Adsorption behaviour and mechanisms of cadmium and nickel on rice straw biochars in single- and binary-metal systems

Pristine biochar performance investigation to remove metals in primary and secondary treated municipal wastewater for groundwater recharge application

In this study, pristine biochar derived from date palm at 500°C was used in batch reactors (simulating blending adsorbent in aeration tank) and fixed-bed columns (simulating holding adsorbent in fixed-bed reactors). The removal performance of the biochar was assessed toward single and mixed-metal solutions as well as synthetic primary and secondary treated wastewater for copper (Cu2+), iron (Fe2+), nickel (Ni2+) and zinc (Zn2+). The order of maximum adsorption capacities of the metal ions at pH 7 followed: Fe2+ (2.92/2.94 mg/g)>Cu2+(2.69/2.78 mg/g) >Zn2+(2.03/2.19 mg/g)>Ni2+(1.69/1.02 mg/g) in single/mixed-metal solutions and Zn2+(2.91/11.26 mg/g)>Fe2+(0.60/5.29 mg/g)>Cu2+(0.56/5.05 mg/g)>Ni2+(0.13/2.02 mg/g) in synthetic primary/secondary treated wastewater. Blending biochar in aeration tank reduced metal concentrations. The metal ion concentrations in the final effluent were below the World Health Organization drinking water limits (2, 0.3, 0.1 and 3 mg/L for Cu2+, Fe2+, Ni2+ and Zn2+, respectively) suggesting that treated secondary wastewater can be spread into potable aquifers following disinfection. The Freundlich and the Pseudo-second order models fit best the batch experimental data. Experimental data from column analysis fit well to the Thomas model. The adsorption of metal ions on the surface of biochar was confirmed by Scanning electron microscopy, Energy dispersive X-ray studies, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Desorption studies using different eluents demonstrated the reusability potential of the studied biochar.

Biosorbent derived from coffee husk for efficient removal of toxic heavy metals from wastewater

In this study, we investigated the feasibility on the utilization of coffee husk as biosorbents for the removal of heavy metal ions such as Pb²⁺ and Cd²⁺ from wastewater. Biochar was produced from coffee wastes and modified with sodium hydroxide to create functional groups on the surface and increase the specificic surface area. The resultant products were characterized by using various analytical methods such as scanning electron microscopy, specific area, surface functional group and zeta potential analysis. The as-prepared materials were employed as adsorbent to remove Pb²⁺ and Cd²⁺ ions from wastewater. The maximum sorption capacities of biosorbents were measured to be 116.3 and 139.5 mg g^-1 for Cd²⁺ and Pb²⁺, respectively, which is comparable to the conventional adsorbents. Kinetic studies showed that the sorption of Pb²⁺ and Cd²⁺ on biosorbents can be described by the Freundlich isotherm and second-order kinetic model. The coffee husk-derived biosorbent was capable of removing 89.6% of Pb²⁺ and 81.5% Cd²⁺ ions from wastewater, and therefore can be considered as low-cost and efficient adsorbent to remove heavy metal ions from wastewater.

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Characterization of Biochars Produced by Co-Pyrolysis of Hami Melon (Cantaloupes) Straw Mixed with Polypropylene and Their Adsorption Properties of Cadmium

Reuse of waste from Hami melon (cantaloupes) straws (HS) mingled with polypropylene (PP) ropes is necessary and beneficial to mitigate environmental pollution. The objective of this study was to investigate the characteristics and mechanisms of Cd2+ adsorption on biochars produced by co-pyrolysis of HS-PP with various mixing ratios. N2-sorption, scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), elemental analysis, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal gravity, and differential thermal gravity (TG/DTG) were applied to evaluate the physicochemical properties of materials. Batch adsorption experiments were carried out for investigating the effects of initial pH, Cd2+ concentration, and adsorption time. It was found that the Langmuir and pseudo-second-order models fitted best for the experimental data, indicating the dominant adsorption of co-pyrolysis biochars is via monolayer adsorption. Biochar derived at 4/1 mixing ratio of HS/PP by weight percentage had the highest adsorption capacity of 108.91 mg·g-1. Based on adsorption isotherm and kinetic analysis in combined with EDS, FTIR, and XRD analysis, it was concluded that the main adsorption mechanism of co-pyrolysis biochar involved the surface adsorption, cation exchange, complexation of Cd2+ with surface functional groups, and chemical precipitation. This study also demonstrates that agricultural wastes to biochar is a sustainable way to circular economy.

Synthesis of Magnetic Adsorbents Based Carbon Highly Efficient and Stable for Use in the Removal of Pb(II) and Cd(II) in Aqueous Solution

In this study, two alternative synthesis routes for magnetic adsorbents were evaluated to remove Pb(II) and Cd(II) in an aqueous solution. First, activated carbon was prepared from argan shells (C). One portion was doped with magnetite (Fe₃O₄+C) and the other with cobalt ferrite (CoFe₂O₄+C). Characterization studies showed that C has a high surface area (1635 m² g⁻¹) due to the development of microporosity. For Fe₃O₄+C the magnetic particles were nano-sized and penetrated the material’s texture, saturating the micropores. In contrast, CoFe₂O₄+C conserves the mesoporosity developed because most of the cobalt ferrite particles adhered to the exposed surface of the material. The adsorption capacity for Pb(II) was 389 mg g⁻¹ (1.88 mmol g⁻¹) and 249 mg g⁻¹ (1.20 mmol g⁻¹); while for Cd(II) was 269 mg g⁻¹ (2.39 mmol g⁻¹) and 264 mg g⁻¹ (2.35 mmol g⁻¹) for the Fe₃O₄+C and CoFe₂O₄+C, respectively. The predominant adsorption mechanism is the interaction between -FeOH groups with the cations in the solution, which are the main reason these adsorption capacities remain high in repeated adsorption cycles after regeneration with HNO₃. The results obtained are superior to studies previously reported in the literature, making these new materials a promising alternative for large-scale wastewater treatment processes using batch-type reactors.

