanoparticles. In addition, SmtA-SeNPs were immobilized with a membrane filter to produce a SmtA-SeNPs filter, and the percentage removal of Cd(II) and Pb(II) increased from 26.75% to 98.13% for Cd(II) and from 9.95% to 99.20% compared with the blank filter. Moreover, the SmtA-SeNPs filter was regenerated using subacid deionized water, and the filter exhibited a stable removal ratio of Cd(II) and Pb(II) in ten continuous cycles of Cd(II)- or Pb(II)-containing wastewater treatment. The residual amounts of Cd and Pb met national standard levels of wastewater discharge.

Corncob biochar combined with Bacillus subtilis to reduce Cd availability in low Cd-contaminated soil

Soil contamination by heavy metals such as Cd can pose a risk to the environment and human health. However, Cd is difficult to immobilize at low concentration levels in soil. Individually, Bacillus subtilis and biochar have been shown to be inefficient at immobilizing Cd in soil. In this study, corncob biochar was generated at different pyrolysis temperatures (300 °C-550 °C), and the Cd immobilization efficiency and performance of corncob biochar loaded with B. subtilis (CB@B) and corncob biochar alone (CB) were evaluated in solutions and in soil. The characterization (SEM and FTIR) of CB generated at different pyrolysis temperatures and CB generated at different pyrolysis temperatures in CB@B (300 °C-550 °C) indicated that a superior pore structure and abundant O-functional groups were obtained at a pyrolysis temperature of 400 °C for both CB@B and CB. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the formation of Cd compounds was associated with the positive combined biosorption effect of the bacteria and biochar, electronic adsorption, activity of the O-functional groups (C[double bond, length as m-dash]O, COOH, OH, and Si-O-Si), and complexation between extracellular substances and Cd²⁺. Adsorption experiments were conducted in a solution to assess the effects of various operating parameters such as the time, pH, and adsorbent dose. The 400 °C-CB@B and 400 °C-CB samples achieved the largest reductions in the Cd concentration at 81.21% and 5.70%, respectively. Then, CaCl₂ extraction experiments were conducted in soil, and using 0.25%-CB@B, a 55.21% decrease was realized in the Cd concentration after 56 days and a 16.71% increase was realized in soil pH to 8.38. No significant difference was observed in the CB-treated groups, among which 1.0%-CB achieved the largest reduction of 26.08% after 56 days and a 3.20% increase in the soil pH to 7.41. The Tessier sequential extraction method obtained similar trends. Overall, 400 °C-CB@B demonstrated outstanding immobilization efficiency and durability, indicating that it provided a safe and nutrient-rich habitat for B. subtilis to realize a synergistic effect for Cd immobilization.

Highly efficient removal of cadmium from aqueous solution by ammonium polyphosphate-modified biochar

Phosphorus-modified biochars are considered as good materials for the removal of heavy metals from wastewater. However, the efficacy of ammonium polyphosphate-modified biochar in cadmium (Cd(II)) adsorption remains largely unknown. In this work, the biochar was respectively modified with ammonium polyphosphate (PABC), phosphoric acid (PHBC) and ammonium dihydrogen phosphate (PNBC) to enhance its adsorption performance for heavy metals from wastewater. The properties of biochar before and after modification and P speciation on the surface of the modified biochar were investigated with FTIR, SEM-EDS, XPS, XRD and ³¹P NMR, and the adsorption capacity was evaluated by batch adsorption experiments. The results demonstrated that the optimal adsorption performance could be achieved at the solution pH = 4, and the pseudo-second-order and Langmuir models could well describe the Cd(II) adsorption process. The maximum adsorption capacity of PABC, PHBC and PNBC for Cd(II) was 155, 138 and 99 mg g^-1, which were 4.84, 4.32 and 3.10 folds that of original biochar, respectively. The ³¹P NMR showed that orthophosphate accounted for 82.1%, 62.8% and 54.5% of P in PABC, PHBC and PNBC, respectively, which decreased to 28.24%, 33.51% and 29.34% after Cd(II) adsorption, indicating that the orthophosphate ratio in P-modified biochar surface could significantly affect Cd adsorption by forming phosphate precipitate. This work implies that the PABC has greater potential in the removal of Cd from wastewater relative to PHBC and PNBC.

