Chromium Removal Efficiency Research Articles

Trivalent chromium removal from tannery wastewater with low cost bare magnetic Fe3O4 nanoparticles

In this work, a new method is proposed to remove Cr (III) in tanning wastewater with low cost bare magnetic Fe3O4 nanoparticles. It has achieved ultra-high chromium capture capacity under high selectivity. The maximum capture capacity of magnetic Fe3O4 nanoparticles for Cr (III) in chromium containing tanning wastewater is 456.20 mg/g at optimal pH 8. In a pilot scale apparatus running continuously at 18 L/h for 8 h, the chromium removal efficiency could be stabilized above 98.5% with chromium concentration reduced from 1065 mg/L to about 15 mg/L at the primary treatment. After secondary treatment, the outlet chromium concentration drops to 0.2 mg/L (lower than 0.5 mg/L, the maximum allowable concentration of Cr total in tanning wastewater determined by China), and the chromium removal efficiency is steadily above 97.8%. The results revealed that the method could be used economically as an efficient technique for removal of Cr (III) in chromium containing leather tanning wastewater and has great potential in heavy metal wastewater treatment.

Adsorption of chromium ions from tannery effluents onto activated carbon prepared from rice husk and potato peel by H3PO4 activation

Two biomass agricultural waste materials; rice husks (RH) and potato peels (PP) were used as precursors for preparation of activated carbons by chemical activation using phosphoric acid for adsorption of hexavalent chromium [Cr(VI)] from tannery effluents. The prepared rice husk (RH–AC) and potato peel activated carbon (PP–AC) were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. Adsorption experiments were performed by varying pH, agitation speed, contact time, adsorbent dose and initial metal ion concentration. Freundlich, Langmuir and Temkin isotherms were used to analyze the equilibrium data obtained at different adsorption conditions. It was found that the adsorption isotherms were well fitted by the Freundlich equation and the adsorption process was found to follow pseudo-second-order rate kinetics. Adsorption results obtained show a maximum Cr(VI) uptake being attained at pH 2.0, with chromium removal efficiency of 99.88% and 99.52% for RH–AC and PP–AC, respectively. RH–AC and PP–AC are effective adsorbent for the removal of chromium(VI) ions from wastewater.

Synthesis, Optical Characterization, and Adsorption of Novel Hexavalent Chromium and Total Chromium Sorbent: A Fabrication of Mulberry Stem Biochar/Mn-Fe Binary Oxide Composite via Response Surface Methodology

In this study, a new generation chromium sorbent, mulberry stem biochar/Mn-Fe binary oxide composite (MBC-MFC), was fabricated by chemical precipitation on carbonized mulberry stem according to response surface methodology (RSM) results. RSM was more convenient to figure out the optimized preparation condition of MBC-MFC theoretically for achieving a maximum removal efficiency of Cr(VI) and total chromium (TCr), compared to labor-intensive orthogonal experiments. The RSM results showed that Fe/Mn concentration (CFe; CMn), MBC activation temperature after soaking in KOH solution (T), and pH during precipitation of Fe-Mn oxide were three main factors to significantly affect the efficiency of MBC-MFC (p < 0.05) in Cr(VI) and TCr removal. With the selected condition (CFe = 0.28 mol/L; CMn = 0.14 mol/L; T = 790°C; pH = 9.0), MBC-MFC was synthesized with a large surface area (318.53 m2/g), and the point of zero charge values of MBC-MFC was 5.64. The fabricated MBC-MFC showed excellent adsorption performance of Cr(VI) and TCr in an aqueous solution. The maximum Cr(VI) and TCr removal capacity of MBC-MFC was 56.18 and 54.97 mg/g (T = 25°C, pH = 3.0, t = 48 h, and dosage = 0.10 g/50 ml), respectively, and the maximum Cr(VI) adsorption of MBC-MFC was 4.16 times that of bare MBC, suggesting the synergistic effects of Fe/Mn oxides and MB on the performance of MBC-MFC in Cr(VI) and TCr removal. The adsorption mechanism of MBC-MFC on chromium was mainly contributed by surface complexation and electrostatic attraction. Our study offers valuable outlooks to develop high-performance biochar-based sorbents for heavy metal removal and sustainable environmental remediation.

