Unraveling sorption of nickel from aqueous solution by KMnO4 and KOH-modified peanut shell biochar: Implicit mechanism

Adsorption performance of Ni(II) by KOH-modified biochar derived from different microalgae species

Microalgae biochar is potential adsorbents to remove heavy metals from wastewater due to abundant functional groups, high porosity and wide sources, but performance is not fully developed since it depends on microalgae species attributing to distinct morphology and biomass compositions. Here, two microalgae species Chlorella Pyrenoidosa and Scenedesmus Obliquus were used for biochar preparation via KOH-modification, biochar properties and their influences on Ni(II) adsorption were investigated. Ni(II) adsorption performances responding to biochar properties and operating conditions were upgraded via progressive optimization and response surface methodology. Together, adsorption isotherms and kinetics were analyzed to obtain significant factors for Ni(II) removal. As results, 100 % of Ni(II) removal was achieved under 100 mg/L initial Ni(II) concentration as pH was higher than the biochar zero-charge point of 6.87 with low biochar dosage (0.5 g/L), which provides an efficient approach for heavy metal removal from wastewater with microalgae biochar.

Highly efficient Ni(II) adsorption by industrial lignin-based biochar: a pivotal role of dissolved substances within biochar

In the context of carbon neutrality, promoting resource utilization of industrial alkali lignin addressing heavy metal pollution is crucial for China's pollution alleviation and carbon reduction. Microwave pyrolysis produced functionalized biochar from industrial alkali lignin for Ni(II) adsorption. LB400 achieved 343.15 mg g-1 saturated adsorption capacity in 30 min. Pseudo-second-order kinetic and Temkin isotherm models accurately described the adsorption, which was endothermic and spontaneous (ΔGϴ < 0, ΔHϴ > 0). Quantitative analysis revealed that both dissolved substances and carbon skeleton from biochar contributed to adsorption, with the former predominates (93.76%), including mineral precipitation NiCO3 (Qp) and adsorption of dissolved organic matter (QDOM). Surface complexation (Qc) and ion exchange (Qi) on the carbon skeleton accounted for 6.3%. Higher biochar preparation temperature reduced Ni(II) adsorption by dissolved substances. Overall, biochar which comes from the advantageous disposal of industrial lignin effectively removes Ni(II) contamination, encouraging ecologically sound treatment of heavy metal pollution and sustainable resource utilization.

Effect of Modified Biochar Prepared by Co-pyrolysis of MgO on Phosphate Adsorption Performance and Seed Germination

Biochar is currently used as a phosphate adsorbent in water and subsequently as a soil amendment. In this study, modified biochar was prepared directly by co-pyrolysis of MgO and rice straw, and a preliminary ecotoxicological assessment was performed before the application of modified biochar to soil. The effects of single factors, such as pyrolysis temperature, dosage, pH, and coexisting ions, on phosphate adsorption performance were investigated. In addition, after phosphate adsorption, the effects of modified biochar leachate on the germination of corn and rice seeds were examined. The results showed that phosphate adsorption by the modified biochar first increased and then decreased as the pyrolysis temperature increased, with modified biochar prepared at 800 °C showing the greatest adsorption. In addition, a comprehensive cost analysis showed that the best phosphate adsorption effect of modified biochar was achieved at a dosage of 0.10 g and a solution pH of 3. In contrast, the presence of competitive coexisting ions, Cl- , NO3 - , CO3 2- , and SO4 2- , reduced the phosphate adsorption capacity of the modified biochar. The adsorption kinetics results revealed that the process of phosphate adsorption by the modified biochar was more in line with the pseudo-second-order model and dominated by chemisorption. Moreover, the adsorption isotherm results indicated that the process was more in line with the Langmuir model and dominated by monomolecular layer adsorption, with a maximum adsorption of 217.54 mg/g. Subsequent seed germination tests showed that phosphate-adsorbed modified biochar leachate had no significant effect on the germination rate of corn seeds, whereas it improved the germination rate of rice seeds. Together, these results provide guidance for the application of modified biochar firstly as an adsorbent of phosphate and subsequently as a soil remediator.

Acid-modified red mud biochar for the degradation of tetracycline: Synergistic effect of adsorption and nonradical activation

In this study, a novel acid-modified red mud biochar catalyst (MMBC) was synthesized by industrial waste red mud (RM) and peanut shell (PSL) to activate peroxodisulfate (PDS) for the degradation of TC. Meanwhile, MMBC exhibited remarkable adsorption capacity, reaching a 60% removal ratio of TC within 60 min (equilibrium adsorption capacity = 12 mg/g). After adding PDS, MMBC/PDS system achieved a 93.8% removal ratio of TC within 60 min. Quenching experiments and electron paramagnetic resonance (EPR) results showed that 1O2 played a dominant role in the degradation of TC and O2•- was the mainly precursor for the production of 1O2 in the MMBC/PDS system. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis showed that the surface Fe(II), -OH and -COOH provided the active sites for the activation of PDS by MMBC. In addition, acid modification optimised the surface structure of the catalyst and enhanced the conversion of Fe (mainly Fe(III) to Fe(II)), thereby improving the adsorption and catalytic efficiency of MMBC. This study confirmed that modified red mud biochar is an efficient composite with both adsorption and catalysis, providing new ideas for the practical treatment of antibiotic wastewater and the resource utilization of red mud.