Biological denitrification potential of cellulase-producing Cupriavidus sp. ZY7 and denitrifying Aquabacterium sp. XL4 at low carbon-to-nitrogen ratio: Performance and synergistic properties

This study emphasizes on the cellulase production characteristics of strain ZY7 and its collaboration with nitrate-dependent ferrous oxidizing (NFO) strain XL4 to achieve efficient denitrification at low carbon-to-nitrogen (C/N) ratio. Results indicated that the denitrification efficiency increased from 65.47 to 97.99% at 24 h after co-culture at C/N of 1.0. Three-dimensional fluorescence excitation-emission matrix (3D-EEM) showed significant changes in the intensity of soluble microbial products (SMP), fulvic-like materials, and aromatic proteins after co-culture. Bio-precipitates were characterized by Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), and X-ray diffraction (XRD), which showed that cellulose structure was disrupted and the metabolites were potential carbon source for denitrification. In addition, cellulase activity suggested that the hydrolysis of β-1,4-glycosidic bonds and oligosaccharides may be the rate-limiting steps in cellulose degradation. This work promoted the understanding of denitrification characteristics of co-culture and expanded the application of cellulose degrading bacteria in sewage treatment.

Removal mechanisms of Cd from water and soil using Fe-Mn oxides modified biochar

The development of remediation materials simultaneously suitable for Cd-contaminated water and soil is of great significance. In this study, the functional biochar (FM-RBC and FM-DBC) was prepared using branch and durian shell biochar (RBC and DBC, respectively) with iron-manganese oxide (Fe-Mn oxide) modification. The behaviors and mechanisms of Cd adsorption and stabilization in water and alkaline soil treated with FM-RBC and FM-DBC were explored. The results showed that the adsorption capacities of RBC and DBC for Cd had increased by 40-80 mg/g after the Fe-Mn oxide modification. The Cd adsorption was conformed to pseudo-second-order kinetic and the Langmuir isothermal models. After 35 days of soil cultivation, the maximum reduction rate of DTPA-Cd occurred in 3% FM-DBC treatments (37.73%), followed by in 3% FM-RBC (30.08%), all of which were significantly higher than that observed in 3% BC treatments (12.55-18.91%). Notably, the FM-RBC and FM-DBC treatments promoted the conversion of the exchangeable to the carbonate-bound and Fe/Mn oxyhydroxide fractions of Cd. The XRD, FTIR, and XPS analyses demonstrated that the loading amount of Fe-Mn oxide was positively correlated with the oxygen-containing functional group of biochar. CdO, Cd₂Mn₃O₈ and CdCO₃ were loaded on the FM-BC, indicating the existence of two main adsorption mechanisms: (1) the complexation with M-O (M: Fe, Mn) and acid oxygen-containing functional groups, (2) the precipitation with carbonate of Cd. In this work, we prepared two functional biochar that rapidly removes Cd from water and effectively fixes Cd in alkaline soil, thus, debasing the risk of Cd entry into the food chain.

Optimization of target biochar for the adsorption of target heavy metal ion

The purpose of this work is to study the pyrolysis conditions of target biochar suitable for target heavy metal ion, to characterize the optimized target biochar, and to study the adsorption performance of biochar. With Cu²⁺ and Zn²⁺ as the target pollutants, the pyrolysis conditions involved in the preparation process as pyrolysis temperature, pyrolysis time, and heating rate were evaluated and optimized from Box–Behnken Design (BBD), response surface methodology (RSM) and desirability function, the optimized pyrolysis conditions of target biochar for Cu²⁺ (Cu-BC) and Zn²⁺ (Zn-BC) were obtained. The optimum pyrolysis parameters for Cu-BC and Zn-BC were pyrolysis time of 3.09 and 2.19 h, pyrolysis temperature of 425.27 and 421.97 °C, and heating rate of 19.65 and 15.88 °C/min. The pseudo-second-order kinetic and Langmuir isotherm model proved to be the best fit for the equilibrium data, with a maximum adsorption capacity (Q_max) fitted by Langmuir model were 210.56 mg/g for Cu²⁺ by Cu-BC and 223.32 mg/g for Zn²⁺ by Zn-BC, which were both higher than the Q_max of unoptimized biochar (BC) for Cu²⁺ (177.66 mg/g) and Zn²⁺ (146.14 mg/g). The physical properties, chemical structure, surface chemistry properties of Cu-BC and Zn-BC were characterized by Zeta potential meter, Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). This study puts forward a new perspective for optimizing target biochar production for special environmental application.