Effects of biochar derived from sewage sludge and sewage sludge/cotton stalks on the immobilization and phytoavailability of Pb, Cu, and Zn in sandy loam soil

Co-pyrolysis of sewage sludge and straws has been used to improve the pore structure and reduce the ecological risks of heavy metals in sewage sludge-derived biochars. However, to date, no study has focused on the effects of biochar derived from sewage sludge/straws on the immobilization and phytoavailability of heavy metals in soil. Here, we studied the effects of biochar derived from sewage sludge/cotton stalks (SCB) and that derived from sewage sludge alone (SSB) on the remediation of sandy loam soil contaminated by Pb, Cu, and Zn. SCB amendment decreased the bioavailable forms of Pb, Cu, and Zn in the soil by 19.0%, 34.9%, and 18.2%, respectively, and reduced their accumulation in ryegrass by 28.6%, 50.1%, and 30.0%, respectively, compared with those by SSB amendment. Furthermore, SCB amendment transformed more metals from the acid-soluble fraction to the oxidizable fraction than SSB amendment, indicating that complexation played a more critical role in SCB amendment than in SSB amendment. Both biochar amendments effectively improved soil water holding capacity, increased the supply of available P, N, and K, and promoted ryegrass growth. The findings of this study show the benefits of SCB over SSB for the remediation of heavy metal-contaminated soil.

Nickel in soil and water: Sources, biogeochemistry, and remediation using biochar

Nickel (Ni) is a potentially toxic element that contaminates soil and water, threatens food and water security, and hinders sustainable development globally. Biochar has emerged as a promising novel material for remediating Ni-contaminated environments. However, the potential for pristine and functionalized biochars to immobilize/adsorb Ni in soil and water, and the mechanisms involved have not been systematically reviewed. Here, we critically review the different dimensions of Ni contamination and remediation in soil and water, including its occurrence and biogeochemical behavior under different environmental conditions and ecotoxicological hazards, and its remediation using biochar. Biochar is effective in immobilizing Ni in soil and water via ion exchange, electrostatic attraction, surface complexation, (co)precipitation, physical adsorption, and reduction due to the biogeochemistry of Ni and the interaction of Ni with surface functional groups and organic/inorganic compounds contained in biochar. The efficiency for Ni removal is consistently greater with functionalized than pristine biochars. Physical (e.g., ball milling) and chemical (e.g., alkali/acidic treatment) activation achieve higher surface area, porosity, and active surface groups on biochar that enhance Ni immobilization. This review highlights possible risks and challenges of biochar application in Ni remediation, suggests future research directions, and discusses implications for environmental agencies and decision-makers.

Crop straw-derived biochar alleviated cadmium and copper phytotoxicity by reducing bioavailability and accumulation in a field experiment of rice-rape-corn rotation system

Biochar has the potential to control the bioavailability and transformation of heavy metals in soil, thereby ensuring the safe crop production. A three seasons field experiment was conducted to investigate the effect of crop straw-derived biochar on the bioavailability and crop accumulation of Cd and Cu in contaminated soil. Wheat straw biochar (WSB), corn stalk biochar (CSB), and rice husk biochar (RHB) were applied at the rate of 0, 1.125, and 2.25 × 10⁴ kg ha^-1, respectively. The results showed that all types of biochar significantly increased soil pH, organic carbon and cation exchangeable capacity (CEC), compared to the control. The reduction in DTPA extractable Cd and Cu contents was much greater under high dosage biochar application, with a prominence at RHB treatment throughout the three cropping seasons, compared to the control. Moreover, the biological accumulation of Cd and Cu in the grains of rapeseed and corn significantly decreased after biochar application. Linear regression also confirmed the effective role of biochar in controlling the translocation and accumulation of Cd and Cu due to their inactive bioavailability. In addition, the sequential extraction indicated that exchangeable fraction (EXF) of Cu and Cd had decreased, while residual fraction (RSF) had increased under all biochar amendments. Contrarily, the oxidizable fraction (OXF) of Cd decreased while OXF of Cu increased under biochar treatments. Biochar application, especially RHB, could be an effective measure to enhance Cd and Cu adsorption and immobilization in polluted soils and thereby reducing its uptake and translocation to crops.

Application of pinewood waste-derived biochar for the removal of nitrate and phosphate from single and binary solutions

We developed biochar by pyrolysis of pinewood wastes at different temperatures and investigated its potential to nitrate and phosphate from single and binary solutions. An in-depth characterization of biochar was carried out to study its physical, surface morphological and chemical characteristics using X-ray diffraction, Fourier transform infrared and scanning electron microscopy analyses. The impact of pyrolysis temperatures (300-600 °C) on the biochar yield, the biochar's elemental composition, and its adsorption characteristics was examined. Biochar produced at 600 °C showed a maximum uptake for both nitrate and phosphate due to its high C content (63.8%), pore volume (0.201 cm³/g), surface area (204.2 m²/g) and reduced acidic binding groups. The influence of pH, initial solute concentrations, contact time on the removal of a single solute at a time by biochar was examined. Results revealed that pinewood-derived biochar had its maximum performance at pH 2, with predicted equilibrium uptakes of 20.5 and 4.20 mg/g for phosphate and nitrate, respectively at initial solute concentrations of 60 mg/L within 360 min. The single solute isotherm was studied using the Freundlich, Langmuir and Toth models, and kinetics was described using the pseudo-first and -second order models. While using dual-solutes, biochar showed preference towards phosphate as confirmed by high affinity factor. The dual-solute kinetic experiments showed that around 95% of phosphate was removed within 45 min, whereas it took 240 min to achieve 95% total nitrate removal from the mixture. Thus, the biochar removes phosphate preferentially with high selectivity as compared to nitrate.