Ba-modified peanut shell biochar (PSB): preparation and adsorption of Pb(II) from water

The impact of Ba-modified peanut shell biochar (Ba-PSB) on Pb(II) removal was studied and BaCl2 was used as a modifier. It was shown that the PSB obtained at 750 °C had the best adsorption effect, and the Ba-PSB had a larger specific surface area and a good adsorption effect on Pb(II). At pH = 5, concentration was 400 mg/L, time was 14 h, and temperature was 55 °C, the loading amount of black peanut shell biochar (BPSB), red peanut shell biochar (RPSB), Ba-BPSB, and Ba-RPSB reached 128.050, 98.217, 379.330, and 364.910 mg/g, respectively. In addition, based on the non-linear fitting, it was found that the quasi-second-order kinetic model, and isothermal model could be applied to describe Pb(II) adsorption on PSB and Ba-PSB. The adsorption behavior of PSB unmodified and modified was a spontaneous process. Moreover, chemical modification of BPSB, RPSB, Ba-BPSB, and Ba-RPSB for hindering of -COOH and -OH groups revealed 81.81, 77.08, 86.90, and 83.65% removal of Pb(II), respectively, which was due to the participation of -COOH, while 17.61, 21.70, 12.77, and 15.06% was from -OH group, respectively. The increase of cation strength (Na+, K+, Ca2+, and Mg2+) will reduce the adsorption capacity of PSB for Pb(II).

Removal Performance of KOH-Modified Biochar from Tropical Biomass on Tetracycline and Cr(VI)

Biochar can be used to address the excessive use of tetracycline and micronutrient chromium (Cr) in wastewater that potentially threatens human health. However, there is little information about how the biochar, made from different tropical biomass, facilitates tetracycline and hexavalent chromium (Cr(VI)) removal from aqueous solution. In this study, biochar was prepared from cassava stalk, rubber wood and sugarcane bagasse, then further modified with KOH to remove tetracycline and Cr(VI). Results showed that pore characteristics and redox capacity of biochar were improved after modification. KOH-modified rubber wood biochar had the highest removal of tetracycline and Cr(VI), 1.85 times and 6 times higher than unmodified biochar. Tetracycline and Cr(VI) can be removed by electrostatic adsorption, reduction reaction, π-π stacking interaction, hydrogen bonding, pore filling effect and surface complexation. These observations will improve the understanding of the simultaneous removal of tetracycline and anionic heavy metals from wastewater.

Untreated Opuntia ficus indica for the Efficient Adsorption of Ni(II), Pb(II), Cu(II) and Cd(II) Ions from Water

The raw cladode of Opuntia ficus indica (OFI) was evaluated as a sustainable biosorbent for the removal of heavy metals (Ni, Pb, Cu, and Cd) from aqueous solutions. The functional groups of OFI were identified by employing DRIFT-FTIR and CP-MAS-NMR techniques before and after contact with the ions in an aqueous media, showing a rearrangement of the biomass structure due to the complexation between the metal and the functional groups. The adsorption process was studied in both single- and multi-component systems under batch conditions at different pHs (4.0, 5.0, and 6.0), different metal concentrations, and different biomass amounts. The results show that the raw OFI had a removal capacity at room temperature of over 80% for all metals studied after only 30 min of contact time, indicating a rapid adsorption process. Biosorption kinetics were successfully fitted by the pseudo-second-order equation, while Freundlich correctly modelled the biosorption data at equilibrium. The results of this work highlight the potential use of the untreated cladode of OFI as an economical and environmentally friendly biosorbent for the removal of heavy metals from the contaminated aqueous solution.

Comparative study for sorption of arsenic on peanut shell biochar and modified peanut shell biochar

In this study, arsenite [As(III)] and arsenate [As(V)] removal efficiency of peanut shell biochar (PSB) and modified peanut shell biochar (MPSB) was compared in aqueous solutions. The modification was carried out with KMnO₄ and KOH. Sorption efficiency of MPSB was relatively higher than PSB at pH 6 for As(III) (86%) and for As(V) (91.26%) for initial concentration of 1 mg/L, adsorbent dose of 0.5 g/L and 240 min equilibrium time at 100 rpm. Freundlich isotherm and pseudo-second order kinetic model suggested possible multilayer chemisorption. Fourier transform infrared spectroscopy showed that -OH, C-C, CC and C-O-C groups contributed significantly in adsorption for both PSB and MPSB. Thermodynamic study showed that the adsorption process was spontaneous and endothermic. Regeneration studies revealed that PSB and MPSB can be successfully used for three cycles. This study established that peanut shell is a low-cost, environment friendly and efficient biochar for removal of arsenic from water.

