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Phosphorus-modified biochar has been proven to enhance the precipitation and complexation of heavy metal ions from wastewater. However, the current modification methods require large amounts of exogenous P and have high energy consumption. Hence, this study proposes and analyzes a strategy integrating biochar production, phosphorus wastewater treatment, dephosphorization waste recovery, and heavy metal removal. "BC-Ca-P" was derived from Ca-modified biochar after phosphorus wastewater treatment. The adsorption of Pb(II) by BC-Ca-P followed the Langmuir isotherm and pseudo–second–order kinetic models. The maximum adsorption capability of 361.20 mg·g−1 at pH 5.0 for 2 h was markedly greater than that of external phosphorous-modified biochar. The adsorption mechanisms were dominated by chemical precipitation and complexation. Furthermore, density functional theory calculations indicated that oxygen-containing functional groups (P-O and C-O) contributed the most to the efficient adsorption of Pb(II) onto BC-Ca-P. To explore its practical feasibility, the adsorption performance of BC-Ca-P recovered from an actual environment was evaluated. The continuous-flow adsorption behavior was investigated and well-fitted utilizing the Thomas and Yoon–Nelson models. There was a negligible P leakage risk of BC-Ca-P during heavy metal treatment. This study describes a novel and sustainable method to utilize dephosphorization waste for heavy metal removal. Article Highlights: Dephosphorization biochar waste was used to sustainably remove heavy metals from wastewater. Field-recovered dephosphorization biochar waste displayed high Pb adsorption capacity. Dephosphorization biochar for heavy metal removal is an eco–friendly waste–reduction and resource–utilization method. [ABSTRACT FROM AUTHOR]

Bioremediation has drawn widespread concern in passivating heavy metals, but the intense toxicity of heavy metals to biological cells limits the application of functional strains. Herein, goethite-modified biochar (GMB) was chosen as the carrier to immobilize phosphate-solubilizing bacteria (PSB) of strain L1 for lead and cadmium remediation. Batch experiments showed that the GMB-L1 possessed excellent adsorption performance with a maximum adsorption of 496.54 and 178.18 mg/g for Pb and Cd, respectively. Moreover, adding GMB-L1 in contaminated soil converted heavy metals (Pb and Cd) into more stable fractions and reduced TCLP-extracted heavy metal concentrations (73.24% of Pb and 57.25% of Cd). The GMB-L1 was proved to accomplish Pb and Cd remediation via the process of chemical precipitation, surface complexation, electrostatic attraction, and biomineralization, which was accompanied by the transformation of heavy metals into a more stable crystal structure, such as Pb5(PO4)3OH and Cd5(PO4)3OH. Therefore, the co-system of GMB and strain L1 could be regarded as a prospective option for efficiently remedying environmental heavy metal pollution. [ABSTRACT FROM AUTHOR]