Removal of Hexavalent Chromium using Iron Nanoparticles Prepared using Date Seed Extract

Removal of hexavalent chromium from contaminated water systems is critical due to their high toxicity to aquatic and human health. Iron based nanoparticles (FeNPs) have emerged as promising materials for chromium removal. However, greener alternatives to the chemical synthesis routes of FeNPs are highly desirable while retaining their remediation ability. In this study we evaluate the removal efficiency of chromium using iron nanoparticles synthesized using aqueous extracts of date tree seeds (ds-FeNPs). Characterization of ds-FeNPs reveal the presence of 20-100 nm spherical nanoparticles containing Fe, C, O and S elements. Batch experiments demonstrated that the removal efficiency increased with increase in nanoparticles dose for a fixed chromium concentration (from 18 to 98% at nanoparticles dose of 166 to 1000 mg/L), whereas an opposite trend was observed for varying chromium concentrations at fixed nanoparticles dose. Removal efficiency was also probed at different initial pH levels and results indicate complete removal of chromium in acidic pH (100% at pH 3) whereas basic pH hindered chromium removal.

Reduced graphene oxide supported ZnO/CdS heterojunction enhances photocatalytic removal efficiency of hexavalent chromium from aqueous solution

The removal of toxic and harmful heavy metal contaminants from wastewater is of great importance for global environmental health. The development of efficient photocatalysts is attracting increasing interest with a current focus on material design for improved efficiency. Accordingly, this study aims to optimize the conformation of nanocomposite prepared from a CdS/ZnO heterojunction on reduced graphene oxide (RGO) for boosting the photocatalytic removal of heavy metal contaminants of aqueous systems. Under visible light, the candidate nanocomposites exhibited a range of photocatalytic activity in reducing hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] at room temperature. Among these different nanocomposites, the photocatalytic removal rate constant of Cr(VI) ranged as follows: ZnO/CdS6:5/RGO6 (0.106 min−1) > ZnO/CdS6:5 (0.0630 min−1) > CdS (0.0335 min−1) > ZnO (0.00121 min−1). Moreover, after five cycles of use, the photocatalytic reduction rate of ZnO/CdS6:5/RGO6 was 93.2 %, which signifies its strong re-cycling performance. These results reveal the feasibility of using CdS/ZnO6:5/RGO6 to reduce heavy metal ions from wastewater and provide insights for efficiently removing heavy metal ions without additional chemical trapping agents in the photocatalytic process.

Bacterial cellulose/PANi mat for Cr(VI) removal at acidic pH

AbstractRemediation of hexavalent chromium ‐ Cr(VI) at acidic pH using polyaniline coated bacterial cellulose porous mat (BC/PANi) is presented and the possible mechanism is discussed. The efficacy of BC/PANi mats in remediation of Cr(VI) was studied by varying pH (pH 1, 2, 3, and 5) and initial Cr(VI) concentrations (250–1000 ppm) of the solution. The BC/PANi (50 mg) mat was able to completely reduce 2000 ppm Cr(VI) into Cr(III) in a 20 ml solution at pH ~ 1 in 24 h. An increasing chromium removal efficiency was observed with decreasing solution pH; reaching a maximum removal capacity of ~920 mg/g at pH 1. The proposed mechanism of negatively charged Cr(VI) ions removal by BC/PANi mat is adsorption and simultaneous reduction into Cr(III), followed by desorption of Cr(III) from the mat. The role of temperature and co‐existing anions like sulphate, nitrate and chloride found in industrial sludge were also investigated for removal efficiency of Cr(VI) at acidic pH ~ 1. The adsorption kinetics of Cr(VI) on polyaniline surface followed a pseudo‐second‐order model with reduction of Cr(VI) into Cr(III) as rate‐limiting step. The reduced Cr(III) from the media was further recovered by neutralizing the pH of the solution.