Engineering and application of polysaccharides and proteins-based nanobiocatalysts in the recovery of toxic metals, phosphorous, and ammonia from wastewater: A review

Global waste production is anticipated reach to 2.59 billion tons in 2030, thus accentuating issues of environmental pollution and health security. 37 % of waste is landfilled, 33 % is discharged or burned in open areas, and only 13.5 % is recycled, which makes waste management poorly efficient in the context of the circular economy. There is therefore a need for methods to recycle waste into valuable materials through resource recovery process. Progress in the field of recycling is strongly dependent on the development of efficient, stable, and reusable, yet inexpensive catalysts. In this case, a growing attention has been paid to development and application of nanobiocatalysts with promising features. The main purpose of this review paper is to: (i) introduce nanobiomaterials and describe their effective role in the preparation of functional nanobiocatalysts for the recourse recovery aims; (ii) provide production methods and the efficiency improvement of nanobaiocatalysts; (iii) give comprehensive description of valued resource recovery for reducing toxic chemicals from the contaminated environment; (iv) describe various technologies for the valued resource recovery; (v) state the limitation of the valued resource recovery; (vi) and finally economic importance and current scenario of nanobiocatalysts strategies applicable for the resource recovery processes.

A study on and adsorption mechanism of ammonium nitrogen by modified corn straw biochar

Using corn stover as raw material, the adsorption mechanism of ammonium nitrogen by biochar prepared by different modification methods was studied. The biochar was characterized by Fourier transform infrared spectroscopy, surface-area analysis and scanning electron microscopy. The results showed that the adsorption of NH 4 + - N by different modified biochars confirmed the quasi-second-order kinetic equation (R ² > 0.95, p ≤ 0.05), the adsorption isotherms of the Langmuir equation (R ² ≥ 0.96, p ≤ 0.05). ΔG ^θ < 0, ΔH ^θ > 0 indicated that the adsorption of NH 4 + - N by different modified biochars was a spontaneous endothermic reaction. With the increase in adsorption temperature, the adsorption capacity of biochar to ammonium nitrogen increased gradually. The adsorption was monolayer adsorption and was controlled by a fast reaction. Both KOH and FeCl₃ modified biochars significantly improved the adsorption capacity of NH 4 + - N , and the adsorption mechanism was different. The adsorption capacity of NH 4 + - N by FeCl₃ modified biochars mainly increased the specific surface area and micropore volume. The adsorption of ammonium nitrogen after KOH modification primarily depended on the wealthy oxygen-containing functional groups. The adsorption effect of ammonium nitrogen modified by KOH was better than that of biochar modified by FeCl₃.

Pseudomonas stutzeri Immobilized Sawdust Biochar for Nickel Ion Removal

Nickel ions generated from the electroplating industry and stainless steel and battery manufacturing industries contribute to water pollution, harm human health, and pose environmental risks. A long-term, sustainable, and efficient treatment method should be developed to address this issue. Bioremediation in the presence of biochar and microorganisms is a potential approach for metal ion abatement. This study evaluates the feasibility of Pseudomonas stutzeri immobilized sawdust biochar (PSDB) for Ni2+ removal. Sawdust biochar was prepared by pyrolyzing in a muffle furnace and was characterized using SEM, FTIR, and BET. The influence of biochar preparation parameters such as pyrolysis temperature, time on biochar yield, and impact on cell immobilization was investigated. The effect of various parameters, such as incubation time, pH, temperature, and biocatalyst dosage, was studied. The total Ni2+ in solution was analyzed using inductively coupled plasma optical emission spectrometry. PSDB showed an 83% Ni2+ removal efficiency and reusability up to three cycles. FT-IR analysis revealed that the mechanism of Ni2+ removal by PSDB was the synergistic effect of adsorption by biochar and bioaccumulation by P. stutzeri. This study presents a novel approach for environmental application by utilizing waste biomass-derived biochar as a carrier support for bacteria and an adsorbent for pollutants.

Chemical Fractionations of Lead and Zinc in the Contaminated Soil Amended with the Blended Biochar/Apatite