Biochar-based sulfidized nano-sized zero-valent iron (SNZVI/BC) can effectively immobilize cadmium (Cd) in contaminated paddy soils. However, the synergistic effects between biochar and SNZVI on Cd immobilization, as well as the underlying mechanisms remain unclear. Herein, a soil microcosm incubation experiment was performed to investigate the immobilization performance of SNZVI/BC towards Cd in the contaminated paddy soil. Results indicated that the addition of SNZVI/BC at a dosage of 3% significantly lessened the concentration of available Cd in the contaminated soil from 14.9 (without addition) to 9.9 mg kg−1 with an immobilization efficiency of 33.3%, indicating a synergistic effect. The sequential extraction results indicated that the proportion of the residual Cd in the contaminated soil increased from 8.1 to 10.3%, manifesting the transformation of the unstable Cd fractions to the steadier specie after application of SNZVI/BC. Also, the addition of SNZVI/BC increased soil pH, organic matter, and dissolved organic carbon, which significantly altered the bacterial community in the soil, enriching the relative abundances of functional microbes (e.g., Bacillus, Clostridium, and Desulfosporosinus). These functional microorganisms further facilitated the generation of ammonium, nitrate, and ferrous iron in the contaminated paddy soil, enhancing nutrients' availability. The direct interaction between SNZVI/BC and Cd2+, the altered soil physicochemical properties, and the responded bacterial community played important roles in Cd immobilization in the contaminated soil. Overall, the biochar-based SNZVI is a promising candidate for the effective immobilization of Cd and the improvement of nutrients' availability in the contaminated paddy soil. Highlights: Biochar-based sulfidized nano-sized zero-valent iron (SNZVI/BC) synergistically immobilized Cd in the contaminated soil. SNZVI/BC effectively enhanced nutrients' availability in the contaminated soil. Nitrate-, Iron-, and sulfate-reducing bacteria were enriched in the SNZVI/BC-treated soil. Precipitation and complexation played an important role in the immobilization of Cd. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) water pollution threatens environmental systems and human health. Adsorption is the preferred method for purifying water bodies polluted by Cd, and the development of effective adsorption materials is critical. The performance of original phosphate rock powder (PRP) as an adsorption medium for purifying water bodies polluted by Cd was compared with that of phosphate rock powder modified with fulvic acid, chitosan, MnO2, and sulfhydryl, respectively, and their appearance and adsorption properties were investigated. The surface structures of all modified powders were rougher than the original, and their functional groups were richer. The greatest Cd2+ adsorption capacity, 1.88 mg g−1, was achieved with chitosan-modified PRP (CMPRP). This was 106.59% greater than that of PRP. The capacities of fulvic acid and MnO2 were 15.38% and 4.40% greater than that of the original, respectively. When the fulvic acid-modified PRP, CMPRP, and manganese dioxide PRP reached adsorption equilibrium, the removal rates of Cd2+ were 51.86%, 93.26%, and 46.70%, respectively. Moreover, the removal rate of Cd2+ by CMPRP was 104.43% higher than that of PRP. The main Cd2+ adsorption mechanisms for the MPRPs were electrostatic interactions, ion exchange, co-precipitation, and complexation. Moreover, the processing of the phosphate rock powder was straightforward, harmless to the environment, and could be effectively used for the removal of Cd. These results show that CMPRP is promising as a new adsorption material to treat Cd-contaminated water. [ABSTRACT FROM AUTHOR]

Water contamination currently threatens human health, which is still a major environmental issue. Scientists are paying attention, in particular, to lead poisoning of water caused by industrial wastes on a global scale. In order to reduce agricultural waste and promote sustainable development, this study created a straightforward process for using leftover rice husks to create biochar. At first, the rice husk biochar was prepared; then, following the immersion of biochar with precursors of Fe2+ and Fe3+ and precipitation under alkaline condition, the Fe3O4 was formed and laid onto biochar to create another magnetic adsorbent known as ferrous-modified biochar. The success of loading Fe3O4 was confirmed by SEM, XRD, FTIR, and BET measurements. The delivered ferrous-modified biochar has a high surface area and correct functional groups for the adsorption process. In order to remove Pb (II) from wastewater, rice husk biochar and ferrous-modified biochar materials were used. Under optimized conditions, synthesized ferrous-modified biochar has a lead adsorbent effectiveness of 95.0% that is related to varying pathways as co-precipitation reaction, complexation reaction, conjugation adsorption, ion exchange, and Fe–O coordination. The Pb2+ adsorption capacity of modified biochar is three times greater than rice husk biochar with 73.68 mg/g. Another evidence of the ferrous-modified biochar adsorbent's excellent recyclable properties is the remaining lead efficiency, which was over 41.2% even after six recycling cycles. Therefore, by this approach of synthesizing Fe3O4 loaded on biochar, the research provided new opportunities for developing low-cost and highly efficient adsorbent to remove heavy metals from water. [ABSTRACT FROM AUTHOR]

The serious environmental risks caused by Pb(II) and Sb(V) co-contamination increase the need for their efficient and simultaneous removal. In this study, the remediation feasibility by Fe-doped phosphogypsum (FPG) was elucidated for single systems with Pb or Sb pollutant and coexisting systems with both from water. As for single systems, Fe doping effectively enhanced the Pb(II) removal performance by phosphogypsum (PG) at low Pb(II) concentrations of below 100 mg/L via the combination of precipitation and complexation. The optimal removal rate of Sb(V) by FPG increased by 2.08–3.31 times as compared to that of by PG (10–120 mg/L), mainly due to the strong affinity of iron hydroxyl (≡Fe–O–H) towards Sb(V). Compared with the single systems, the coexistence greatly enhanced the Pb(II) and Sb(V) removal performance by FPG, and the interaction behavior between Pb(II) and Sb(V) on the FPG was concentration dependent. Briefly, the sorption of FPG controlled the elimination of low coexisting concentrations of Pb(II) and Sb(V), whereas the co-precipitation process between Pb(II) and Sb(V) predominated with high ions concentration. The significant synergistic effects were found during the removal of Pb(II) and Sb(V) on FPG in the coexisting system, which mainly attributed to precipitation, bridging complexation and electrostatic attraction. Considering the advantages such as facile preparation, low cost and high removal capacity, FPG is a promising material to uptake Pb(II) and/or Sb(V) from contaminated water. [ABSTRACT FROM AUTHOR]

