A novel composite of SiO2 decorated with nano ferrous oxalate (SDNF) for efficient and highly selective removal of Pb2+ from aqueous solutions

Modification of iron-containing silicate tailings with oxalic acid to develop a long-efficacy utilization peroxymonosulfate-based system for the efficient decomplexation and removal of Cr(III)-ethylenediamine tetraacetic acid

Ferrous oxalate (FeC2O4)-based composite has been recognized as an eminent catalyst for Cr(III)-ethylenediamine tetraacetic acid (Cr(III)-EDTA) decomplexation. However, their practical application has been limited by low cycling capacity and an ambiguous mechanism. In this research, a composite catalyst consisting of biotite loaded with nano FeC2O4 (CFS90) was prepared directly from iron-containing silicate tailing. The removal efficiency (91.3 %, kobs = 0.0185 min-1) of Cr(III)-EDTA by CFS90/peroxymonosulfate (PMS) system was remarkably higher than that of other typical systems. The Si site in biotite lost electrons while the electron cloud density around the Fe atom in FeC2O4 increased, which facilitates the activation of PMS and the generation of reactive oxygen species (ROS). In this system, abundant singlet oxygen (1O2) was primarily produced via interactions between carbon-centered radicals (CO2·-) and dissolved oxygen (DO), rather than through oxygen vacancies (Ovs) in CFS90. Both CO2·- and Fe(II) provided reducing conditions, preventing the released Cr(III) from being re-oxidized. Notably, the released Cr(III) was effectively precipitated by elevating the solution pH with NaOH, therefore endowing superior stability and deactivation capacity of CFS90 to enable its removal rate of Cr(III)-EDTA to remain above 84.1 % for 18 h in a fix-bed reactor. These findings provide an in-depth analysis of the enhanced Cr(III)-EDTA removal mechanism and highlight the environmental remediation potential of iron-containing silicate tailings.

Biotransformation of Pb and As from sewage sludge and food waste by black soldier fly larvae: Migration mechanism of bacterial community and metalloregulatory protein scales

The accumulation and transformation of lead (Pb) and arsenic (As) during the digestion of sewage sludge (SS) by black soldier fly larvae (BSFL) remain unclear. In this study, we used 16 s rRNA and metagenomic sequencing techniques to investigate the correlation between the microbial community, metalloregulatory proteins (MRPs), and Pb and As migration and transformation. During the 15-day test period, BSFL were able to absorb 34-48 % of Pb and 32-45 % of As into their body. Changes in bacterial community abundance, upregulation of MRPs, and redundancy analysis (RDA) results confirmed that ZntA, EfeO, CadC, ArsR, ArsB, ArsD, and ArsA play major roles in the adsorption and stabilization of Pb and As, which is mainly due to the high contribution rates of Lactobacillus (48-59 %) and Enterococcus (21-23 %). Owing to the redox reaction, the regulation of the MRPs, and the change in pH, the Pb and As in the BSFL residue were mainly the residual fraction (F4). The RDA results showed that Lactobacillus and L.koreensis could significantly (P < 0.01) reduce the reducible fraction (F2) and F4 of Pb, whereas Firmicutes and L.fermentum can significantly (P < 0.05) promote the transformation of As to F4, thus realizing the passivation Pb and As. This study contributes to the understanding of Pb and As in SS adsorbed by BSFL and provides important insights into the factors that arise during the BSFL-mediated migration of Pb and As.

The remediation potential and kinetics of Pb2+ adsorbed by the organic frameworks of Cladophora rupestris

Cladophora rupestris is ubiquitous in many kinds of waterbodies, and C. rupestris biomass can serve as a carrier for adsorbing and transferring heavy metals. Batch experiments and characterization were performed. Results showed that the organic frameworks of C. rupestris (CROF) had a specific surface area of 2.58 m2/g and an external surface area of 2.06 m2/g. Many mesopores were present in CROF, mainly distributed in 2.5-7.5 nm. The zeta potentials were within the range of - 4.46 to - 13.98 mV in the tested pH of 2.0-9.0. CROF could effectively adsorb Pb2+ in large pH range. The maximum adsorption capacity (qmax) of Pb2+ on CROF was 15.02 mg/g, and 97% of Pb2+ was adsorbed onto CROF after 25 min. CROF had a preferential adsorption of Pb2+. The protein secondary structures and carbon skeletons of CROF all worked in adsorption. The main Pb2+ adsorption mechanisms were pore filling, electrostatic attraction, Pb-π interaction, and surface complexation. Therefore, it is valuable as a biosorbent for the removal of Pb2+ from waterbodies.