Heavy metal contamination in agricultural land is an alarming issue in Vietnam. It is necessary to develop suitable remediation methods for environmental and farming purposes. The present study investigated the effectiveness of using peanut shell-derived biochar to remediate the two heavy metals Zn and Pb in laboratory soil assays following Tessier’s sequential extraction procedure. The concentration of heavy metals was analyzed using Inductively coupled plasma mass spectrometry (ICP-MS). This study also compared the effectiveness of the blend of biochar and apatite applied and the mere biochar amendment on the chemical fractions of Pb and Zn in the contaminated agricultural soil. Results have shown that the investigated soil was extremely polluted by Pb (3047.8 mg kg−1) and Zn (2034.3 mg kg−1). In addition, the pH, organic carbon, and electrical conductivity values of amended soil samples increased with the increase in the amendment’s ratios. The distribution of heavy metals in soil samples was in the descending order of carbonate fraction (F2) > residue fraction (F5) > exchangeable fraction (F1) > Fe/Mn oxide fraction (F3) > organic fraction (F4) for Pb and F5 ≈ F2 > F1 > F3 > F4 for Zn. The peanut shell-derived biochar produced at 400 °C and 600 °C amended at a 10% ratio (PB4:10 and PB6:10) could significantly reduce the exchangeable fraction Zn from 424.82 mg kg−1 to 277.69 mg kg−1 and 302.89 mg kg−1, respectively, and Pb from 495.77 mg kg−1 to 234.55 mg kg−1 and 275.15 mg kg−1, respectively, and immobilize them in soil. Amending the biochar and apatite combination increased the soil pH, then produced a highly negative charge on the soil surface and facilitated Pb and Zn adsorption. This study shows that the amendment of biochar and biochar blended with apatite could stabilize Pb and Zn fractions, indicating the potential of these amendments to remediate Pb and Zn in contaminated soil.

Comparative Study of Biochar Modified with Different Functional Groups for Efficient Removal of Pb(II) and Ni(II)

The potential application of biochar in water treatment is attracting interest due to its sustainability and low production cost. In the present study, H₃PO₄-modified porous biochar (H-PBC), ethylenediaminetetraacetic acid-modified porous biochar (E-PBC), and NaOH-modified porous biochar (O-PBC) were prepared for Ni(II) and Pb(II) adsorption in an aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller analysis (BET), and Fourier-transform infrared (FT-IR) spectroscopy were employed to characterize the as-obtained samples, and their capacities for Ni(II) and Pb(II) adsorption were determined. SEM showed that H-PBC retained the hierarchical porous structure of pristine biochar. FT-IR showed that H-PBC possessed abundant oxygen-containing and phosphorus-containing functional groups on the surface. BET analysis demonstrated that the surface areas of H-PBC (344.17 m²/g) was higher than O-PBC (3.66 m²/g), and E-PBC (1.64 m²/g), respectively. H-PBC, E-PBC, and O-PBC all exhibited excellent performance at Ni(II) and Pb(II) adsorption with maximum adsorption capacity of 64.94 mg/g, 47.17 mg/g, and 60.24 mg/g, and 243.90 mg/g, 156.25 mg/g, and 192.31 mg/g, respectively, which were significantly higher than the adsorption capacity (19.80 mg/g and 38.31 mg/g) of porous biochar (PBC). Pseudo-second order models suggested that the adsorption process was controlled by chemical adsorption. After three regeneration cycles, the Ni(II) and Pb(II) removal efficiency with H-PBC were still 49.8% and 56.3%. The results obtained in this study suggest that H-PBC is a promising adsorbent for the removal of heavy metals from aqueous solutions.

Preparation of biochar from constructed wetland plant and its adsorption performance towards Cu2

In order to solve problems in the treatment and disposal of huge production of artificial wetland plants and heavy metal pollution, two constructed wetland plants of reed and gladiolus were selected as raw materials to prepare biochar for adsorbing heavy metals from aqueous solutions. The experimental results showed that reed biochar prepared at 600℃ and activated by KOH with an impregnation ratio of 1:3 (KRAC-3) exhibited relatively high adsorption ability towards Cu²⁺. The optimal results analyzed by Design-Expert software showed that the maximum adsorption rate of KRAC-3 towards Cu²⁺ was obtained under the optimal conditions of adsorbent dosage of 1.2 g/L, pH of 4.96, and reaction time of 137.43 min. The adsorption of Cu²⁺ followed pseudo-second-order kinetics and the Langmuir adsorption model. The theoretical maximum adsorption capacity of KRAC-3 calculated from the Langmuir isotherm model was 148.08 mg/g. Microscopic tests with the help of SEM, EDS, and XRD revealed that physical adsorption, ion exchange, electrostatic adsorption, surface complexation, and precipitation were the main adsorption mechanism of Cu²⁺ loading onto KRAC-3. This study will provide a theoretical basis for the application of biochar prepared from constructed wetland plants and the treatment of heavy metal-containing wastewater.