Efficient removal of chromium(VI) from dilute aqueous solutions using agro-industrial residue based on parboiled-rice husk ash

The removal of Cr(VI) from wastewater by adsorption from agro-industrial residues remain an attractive option since combines reasonable cost with the quality of effluents treated. This paper employs of parboiled-rice husk ash (RHA) and parboiled-rice husk ash chemically treated (RHAH+) as adsorbents for Cr(VI). The RHA and RHAH+ were characterized. It was studied the adsorption efficiency on adsorbent dosage, pH, chromium concentration, and interaction time. RHAH+ presented superior Cr(VI) removal, although both adsorbents have shown satisfactory results. The best results are obtained at pH 1.0, presenting 90.9% and 97.7% of Cr(VI) removal for RHA and RHAH+, respectively, in 5 mg L−1 of Cr(VI) concentration at about 30 minutes. The adsorption of RHAH+ is governed by the Freundlich isotherm (R2 adj = 0.989) and kinetically by the pseudo-second order model (R2 adj = 0.991). The rice rusk ash represents an alternative low-cost and environment-friendly material that efficiently removes Cr(VI) from dilute aqueous solutions.

Efficient Removal of Chromium(VI) Anionic Species and Dye Anions from Water Using MOF-808 Materials Synthesized with the Assistance of Formic Acid.

This study presents a simple approach to prepare MOF-808, an ultra-stable Zr-MOF constructed from 6-connected zirconium clusters and 1,3,5-benzene tricarboxylic acid, with tailored particle sizes. Varying the amount of formic acid as a modulator in the range of 200–500 equivalents results in MOF-808 materials with a crystal size from 40 nm to approximately 1000 nm. Apart from the high specific surface area, a combination of a fraction of mesopore and plenty of acidic centers on the Zr-clusters induces a better interaction with the ionic pollutants such as K2Cr2O7 and anionic dyes. MOF-808 shows uptakes of up to 141.2, 642.0, and 731.0 mg/g for K2Cr2O7, sunset yellow, and quinoline yellow, respectively, in aqueous solutions at ambient conditions. The uptakes for the ionic dyes are significantly higher than those of other MOFs reported from the literature. Moreover, the adsorption capacity of MOF-808 remains stable after four cycles. Our results demonstrate that MOF-808 is a promising ideal platform for removing oxometallates and anionic dyes from water.

To improve the performance of focusing phenomenon related to energy consumption and removal efficiency in electrokinetic remediation of Cr-contaminated soil

The focusing phenomenon is a difficult point during the electrokinetic remediation (EKR) of contaminated soil. It restricts the extraction and removal of heavy metals. There is still a lack of methods to discern focusing position rapidly and take proper measures. Therefore, a total of seven tests with or without intervening and regulating measures were conducted. Among the four tests without regulating and intervening measures, focusing position often appeared in low-voltage region after three days’ treatment. When using ammonium citrate as electrolyte, the highest removal efficiency of total chromium (Cr) (32.20%) was achieved. The intervening measure that adding citric acid near section 4 decreased the area of high-voltage and made it move towards cathode. Meanwhile, the removal efficiency of Cr(VI) (60.17%) was significantly improved. Using sodium dodecyl sulfate (SDS) as pretreatment agent and electrolyte made the position of high-voltage area move towards anode and removed 35.80% of total Cr and 53.47% of Cr(VI) eventually. Simultaneously, the energy consumption per gram of removed Cr was also the lowest. The focusing degree was reduced with intervening and regulating measures conducted but focusing position still existed in low voltage area, which further indicated that focusing position preferred to appear in low voltage area and we could discern focusing position through voltage distribution across the soil roughly.