Facile activation of natural calcium-rich sepiolite with oxalic acid for selective Pb(II) removal: Highly-efficient performance, mechanisms and site energy distribution

The design and development of adsorbents with high efficiency, selectivity, and economy for Pb(II) are essential to environmental governance and ecological safety. Herein, an oxalic acid (OA) activated natural sepiolite (nSEP) composite for highly efficient Pb(II) removal was prepared by a facile impregnation strategy. The OA activated nSEP nanocomposite (OA-nSEP) was characterized by various instrumental techniques and its adsorption performance towards Pb(II) was further evaluated through a series of static and dynamic experiments under various environmental conditions. Results revealed that OA reacted with the calcium impurities in nSEP to form calcium oxalate, causing mesoporous structure and larger specific surface area of OA-nSEP. The obtained OA-nSEP possessed super high Pb(II) adsorption capacities (858.4-1252 mg/g), which were much higher than that of most modified clays or conventional materials. The average adsorption site energy and the standard deviation of the site energy distribution were analyzed to investigate the strength of Pb(II) binding onto OA-nSEP and the adsorption site heterogeneity. Mechanism studies confirmed that oxalate groups exerted a primary role in the adsorption process. X-ray diffraction and X-ray photoelectron spectrometry (XPS) unveiled that the coordination of oxalate with Pb(II) and precipitation of lead oxalate was responsible for the high efficiency and selectivity. Distinguishing feature of high adsorption capacity, specific selective adsorption, abundant availability, and splendid reusability make the OA-nSEP a promising candidate for eliminating Pb(II) in practical scenarios.

Pb(II) bioremediation using fresh algal-bacterial aerobic granular sludge and its underlying mechanisms highlighting the role of extracellular polymeric substances

Lead (Pb) discharged from rural industries poses a significant threat to the environment and human health. Algal-bacterial aerobic granular sludge (A-B AGS) is a promising alternative for sewage treatment with high efficiency and good settleability. In this study, Pb(II) biosorption using fresh A-B AGS was investigated for the first time. The important role of extracellular polymeric substances (EPS) was revealed with the involved mechanisms being clarified. The desorbents for Pb recovery from Pb-loaded A-B AGS were also screened. Results showed that A-B AGS has an excellent maximum Pb adsorption capacity of 72.4 mg·g^-1 at pH 6.0. EPS plays an important role in keeping microbial activity, Pb bonding, and providing metal ions (Ca, Na and Mg) for Pb ion exchanges. Electrostatic interaction, ion exchange, and bonding to functional groups may occur orderly in the Pb biosorption process and the formation of pyromorphite (Pb₅(PO₄)₃Cl) contributes to Pb biosorption. About 66 % of the adsorbed Pb was accumulated in the A-B AGS microbial cells. Na₂EDTA (0.05 M) can recover 60.3 % of the loaded Pb with the highest microbial activity of granules being remained. All the findings will provide the theoretical basis for the large-scale application of A-B AGS to bioremediate Pb(II)-containing wastewater.

Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal

An oxalate-doped hydroxyapatite (O-HAP) was hydrothermally synthesized for aqueous lead (Pb) removal based on the solubility-limiting ability of oxalate and phosphate over pH range 4-9. Free Pb²⁺ activities in oxalate and/or phosphate systems were controlled by oxalate to form soluble ion pairs Pb-Ox (aq) and Pb-Ox₂^2- at pH 4-7 while in preference to persist as PbHPO₄ (aq) when pH ≥ 8. Both phosphate and oxalate exhibited excellent efficiency in reducing Pb solubility, causing over 99 % of Pb precipitated from solution following oxalate < oxalate-phosphate < phosphate. The Visual MINTEQ model overestimated dissolved Pb and free Pb²⁺ in nearly all of the reaction systems due to the ill-defined stability constants and solubility products for Pb ion-pair formation. The addition of phosphate acting as a buffer in Pb-oxalate systems tended to lessen the spontaneous pH shifts within 24 h to equilibrate proton release from Pb precipitation and hydrolysis, indicating lower solubility products and faster kinetics of Pb-phosphate mineral formation. The TEM-EDS, FTIR and XRD identified a block-shaped Pb-oxalate mineral phase as the only precipitate at acidic pH while substituted by phosphate to form rod-shaped Pb₅(PO₄)₃OH and Pb₃(PO₄)₂ precipitates as pH increased. The optimum hydrothermal conditions of O-HAP were 433 K, pH 9 and P/Ox doping ratio of 0.5 for 24 h. Batch experiments revealed the endothermic process of O-HAP toward Pb with the maximum adsorption capacity reaching 2333 mg/g at a pH of 7, reaction time of 12 h, initial Pb concentration of 600 mg/L and temperature of 308 K, which were best fitted with the pseudo-second-order kinetic model and Langmuir isotherm. The synergetic mechanisms of O-HAP for Pb removal involved dissolution-precipitation, adsorption and ion exchange. This study provides an insight in developing effective remediation strategies for heavy metal contamination by interacting between low-molecular-weight organic acids and secondary mineral phases.