Research Progress on Adsorption of Arsenic from Water by Modified Biochar and Its Mechanism: A Review

Arsenic (As) is a non-metallic element, which is widely distributed in nature. Due to its toxicity, arsenic is seriously harmful to human health and the environment. Therefore, it is particularly important to effectively remove arsenic from water. Biochar is a carbon-rich adsorption material with advantages such as large specific surface area, high porosity, and abundant functional groups, but the original biochar has limitations in application, such as limited adsorption capacity and adsorption range. The modified biochar materials have largely enhanced the adsorption capacity of As in water due to their improved physicochemical properties. In this review, the changes in the physicochemical properties of biochar before and after modification were compared by SEM, XRD, XPS, FT-IR, TG, and other characterization techniques. Through the analysis, it was found that the adsorbent dosage and pH are the major factors that influence the As adsorption capacity of the modified biochar. The adsorption process of As by biochar is endothermic, and increasing the reaction temperature is conducive to the progress of adsorption. Results showed that the main mechanisms include complexation, electrostatic interaction, and precipitation for the As removal by the modified biochar. Research in the field of biochar is progressing rapidly, with numerous achievements and new types of biochar-based materials prepared with super-strong adsorption capacity for As. There is still much space for in-depth research in this field. Therefore, the future research interests and applications are put forward in this review.

Ni(II), Cr(VI), Cu(II) and nitrate removal by the co-system of Pseudomonas hibiscicola strain L1 immobilized on peanut shell biochar

At present, the improvement of nitrate and mixed heavy metals removal in wastewater by microorganism are urgently needed. Previous studies have shown that Pseudomonas hibiscicola strain L1 exhibited Ni(II) removal ability under aerobic denitrification. In this study, the characteristics of the free strain L1, peanut shell biochar (PBC) and further the co-system of strain L1 immobilized on PBC were investigated for the removal of Ni(II), Cr(VI), Cu(II) and nitrate in mix-wastewater. The results illustrated that strain L1 could remove 15.51% - 32.55% of Ni(II) (20-100 mg·L^-1), and removal ratios by co-system were ranked as Ni(II) (81.17%) > Cu(II) (45.84%) > Cr(VI) (38.21%). Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) images indicated that the strain L1 immobilized well on PBC and had vigorous biological activity; the crystals of Ni(OH)₂, Cu(OH)₂ and CrO(OH) etc. were formed on surface of co-system with various functional groups participated in. In Sequential Batch Reactor (SBR), the pollutant removal ratios by co-system were higher than that by free strain L1. This study illustrated that the co-system of strain L1 immobilized on PBC was qualified to be applied for practical scenarios of effective heavy metal removal of electroplating mix-wastewater.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.

Nickel Hyperaccumulator Biochar as a Ni-Adsorbent and Enhanced Bio-ore

Increasing nickel (Ni) demand may spur the need for creative Ni production methods. Agromining (farming for metals) uses plants that can accumulate high concentrations of metal in their biomass, called bio-ore, as a metal extraction strategy. Furthermore, biochar, produced by biomass pyrolysis under low-oxygen conditions, can be used to remove Ni from contaminated wastewaters. In this work we investigate whether biochar synthesized from the Ni-hyperaccumulating plant Odontarrhena chalcidica (synonymous Alyssum murale) can be used as a Ni-adsorbing biochar. We grew O. chalcidica on soils with varying Ni concentration, characterized the plants and resultant biochars synthesized at different pyrolysis temperatures, and analyzed Ni batch adsorption results to determine the adsorption capacity of O. chalcidica biochar. We found that Ni concentration in O. chalcidica increases with increasing soil Ni but reaches an accumulation limit around 23 g Ni kg^–1 dry weight in dried leaf samples. Pyrolysis concentrated Ni in the biochar; higher pyrolysis temperatures led to higher biochar Ni concentrations (max. 87 g Ni kg^–1) and surface areas (max. 103 m²/g). Finally, the O. chalcidica biochar adsorption results were comparable to high-performing Ni adsorbents in the literature. The adsorption process greatly increased the Ni concentration in some biochars, indicating that synthesizing biochar from O. chalcidica biomass and using it as a Ni adsorbent can produce a Ni-enhanced bio-ore with nickel content higher than all nickel-rich veins currently mined.

Chemically Dual-Modified Biochar for the Effective Removal of Cr(VI) in Solution

Here, a dual-modification strategy using KMnO4 (potassium permanganate) and AlCl3·6H2O (aluminum chloride, hexahydrate) as co-modifiers to improve the Cr(VI) removal capacity of K2CO3 activated biochar is introduced. As a result, the dual-modified biochar with KMnO4 and AlCl3·6H2O has the calculated adsorption energy of −0.52 eV and −1.64 eV for HCrO4−, and −0.21 eV and −2.01 eV for Cr2O72−. The Al2O3 (aluminum oxide) and MnO (manganese oxide) embedded on the surface of dual-modified biochar bring more Cr(VI) absorption sites comparing to single-modified biochar, resulting in a maximum Cr(VI) saturated adsorption capacity of 152.86 mg g−1. The excellent removal performance is due to the synthetic effect of electrostatic attraction, reduction reaction, complexation reaction, and physical adsorption. The experimental results also indicated that the spontaneous adsorption process agreed well with the pseudo-second order and Langmuir models. This dual-modification strategy is not limited to the treatment of Cr(VI) with biochar, and may also be incorporated with the treatment of other heavy metals in aqueous environment.

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.