Development of phosphorus composite biochar for simultaneous enhanced carbon sink and heavy metal immobilization in soil

As a porous and carbon material, biochar is focused on respectively in sequestrating carbon and stabilizing metals in soil, while few studies attempted to design biochar for simultaneously achieving these two targets. This study proposed to produce phosphorus-composite biochar for synchronously enhancing carbon sequestration and heavy metals immobilization. Two phosphorus materials from tailings, Ca(H₂PO₄)₂ and Ca₅(PO₄)₃(OH), were selected as modifier to load into biomass prior to pyrolysis. Results showed that incorporating P not only increased pyrolytic C retention in biochar by 36.1-50.1%, but also obtained biochar with higher stability by chemically formation of COP, C-PO₃ and C₂-PO₂. After 90-day incubation with soil, more C was sequestrated in the P-biochar amended soil (59.6-67.0%) than those pristine biochar (43.2-46.6%). Highly soluble Ca(H₂PO₄)₂ was more efficient than Ca₅(PO₄)₃(OH) in this regard. Meanwhile, these P-composite biochar exhibited more Pb/Cd immobilization (31.3-92.3%) compared with the pristine biochar (9.5-47.2%), which was mainly due to the formation of stable precipitates Pb₅(PO₄)₃Cl and Cd₃(PO₄)₂, especially for Ca₅(PO₄)₃(OH) modification. Additionally, P-composite biochar "intelligently" altered soil microbial community, i.e., they suppressed Actinobacteria proliferation, which is correlated to carbon degradation, while promoted Proteobacteria growth, facilitating phosphate dissolution for ready reaction with heavy metals to form precipitate, benefiting the Pb and Cd immobilization. A dual functions biochar was engineered via simply loading phosphorous prior to pyrolysis and simultaneously enhanced carbon sequestration and heavy metal immobilization.

A review of prospects and current scenarios of biomass co-pyrolysis for water treatment

With ever-growing population comes an increase in waste and wastewater generated. There is ongoing research to not only reduce the waste but also to increase its value commercially. One method is pyrolysis, a process that converts wastes, at temperatures usually above 300 °C in a pyrolysis unit, to carbon-rich biochars among with other useful products. These chars are known to be beneficial as they can be used for water treatment applications; certain studies also reveal improvements in the biochar quality especially on the surface area and pore volume by imparting thermal and chemical activation methods, which eventually improves the uptake of pollutants during the removal of inorganic and organic contaminants in water. Research based on single waste valorisation into biochar applications for water treatment has been extended and applied to the pyrolysis of two or more feedstocks, termed co-pyrolysis, and its implementation for water treatment. The co-pyrolysis research mainly covers activation, applications, predictive calculations, and modelling studies, including isotherm, kinetic, and thermodynamic adsorption analyses. This paper focuses on the copyrolysis biochar production studies for activated adsorbents, adsorption mechanisms, pollutant removal capacities, regeneration, and real water treatment studies to understand the implementation of these co-pyrolyzed chars in water treatment applications. Finally, some prospects to identify the future progress and opportunities in this area of research are also described. This review provides a way to manage solid waste in a sustainable manner, while developing materials that can be utilized for water treatment, providing a double target approach to pollution management.

Qualitative and quantitative investigation on adsorption mechanisms of Cd(II) on modified biochar derived from co-pyrolysis of straw and sodium phytate

Developing effective modification methods and obtaining a comprehensive understanding of adsorption mechanisms are essential for the practical application of biochars for the removal of heavy metals from solutions. In this study, rice straw was impregnated with sodium phytate and pyrolyzed at 350 °C, 450 °C, and 550 °C to synthesize modified biochars (i.e., MBC350, MBC450, and MBC550). The Cd(II) adsorption capacities and contributions of different mechanisms, including the effects of biochar-derived dissolved organic matter (BDOM), were investigated using batch sorption experiments and characterization analyses. The modification of sodium phytate promoted the pyrolysis of biomass, thereby increasing the BDOM content and aromatic structures at low and high pyrolysis temperatures, respectively. Moreover, the modification also increased the exchangeable Na⁺ and carbonate contents in the modified biochars. Compared with the raw biochars, the Cd(II) adsorption capacities of modified biochars increased by 3.3-4.3 times, and MBC550 had the highest Cd(II) adsorption capacity (126.5 mg/g), of which precipitation with minerals and interaction with π-electrons contributed 41.7% and 45.8%, respectively. However, at a lower pyrolysis temperature, the Cd(II) adsorption attributed to ion exchange and co-deposition with BDOM significantly increased, especially on MBC350 (33.9 and 12.6 mg/g, respectively). These results indicate that modification by sodium phytate effectively enhanced various adsorption mechanisms, thereby increasing the Cd(II) adsorption capacity. In addition, the contribution of co-deposition with BDOM to adsorption was unneglectable for the biochars pyrolyzed at low temperatures.

