Engineered phosphorous-functionalized biochar with enhanced porosity using phytic acid-assisted ball milling for efficient and selective uptake of aquatic uranium

Biochar boost: revolutionizing functionalization of a difficult material

The challenge with synthetically modified biochars is that they are notoriously difficult to characterize, and a new characterization approach that circumvents the challenges posed by overlapping bands in IR spectra is needed. We report multinuclear NMR approaches successful in the easy identification and quantification of covalently-bound functional groups on the biochar surface using 31P{1H} CPMAS NMR spectroscopy.

Advancing modified biochar for sustainable agriculture: a comprehensive review on characterization, analysis, and soil performance

Biochar is a carbon-rich material produced through the pyrolysis of various feedstocks. It can be further modified to enhance its properties and is referred to as modified biochar (MB). The research interest in MB application in soil has been on the surge over the past decade. However, the potential benefits of MB are considerable, and its efficiency can be subject to various influencing factors. For instance, unknown physicochemical characteristics, outdated analytical techniques, and a limited understanding of soil factors that could impact its effectiveness after application. This paper reviewed the recent literature pertaining to MB and its evolved physicochemical characteristics to provide a comprehensive understanding beyond synthesis techniques. These include surface area, porosity, alkalinity, pH, elemental composition, and functional groups. Furthermore, it explored innovative analytical methods for characterizing these properties and evaluating their effectiveness in soil applications. In addition to exploring the potential benefits and limitations of utilizing MB as a soil amendment, this article delved into the soil factors that influence its efficacy, along with the latest research findings and advancements in MB technology. Overall, this study will facilitate the synthesis of current knowledge and the identification of gaps in our understanding of MB.

Graphical Abstract

Leaching Peculiarity of Uranium-Containing Layered Double Hydroxide Sediment Varied with Environmental Anions

In this research, we focus our attention on the leaching peculiarity of uranium-containing Mg-Al layered double hydroxide (LDH) which is one kind of waste sediment in uranium tailings, generated by the alkalinization of uranyl raffinate. The effect of inorganic (CO32-, SO42-, PO43-) and organic (C2O42-, C6H6O72-, C6H16O24P62-) anions were investigated. Atomic force microscopy result showed that the thickness of CO32--LDH increased to 8.6 nm compared to original LDH whose thickness was 6.7 nm. Compared with the control sample (5.58 μm), the grain size with C6H16O24P62- anion grew to 7.04 μm. A large amount of CO32- can stay in LDH, up to 1.78 mol percent, while the C6H16O24P62- anion was only 0.41 mol percent. X-ray diffraction results showed that the anions could change the crystal structure of LDH, especially the C6H18O24P6 anion, and theoretical calculation also conformed this result. The leaching tests showed that the introduction of anions improved the leaching efficiency of UO22+ from LDH. The introduction of anions destroyed the super buffer property of LDH. Theoretical calculation results indicated that the anions could grab UO22+ and help the UO22+ escape from the LDH. This research gave guidance for long-term disposal of uranium-containing tailings.

Prediction of Biochar Adsorption of Uranium in Wastewater and Inversion of Key Influencing Parameters Based on Ensemble Learning

With the rapid development of industrialization, the problem of heavy metal wastewater treatment has become increasingly serious, posing a serious threat to the environment and human health. Biochar shows great potential for application in the field of wastewater treatment; however, biochars prepared from different biomass sources and experimental conditions have different physicochemical properties, resulting in differences in their adsorption capacity for uranium, which limits their wide application in wastewater treatment. Therefore, there is an urgent need to deeply explore and optimize the key parameter settings of biochar to significantly improve its adsorption capacity. This paper combines the nonlinear mapping capability of SCN and the ensemble learning advantage of the Adaboost algorithm based on existing experimental data on wastewater treatment. The accuracy of the model is evaluated by metrics such as coefficient of determination (R2) and error rate. It was found that the Adaboost-SCN model showed significant advantages in terms of prediction accuracy, precision, model stability and generalization ability compared to the SCN model alone. In order to further improve the performance of the model, this paper combined Adaboost-SCN with maximum information coefficient (MIC), random forest (RF) and energy valley optimizer (EVO) feature selection methods to construct three models, namely, MIC-Adaboost-SCN, RF-Adaboost-SCN and EVO-Adaboost-SCN. The results show that the prediction model with added feature selection is significantly better than the Adaboost-SCN model without feature selection in each evaluation index, and EVO has the most significant effect on feature selection. Finally, the correlation between biochar adsorption properties and production parameters was discussed through the inversion study of key parameters, and optimal parameter intervals were proposed to improve the adsorption properties. Providing strong support for the wide application of biochar in the field of wastewater treatment helps to solve the urgent environmental problem of heavy metal wastewater treatment.