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Cadmium (Cd) pollution in aqueous solution has caused great threat to human health. A novel chitosan and biochar supported sulfide-modified nZVI composite (CB-S-nZVI) was synthesized by liquid phase reduction method and applied to the removal of Cd2+ from wastewater. The synthesized materials were characterized by SEM, BET, XRD, FTIR, and zeta potential. Batch experiments showed that the optimum synthesis conditions of CB-S-nZVI were the S/Fe molar ratio of 0.56 and the Fe/BC mass ratio of 2. The removal capacity of Cd2+ by CB-S-nZVI increased with the increase of pH and reached the maximum of 249.92 mg/g at pH of 9. Among the competitive cations, Pb2+ and Cu2+ had a strong inhibition to the removal of Cd2+. The removal process of Cd2+ conformed to the pseudo-second-order kinetic model and the Freundlich model, and it was exothermic. XPS analysis suggested that the removal mechanism of Cd2+ was mainly through electrostatic attraction, precipitation, and complexation. Overall, these findings provide new insights into the development of new nZVI-modified material, and CB-S-nZVI is promising in removing heavy metals from wastewater. [ABSTRACT FROM AUTHOR]

In this study, we investigated the removal of hexavalent chromium (Cr(VI)) through an innovative approach, which employed iron sulfide nanoparticles synthesized via a green chemistry technique, utilizing extracts derived from date palm seeds (referred to as ds-FeS). Batch studies, which were well represented by the Langmuir isotherm model, were conducted to determine the maximum removal capacities (qm) of ds-FeS nanoparticles at three different initial pH conditions (pH = 3, 7, and 9). Additionally, batch kinetic studies were conducted under varying conditions of initial Cr(VI) load (3.5, 9, 27, and 38 mg/g of nanoparticles), nanoparticle dose (25, 37, 50, and 75 g/g of Cr(VI)), and initial pH (3, 5, 7, and 9). Results demonstrated the positive impact of acidic pH during Cr(VI) removal by ds-FeS wherein the highest qm of 31.3 mg/g and initial rate of 6.95 mg/g·min (pseudo-second order kinetics) were observed at pH 3. Conversely, with an increase in pH to neutral and alkaline conditions, a decline in both qm and initial rates was observed. Measurements of solution pH, total chromium, and particle surface chemistry using X-ray diffraction and Fourier transform infrared spectrometry techniques revealed the crucial roles of reduction, surface precipitation, and complexation processes in Cr(VI) removal by ds-FeS nanoparticles. Overall, this study demonstrates the promising potential of environmentally friendly, date palm seed–derived iron sulfide nanoparticles for Cr(VI) removal. [ABSTRACT FROM AUTHOR]

Effective treatment of uranium-containing wastewater is of great significance to the sustainable development of nuclear power and the protection of ecological environment. In this study, a highly efficient uranium adsorbent, graphene oxide (GO)/nano-hydroxyapatite (nHA) composite microspheres (nHA@rGO) was synthesized, which could effectively remove uranium from aqueous solution. Under the condition of pH = 3.5, T = 298 K, the maximum adsorption capacity reached 1672.96 mg/g. The results of batch experiments showed that the adsorption capacity of nHA@rGO microspheres was higher than that of nHA microspheres, indicating the enhancement of GO. The adsorption kinetics conformed to the pseudo second-order model. The changes of nHA@rGO microspheres before and after uranium adsorption were analyzed by FT-IR, XPS and XRD. The mechanisms of U(VI) ions adsorption onto nHA@rGO microspheres involved precipitation, surface complexation and ion exchange, in which the hydroxyl and phosphoric acid groups played important roles. The results showed that the prepared nHA@rGO microspheres can be used as an efficient and promising adsorbent for the treatment of uranium-containing wastewater. [ABSTRACT FROM AUTHOR]