Biochar produced from the straw of common crops simultaneously stabilizes soil organic matter and heavy metals

The simultaneous stabilization of heavy metals and organic matter in polluted soil has received little research attention. In this study, we studied the immobilization of Cu and Cd and the mineralization of organic matter in the acidic soil amended with biochar produced from rice, wheat, corn, and rape straws through incubation experiments. Compared with that in the control treatment, the availability of Cu and Cd in the biochar amended soils decreased by 17-31% and 3-17%, respectively. The cumulative amount of CO₂ released from each treatment in 60 days of incubation followed the order: control treatment (399 mg CO₂-C kg^-1) > rape straw biochar treatment (388 mg CO₂-C kg^-1) > rice straw biochar treatment (374 mg CO₂-C kg^-1) > corn straw biochar treatment (355 mg CO₂-C kg^-1) > wheat straw biochar treatment (288 mg CO₂-C kg^-1). The information implied that biochar produced from the straw of common crops can simultaneously stabilize both heavy metals and organic matter in the acidic soil. The transformation of Cu and Cd from acid soluble fraction to residual fraction was the potential mechanism of biochar in facilitating soil heavy metal immobilization. The significant decrease in soil β-glucosidase activity, which controlled the degradation of soil organic matter, was an important potential pathway of biochar in decreasing soil organic matter mineralization. A significant decrease in the content and a substantial increase in the structural complexity of soil dissolved organic matter could further the decrease of wheat straw biochar in soil organic matter mineralization. Thus, biochar produced from the straw of common crops is a promising amendment for simultaneously stabilizing both heavy metals and organic matter in the acidic soil.

Removal of Ni(II) Ions by Poly(Vinyl Alcohol)/Al2O3 Nanocomposite Film via Laser Ablation in Liquid

Al₂O₃-poly(vinyl alcohol) nanocomposite (Al₂O₃-PVA nanocomposite) was generated in a single step using an eco-friendly method based on the pulsed laser ablation approach immersed in PVA solution to be applicable for the removal of Ni(II) from aqueous solution, followed by making a physicochemical characterization by SEM, XRD, FT-IR, and EDX. After that, the effect of adsorption parameters, such as pH, contact time, initial concentration of Ni(II), and medium temperature, were investigated for removal Ni(II) ions. The results showed that the adsorption was increased when pH was 5.3, and the process was initially relatively quick, with maximum adsorption detected within 90 min of contact time with the endothermic sorption process. Moreover, the pseudo-second-order rate kinetics (k₂ = 9.9 × 10⁻⁴ g mg⁻¹ min⁻¹) exhibited greater agreement than that of the pseudo-first-order. For that, the Ni(II) was effectively collected by Al₂O₃-PVA nanocomposite prepared by an eco-friendly and simple method for the production of clean water to protect public health.

Adsorption and immobilization of soil lead by two phosphate-based biochars and phosphorus release risk assessment

Phosphorus-based biochar can effectively immobilize lead (Pb) in soils, but the effects of soluble and insoluble phosphate on the remediation efficiency of Pb and phosphorus (P) release risks remain largely unknown. In this study, three biochars were produced from reed (Phragmites australis L.) straw, potassium dihydrogen phosphate (PDP, soluble) and hydroxyapatite (HAP, insoluble) modified reed straws and marked as BC, BCP, and BCH, respectively. Pb adsorptions and immobilizations by the three biochars and their P release risks were investigated. The P release kinetics of the three biochars were all fitted with the pseudo-second-order kinetic model and the P-release capacity followed the order of BCP > BCH > BC. The sorption isotherms of Pb²⁺ by three biochars were better described using the Langmuir model and the maximum adsorption capacities of BCP (59.3 mg/g) and BCH (58.8 mg/g) were higher than that of BC (48.1 mg/g). However, the P concentrations remained in BCP treated solution were significantly higher than those in BCH and BC under initial Pb²⁺ concentrations in the ranges of 5-25 mg/L. Soil pH and available P were increased with the increasing dosage of BCP and BCH, decreasing CaCl₂-extractable Pb concentrations. BCH was more effective to decrease the exchangeable Pb and transform it into iron/manganese oxides and residual fractions. Compared to BC, BCH applications in the range of 2-5% can significantly increase labile P by 15.2-17.7%, but 21.0-33.6% for BCP, indicating BCP had a higher P release risk. The major implication is that HAP-modified biochar can effectively immobilize Pb and decrease P release risks compared to soluble P-modified biochar.