Encapsulation of Bamboosa vulgaris culms derived activated biochar into hierarchical permeable, phosphate rich and functionalized alginate aerogel composites and its contribution in U(VI) adsorption

In this study, a facile methodology was designed to encapsulate Bamboosa vulgaris culms derived activated biochar (BVC) in a variable mass ratio, into a three-dimensional hierarchical porous and permeable and amino-thiocarbamated alginate (TSC) to prepare hybrid biosorbents (BVC-MSA). These ultralight and lyophilized phosphate rich macroporous sorbents were rationally characterized through FTIR, XRD, BET, SEM-EDS, elemental mapping, XPS techniques and employed for efficient UO22+ adsorption from aqueous solutions. The phytic acid (PA) was found to be a suitable hydrophilic and phosphorylating agent for the TSC matrix through hydrogen-bonded crosslinking when employed in a correct mass ratio (1:3). The SEM-EDS and XPS analyses confirmed the UO22+ sorption onto BVC-MSA-3 (the most suitable composite with a BVC/TSC mass ratio of 30.0 % w/w) and provided evidence of heteroatom involvement in developing the physico-chemical interactions. The BCV-MSA-3 exhibited the best response as a sorbent during kinetics/sorption process, therefore, it was selected to study the equilibrium sorption studies. The BCV-MSA-3 removal efficiency increased from 12.1 to 94.2 % using 0.2 to 1.8 g/L sorbent dose at pH (4.5). The mentioned sorbent displayed a significant maximum sorption capacity qm (309.55 mg/g at 35 °C) calculated through the best-fitted Langmuir and Temkin models (R2 ≈ 0.99). The sorption kinetics followed the pseudo-second-order (PSORE) model and exhibited fast sorption rate teq (180 min). Thermodynamic parameters clarified that the sorption process is feasible ΔGo (-25.3 to -27.6 kJ/mol kJ/mol), endothermic ΔHo (27.17 kJ/mol), and proceeds with a positive entropy (0.176 kJ/mol.K). The study shows that BCV-MSA-3 could be an alternative and auspicious sorbent for uranium removal from aqueous solution.

A sodium alginate gel bead adsorbent doping with amidoxime-modified hydroxyapatite for the efficient adsorption of uranium

In this work, the modified‑sodium alginate gel beads were prepared by sol-gel method. Due to the presence of water channels in the sodium alginate gel bead, amidoxime groups and PO43- were exposed to the surface of the adsorbent to the maximum extent, resulting in the excellent adsorption capacity of modified‑sodium alginate gel beads. The introduction of amidoxime-modified hydroxyapatite significantly improved the adsorption capacity and the adsorption rate of the gel beads. The adsorption capacity increased from 308.7 to 466.0 mg/g and the adsorption equilibrium time was shortened from 300 min to 120 min. The modified‑sodium alginate gel bead possessed the advantages of short adsorption time, high adsorption efficiency and large adsorption capacity, which could be regarded as a potential adsorbent for uranium. Moreover, the uranium removal ability on the modified gel beads was mainly attributed to the Coulomb force between PO43- and uranium and the complexation between uranium and amidoxime groups. In summary, this work would provide a new idea for the modification and application of sodium alginate-based materials.

Prediction of Uranium Adsorption Capacity in Radioactive Wastewater Treatment with Biochar