In this study we investigated the efficacy of a novel material parthenium weed (Parthenium hysterophorus L.) biochar (PBC), iron doped zinc oxide nanoparticles (nFe-ZnO), and biochar modified with nFe-ZnO (Fe-ZnO@BC) to adsorb heavy metals (HMs) and reduce their uptake by wheat (Triticum aestivum L.) in a highly chromite mining contaminated soil. The co-application of the applied soil conditioners exhibited a positive effect on the immobilization and restricted the HMs uptake below their threshold levels in shoot content of wheat. The maximum adsorption capacity was because of large surface area, cation exchange capacity, surface precipitation, and complexation of the soil conditioners. The scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) showed porous smooth structure of parthenium weed derived biochar that helped in HMs adsorption, increase the efficiency of soil fertilizers and nutrients retention which help in the enhancement soil condition. Under different application rates the highest translocation factor (TFHMs) was obtained at 2 g nFe-ZnO rate followed the descending order: Mn > Cr > Cu > Ni > Pb. The overall TFHMs was found <1.0 indicating that low content of HMs accumulation in roots from soil slight transferred to shoot, thus satisfying the remediation requirements. Wheat is considered as an important staple food which is grown in a chromite mining contaminated soil containing toxic HMs releasing from weathering of mafic and ultramafic rocks in the study area. The present research work is significantly beneficial in identifying the efficiency of treatment technologies to immobilize toxic HMs in soil. Parthenium weed derived biochar and biochar modified with nFe-ZnO (Fe-ZnO@BC) reduce the HMs uptake by wheat plant. [ABSTRACT FROM AUTHOR]

Groundwater pollution caused by lead ions has become a widespread issue worldwide due to the ever-increasing development of industrial activities. Such pollution poses significant threats to both humans and the environment. Oyster shell powder–peanut shell biochar mixture (OSP–PSB mixture) was used for lead-contaminated groundwater treatment by permeable reactive barrier (PRB) technology. Basic characteristics of materials proved that OSP–PSB mixture has good adsorption properties; OSP with particle sizes ranging from 0.85 to 1.18 mm was used in this research; according to engineering and adsorption characteristics, OSP–PSB mixture (5:1) showed excellent permeability (4.35 × 10−4 cm/s) and lead adsorption capacity(27 mg/g); long-term permeability of the OSP–PSB mixture slightly decreased over time and met the permeability requirements for PRB; the removal mechanisms of lead ions by OSP–PSB mixture include precipitation, surface complexation, ion exchange, and physical adsorption. The experiment results showed that the OSP–PSB mixture fulfills the actual project requirements of PRB. [ABSTRACT FROM AUTHOR]

• Rice straw-derived dissolved organic matter (DOM) included four main components. • The presence of goethite significantly promotes the straw decomposition process. • OM's adsorption capacity for Cd increased with the straw decomposition time. • The presence of minerals promoted the OM's adsorption capacity and affinity of Cd. • Surface precipitation and complexation dominant Cd adsorption by OM. Organic matter (OM) derived from the decomposition of crop residues plays a key role as a sorbent for cadmium (Cd) immobilization. Few studies have explored the straw decomposition processes with the presence of minerals, and the effect of newly generated organo-mineral complexes on heavy metal adsorption. In this study, we investigated the variations in structure and composition during the rice straw decomposition with or without minerals (goethite and kaolinite), as well as the adsorption behavior and mechanisms by which straw decomposition affects Cd immobilization. The degree of humification of extracted straw organic matter was assessed using excitation-emission matrix (EEM) fluorescence and Ultraviolet-visible spectroscopy (UV-vis), while employing FTIR spectroscopy and XPS to characterize the adsorption mechanisms. The spectra analysis revealed the enrichment of highly aromatic and hydrophobic components, indicating that the degree of straw decomposition and humification were further intensified during incubation. Additionally, the existence of goethite (SG) accelerated the humification of OM. Sorption experiments revealed that the straw humification increased Cd adsorption capacity. Notably, SG exhibited significantly higher adsorption performance compared to the organic matter without minerals (RS) and the existence of kaolinite (SK). Further analysis using FT-IR spectroscopy and XPS verified that the primary mechanisms involved in Cd immobilization were complexion with —OH and —COOH, as well as the formation of Cd-π binds with aromatic C=C on the surface of solid OMs. These findings will facilitate understanding the interactions of the rice straw decomposing with soil minerals and its remediation effect on Cd-contaminated farmland. [Display omitted] [ABSTRACT FROM AUTHOR]