Efficient removal of Cd(II) by phosphate-modified biochars derived from apple tree branches: Processes, mechanisms, and application

Phosphate (P)-modified biochar is a good material for cadmium (Cd) immobilization, and the pore-forming effect of potassium ions (K⁺) can favor the P loading on biochar. However, few studies have been done specifically on Cd(II) removal by composites of potassium phosphates with biochar, and the removal potential and mechanisms are not clear. Herein, apple tree branches, a major agricultural waste suitable for the development of porous materials, were pyrolyzed individually or together with KH₂PO₄, K₂HPO₄·3H₂O, or K₃PO₄·3H₂O to obtain biochars to remove Cd(II), denoted as pristine BC, BC-1, BC-2, and BC-3, respectively. The results showed that the orthophosphates containing more K⁺ enlarged the specific surface area, total pore volume and phosphorus loading of biochar. Co-pyrolysis of apple tree branches and P promoted the thermochemical transformation of P species. Only weak signal of orthophosphate was observed in the pristine BC, while the presence of orthophosphate, pyrophosphate and metaphosphate were detected in BC-1, and BC-2 and BC-3 showed the presence of orthophosphate and pyrophosphate. The maximum Cd(II) adsorption capacities of pristine BC, BC-1, BC-2 and BC-3 were 10.4, 88.5, 95.8, and 116 mg·g^-1, respectively. Orthophosphate modification enhanced the Cd(II) adsorption capacity due to the formation of Cd-P-precipitates, namely Cd₅(PO₄)₃Cl, Cd₅(PO₄)₃OH, Cd₃(PO₄)₂, Cd₂P₂O₇, and Cd(PO₃)₂. Furthermore, higher cation exchange efficiencies between Cd(II) and K⁺ in P-modified biochars also contributed to their high Cd(II) adsorption capacity. Cd(II) removal by BC-3 from artificially polluted water bodies showed more than 99.98% removal rates. Application of BC-3 also reduced the diethylene triamine pentaacetic acid-extracted Cd(II) in soil by 69.1%. The co-pyrolysis of apple tree branches and potassium phosphates shows great prospect in Cd(II) wastewater/soil treatment and provide a promising solution for agricultural waste utilization and carbon sequestration.

Simultaneous adsorption of As(III) and Cd(II) by ferrihydrite-modified biochar in aqueous solution and their mutual effects

A simply synthetic ferrihydrite-modified biochar (Fh@BC) was applied to simultaneously remove As(III) and Cd(II) from the aqueous solution, and then to explore the mutual effects between As(III) and Cd(II) and the corresponding mechanisms. The Langmuir maximum adsorption capacities of As(III) and Cd(II) in the single adsorbate solution were 18.38 and 18.18 mg g⁻¹, respectively. It demonstrated that Fh@BC was a potential absorbent material for simultaneous removal of As(III) and Cd(II) in aqueous solution. According to the XRF, SEM–EDS, FTIR, XRD, and XPS analysis, the mechanisms of simultaneous removal of As(III) and Cd(II) by Fh@BC could be attributable to the cation exchange, complexation with R-OH and Fe-OH, and oxidation. Moreover, the mutual effect experiment indicated that Cd(II) and As(III) adsorption on Fh@BC in the binary solution exhibited competition, facilitation and synergy, depending on their ratios and added sequences. The mechanisms of facilitation and synergy between Cd(II) and As(III) might include the electrostatic interaction and the formation of both type A or type B ternary surface complexes on the Fh@BC.

Preparation of ball-milled phosphorus-loaded biochar and its highly effective remediation for Cd- and Pb-contaminated alkaline soil

Pyrolytic biochar is a good material for remediating soils contaminated with heavy metals; however, it exhibits strong alkalinity, which easily causes soil alkalization and fertility reduction. Herein, a series of novel biochar materials (BPBCs) were prepared by combined ball milling and phosphorus (P)-loading. The optimized BPBC were fabricated in the basis of Cd and Pb adsorption capacities of the biochar, with pyrolysis at 700 °C, ball milling for 12 h and the addition of 5% red P (BPBC700). Ball milling could effectively grind pristine biochar into submicron particles and nanoscale P particles could be uniformly loaded on BPBC700. Moreover, the oxidative conversion of red P into phosphorus oxides, phosphoric acid and (hydro)phosphates was promoted due to reactions with the carbonates, alkaline minerals and O-containing functional groups of biochar. These reactions also decreased the biochar and soil pH to nearly neutral by acid-base neutralization. Pot experiments showed that BPBC700 had better effects than the pristine or ball-milled biochar in improving soil properties (e.g., cation exchange capacity and organic carbon), increasing the concentrations of soil nutrients (e.g., N and P), promoting alkaline phosphatase, catalase and urease activities, decreasing soil mobility and plant accumulation of Cd and Pb, and alleviating Cd and Pb stress on maize plants. Thus, BPBC is a promising and ecofriendly amendment to enhance its adsorption ability on Cd and Pb, soil quality and plant productivity in contaminated soil.