Impact of Biochar on Soil Properties, Pore Water Properties, and Available Cadmium

Some effects of biochar on soil properties (such as pore water DOC) are not very clear. The changes of soil properties [cation exchange capacity (CEC)], pore water properties [pH, dissolved organic carbon (DOC), and Cd concentration (C_PW-Cd)], Cd concentration measured by diffusive gradients in thin films (C_DGT-Cd), and available Cd content (Cd in weak acid extractable state and reducible state, C_BCR-Cd) determined by the BCR sequential extraction procedure over time after biochar addition were studied by soil incubation and potted corn experiments with five soils from a mining area. The results showed increases of 20.3%-64.6% in CEC and 0.34-1.02 in pH (both p < 0.05) in the soil incubation after adding biochar. The DOC concentration was reduced by 8.2%-33.2% (p < 0.05). C_PW-Cd, C_DGT-Cd, and C_BCR-Cd decreased by 14.2%-47.2%, 15.3%-47.9%, and 22.3%-61.4%, respectively. During the corn cultivation phase, CEC increased by 5.1%-29.0%, and DOC concentration decreased by 10.4%-41.3% (p < 0.05). C_PW-Cd, C_DGT-Cd, and C_BCR-Cd decreased by 5.9%-22.4%, 7.2%-25.1%, and 10.5%-64.8%, respectively. Biochar effectively increased the biomass of corn roots and reduced the concentration of Cd in the roots. Biochar altered the properties of soil and pore water, reduced the bioavailability of Cd in soil, and mitigated the harm to corn caused by Cd.

Rapid Separation and Efficient Removal of Cd Based on Enhancing Surface Precipitation by Carbonate-Modified Biochar

The high buoyancy of biochar makes its application difficult in Cd removal. In this paper, the content of minerals was increased by modifying carbonate on the biochar surface using the vacuum impregnation method. Enhancing surface precipitation between minerals and Cd introduced a correspondingly great number of Cd precipitates on the biochar surface, leading to the rapid precipitation and separation of buoyant biochar. The physical and chemical properties of carbonate-modified biochar and the adsorption mechanism of Cd were comprehensively studied by jar tests, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results showed that the adsorption of Cd by carbonate-modified biochar was controlled by multiple mechanisms, including surface precipitation, surface complexation, and Cd-π interaction. Surface precipitation dominated the removal of Cd. The contributions of Cd removal mechanisms indicated that the contribution proportions of minerals increased from 89.73 to 97.9% when the pyrolysis temperature increased from 300 to 600 °C, while the contribution proportions of Cd-π binding decreased from 9.99 to 2.08%. Meanwhile, oxygen functional groups have only a marginal effect on Cd adsorption. Besides, the results revealed that the higher surface hydrophobicity and the lower polarity were conducive to biochar separation from water. The Cd removal method can provide efficient adsorption and rapid separation, making it possible to use biochar in water treatment.

Biochar heavy metal removal in aqueous solution depends on feedstock type and pyrolysis purging gas

The effectiveness of biochar as a sorptive material to remove contaminants, particularly heavy metals, from water is dependent on biomass type and pyrolysis condition. Biochars were produced from pulp mill sludge (PMS) and rice straw (RS) with nitrogen (N₂) or carbon dioxide (CO₂) as the purging gas. The sorptive capacity of the biochars for cadmium(II), copper(II), nickel(II) and lead(II) was studied. The heavy metal adsorption capacity was mainly affected by biomass type, with biochars adsorption capacities higher for lead(II) (109.9-256.4 mg g^-1) than for nickel(II) (40.2-64.1 mg g^-1), cadmium(II) (29.5-42.7 mg g^-1) and copper(II) (18.5-39.4 mg g^-1) based on the Langmuir adsorption model. The highest lead(II) adsorption capacities for PMS and RS biochars were 256.4 and 133.3 mg g^-1, respectively, when generated using N₂ as the purging gas. The corresponding lead(II) adsorption capacities were 250.0 and 109.9 mg g^-1, respectively, when generated using CO₂ as the purging gas. According to the intraparticle diffusion model, 30-62% of heavy metal adsorption was achieved in 1 h; film diffusion was the rate-dominating step, whereas pore diffusion was a rate-limiting step. Ion exchange and complexation between heavy metals and biochar surface functional groups such as carbonyl and hydroxyl groups were effective mechanisms for heavy metal sorption from the aqueous solution. We conclude that proper selection of both the feedstock type and the purging gas is important in designing biochars for the effective removal of potentially toxic metals from wastewater.

Mechanism and industrial application feasibility analysis on microwave-assisted rapid synthesis of amino-carboxyl functionalized cellulose for enhanced heavy metal removal

The study presented the successful microwave-assisted (MW-assisted) preparation of a novel adsorbent derived from rice straw (RS_MW-AC) and explored its adsorption performance toward heavy metal ions from water. The RS_MW-AC was rapidly synthesized through pretreatment and one step grafting via the MW-assisted approach. The quantitative predictive correlations between target performance of RS_MW-AC and process parameters were obtained through the response surface methodology (RSM). Meanwhile, the optimal preparation process conditions were determined: NaOH solution concentration, 20%; MW irradiation temperature for pretreatment, 100 and 150 °C; MW irradiation time for pretreatment and grafting, 10 and 60 min; EDTAD-RS mass ratio, 3. The RS_MW-AC showed a good adsorption of different heavy metal ions from water (152.39, 55.46, 52.91, 35.60 and 20.11 mg g^-1 for Pb(Ⅱ), Mn(Ⅱ), Cd(Ⅱ), Cu(Ⅱ) and Ni(Ⅱ), respectively). The adsorption behaviors followed the Langmuir model and pseudo second-order kinetics model with a highly significant correlation. Also of note was that amino and carboxyl groups were successfully introduced on the rice straw based on characterization results. Furthermore, preparation mechanism was explored to reveal reasons why microwave irradiation could accelerate the preparation of the adsorbent; its adsorption process was dominated by electrostatic attraction and chelation. Finally, the study made the industrial application feasibility analysis of MW-assisted approach used for pretreatment and graft reaction of agro-waste biomass.

Adsorption of sulfonamides on biochars derived from waste residues and its mechanism

Waste residues have been prepared as biochar (BC) adsorbents to remove sulfonamides (SAs) at low cost, but the mechanisms of the differences in the SA adsorption performance of different BCs are not clear. Thus, the adsorption characteristics of two SAs (sulfadiazine and sulfathiazole) on three BCs derived from waste residues (sewage sludge (SB), pig manure (PB), and rice straw (RB)) were investigated. The results showed that the adsorption mechanism was chemisorption and RB was the preferred BC under the different tested conditions (pH, Ca²⁺, and humic acid), followed by PB and SB. To interpret the phenomena, FTIR, XRD, and XPS analyses were performed and results indicated that SB had the lowest C content, and there was a very significant difference in the concentrations of the two O functional groups (C˭O and C‒O) for PB and RB (P < 0.01). Density functional theory calculations revealed that the mechanisms of SA adsorption onto BCs were mainly through π-π electron donor acceptor interactions and H bonds. There was no significant difference in the π interactions between the SAs-BC containing C‒O (BC(OH)) and the SAs-BC containing C˭O (BC(C˭O)), whereas the H bond strength of SAs-BC(OH) was much stronger than that of SAs-BC(C˭O).