Development of iron-based biochar for enhancing nitrate adsorption: Effects of specific surface area, electrostatic force, and functional groups

The problem of nitrate contamination in water has attracted widespread attention. Original biochar has a poor adsorption capacity for nitrate adsorption. Iron impregnation and acid protonation (base deprotonation) are common modification methods for biochar. In order to develop iron-mediated biochar containing multi-functional groups for enhancing nitrate adsorption, Fe-BC@H and Fe-BC@OH were prepared using a two-stage development process, including an iron-based carbon pyrolysis followed by acid protonation (or base deprotonation). The pseudo-second-order kinetic and Langmuir models can well describe the adsorption process which is a physicochemical complex monolayer adsorption. The data proved that Fe-BC@H (9.35 mg/g NO₃^--N) had a stronger adsorption capacity than Fe-BC@OH (2.95 mg/g NO₃^--N). Surface morphologies, functional groups, and mineral compositions of Fe-BC@H and Fe-BC@OH were analyzed through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Characterization results showed that acid protonation can further improve the specific surface area (SSA), pore volume, and Zeta potential of Fe-based biochar, providing more adsorption sites for nitrate and enhancing the electrostatic force between nitrate and biochar. However, these effects were suppressed through base deprotonation. In addition, acid protonation can significantly increase the type and number of functional groups of biochar to enhance the chemisorption of nitrate. Such results suggested that the acid protonation can further improve the adsorption capacity of Fe-based biochar for nitrate, while base deprotonation had an inhibitory effect on that of Fe-based biochar. Overall, this study reveals that specific surface area, electrostatic force, and functional groups are crucial effects of the nitrate adsorption on acid/base modified biochar.

Technological trends in nanosilica synthesis and utilization in advanced treatment of water and wastewater

Water and wastewater treatment applications stand to benefit immensely from the design and development of new materials based on silica nanoparticles and their derivatives. Nanosilica possesses unique properties, including low toxicity, chemical inertness, and excellent biocompatibility, and can be developed from a variety of sustainable precursor materials. Herein, we provide an account of the recent advances in the synthesis and utilization of nanosilica for wastewater treatment. This review covers key physicochemical aspects of several nanosilica materials and a variety of nanotechnology-enabled wastewater treatment techniques such as adsorption, separation membranes, and antimicrobial applications. It also discusses the prospective design and tuning options for nanosilica production, such as size control, morphological tuning, and surface functionalization. Informative discussions on nanosilica production from agricultural wastes have been offered, with a focus on the synthesis methodologies and pretreatment requirements for biomass precursors. The characterization of the different physicochemical features of nanosilica materials using critical surface analysis methods is discussed. Bio-hybrid nanosilica materials have also been highlighted to emphasize the critical relevance of environmental sustainability in wastewater treatment. To guarantee the thoroughness of the review, insights into nanosilica regeneration and reuse are provided. Overall, it is envisaged that this work's insights and views will inspire unique and efficient nanosilica material design and development with robust properties for water and wastewater treatment applications.

Efficient removal of Cd2+ from aqueous solution with a novel composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides prepared from biotite

Taking low cost silicate minerals to develop efficient Cd²⁺ adsorption materials was favorable to the comprehensive utilization of minerals and remediation of environmental pollution. In this study, a composite of silicon supported nano iron/aluminum/magnesium (hydr)oxides was prepared with biotite by combining acid leaching and base precipitation process, which was used to remove Cd²⁺. Cd²⁺ adsorption behaviors were in accordance of pseudo-second order kinetic model and Langmuir model, and the obtained maximal Cd²⁺ adsorption capacity was 78.37 mg/g. Increasing pH and temperature could accelerate the removal of Cd²⁺. The activation energy was calculated as 66.05 kJ/mol, meaning that Cd²⁺ removal process was mainly depended on chemical adsorption. XRD and SEM results showed that this composite was a micro-nano structure of layered silica supported nano iron/aluminum/magnesium (hydr)oxides. Cd²⁺ removal mechanisms were consisted of surface complexation and ion exchange between Cd²⁺ and other metal ions, and the ion exchange interaction played the major role. These results indicated that a novel efficient utilization way for silicate minerals was developed.