Remediation of petroleum-contaminated soil by ball milling and reuse as heavy metal adsorbent

A simple mechanochemical (MC) method is used to treat petroleum-contaminated soil and prepare a heavy metal adsorbent in one step. XRD, Raman, FT-IR, VSM, BET, and XPS were used to characterize the adsorbent. After MC treatment, the dissolved total petroleum hydrocarbons of the adsorbent is less than 1 mg·L^-1, and a porous structure and carbonization phenomenon are evident. The specific surface area and cumulative void volume increase, and the adsorption pore size decreases. On the surface of soil, the percentages of iron oxides, carbonates, CO, -C-O-H, -COOH, and π unsaturated bonds increase. The Langmuir model shows that the maximum adsorption capacity of Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ are 338.58, 51.61, 32.34, and 25.05 mg·g^-1, respectively. The pseudo-second-order kinetic model fits the Pb adsorption process, indicating the domination of chemical adsorption. GC-MS shows that petroleum hydrocarbons are completely degraded. The Tessier continuous extraction result shows that heavy metals are bound to carbonate, iron manganese oxide, and organic matter. The MC treatment achieves deep cleanup and resource utilization of petroleum-contaminated soil through the formation of amorphous carbon, carbonates, and iron oxides on the surface of soil particles. The material is magnetic and can be recycled when used in wastewater treatment.

Synergistic effects of ball-milled biochar-supported exfoliated LDHs on phosphate adsorption: Insights into role of fine biochar support

Although biochar supports were widely adopted to fabricate the biochar (BC) supported layered double hydroxides (LDHs) composites (LDH-BC) for efficient environmental remediation, few studies focus on the important role of biochar support in alleviating the stacking of LDHs and enhancing LDH-BC's performance. Through the analysis of the material structure-performance relationship, the "support effect" of fine biochar prepared by ball milling was carefully explored. Compared with the original LDHs on LDH-BC, the LDHs on ball milled biochar (LDH-BMBC) had smaller particle size (from 1123 nm to 586 nm), crystallite size (from 20.5 nm to 6.56 nm), more abundant O-containing functional groups, and larger surface area (370 m² g^-1) and porous structure. The Langmuir model revealed that the maximum theoretical phosphate adsorption capacity of LDH-BMBC (56.2 mg P g^-1) was significantly higher than that of LDH-BC (27.6 mg P g^-1). The leaching experiment proved that the addition of LDH-BMBC in calcareous soil could significantly reduce the release of soil total phosphate (46.1%) and molybdate reactive phosphate (40.4%), even though pristine BC and BMBC significantly enhanced the soil phosphate leaching. This work fabricated high-performance and eco-friendly LDH-BMBC for phosphate adsorption in solution and phosphate retention in soil and also provide valuable insights into fine biochar support effect on LDHs exfoliation, extending the practical use of the engineered ball milled biochars in environment remediation.

A critical review of biochar-based materials for the remediation of heavy metal contaminated environment: Applications and practical evaluations

The contamination of heavy metals (HMs) in the environment has aroused a global concern. The valid remediation of HM contaminated environment is a highly significant issue. As alternative to carbon materials, biochar has been vastly documented for the remediation of HM contaminated environment. However, there are some possible imperfections to meet the actual remediation tasks as the finite properties of raw biochar, and the remediation process is complex and unexpectedly. This review focuses on the progress made on environmental HM remediation by biochar-based materials within the past six years. The property analysis and key modifications of biochar are summarized inspired by their applicability or necessity for HM decontamination, and the environmental remediation as well as the implicated mechanisms are thoroughly elaborated from multiple pivotal sides. The evaluations of practical application associated with biochar amendment are also presented. Finally, some pertinent improvements and research directions are proposed. To our knowledge, this article is the first time to make a systematic summary on the reliability and practicability of biochar-based materials for environmental HM remediation, and critically pointed out the existing issues to facilitate the judicious design of biochar-based materials and understanding the research trends. It is also aims to provide reference for subsequent research and propel the practical applications.

Optimizing magnetic functionalization conditions for efficient preparation of magnetic biochar and adsorption of Pb(II) from aqueous solution