Recycle of Fenton sludge through one-step synthesis of aminated magnetic hydrochar for Pb2+ removal from wastewater

In order to achieve proper disposal of Fenton sludge, a new recycle method for preparing adsorbents based on one-step hydrothermal carbonization synthesis of aminated hydrochar from Fenton sludge (AHFS) was developed. It was found that AHFS prepared at 340 °C for 60 min showed Pb²⁺ adsorption capacity as high as 359.83 mg g^-1. Adsorption kinetics and thermodynamics results indicated that chemical interaction, intra-particle diffusion and monolayer homogeneous surface of AHFS dominated in adsorption process. The contribution proportion of different mechanisms, including cation-exchange (43.15%), acidic groups complexation (28.17%) and amino groups complexation (24.06%) to overall Pb²⁺ adsorption, demonstrated that complexation of surface functional groups played the dominated role in the adsorption process. Especially, the addition of amino was conducive to the increased adsorption capacity of hydrochar. In addition, according to the regeneration test, the magnetic AHFS exhibited a satisfactory reproducibility and recyclability. These findings illustrated that the synthesis of aminated magnetic hydrochar not only provided an innovative and efficient heavy metal adsorbent to remove Pb²⁺ from wastewater, but also explored a new method for the resource utilization of Fenton sludge.

Removal of iron, zinc, and nickel-ions using nano bentonite and its applications on power station wastewater

Removal of high concentrations of toxic heavy metals from wastewater is very important within the environmental field because heavy metals pollution a serious environmental problem due to them being nonbiodegradable. This study shed some light on the use of Nano bentonite as an adsorbent for the elimination of Iron, Zinc, and Nickel ions from wastewater, and the optimum conditions were evaluated to find out thermodynamic and kinetic parameters and equilibrium adsorption models have been applied. The results showed that adsorption percentage increases with increasing temperature, speed of rotation, and volume of solution, but decreases with adsorbent dose and initial concentration increase. The adsorption process has fit pseudo-second-order kinetic model Langmuir and Freundlich adsorption isotherm models were applied to analyze adsorption data and both were found to apply to these adsorption processes. Thermodynamic parameters e.g., ΔG^o, ΔS^o, and ΔH^o of the adsorption process were found to be endothermic. Finally, the Nano bentonite was observed to be more powerful for the removal of Fe (III), Zn (II), and Ni (II) at the same experimental conditions.

A meta-analysis of heavy metal bioavailability response to biochar aging: Importance of soil and biochar properties

Biochar has been widely applied to remediate the heavy metal-polluted soils, whereas biochar aging can induce the changes of the biochar physic-chemical properties. Afterwards, the bioavailability of heavy metals (BHM) will vary in soils which likely increase the unstable fractions of heavy metals and the following environmental risks. To explore the biochar aging effects on the BHM changes in responses to the variation of experimental conditions and biochar properties, a meta-analysis for the literatures published before May 2020 was conducted. A sum of 257 independent observations from 22 published papers was obtained. The results from the analysis of boosted regression tree showed that the soil pH was the most important factor influencing the BHM changes in biochar amended soil, followed by soil texture, aging time and biochar pyrolysis temperature. The results of this review showed that the BHM was decreased by 16.9%, 28.7% and 6.4% in weakly acid soil (pH 6.00-6.99), coarse- and medium-textured soils, respectively, but increased by 149% and 121% in the alkaline (pH > 8.00) and fine-textured soils. The BHM declined in the soils amended with biochar pyrolyzed at relative high temperature (> 500 °C), and increased during aging in soils amended with biochar pyrolyzed at relatively low temperature (401-500 °C). In terms of diverse immobilized heavy metals, only bioavailable Zn in soil decreased after aging. However, there was no significant changes in Cd, Cu and Pb's bioavalability. Besides, the BHM was decreased by 18.6% within the short-term (less than one year) biochar aging, while showed inverse trend during the longer aging processes. Besides, the application of lignin-enriched biochar may counteract the positive effects of the biochar aging on BHM. Our works may promote the interpretation of the interference factors on the BHM changes and filled the research gaps on biochar aging process in soils.

Sorption of diethyl phthalate and cadmium by pig carcass and green waste-derived biochars under single and binary systems

Potentially toxic elements (PTEs) and phthalic acid esters (PAEs) often coexist in contaminated soils. Their co-existence may affect the mutual sorption behavior, and thereby influence their bioavailability and fate in soils. To our best knowledge, the impacts of plant-and animal-derived biochar on the competitive sorption-desorption of PTEs and PAEs in soils with different organic carbon content have not been studied up to date. Therefore, in this study, batch sorption-desorption experiments were conducted to investigate the influence of biochars derived from pig carcass and Platanus orientalis branches on the mono- and competitive sorption of cadmium (Cd²⁺) and diethyl phthalate (DEP) in soils with high (HS) and low (LS) organic carbon content. The DEP sorption was well described by Freundlich isotherm model, while Cd²⁺ sorption fitted better with the Langmuir isotherm model. Application of both biochars enhanced soil sorption of DEP, which increased as the application doses increased. The HS showed a stronger affinity to both DEP and Cd²⁺ than the LS. In the LS, the pig carcass biochar (PB) addition was more effective to increase the sorption capacity of Cd²⁺ and DEP and to reduce their desorption than woody biochar (WB) treatments. Moreover, the co-existing of Cd²⁺ could reduce the sorption of DEP, especially in the LS. The presence of DEP enhanced Cd²⁺ sorption in LS treated by both biochars, but the sorption of Cd²⁺ was suppressed with DEP addition in the PB-amended HS. In conclusion, the soil sorption capacity of DEP and Cd²⁺ was affected by biochar type, application dose and soil organic carbon content. The reciprocal effect between DEP and Cd²⁺ was also a crucial factor influencing their sorption/desorption by biochar. Therefore, PB and WB, especially PB, can be used for metal/DEP immobilization due to enhanced sorption. This approach is applicable for future remediation of soils contaminated by PTEs and PAEs.