Application of the Organic Waste-Based Sorbent for the Purification of Aqueous Solutions

The effective purification of large-capacity wastewater from heavy non-ferrous metals and organic pollutants using inexpensive sorption technology remains a crucial task. Analyzing the current objectives of sustainable development, biochar obtained from chicken manure has prospects as a source for sorption purification of industrial wastewater. To determine the characteristics of organic material and the composition of the initial and equilibrium phases, the following analysis methods were used: volumetric, complexometric, pH-metric, X-ray fluorescence, chromatographic, spectrophotometric, luminescence-photometric and X-ray diffraction. The thermal nitrogen desorption method was used for determining the specific surface area and pore sizes with the Quantachrome Nova 1000e automatic analyzer. The sorption properties of the reprocessing product of the fresh poultry manure were investigated in relation to organic and inorganic compounds: phenols, benzene, ketones, cations of lead, mercury, manganese and iron. Based on the results obtained, technical conditions were developed for the use of the reprocessed organic waste-based product as a sorption material for household, industrial and technological wastewater purification from organic and inorganic components.

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.

Sorption and transport of Mn2+ in soil amended with alkali-modified pomelo biochar

Owing to its effectiveness and being environment-friendly, biochar has been used for adsorbing and immobilizing pollutants in soil in recent years of studies, which is also suitable for manganese pollution in soil caused by manganese mining and processing activities. In this research, alkali-modified pomelo biochar (MBC) was regarded as a soil amendment, and the improvement of soil physicochemical properties and Mn²⁺ sorption and transport in soil by modifying with MBC were investigated. In incubation experiment, 0-10% (w/w) MBC addition amount significantly improved the physicochemical properties of soil. Due to the amelioration of soil physicochemical properties along with the oxygen-containing functional groups and the developed pore structure of MBC itself, the adsorption capacity of MBC modification soil towards Mn²⁺ (q_e) was enhanced in batch adsorption experiment, and q_e increased by 10-108% when MBC ratio grew from 0 to 10% at 300 mg·L^-1 Mn²⁺ solution. In column transport experiment, the Mn²⁺ retention rate climbed by 13-106% from 0 to 10% MBC addition proportion when adopted the MBC filling way that placed MBC on the soil upper layer, and the reinforced restriction on Mn²⁺ transport in soil amended with MBC might ascribe to the enhanced q_e as well as the reduced saturated hydraulic conductivity. These results proved that MBC effectively augmented adsorption ability and suppressed transport of Mn²⁺ in soil, which could provide an available mind on prevention and remediation of soil Mn contamination.

Sustainable Adsorption Removal of Nickel and Chromium on Eco-Friendly Industrial Waste: Equilibrium Study

Adsorption of nickel and chromium was investigated using fuller’s earth. The experimental data were analyzed using five 2-parameter adsorption models and three 3-parameter models. The maximum adsorption capacities for nickel and chromium were 769 and 556 mg/g, respectively. The Langmuir isotherm model was found to have the best fitting indicating monolayer adsorption. The adsorption was found to have an exothermic nature.

Enhanced Adsorption Capacities of Fungicides Using Peanut Shell Biochar via Successive Chemical Modification with KMnO4 and KOH

This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modifications, using KMnO4 and KOH (PSBOX-A), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. To this end, the physicochemical properties of PSB and PSBOX-A were examined by using the Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer. The effects of temperature, ionic strength, and humic acids on the adsorption of fungicides, using PSB and PSBOX-A, were estimated through batch experiments. Furthermore, adsorption kinetics, isotherms, and thermodynamics were studied. The maximum adsorption capacities of fungicides by PSBOX-A were estimated to be more notable (Qmax of carbendazim = 531.2 μmol g−1, Qmax of pyrimethanil = 467.7 μmol g−1, and Qmax of tebuconazole = 495.1 μmol g−1) than PSB (Qmax of carbendazim = 92.6 μmol g−1, Qmax of pyrimethanil = 61.7 μmol g−1, and Qmax of tebuconazole = 66.7 μmol g−1). These findings suggest that successive chemical modification using KMnO4 and KOH could potentially be used to effectively fabricate PSB to remove fungicides in water-treatment processes.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g^-1 at 0.5 A g^-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm^-2), specific capacity (767 mAh g_Zn^-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

An Efficient Strategy for Enhancing the Adsorption Capabilities of Biochar via Sequential KMnO4-Promoted Oxidative Pyrolysis and H2O2 Oxidation

In this study, sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation were employed to upgrade the adsorption capacities of durian shell biochar for methylene blue (MB) and tetracycline (TC) in an aqueous solution. It was found that the KMnO4/H2O2 co-modification was greatly influenced by pyrolysis temperature and the optimal temperature was 300 °C. Moreover, a low concentration of H2O2 enabled the improvement of the adsorption capabilities greatly with the catalysis of pre-impregnated manganese oxides, addressing the shortcoming of single H2O2 modification. The co-modified biochar exhibited high adsorption capabilities for MB and TC, remarkably surpassed KMnO4- and H2O2- modified biochars as well as pristine biochar. The increase of adsorption capabilities could be mainly contributed to the incorporation of MnOx and carboxyl by KMnO4-promoted oxidative decomposition and Mn-catalyzed H2O2 oxidation. This would provide a novel and efficient method for preparing highly adsorptive biochar using sequential KMnO4-promoted oxidative pyrolysis and H2O2 oxidation.