In view of the treatment of heavy metal wastewater of[ Cd (II) ], [ Cr (VI) ] and[ Pb (II) ], this study modified nano-zero-valent iron (nZVI) by bioehar (BC) and bentonite (BE) to obtain BC-BE-NZVI composite material, and explored the adsorption characteristics of the material for heavy metals through ad-sorption experiments. Adsorption kinetics equation, isothermal adsorption equation fitting, XRD and XPS analysis were used to reveal the adsorption mechanism of BC-BE-nZVI on single and compound heavy metal systems. The results show that BC-BE-nZVI has the strongest effect on the removal of heavy metals, and the removal rate of Cd (II), Cr (VI) and Pb (II) can reach 96. 43%, 97.70% and 95. 69% /respectively, and can adapt to heavy metal wastewater with a wide pH range. The pseudo-second-order kinetic equation and Langmuir isothermal adsorption equation are more suitable for describing the adsorption process of BC-BE-nZVI. In the compound heavy metal system, the adsorption process of BC-BE-nZVI is more suitable for Freundlich isothermal adsorption equation, and the competitive adsorption capacity Cd (II) is higher than Cr (VI). In a single heavy metal system, the removal mechanism of Cd (II) mainly includes adsorption precipitation, Cr (VI) is mainly reduction and adsorption, and Pb (II) is mainly adsorption precipitation. The adsorption mechanism of the compound heavy metal system is mainly precipitation and complexation. [ABSTRACT FROM AUTHOR]

The present investigation applies the stabilization/solidification technique for lead (Pb)-contaminated soil remediation utilizing an organic binder to negate the environmental consequences caused by inorganic binders such as cement. This research synthesized novel biochar by slow pyrolysis of moringa seed cake or de-oiled cake (waste generated after oil recovery) and tested its physicochemical characteristics, which revealed that it possesses a high pH and abundant surface functional groups that can act as potential adsorption sites for lead. Furthermore, the effects of biochar content (0% to 10% w/w) and curing time on the stabilization of soil contaminated with Pb at a concentration of 5,000 mg/kg were evaluated. The toxicity characteristic leaching test showed that treatment with 10% w/w biochar and 28 days of curing reduced Pb leachability to regulatory limits with over 89% immobilization efficiency. Moreover, the soil strength and the pH increased steadily with the biochar content and curing time while maintaining stability after 56 to 90 days of curing. Microstructural characterization revealed the underlying mechanisms in effectively stabilizing lead in soil, including precipitation, surface complexation with functional groups (C═O, O═C─ O), and lead encapsulation in calcium silicate hydrates (C─ S─ H). [ABSTRACT FROM AUTHOR]

Fly ash (FA) is promising for environmental remediation, but how to modify the FA with high remediation efficiency through an environmentally friendly and low-cost modification method is scare. A modified FA (MFA) was prepared through a one-step hydrothermal modification with Ca(OH)2 and KH2PO4. Results indicated that irregular agglomerates occurred on the surface of the MFA and that the specific surface area increased by 1.94 times compared to that of FA. Compared to FA, glassy compositions in MFA were destroyed and amorphous Si/Al and alkaline aluminosilicate gels were formed. The soil application of 0.2–0.6% MFA significantly increased soil pH by 0.23–0.86 units compared to FA and decreased available lead (Pb) and copper (Cu) by 25–97.1% and 13.5–75%, respectively. MFA significantly decreased exchangeable Pb and Cu by 12.5–32% and 11.4–35.2%, respectively, compared to FA. This may be due to the high pH and specific surface area of MFA, which promoted to the formation of amorphous Si/Al, metal–phosphate precipitation, and complexation with functional groups. In addition, MFA slightly increased the biomass of shoots and roots and decreased the uptake of Pb and Cu by ryegrass. This study provides a new modification method for the utilization of FA in the heavy metal-contaminated soils. [ABSTRACT FROM AUTHOR]