Qualitative and quantitative adsorption mechanisms of zinc ions from aqueous solutions onto dead carp derived biochar

The adsorption mechanisms of Zn2+ on carp biochars mainly include precipitation with minerals, exchange with cations, and complexation with OFGs. The pyrolysis temperature of carp biochars has a significant effect on the mechanisms of Zn2+ adsorption.

Competitive and non-competitive zinc, copper and lead biosorption from aqueous solutions onto flax fibers

Competitive and non-competitive batch experiments were conducted on flax fibers to study Zn²⁺, Cu²⁺, and Pb²⁺ ions biosorption performance. Biosorption efficiency was dependent on contact time, pH, and biosorbent concentration. The results under competitive conditions were different from those obtained in non-competitive form. A high affinity of lead, with a selectivity sequence in general of Pb > Cu > Zn was observed. The biosorption data fitted very well the Langmuir model for lead in both types of solutions and for zinc and copper in the monometal form. The fit with the Freundlich model was not as successful, except for copper in the ternary system. Regarding zinc under competitive conditions, the sorption process was quite difficult and thus the equilibrium data could not fit well the adsorption models. The maximum adsorption capacities (mmol.kg^-1) were respectively 112, 122 and 71, for Pb, Cu and Zn in the single metal ion solution and 82, 57 and 8 only in the ternary, showing thus a high competition between metal ions when added simultaneously. Overall, lead could still be efficiently removed in spite of the presence of other ions while zinc would be overcome in the presence of lead and copper.

Mechanisms for the removal of Cd(II) and Cu(II) from aqueous solution and mine water by biochars derived from agricultural wastes

The capacity of biochars derived from agricultural wastes to remove Cd(II) and Cu(II) from aqueous solution and contaminated mine water was evaluated using laboratory-based batch sorption experiments. To examine immobilization of heavy metals, biochars produced in a commercial-scale mobile pyrolizer from feedstocks: poultry litter; lucerne shoot; vetch shoot; canola shoot; wheat straws; and sugar-gum wood, were tested in a liquid-based system. Biochars were characterized by FTIR, XPS and XRD before and after the mine water treatment. Lucerne biochar had the highest Langmuir sorption capacity of Cd(II) (6.28 mg g^-1) and vetch-derived biochar had the highest Cu(II) sorption capacity (18.0 mg g^-1) at pH 5.5. All the biochars exhibited higher sorption capacity for Cu(II) than for Cd(II). The smaller ionic radius and higher electronegativity of Cu(II), and the PO₄^3-, CO₃^2- and N-containing functional groups of biochars enhanced their binding affinity. The results demonstrated that poultry litter-derived biochar was effective at removal of the Cd(II) and Cu(II) from mine water up to the levels recommended by the World Health Organisation. The results revealed that precipitation with CO₃^2- and PO₄^3-, complexation with -OH and -COOH groups and electrostatic interaction with O-containing surface functional groups were the main mechanisms involved in the removal of multi-metals by biochars, and that selection of feedstock materials for biochar production is important to maximise remediation of multi-metals in contaminated water.

Adsorption of As(V) and Ni(II) by Fe-Biochar composite fabricated by co-pyrolysis of orange peel and red mud

This study aimed to compare the adsorption performance of Fe-biochar composites (Fe-C-N₂ and Fe-C-CO₂), fabricated by co-pyrolysis of red mud and orange peel in N₂ and CO₂, for As(V) and Ni(II). By the syngas production comparison test, it was confirmed that CO₂ was more advantageous than N₂ as a pyrolytic medium gas to produce more CO. The resulting Fe-biochar composite showed the aggregate morphology consisting of different Fe phases (magnetite or metal Fe) from the inherent hematite phase in red mud and carbonized carbon matrix, and there was no distinct difference between the structural shapes of two Fe-biochar composites. Adsorption experiments showed that the adsorption capacities for As(V) and Ni(II) in single mode were almost similar with 7.5 and 16.2 mg g^-1 for Fe-C-N₂ and 5.6 and 15.1 mg g^-1 for Fe-C-CO₂, respectively. The adsorption ability of Fe-C-CO₂ for both As(V) and Ni(II) was further enhanced in binary adsorption mode (As(V): 13.4 mg g^-1, Ni(II):17.6 mg g^-1) through additional removal of those ions by Ni(II)-As(V) complexation. The overall results demonstrated CO₂-assisted pyrolysis can provide a viable platform to convert waste materials into fuel gases and environmental media for co-adsorption of cationic and anionic heavy metals.

Qualitative and quantitative characterization of adsorption mechanisms for Cd2+ by silicon-rich biochar

The adsorption characteristics of rice-husk biochar (RHB) rich in silicon (Si) for Cd²⁺ in solution and soil were investigated. Three biochars were produced at different pyrolytic temperatures of 300 °C(RHB300), 500 °C(RHB500) and 700 °C (RHB700). The pH effect, adsorption kinetics and isotherms were examined, and chemical analyses of Cd²⁺-loaded biochars were conducted by SEM-EDS, FTIR, XRD and Boehm titration. Biochars produced at higher temperature have much larger pH and surface area, resulting in greater adsorption capacities and faster adsorption kinetics. Maximum adsorption capacities calculated from Langmuir isotherm were 62.75, 77.37 and 93.50 mg/g for RHB300, RHB500 and RHB700, respectively. Cd²⁺ adsorption was primarily attributed to cation exchange and precipitation, which jointly contributed 59.55% (RHB300) to 76.05% (RHB700) of the total adsorption, but the mechanisms of complexation and coordination were of minor importance in total adsorption. The relationship of each mechanism with biochar's properties was further discussed. Si-containing minerals within biochar made a much larger contribution to precipitation than total adsorption, as the respective contribution proportion were 33.92% and 8.33% on average. When added to highly Cd-polluted soil, the biochars could effectively reduce the availability of Cd²⁺ after incubation for 35 days, and ameliorate soil acidification through the speediness of Si released into soil solutions. These demonstrate that rice husk-derived biochar, produced at high temperatures, can be suitable applied to mitigate Cd-contamination of soil and water, and the presented analyses shed light on the mechanisms underlying the adsorption by this Si-rich biochar.