EDTAD-modified cassava stalks loaded with Fe3O4: highly efficient removal of Pb2+ and Zn2+ from aqueous solution

In this study, a novel magnetic cassava stalk composite (M-EMCS) was prepared through modification with ethylenediamine tetraacetic anhydride (EDTAD) and loading of Fe₃O₄. The surface morphology, molecular structure, and magnetic characteristics of the composite were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), vibrating-sample magnetometer (VSM), and X-ray diffraction (XRD). It was shown that EDTAD and Fe₃O₄ were successfully modified and loaded in cassava straw (CS), respectively. The capacity of M-EMCS to absorb heavy metals under different influencing factors was tested by atomic absorption spectroscopy. The adsorption processes of both Pb²⁺ and Zn²⁺ were suitably described by second-order kinetic models and Langmuir models, indicating monolayer chemisorption. M-EMCS had high adsorption rates and adsorption capacities for these two metal ions. The adsorption of Pb²⁺ and Zn²⁺ reached a plateau after 10 min, and the adsorption capacity of Pb²⁺ (163.93 mg/g) was higher than that of Zn²⁺ (84.74 mg/g). Thermodynamic analysis showed that the adsorption of two metals by M-EMCS was spontaneous, endothermic, and irreversible. XPS analysis showed that M-EMCS mainly removes Pb²⁺ and Zn²⁺ through ion exchange, chelation, and redox. Graphical abstract.

Green synthesis of reusable super-paramagnetic diatomite for aqueous nickel (II) removal

Adsorption is an effective method for treating wastewater containing nickel due to its minimal equipment requirements and flexible operation. Therefore, an environmental friendly, inexpensive, efficient and recyclable adsorbent is needed. In this work, a reusable dual-functional super-paramagnetic adsorbent was prepared by combining APTES (3-Aminopropyltriethoxysilane) and EDTA (ethylenediaminetetraacetic acid disodium) with magnetic diatomite for the removal of Ni²⁺. It is named diatomite/CoFe₂O₄@APTES-EDTA (DECFASEs). The synthetic material was characterized and studied by XRD (X-ray Powder Diffractometer), FTIR (Fourier Transform Infrared Spectrometer), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), EDS (Energy Dispersive Spectrometer), VSM (Vibrating-Sample Magnetometer), BET (Brunauer-Emmett-Teller) method, Zeta potential analyzer and XPS (X-ray Photoelectron Spectroscopy), respectively. The performance of adsorption Ni²⁺ by DECFASEs was studied on effect of pH, reaction time and initial concentrations. The adsorption and desorption capacity and recyclability of the adsorbent material were estimated. A adsorption kinetic data had a significant correlation with the pseudo second-order kinetic and also adsorption isotherm data corresponded well with Freundlich adsorption isotherm. The maximum adsorption capacity of the adsorbent material was 19.22 mg/g. The Ni²⁺ adsorption capacity of DECFASEs decreased slightly from 9.11 to 8.25 mg/g after 4 recycles. The XPS results of DECFASEs before and after Ni²⁺ uptake showed N and O participated in the complexation of Ni²⁺ in the adsorption process, which verified the chemical interaction between Ni²⁺ and DECFASEs. Modified-diatomite is a promising adsorbent for aqueous Ni²⁺ removal.

Porous biochar-nanoscale zero-valent iron composites: Synthesis, characterization and application for lead ion removal

Nano-zero-valent iron has been used in combination with a variety of support carriers to remove heavy metals in solution. However, pre-treatment of the carrier can reflect a better synergistic effect and thus achieve high heavy metal removal capabilities. In this study, the hydrophilic biochar obtained by an acid ammonium persulfate oxidation has an adsorption capacity of up to 135.4 mg g^-1 for Pb²⁺ (25 °C, pH = 6 with adsorbent amount of 10 mg and Pb²⁺ concentration of 50 mg L^-1). Due to the strong Fe-C-O covalent bond, nZVI increases the binding force with the carbon matrix. Benefitting from the high specific surface area, porous structure and rich oxygen-containing functional groups, the resultant nZVI-HPB samples are favourable for Pb²⁺ diffusion and adsorption, exhibiting maximum adsorption capacity of 480.9 mg g^-1 (pH = 6, 25 °C with adsorbent amount of 10 mg and Pb²⁺ concentration of 200 mg L^-1). The multiple interaction mechanisms in the Pb²⁺ removal process such as the reduction reaction, complexation and co-precipitation proceed simultaneously are concluded by the analyses of Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectra.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Facile preparation of porous biomass charcoal from peanut shell as adsorbent