Recently, Japan's discharge of wastewater from the Fukushima nuclear disaster into the ocean has attracted widespread attention. To effectively address the challenge of separating uranium, the focus is on finding a healthy and environmentally friendly way to adsorb uranium using biochar. In this paper, a BP neural network is combined with each of the four meta-heuristic algorithms, namely Particle Swarm Optimization (PSO), Differential Evolution (DE), Cheetah Optimization (CO) and Fick's Law Algorithm (FLA), to construct four prediction models for the uranium adsorption capacity in the treatment of radioactive wastewater with biochar: PSO-BP, DE-BP, CO-BP, FLA-BP. The coefficient of certainty (R2), error rate and CEC test set are used to judge the accuracy of the model based on the BP neural network. The results show that the Fick's Law Algorithm (FLA) has a better search ability and convergence speed than the other algorithms. The importance of the input parameters is quantitatively assessed and ranked using XGBoost in order to analyze which parameters have a greater impact on the predictions of the model, which indicates that the parameters with the greatest impact are the initial concentration of uranium (C0, mg/L) and the mass percentage of total carbon (C, %). To sum up, four prediction models can be applied to study the adsorption of uranium by biochar materials during actual experiments, and the advantage of Fick's Law Algorithm (FLA) is more obvious. The method of model prediction can significantly reduce the radiation risk caused by uranium to human health during the actual experiment and provide some reference for the efficient treatment of uranium wastewater by biochar.

Fabrication of electrospun cellulose/chitosan/ball-milled bone char membranes for efficient and selective sorption of Pb(II) from aqueous solutions

Separation materials have received increasing attention given their broad applications in the management of environmental pollution. It is desired to balance the contradiction between high separation efficiency and selectivity of separation materials. The integration of ball-milled bone chars with electrospun membranes might achieve this balance. In this study, electrospun cellulose/chitosan/ball-milled bone char (CL/CS/MB) membranes were by well-dispersing ball-milled bone chars with nanoscale size (98.9-167.5 nm) and developed porosity (40.2-373.1 m2/g) in the electrospinning solvent. The synergistic integration of distributed MBs (5.4-31.5 wt.% of loading hydroxyapatite on the membrane matrix) allowed the efficient sorption of Pb(II) with fast kinetics (20.0 min), excellent capacity (219.9 mg/g at pH 5.0, T 298 K), and favorable selectivity coefficients (2.76-6.79). The formation of minerals was dominant for the selective sorption of Pb(II) by combining the spectral analysis and quantitative determination. The surface complexation with O-/reductive N-species, the cation exchange with inorganic Ca2+, the electrostatic attraction with deprotonated O-, and the cation-π coordination with the aromatic carbon via the π-electrons should be not ignored for the capture of Pb(II). This work demonstrated the feasibility of electrospun CL/CS/MB membranes as a promising candidate for the remediation of aquatic pollutants.

Efficient removal of uranium(VI) from aqueous solution by a novel phosphate-modified biochar supporting zero-valent iron composite

Uranium (U) is an important strategic resource as well as a heavy metal element with both chemical and radiotoxicity. At present, the rapid and efficient removal of uranium from wastewater remains a huge challenge for environmental protection and ecological security. In this paper, phosphate-modified biochar supporting nano zero-valent iron (PBC/nZVI) was triumphantly prepared and fully characterized. The introduction of polyphosphate can greatly increase the specific surface area of biochar pores, and then the zero-valent iron can be evenly distributed on the surface of material, thus leading to excellent removal performance of the PBC/nZVI for U(VI). The theoretical maximum U(VI) removal capacity of PBC/nZVI was up to 967.53 mg/g at pH 5. The results of adsorption kinetics, isotherm, and thermodynamics showed that the adsorption of uranium by PBC/nZVI was a monolayer physical adsorption and endothermic reaction. And the PBC/nZVI has favorable selectivity toward uranium against the interference of coexisting metal ions. Further mechanism studies show that the excellent uranium removal performance of PBC/nZVI is mainly attributed to the synergistic effect of physical adsorption and chemical reduction. This work proves that the PBC/nZVI has a wide application prospect in the field of uranium wastewater treatment.

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.

Efficient removal of uranium from wastewater using pig manure biochar: Understanding adsorption and binding mechanisms

In this work, three kinds of biochars (PMBC-H₂O, PMBC-PP and PMBC-HP) with excellent adsorption performance were obtained by carbonizing pig manure pre-treated with different agents. These biochars had the ordered mesoporous structures and possessed abundant active functional groups on their surface. The adsorption behaviors of the biochars towards U_VI under various conditions were evaluated by batch experiment. The results showed that KMnO₄ and H₂O₂ could enormously improve the adsorption performance of PMBC to U_VI. After KMnO₄ and H₂O₂ pretreatment, the maximum adsorption capacities of PMBC-PP (979.3 mg/g) and PMBC-HP (661.7 mg/g) were about 2.6 and 1.8 times higher than that of PMBC-H₂O (369.9 mg/g), respectively, which was much higher than previously reported biochar-based materials. Obviously, KMnO₄ pretreatment leaded to a higher enhancement than that of H₂O₂. The removal mechanism of U_VI on PMBC-PP was discussed in-depth. The interaction between U_VI species and PMBC-PP was mainly ascribed to the abundant active sites on the surface of PMBC-PP. In a word, conversion of pig manure pre-treated with KMnO₄ into biochar not only demonstrates that PMBC-PP has great potential in the treatment of actual uranium-containing wastewater, but also provides a method for the rational utilization of pig manure to reduce the pollution.