Recoverable magnetic biochar has great potential for treating wastewater contaminants such as Pb(II). However, whether magnetic modification could enhance metal adsorption efficiency is currently contradictory in the literature mainly due to the differences in selecting various magnetic functionalization conditions. Considering this gap in knowledge, the effects of magnetic functionalization method (impregnation and precipitation), concentration of precursor iron solution (0.01-1 M), and pyrolysis temperature (300-700 °C) on the characteristics and Pb(II) adsorption capacity of biochar were systematically investigated in this paper. Results indicated that Fe₃O₄ was the main product for magnetic biochars synthesized using the impregnation (denoted as FWFe(3)) and precipitation methods (denoted as FWFe(2)). Magnetic functionalization resulted in remarkably increased pH and more negative zeta potential for FWFe(2) samples, whereas FWFe(3) samples showed the opposite trends. The adsorption of Pb(II) on different biochars fitted the pseudo-second order model and the Langmuir model. The maximum adsorption capacity was 817.64 mg/g for FWFe(2)1M700C (precipitation by 1 M of Fe(II)/Fe(III), pyrolysis at 700 °C), outperforming FWFe(3) and pristine biochar samples by around 5-13 times. Mechanism study indicated that the adsorption mainly involved electrostatic attraction, ion exchange, co-precipitation, and complexation. Pb(II) adsorption capacity was strongly dependent on the alkali pH of biochar. However, this efficiency was less affected by biochar surface area and its morphology. The higher pH of FWFe(2) samples not only led to an increased surface charge for stronger electrostatic attraction and ion exchange but also favored the formation of co-precipitates. By contrast, FWFe(3) samples showed a decreased adsorption capacity for Pb(II) with increased concentration of embedded iron. Overall, magnetic biochar, prepared using precipitation followed by high-temperature pyrolysis (such as, FWFe(2)1M700C), can be a promising adsorbent for Pb(II) adsorption from wastewater.

Highly efficient and rapid Pb(ii) removal from acidic wastewater using superhydrophilic polystyrene phosphate resin

Novel superhydrophilic polystyrene phosphate resin was synthesized for efficient and rapid Pb(ii) removal from acidic wastewater.

Sustainable remediation of hazardous environmental pollutants using biochar-based nanohybrid materials

Biochar is a well-known carbon material with diversified functionalities and excellent physicochemical characteristics with high wastewater treatment potential. This review aims to summarize recent advancements in the development of biochar and biochar-based nanohybrid materials as a potential tool for the removal of harmful organic compounds such as synthetic dyes/effluents. The formation of biochar using pyrolysis of renewable feedstocks and their applications in various industries are explained hereafter. The characteristics and construction of biochar-based hybrid materials are explained in detail. Diversity of feedstocks, including municipal wastes, industrial byproducts, agricultural, and forestry residues, endows different biochar types with a wide structural variety. The production of cost-effective biochar drives the interest in manipulating biochars and induces desire functionality using nanoscale reinforcements. Various types of biochars, such as magnetic biochar, layered nanomaterial coated biochar, nanometallic oxide composites, chemically and physically functionalized biochar, have been produced. With the aid of nanomaterial, hybrid biochar exhibits a high potential to remove toxic contaminants. Depending upon biochar type, dyes/effluents can be removed via different mechanisms, including the Fenton process, photocatalytic degradation, π-π interaction, electrostatic interaction, and physical adsorption. In conclusion, desired physicochemical features, and tunable surface properties of biochar present high potential material in removing organic dyes and other effluents. The blended biochar with different materials/nanomaterials endows broader development and multi-functional opportunities for treating dyes/effluents.

A State-of-the-Art Review on Innovative Geopolymer Composites Designed for Water and Wastewater Treatment

There is nothing more fundamental than clean potable water for living beings next to air. On the other hand, wastewater management is cropping up as a challenging task day-by-day due to lots of new additions of novel pollutants as well as the development of infrastructures and regulations that could not maintain its pace with the burgeoning escalation of populace and urbanizations. Therefore, momentous approaches must be sought-after to reclaim fresh water from wastewaters in order to address this great societal challenge. One of the routes is to clean wastewater through treatment processes using diverse adsorbents. However, most of them are unsustainable and quite costly e.g. activated carbon adsorbents, etc. Quite recently, innovative, sustainable, durable, affordable, user and eco-benevolent Geopolymer composites have been brought into play to serve the purpose as a pretty novel subject matter since they can be manufactured by a simple process of Geopolymerization at low temperature, lower energy with mitigated carbon footprints and marvellously, exhibit outstanding properties of physical and chemical stability, ion-exchange, dielectric characteristics, etc., with a porous structure and of course lucrative too because of the incorporation of wastes with them, which is in harmony with the goal to transit from linear to circular economy, i.e., "one's waste is the treasure for another". For these reasons, nowadays, this ground-breaking inorganic class of amorphous alumina-silicate materials are drawing the attention of the world researchers for designing them as adsorbents for water and wastewater treatment where the chemical nature and structure of the materials have a great impact on their adsorption competence. The aim of the current most recent state-of-the-art and scientometric review is to comprehend and assess thoroughly the advancements in geo-synthesis, properties and applications of geopolymer composites designed for the elimination of hazardous contaminants viz., heavy metal ions, dyes, etc. The adsorption mechanisms and effects of various environmental conditions on adsorption efficiency are also taken into account for review of the importance of Geopolymers as most recent adsorbents to get rid of the death-defying and toxic pollutants from wastewater with a view to obtaining reclaimed potable and sparkling water for reuse offering to trim down the massive crisis of scarcity of water promoting sustainable water and wastewater treatment for greener environments. The appraisal is made on the performance estimation of Geopolymers for water and wastewater treatment along with the three-dimensional printed components are characterized for mechanical, physical and chemical attributes, permeability and Ammonium (NH4+) ion removal competence of Geopolymer composites as alternative adsorbents for sequestration of an assortment of contaminants during wastewater treatment.