Catalytic performance and periodate activation mechanism of anaerobic sewage sludge-derived biochar

Periodate (PI)-based advanced oxidation processes are a newly discovered approach for effective pollutant elimination. In this study, we demonstrated that biochar obtained from pyrolysis of anaerobic sewage sludge without any pretreatment can be used for PI activation. The biochar obtained at 800 °C (SBC-800) exhibited the best PI activation capacity using acid organic II (AO7) as substrate. The PI activation was strongly dependent on pH and exhibited the highest AO7 removal rate at pH 3.0. Meanwhile, the anti-interference capacity with common wastewater components and reusability of the SBC-800/PI system were confirmed. Combined with the results of chemical quenching, reactive oxygen species (ROS) trapping, X-ray photoelectric spectroscopy (XPS), electrochemical and density function theory (DFT)-based calculations, singlet oxygen production and electron transfer mediated by the SBC-800-PI complex were the dominant AO7 oxidation mechanisms. This study provides easily prepared catalysts for PI activation and paves the way for solid waste recycling and reuse.

Mesoporous maltose/calcium oxalate hybrid material with abundant reaction sites and its efficient Pb(ii) removal from diverse water bodies

Maltose/calcium oxalate exhibits high capacity and selective adsorption of Pb(ii) due to the synergistic mechanism of ion exchange, electrostatic and complexation.

A Novel Calcium Oxalate/Sepiolite Composite for Highly Selective Adsorption of Pb(II) from Aqueous Solutions

Synthesizing functional nanomaterials from naturally abundant clay has always been of vital importance for resource utilization, however, the lack of new methods to effectively utilize low-grade clay presents a significant challenge. Herein, a calcium oxalate/sepiolite nanocomposite (SMN-x) was prepared by using the water bath heating method to convert the associated calcium carbonate in low-grade sepiolite into calcium oxalate. The developed composite was subsequently used to remove Pb(II) from the aqueous solutions. The SMN-3 adsorbent prepared by heating in a water bath at 90 °C for 3 h (with a high specific surface area of 234.14 m2·g−1) revealed the maximum Pb(II) adsorption capacity of 504.07 mg·g−1 at pH 5, which was about five times higher than that of sepiolite (105.57 mg·g−1). Further, the SMN-3 adsorbent possessed a much higher selectivity for Pb(II) as compared to the other metal ions. Moreover, the residue was noted to be stable and safe. The adsorption kinetics and isotherms conformed to the quasi-second-order kinetic and Langmuir models. During the adsorption process, ion exchange was noted to the main mechanism, however, it was also accompanied by electrostatic attraction. This study provides a novel strategy for the sustainable development of simple and efficient adsorbents by utilizing low-grade clay minerals.

Adsorption and Separation of Crystal Violet, Cerium(III) and Lead(II) by Means of a Multi-Step Strategy Based on K10-Montmorillonite

A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common contaminants, i.e., crystal violet dye (CV), Ce(III) and Pb(II) were chosen as “model” pollutants. The main factors affecting the pollutants’ sorption were investigated. The experimental data were correlated with adsorption isotherms and kinetic models to obtain a deeper insight into the adsorption processes. The affinity of the clay toward the pollutants is favored by an increasing pH and follows the order CV > Pb(II) > Ce(III). Whereas Ce(III) metal ions do not adsorb onto clay under strongly acidic conditions, both Pb(II) and CV can adsorb under all the investigated pH conditions. The analysis of isotherms and kinetic profiles revealed that CV adsorbs onto clay through a mechanism consisting of two parallel processes, namely cation exchange on the external mineral surface and in the interlayer and surface complexation at the edge sites, while metal ion uptake is due solely to cation exchange processes involving mineral surfaces. The time required for the complete removal of pollutants follows the order CV > Ce(III) >> Pb(II). The possibility to modulate the adsorption features by changing experimental conditions was successfully employed to propose the best strategy for the progressive removal of different components from aqueous solutions.