Artificial intelligence (AI) applications in adsorption of heavy metals using modified biochar

The process of removal of heavy metals is important due to their toxic effects on living organisms and undesirable anthropogenic effects. Conventional methods possess many irreconcilable disadvantages pertaining to cost and efficiency. As a result, the usage of biochar, which is produced as a by-product of biomass pyrolysis, has gained sizable traction in recent times for the removal of heavy metals. This review elucidates some widely recognized harmful heavy metals and their removal using biochar. It also highlights and compares the variety of feedstock available for preparation of biochar, pyrolysis variables involved and efficiency of biochar. Various adsorption kinetics and isotherms are also discussed along with the process of desorption to recycle biochar for reuse as adsorbent. Furthermore, this review elucidates the advancements in remediation of heavy metals using biochar by emphasizing the importance and advantages in the usage of machine learning (ML) and artificial intelligence (AI) for the optimization of adsorption variables and biochar feedstock properties. The usage of AI and ML is cost and time-effective and allows an interdisciplinary approach to remove heavy metals by biochar.

Phosphate modified hydrochars produced via phytic acid-assisted hydrothermal carbonization for efficient removal of U(VI), Pb(II) and Cd(II)

Phosphate species can complex with nuclides and heavy metals from aqueous solutions strongly. The introduction of phosphate groups onto the surface of biochar sorbents (mostly <1.0 at.% of P) is highly desired. In this study, phosphate modified hydrochars (HTBs) were prepared through the hydrothermal carbonization of bamboo sawdust with various duration (2, 12, 24 h) in the presence of phytic acid (0-70 wt%). The results showed that the addition of PA with a low concentration of 10 wt% carbonized at 2 h generated hydrogen protons to etch the pristine sawdust, inducing the granulation of surfaces and a 5.5-fold enhancement of surface area. While HTBs carbonized with increasing PA concentrations (30-70 wt%) and longer duration (12 and 24 h) presented more carbonaceous particles with rising sizes from <100 nm to 2.5 μm, which should be due to the cross-linkage of dehydrated phosphate-containing organic carbon components to the matrix, enabling the resultful surface modification (maximum of 2.1 wt% of P). The uptake of U(VI), Pb(II) and Cd(II) on HTBs was investigated given various geochemical conditions including contact time, pH, ionic strength, humic acid and temperature. HTBs could capture U(VI), Pb(II) and Cd(II) efficiently from the ideal and simulated wastewaters, and be reused well after six recycles. This work opened a new strategy for the potential of phosphate-hydrochars in the aqueous remediation.

Soybean residue based biochar prepared by ball milling assisted alkali activation to activate peroxydisulfate for the degradation of tetracycline

The advanced oxidation process (AOPs) has caused great concern in recent years. Among them, biochar has been widely studied as a catalyst for advanced oxidation process because of its low price and low environmental risk. In this study, a novel ball milling assisted KOH activation biochar (MKBC) was prepared and applied in peroxydisulfate (PDS) activation to degrade tetracycline hydrochloride (TC-H). In comparison with the oxidation (3.48%) by PDS alone and adsorption (36.19%) by MKBC alone, the removal rate of TC-H was increased to 84.15% in the MKBC/PDS system, indicating that MKBC can successfully activate PDS. Besides, the catalytic activity of the MKBC to activate PDS for the degradation of TC-H is 58.33% higher than that of pristine biochar (PBC). In addition, MKBC has outstanding stability that after three repeated experiments, the removal rate of TC-H by the MKBC/PDS system still remains 77.35%. Meanwhile, the mechanism was investigated that the singlet oxygen (1O2) seized the principal position in the degradation of TC-H in the PDS/MKBC system. This study explored a novel, solvent-free and economic method to propose this extraordinary biochar, which provided a new strategy for the future research of biochar.