Activated carbons derived from biomass have been proved to be one of the most promising adsorbents due to their abundance, low cost, reproducibility and environmental friendliness. In this study, a simple, facile and effective pyrolysis method was demonstrated to prepare hierarchical porous biomass charcoal by using peanut shells as precursor without chemical activation in an electric muffle furnace. The obtained products hold porous structure and abundant oxygen-containing functional groups, which were mainly due to in-built template of the structure of peanut shell and the preparation process without nitrogen protection, respectively. Interestingly, the obtained biomass charcoal sample with excellent adsorptive property quickly removed Pb2+ (100 mg/L) and methylene blue (50 mg/L) from water with removal efficiency of 96.5% and 97.1%, and removal capacity of 48 mg/g and 24 mg/g, respectively. The synthetic process was simple and economical, and it could be used as a beneficial reference in the recycling of biomass waste.

Biochar technology in wastewater treatment: A critical review

Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater.

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.

Comparison of adsorption properties for cadmium removal from aqueous solution by Enteromorpha prolifera biochar modified with different chemical reagents

Using biochar to remove heavy metals from water is environmentally beneficial. In this study, three kinds of chemical reagents, including ZnCl₂, H₃PO₄ and KMnO₄, were introduced to modify the biochar derived from Enteromorpha prolifera. The performance of these modified biochar in removing Cadmium ions (Cd(II)) from water was investigated. The physicochemical properties of activated biochars were characterized by N₂-sorption, thermal gravity and differential thermal gravity (TG/DTG), scanning electron microscopy (SEM), elemental analysis and Fourier transform infrared spectroscopy (FTIR). The results showed that the removal rate of Cd(II) from water by EP biochar modified with H₃PO₄ was significantly increased, and the maximum adsorption capacity of Cd(II) reached to 423 mg/g for PBC. Moreover, the adsorption of Cd(II) from water by phosphoric acid modified biochar was very fast, and the saturation adsorption of Cd(II) was reached within 1 h. Compared with pseudo first-order model, pseudo secondary-order model was much more suitable for analyzing the adsorption kinetics data of Cd(II) onto KBC or ZBC. The adsorption of Cd(II) onto PBC was analyzed by the intra-particle diffusion kinetic model, where the value of R² was high as 0.98. The Langmuir model was fit for phosphoric acid modified biochar.

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.

Ultrahigh adsorbability towards different antibiotic residues on fore-modified self-functionalized biochar: Competitive adsorption and mechanism studies

An ultrasonic-assistant fore-modified method was designed to develop the self-functionalized biochar (SFB) with enhanced adsorbability. Characterized by different morphologies, SFB was presenting particular groups of carbon micro-spheres. Possessing ultrahigh surface area of 2368 m²/g, SFB exhibited excellent adsorption capacity (up to 497 mg/g) towards traditional antibiotic. Besides, more functional groups, which played important roles on the solid-liquid interface interaction, posed on the surface of SFB. The removal efficiency of levofloxacin was up to 99.93 % in the competitive system. Adsorption mechanism was analyzed based on the results of FTIR, kinetics, isotherms and competitive adsorption experiments. The chemisorption affinity on the solid-liquid interface was strong enough, which was proved by isotherms, thermodynamics and K_d analyses. Meanwhile, SFB has presented a good resistance against humid acid interference in aqueous environment. Thus, the ultrasonic-assistant fore-modified method was potential in dramatically improving the feature of biochars. SFB presented excellent adsorbability to antibiotics and exhibits extraordinary potential in wastewater treatment.

Nano-manganese oxides-modified biochar for efficient chelated copper citrate removal from water by oxidation-assisted adsorption process

Removal of chelated copper from wastewater is more difficult than that of copper ions owing to its stable structure, wide range of pH tolerance, and stronger mobility. Copper citrate (CuCA) widely exists in the water system and inevitably poses serious hazards to human health and environment. Biochar as economic functional material has been widely used for environmental applications, especially in wastewater treatment. This study focused on the performance of manganese oxide-modified biochar (BC-MnO_x) toward uptake and removal of CuCA and to understand the related mechanism. The result indicated that the CuCA removal efficiency reached up to 99%. High removal efficiency and low concentration of dissolved Mn over a wide pH range proved that the BC-MnO_x is efficient and chemically stable. Furthermore, the removal mechanism may involve the following processes: First, CuCA was removed via the chemical bonds formed between CuCA and MnO_x on the surface of BC. Second, chemisorption due to the oxygen-containing functional groups or physisorption of porous structure in BC worked synergistically on CuCA. Third, CuCA was partially oxidized into low molecular weight acids by means of MnO_x, while the released Cu ions were retained on the adsorbent surface. This study demonstrates that BC-MnO_x is a promising material for the removal of CuCA from 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.