Nowadays, clean-up of heavy metals from wastewaters using waste residue carbon-based material has received increasing attention. In this work, a novel Chinese medicine residue carbon-based nano zero-valent iron composite (CM-nZVI) had been successfully prepared using the combined Chinese medicine residue, FeCl3 and green tea extract. Cr(VI) and/ or Cd(II) removal in water by the CM-nZVI were systematacially investigated with a series of batch experiments. The most relevant findings indicated the adsorption efficiecy and capacity of Cr(VI) by CM-nZVI were respecitvely nearly 98% and 26 mg/g under optimized reaction conditions. The negative influences of the cations on the Cr(VI) removal followed the order of Al3+ > Ca2+ > Mg2+ Na+ > K+, but the anions followed the order of HCO3− > PO43− > NO3− > Cl− > SO42−. Humic acid (HA) and ionic strength with high concentrations severely inhibited Cr(VI) removal. The Cr(VI) adsorption on CM-nZVI fitted well by the pseudo-second-order kinetic and Langmuir models. A monolayer endothermic chemisorption occurred on Cr(VI) adsorption over CM-nZVI, and Cr(VI) removal by CM-nZVI primarily involved in the absorption, reduction, precipitation and complexation processes. Both Cr(VI) and Cd(II) removals had been achieved by CM-nZVI at their low concentrations. This CM-nZVI showed a better reusability proprity for Cr(VI) and Cd(II) removal with the regeneration of CM-nZVI through simple pickling. The outcomes of this work show that CM-nZVI could be used an effective material for heavy metals removal from water. [ABSTRACT FROM AUTHOR]

Copyrolysis biochar derived from rape straw (RSBC) was prepared through oxygen-limited pyrolysis at 500 °C and utilized to investigate its adsorption capability for single and complex trace elements (Fe2+, Mn2+, Cu2+, and Zn2+) in contaminated solutions. The microstructures, functional groups, and adsorption behaviors of RSBC were determined through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and batch adsorption experiments, respectively. From these, the single/complex adsorption results showed that the adsorption capacity of RSBC for Fe2+, Mn2+, Cu2+, and Zn2+ was 32.21/23.78, 8.95/3.41, 28.12/7.19, and 13.77/4.92 mg/g, respectively. The Langmuir isotherm model fit better than that of Freundlich in the mixed adsorption system, while the pseudo-second-order kinetic model was the most suitable for single adsorption. Thermodynamic adsorption analysis revealed that the removal rate of the four ions by RSBC was 22.14%, 8.95%, 18.75%, and 13.77%, respectively. Moreover, the adsorption mechanism was primarily chemical adsorption, including ion exchange, precipitation, and complexation, because of the binding effects of aromatic structures and polar groups. Additionally, biochar, with its porous structure and high ash content also provided favorable conditions for adsorption of those ions. Through this simple procedure, this work provides a potential strategy to produce biochar with a high adsorption capacity to remediate trace elements in contaminated solutions. [ABSTRACT FROM AUTHOR]

With the development of industry, large amounts of heavy metals are eliminated into the environment, which leads to contamination of important water resources, such as ground waters, surface waters, and lake waters. They can also get into drinking water and by ingestion, pollutants can accumulate in the human body where it manifests toxic effects on various systems and organs. In order to minimize the contamination of water resources and wastewater, the removal of heavy metals is being studied more and more through the use of various processes, such as adsorption, membrane filtration, ion exchange or coagulation. The aim of this review paper is a state-of -the-art discussion about the effective applications of different removal processes and sorbent materials for heavy metals removal from water resources. For conducting the study were consulted more than 50 literature sources from the most important electronic databases: Web of Science and SCOPUS. Several platforms such as Science Direct, Springer Link, CAB Abstracts and Taylor and Francis were also consulted. Processes we are talking about include the use of adsorbent materials, such as activated carbon, nanotubes, bio-sorbents and bio-chars, or various filtration processes, that include ultrafiltration, microfiltration, nanofiltration or reverse osmosis. However, of all the adsorbent materials, bio-sorbents have gained considerable attention for applications in water treatment, due to their cost-effectiveness, acceptable performance and high removal capacity. Their most important aspect is eco-friendly character, as most come from agricultural waste (peanuts, rice, lemon peel, cocoa shells, and coffee residues), soil and mineral deposits (bentonite, kaolin, and zeolite) or aquatic and terrestrial biomass (lignin, seaweed, algae). Bio-sorbents may be subjected to processes like electrostatic interaction, precipitation, chelation, complexation, to enhance their adsorption capacity. The research studies demonstrated that the removal rate is influenced by some parameters, like the pH of the aqueous media, the adsorbent dose, concentration of the metal, time of contact, temperature, and mixing or agitation speed. As a conclusion, the removal processes show good adsorption capacities for heavy metals, but further research are needed for successful applications of these methods for removal of chemical pollutants from drinking water. [ABSTRACT FROM AUTHOR]