Transport and transformation of Cd between biochar and soil under combined dry-wet and freeze-thaw aging

We quantified the transport and transformation of Cd in historically contaminated soil (OS) and artificially contaminated soil (NS), treated with 3% (w/w) rice straw biochar prepared at 400 °C (BC400) and 700 °C (BC700) under combined dry-wet and freeze-thaw cycles for 72 days simulating the natural aging process of 8 years. An improved three-layer mesh experiment was developed to simulate the natural situation in field. The result showed that the total Cd concentration increased in the biochar but decreased in the soil, suggesting that Cd was transported from the soil into the biochar during the aging process. The total Cd concentration in BC400 treated with both soils was higher than that in BC700 treated with both soils, however, BC700 displayed stronger ability on immobilizing Cd than BC400 because the Tessier exchangeable Cd fraction in BC700 treated both soils was lower than that in BC400 treated with both soils. The average Tessier exchangeable Cd fraction in the soil and biochar decreased in all treatments during the aging process, indicating that Cd tended to be more stable in the soil for a long term. The result also showed that biochar could immobilizate Cd by decreasing the Tessier exchangeable Cd fraction of soil and biochar, and the quantitative contributions of biochar and soil to Cd immobilization were different in OS and NS treated with BC400 and BC700. The biochar contribution to the reduction in Tessier exchangeable Cd fraction accounted for 40-85% in NS treated with BC400 and 54-82% in NS treated with BC700. However, in OS treated with biochar, the biochar contribution accounted for nearly 100%, and soil had almost no contribution. In summary, OS did not contribute to Cd immobilization, while NS contributed nearly 50% to Cd immobilization, and BC700 was more effective in immobilizing Cd than BC400.

In situ preparation of magnetic hydrochar by co-hydrothermal treatment of waste vinasse with red mud and its adsorption property for Pb(II) in aqueous solution

Herein, a new magnetic hydrochar was prepared through co-hydrothermal treatment of vinasse with red mud, two abundant industrial wastes, and its adsorption property was evaluated on Pb(II), selected model ion in aqueous solution. During co-hydrothermal process, Fe₂O₃ species in red mud was reduced to Fe₃O₄ form, hereby, in situ magnetization of hydrochar was achieved, which was confirmed by characterization studies. Produced hydrochar with porous structure (V_total = 0.071 cm³/g and BET surface area = 23 m²/g) had saturation magnetization (44.7 emu/g), providing easier separation from water by a magnet. Maximum Pb(II) adsorption was favored at pH ≥ 5.0 within 120 min of equilibrium time and Freundlich isotherm model was preferable. The contribution percentage of different mechanisms including cation-exchange (40.8 %), (electrostatic attraction + "cation-π" interaction) (31.2 %), precipitation (25.4 %) and complexation (2.6 %) to overall Pb(II) adsorption indicated that cation-exchange was the dominant mechanism. Finally, application to fortified real water demonstrated that in situ magnetic hydrochar produced by suggested approach was successful at adsorptive removal of Pb(II) from water with no matrix effects.

Synthesis of amino-functionalized biochar/spinel ferrite magnetic composites for low-cost and efficient elimination of Ni(II) from wastewater

Novel amino-modified rice bran biochar/MgFeAlO₄ (RB@MgFeAlO₄-NH₂) magnetic composites were synthesized via a simple one-step solvothermal approach and applied for removing toxic Ni(II) from wastewater. The elimination process and sorption performance of Ni(II) on RB@MgFeAlO₄-NH₂ were analyzed by combining batch experiments and spectral techniques. The sorption isotherms and kinetic data indicated that Ni(II) sorption on RB@MgFeAlO₄-NH₂ was monolayer and rapid. The experimental results confirmed that the obtained RB@MgFeAlO₄-NH₂ magnetic composite had high sorption capacity for Ni(II). The maximum sorption capacity of Ni(II) on RB@MgFeAlO₄-NH₂ was 201.62 mg g^-1. The researches based on the sorption mechanism showed that the ion exchange mechanism accounted for 76.51% of Ni(II) sorption. In addition, the amino, carboxyl and hydroxyl functional groups were also involved in the complexation with Ni(II). In view of its multiple advantages of environmental friendliness, low cost, easy magnetic separation and high sorption capacity, RB@MgFeAlO₄-NH₂ will be an excellent adsorbent for low-cost and efficient elimination of Ni(II) from aqueous solutions.

An experimental study about the effects of phosphorus loading in river sediment on the transport of lead and cadmium at sediment-water interface

Phosphorus (P) in the river sediment plays an important role in the fate and transport of heavy metals at sediment-water interface of the aquatic eutrophication environment. To explicate the effect of P loading, the sediments with different P contents were employed in this study to experimentally investigate the adsorption/desorption of Pb²⁺ and Cd²⁺ and the releasing behavior of P during the adsorption/desorption processes. Results illustrated a strong affinity between Pb²⁺ ions and the P-containing sediments in both single Pb and binary Pb + Cd systems. In single-metal systems, the Pb²⁺ adsorption capacities of all types of sediments (15.04-19.44 mg g^-1) were higher than those for Cd²⁺ (4.68-5.56 mg g^-1). While in binary-metal systems, the Pb²⁺ adsorption was slightly influenced by the coexisting Cd²⁺, but the Cd²⁺ adsorption capacities were decreased by over 5 times. Moreover, the adsorption amount and retention ability of Pb²⁺ on sediment were enhanced by increasing content of P in the sediment. Meanwhile, the releasing of P was also closely depended and significantly inhibited by the Pb²⁺ attached on the sediment. The P release amounts during the desorption processes of Pb- and Pb + Cd-loaded sediments were over 50 times lower than those from the raw sediments (sediments without heavy metals adsorbed), but the values decreased by a factor of two for the single Cd-loaded sediments. Furthermore, the results of X-ray photoelectron spectroscopy indicated the crucial role of P loading in Pb transport in the sediment and overlaying water. The findings in this study showed important implications for the transport of heavy metals and P at the sediment-water interface and offered new insights for further explicating the mechanisms of secondary pollution caused by heavy metals and P in aquatic eutrophication environment.