Comparing the effects of humic acid and oxalic acid on Pb(II) immobilization by a green synthesized nanocrystalline hydroxyapatite

Dissolved organic matter (DOM) is one of the most significant parameters to affect the remediation efficiency of Pb(II) by apatites. Numerous studies chose humic substances as a surrogate of DOM to investigate its influence on Pb(II) immobilization. However, the effect of low-molecular-weight organic acids such as oxalic acid (OA), which is ubiquitous in the environment and a primary component of DOM, in immobilizing Pb(II) was still not fully understood. Herein, humic acid (HA) and OA were examined to distinguish their influence on Pb(II) immobilization by a green synthesized nanocrystalline hydroxyapatite (nHAP). Various parameters were considered to evaluate the removal performance of nHAP towards Pb(II) as affected by HA/OA. Results indicated that Pb(II) immobilization was significantly promoted in the coexistence of OA owing to the precipitation of hydroxypyromorphite (HPY) as well as PbC₂O₄, but was independent on the addition sequence and slightly hindered by HA, disclosing that Pb(II) preferred to bind directly with nHAP instead of via HA. Characterization of the Pb(II) loaded solids by multiple technologies revealed that HPY was the predominant precipitate both in the absence and presence of HA, while the formation of PbC₂O₄ was preferred over that of HPY in the existence of OA. X-ray photoelectron spectroscopy indicated that PbC₂O₄ was the prevalent solid phase with the ratio of 62.97% after Pb(II) immobilization by nHAP in the presence of OA. These findings implied that the transformation efficiency of Pb(II) to HPY by apatites can be overestimated in the presence of OA due to the precipitation of PbC₂O₄.

Ultrafast and efficient removal of Pb(II) from acidic aqueous solution using a novel polyvinyl alcohol superabsorbent

The direct removal of heavy metal ions from acidic wastewater is a hard problem. In this study, a novel superabsorbent, polyvinyl alcohol phosphate ester (PVAP), was designed and prepared to remove Pb(II) from acidic wastewater (pH = 3). The PVAP can absorb water and swell to reach equilibrium within 30 s, which provides the conditions for ultrafast kinetic adsorption. For 100 mg/L Pb(II) solution, the adsorption reaches equilibrium within 5 min, and the removal ratio is more than 99.9% over a wide pH range of 3-6. Adsorption kinetics and isotherm data are consistent with pseudo-second-order and Langmuir model, respectively. The calculated maximum adsorption capacity for Pb(II) is 558.66 mg/g. Thermodynamic results show that the adsorption is spontaneous and exothermic process. The removal ratio for Pb(II) of PVAP still maintains above 99% after ten recycles. The PVAP can also simultaneously remove more than 97% of other heavy metal ions (Cu(II), Cd(II), Zn(II), Co(II), and Ni(II)) from an acidic solution. Moreover, the PVAP can efficiently purify simulated acid mine heavy metal wastewater, and the results meet EPA drinking water standards. The studies of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy prove that the adsorption mechanism involves surface complexation. This new superabsorbent is a promising candidate for acidic heavy metal sewage disposal.

Effect of KH2PO4-modified biochar on immobilization of Cr, Cu, Pb, Zn and as during anaerobic digestion of swine manure

In this study, the immobilization performance and mechanisms of heavy metals (HMs) in swine manure (SM) during anaerobic digestion (AD) with biochar (BC) and KH₂PO₄-modified biochar (BP) were investigated. BC and BP addition decreased DTPA-extractable Cr, Cu, Pb and Zn amount, transformed these HMs to more stable state, and decreased the ecological risks of these HMs by 2 grades accordingly. BP exhibited a higher passivation efficiency for Cr, Cu and Pb and 5% -10% biochar dosage showed the maximum passivation effects. Characterization results showed that Cr, Cu and Pb immobilization with BP were mainly attributed to the formation of phosphate precipitation. However, both DTPA extraction and mobility of As increased with biochar addition, because the release of phosphorus in biochar had negative effect on As immobilization. BP could serve as a novel remediation agent for Cr, Cu, Pb and Zn passivation but special attention should be paid with As presence.