In this study, rice straw biochar (BC), goethite (GT), and goethite-modified biochar (GBC) were prepared and their differences in adsorption characteristics and mechanisms of arsenic were explored to provide theoretical and data reference for future design of modified biochar, aiming to address adsorption mechanism weakness and improve the efficiency of arsenic removal in water. Various characterization methods were employed to evaluate the influence of pH, adsorption kinetics, isotherms, and chemical analyses of the materials. At temperatures of 283 K, 298 K, and 313 K, the maximum actual adsorption capacity followed the order GBC > GT > BC, while at 313 K, the maximum Langmuir adsorption capacity of GBC reached 149.63 mg/g which was 95.92 times that of BC and 6.27 times of GT. Due to precipitation and complexation mechanisms, GBC exhibited more superior arsenic adsorption capacities than BC and GT, contributing to total adsorption ranging from 88.9% to 94.2%. BC was dominated by complexation and ion exchange mechanisms in arsenic adsorption, with contribution proportions of 71.8%–77.6% and 19.1%–21.9%, respectively. In GT, the precipitation mechanism played a significant role in total adsorption, contributing from 78.0% to 84.7%. Although GBC has significant potential for removing arsenic from aqueous solutions, the findings suggest that its ion exchange capacity needs improvement. [ABSTRACT FROM AUTHOR]

The adsorption property of the costless green cellulose acetate (CA) was boosted by the dual modifications: inner modification by incorporating carboxylated graphene oxide (COOH-GO) into the CA spheres and outer modification by the surface modification of the COOH-GO@CA spheres by iminodiacetic acid (IDA) for removing Pb(II). The adsorption experiments of the Pb(II) proceeded in a batch mode to evaluate the adsorption property of the COOH-GO@CA@IDA spheres. The maximal Pb(II) adsorption capacity attained 613.30 mg/g within 90 min at pH = 5. The removal of Pb(II) reached its equilibrium within 20 min, and the removal % was almost 100% after 30 min at the low Pb(II) concentration. The Pb(II) adsorption mechanism was proposed according to the kinetics and isotherms studies; in addition, the zeta potential (ZP) measurements and X-ray Photoelectron Spectroscopy (XPS) analysis defined the adsorption pathways. By comparing the XPS spectra of the authentic and used COOH-GO@CA@IDA, it was deduced that the contributed chemical adsorption pathways are Lewis acid–base, precipitation, and complexation. The zeta potential (ZP) measurements demonstrated the electrostatic interaction participation in adsorbing the cationic Pb(II) species onto the negatively charged spheres (ZP = 14.2 mV at pH = 5). The unique channel-like pores of the COOH-GO@CA@IDA spheres suggested the pore-filling mechanism of Pb(II). The promising adsorption results and the superb recyclability character of COOH-GO@CA@IDA enable it to extend of the bench scale to the industrial scale. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the adsorption properties of La-activated biochar for pollutants in a binary coexistence system. Materials and methods: La was impregnated with walnut shells to prepare biochar and orthophosphate (OP) and inositol hexaphosphate (IHP) were adsorbed in the composite system. Results and discussion: At the same concentration (75 mg L−1), the overall phosphorus adsorption performance of biochar treatment (CK + BC) was considerably better than that of gypsum (CK + GP) and zeolite (CK + ZP). The maximum adsorption capacities of OP and IHP were 0.52 and 1.29 mg g−1, respectively. In the binary coexistence system, there is a competition among phosphorus species because of the number of adsorption sites on the surface of adsorbents and the blockage effect of pores. The fitting results of the adsorption kinetics and adsorption isotherm model show that the adsorption of phosphorus species is primarily controlled by chemical action. Conclusions: The adsorption mechanism may include electrostatic attraction, ligand exchange, precipitation, and complexation. [ABSTRACT FROM AUTHOR]