Valorization of agro-industry residues in the building and environmental sector: A review

Environmental pollution has become a relevant issue as the population rises and resources decrease. Reuse and recycling still have the greatest potential as they turn the waste into a new resource, representing the 'closed-loop' step of a circular economy (CE). Looking for new applications for agro-industry waste represents both an environmental issue, as its incorrect disposal is a cause of pollution, and a chance to exploit zero-cost natural wastes. The present review, with around 200 articles examined, focuses on possible reuses of these residues in (a) building construction, as additives to produce thermal and acoustic insulation panels, and (b) in water treatments, exploited for removal of pollutants. The selected materials (coconut, coffee, corn, cotton and rice) have industry production wastes with suitable applications in both sectors and huge worldwide availability; their reuse may thus represent a new resource, with an impact based on the production rate and the possible replacement of current inorganic materials. Along with possible implementation of the selected materials in the building industry and environmental engineering, a brief description of the production and supply chain are provided.

Competitive adsorption behaviour and mechanisms of cadmium, nickel and ammonium from aqueous solution by fresh and ageing rice straw biochars

In this study, competitive adsorption behaviour and mechanisms of Cd²⁺, Ni²⁺ and NH₄⁺ by fresh and artificially ageing biochars produced from rice straw at 400 and 700 °C (RB400, RB700, HRB400 and HRB700) were investigated. Cd²⁺ competed with Ni²⁺ and NH₄⁺ for the overlapped adsorption sites on the biochars. For Cd²⁺ and Ni²⁺ adsorption, cation exchange (Q_ci) and mineral co-precipitation (Q_cp) were the primary mechanisms for the low-temperature and high-temperature biochars, respectively. However, the other potential mechanisms (Q_co) made the greatest contributions to NH₄⁺ adsorption (>60%). Cd²⁺ and Ni²⁺ competition increased the proportions of mineral co-precipitation (Q_cp) and other potential mechanisms (Q_co) but decreased that of cation exchange (Q_ci) mechanism. Biochar ageing increased the contribution of surface complexation (Q_cf) mechanism, especially for the low-temperature biochars. This study indicated that biochar aging and types and states of adsorbates should be considered when biochars were applied to remove contaminants.

Lead competition alters the zinc adsorption mechanism on animal-derived biochar

In this study, the adsorption behaviors and mechanisms of Pb(II) and Zn(II) by animal-derived biochar (ADB) in single and binary metal systems were comparatively investigated. ADB contains considerable amounts of Ca/P components and is mainly composed of hydroxyapatite (HAP), which plays an important role in the adsorption of Pb(II) and Zn(II). The maximum adsorption capacities of Pb(II) and Zn(II) on ADB were in the order of Zn(II)-single (3.23 mmol g^-1) > Pb(II)-single (2.74 mmol g^-1) ≈ Pb(II)-binary (2.71 mmol g^-1) > Zn(II)-binary (2.31 mmol g^-1). In the single metal system, approximately 99.9% of the adsorbed Pb(II) existed as Pb₅(PO₄)₃Cl, while the dominant adsorption mechanism of Zn(II) was cation exchange, followed by precipitation, accounting for 78.0%-80.6% and 19.4%-21.5% of the adsorption capacity, respectively. These findings were verified by X-ray diffraction refinement, X-ray photoelectron spectroscopy, metal speciation modeling, and Ca(II) exchange experiment. In the binary metal system, the proportion and form of Pb(II) precipitate remained unchanged. However, the binding of Zn(II) to ADB was completely dependent on the cation exchange with Ca(II), and no remarkable Zn(II) precipitation was observed. Phosphate released from HAP preferentially precipitated with Pb(II) than with Zn(II) when they coexisted. Consequently, Pb(II) competition may alter the Zn(II) adsorption mechanism on ADB. Nonetheless, ADB could serve as an efficient biochar for the simultaneous immobilization of Pb(II) and Zn(II) via different mechanisms.

Wheat Straws and Corn Straws as Adsorbents for the Removal of Cr(VI) and Cr(III) from Aqueous Solution: Kinetics, Isotherm, and Mechanism

In this paper, the adsorption properties of wheat straw (WS) and corn straw (CS) for Cr(VI) and Cr(III) in solution were studied. The effects of adsorption time, pH of the solution, temperature, and initial concentration of metal ions on adsorption capacity were investigated. The adsorption mechanism was discussed. The results showed that the adsorption isotherms of WS and CS for Cr(VI) and Cr(III) satisfied the Langmuir equation. By fitting the Langmuir equation, the saturated adsorption capacity of WS for Cr(VI) and Cr(III) can reach 125.6 and 68.9 mg g^-1, and that of CS for Cr(VI) and Cr(III) can reach 87.4 and 62.3 mg g^-1 , respectively. The adsorption kinetics conformed to the pseudo-second-order kinetic equation. The effect of temperature on the adsorption capacity was not significant. Physical diffusion and chemical adsorption coexist in the process of adsorption of metal ions by straws, and chemical adsorption is dominant, and the effect of physical diffusion on the chemical adsorption rate can be neglected. It can be seen from the experimental results that the treatment of chromium-containing wastewater by using cheap and easily available wheat straw and corn straw had a remarkable effect. The adsorbed straw could be completely desorbed and had excellent recyclability, indicating that the straws are ideal adsorbents.

Self-assembly biochar colloids mycelial pellet for heavy metal removal from aqueous solution

To effectively improve the heavy metal removal efficiency and stability of biomass adsorbents, a novel biochar colloids-mycelial pellets (BC-MP) composite was prepared via a biological assembly method. BC-MP was successfully produced with increased surface area and multisorption sites by physical adsorption, electrostatic interaction and hydrogen-bond formation between BC and extracellular polymers on MP. To investigate the performance and mechanisms of heavy metal adsorption by BC-MP, batch experiments were conducted with cadmium (Cd (II)) as the model pollutant. Results showed that BC-MP had higher removal efficiency (57.66%) compared to BC (5.45%) and MP (38.45%), respectively, due to the synergistic effect. The maximum adsorption capacity of Cd (II) on BC-MP was 102.04 mg/g based on Langmuir isotherm model. Adsorption kinetics analysis indicated that chemical sorption was the key factor controlling the adsorption of Cd (II) onto BC-MP. Multiple characterization tests revealed that the main mechanisms of the adsorption process were surface complexation, cation exchange and precipitation. The BC-MP composite showed excellent heavy metal removal efficiency with long-term adsorption stability, suggesting its potential as a promising biosorbent for heavy metal removal from industrial wastewater.

Comparison of adsorption behavior studies of Cd2+ by vermicompost biochar and KMnO4-modified vermicompost biochar

Cd²⁺ pollution in aquatic environments can pose a serious threat to human health. Biochar can remove Cd²⁺ from aquatic environments, but the Cd²⁺adsorption capacity of conventional biochar is low, therefore, we focused on exploring the Cd²⁺ adsorption capacity of modified biochar. In this study, KMnO₄ was used to modify vermicompost biochar (VBC), and static adsorption tests for Cd²⁺ were carried out. The biochar properties and its adsorption efficiency toward Cd²⁺ before and after modification were studied by kinetics and isotherm model fitting, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Additionally, an adsorption mechanism was discussed. The results showed that the KMnO₄-modification resulted in a successful loading of the vermicompost biochar with MnO₂, which greatly improved its adsorption capacity for Cd²⁺. The adsorption of Cd²⁺ by VBC and MVBC was a spontaneous, endothermic, and monolayer chemical adsorption process. Mineral precipitation mechanism accounted for the largest proportion, and CdCO₃ was the main precipitate. After modification the proportion of surface precipitation and other mechanisms (π-electron coordination and the inner/outer sphere surface coordination) increased，while adsorption via cation exchange, oxygen-containing functional groups, physical adsorption and electrostatic attraction reduced. Hence, KMnO₄ modification has a significant effect on the Cd²⁺ adsorption behavior of vermicompost biochar.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Optimization of biochar preparation from the stem of Eichhornia crassipes using response surface methodology on adsorption of Cd2

In this study, preparation of Eichhornia crassipes stem biochar (ECSBC) was optimized and applied for the removal of Cd²⁺ from aqueous solution. To obtain the best adsorption capacity of ECSBC, the response surface methodology (RSM) was used to optimize the preparation conditions of ECSBC (OECSBC). The interactions among heating time (X₁), heating temperature (X₂) and heating rate (X₃) were designed by Box-Behnken Design (BBD) experiments. The software gave seventeen runs experiment within the optimal conditions towards two response variables (removal rate and adsorption capacity for Cd²⁺). The results showed that the mathematical model could fit the experimental data very well and the significance of the influence factors followed the order as heating temperature (X₂) > heating rate (X₃) > heating time (X₁), and the influence of interaction term is: X₁ and X₂ (heating time and heating temperature) > X₂ and X₃ (heating temperature and heating rate) > X₁ and X₃ (heating time and heating rate). Based on the analysis of variance and the method of numerical expected function, the optimal conditions were heating time of 2.42 h, heating temperature of 393 °C, and heating rate of 15.56 °C/min. Under the optimum conditions, the predicted the maximum removal rate and adsorption capacity were 85.2724% and 21.168 mg/g, respectively, and the experimental value of removal rate and adsorption capacity for Cd²⁺ were 80.70% and 20.175 mg/g, respectively, the deviation from the predicted value were 5.36% and 4.69%. The results confirmed that the RSM can optimize the preparation conditions of ECSBC, and the adsorption capacity of OECSB was improved.

The application of machine learning methods for prediction of metal sorption onto biochars

The adsorption of six heavy metals (lead, cadmium, nickel, arsenic, copper, and zinc) on 44 biochars were modeled using artificial neural network (ANN) and random forest (RF) based on 353 dataset of adsorption experiments from literatures. The regression models were trained and optimized to predict the adsorption capacity according to biochar characteristics, metal sources, environmental conditions (e.g. temperature and pH), and the initial concentration ratio of metals to biochars. The RF model showed better accuracy and predictive performance for adsorption efficiency (R² = 0.973) than ANN model (R² = 0.948). The biochar characteristics were most significant for adsorption efficiency, in which the contribution of cation exchange capacity (CEC) and pH_H2O of biochars accounted for 66% in the biochar characteristics. However, surface area of the biochars provided only 2% of adsorption efficiency. Meanwhile, the models developed by RF had better generalization ability than ANN model. The accurate predicted ability of developed models could significantly reduce experiment workload such as predicting the removal efficiency of biochars for target metal according to biochar characteristics, so as to select more efficient biochar without increasing experimental times. The relative importance of variables could provide a right direction for better treatments of heavy metals in the real water and wastewater.

Adsorption and sequestration of cadmium ions by polyptychial mesoporous biochar derived from Bacillus sp. biomass

Bacteria-derived biochars from Bucillus sp. biomass under different pyrolysis temperature (250 °C, 350 °C, 450 °C, and 550 °C, respectively) were prepared, forming polyptychial, mesoporous graphite-like structure. The adsorption and sequestration efficiencies of Cd²⁺ by these biochars were evaluated, and the underlying mechanisms were then discussed. Cd²⁺ sorption data could be well described by Langmuir mode while the pseudo-second-order kinetic model and Elovich model best fitted the kinetic data. The functional groups complexation, cation-π interactions, and interaction with minerals (including surface precipitation with phosphorus and ion exchange) jointly contributed to Cd²⁺ sorption and sequestration on biochar, but the interaction with minerals played a dominant role by forming insoluble cadmium salt composed by polycrystalline and/or amorphous phosphate-bridged ternary complex. The maximum sorption capacity of BBC350 in simulated water phase of soil for Cd²⁺ was 34.6 mg/g. Furthermore, the addition of bacteria-derived biochars (1%, w/w) decreased the fractions easily absorbed by plants for Cd in the test paddy soils by 1.9-26% in a 10-day time. Results of this study suggest that bacteria-derived biochar would be a promising functional material in environmental and agricultural application.