Hexavalent chromium adsorption onto crosslinked chitosan and chitosan/β-cyclodextrin beads: Novel materials for water decontamination

The primary aim of the present research was the development and testing of novel synthesized crosslinked beads consisting of plain chitosan and/or with β-cyclodextrin as hexavalent chromium adsorption agents. Their effectiveness was evaluated in batch experiments, whereby the effects of pH, initial hexavalent chromium concentration, initial adsorbent concentration, and temperature were investigated. Between the two beads, chitosan/β-cyclodextrin provided higher hexavalent chromium removal efficiency than the chitosan beads. Further, it achieved higher amount of adsorbed hexavalent chromium in the majority of the experiments. The adsorption was exothermic and more spontaneous at low temperature (15 °C). The optimum hexavalent chromium removal conditions were identified at pH = 4, initial concentration of adsorbent 20 g/L, and temperature of 15 °C; at high initial concentrations of hexavalent chromium (75 and 100 mg/L) a decrease in the removal efficiency was observed. The maximum reported adsorption capacity was 400.00 and 555.56 mgCr(VI)/gadsorbent for plain chitosan and chitosan with β-cyclodextrin beads produced by crosslinking, respectively. Moreover, the adsorption of hexavalent chromium onto both beads was revealed to follow the kinetic model of pseudo-second. Both the adsorption and the characterization of the beads were evaluated prior and after the adsorption process by FTIR and SEM analyses. Finally, the synthesized beads provided satisfactory regeneration results after four adsorption/desorption cycles. Therefore, they constitute a promising novel class of adsorbents for the efficient decontamination of aqueous streams with concentrations of hexavalent chromium that exceed legislation limits.

Batch Electrocoagulation Process for Removal of Chromium from Tannery Wastewater

This study was aimed to investigate the chromium removal from the tannery wastewater through electrocoagulation. The zinc and copper plates were used as electrodes for the electrocoagulation process. The effectiveness of the electrocoagulation for chromium removal efficiency was examined investigating various parameters: applied voltage, time, and current density. In batch experiment, 500 mL chromium-containing wastewater was used for electrocoagulation. Chromium content in the raw wastewater and after treatment at optimized conditions was 340.1 and 6.9 mg/L, respectively. The efficiency of chromium removal and reduction of biochemical oxygen demand (BOD) was at 98.0 and 64.6%, accordingly. Although total dissolved solids (TDS) was slightly increased. The increment of current density enhances forming zinc hydroxide which causes the damage of electrodes. Electrocoagulation is an effective technique to remove chromium from the wastewater especially from the tannery wastewater.
 Journal of Engineering Science 12(1), 2021, 29-34

Electrochemical treatment of high strength chrome bathwater: A comparative study for best-operating conditions

In this study, high strength chromium (1500 ​ppm) wastewater was treated by electrochemical and chemical precipitation. Preliminary experiments using synthetic wastewater were carried out to optimize the process parameters viz. pH, current density and treatment time by systematically varying these variables as per response surface methodology (RSM) approach. The results showed that 97.5% chromium removal efficiency was achieved under optimized process conditions, i.e. pH 5, current density 68 A/m2 and treatment time 17 ​min. The electrolyte concentration beyond 4 ​g/L does not significantly improve chromium removal efficiency. The optimized process conditions from simulated solution were used to treat real chrome bathwater, but due to the highly acidic nature of the chrome bath, negligible chromium removal was obtained. Thus, two industrial wastewater management approaches were used to improve the chromium removal efficiency (i) dilution of the chrome bathwater (ii) chemical precipitation before electrocoagulation. Electrocoagulation treatment of five-fold diluted chrome bathwater has 99.9% chromium removal efficiency in 55 ​min of treatment time consuming specific energy consumption (SEC) of 10.3 ​KWh/kg of chromium. By integration of chemical precipitation and electrochemical treatment, the chromium removal efficiency of 97.3% was observed in 240 ​min of treatment time with SEC of 27.3 ​kWh/kg of chromium. Integration of reduction-precipitation before electrochemical treatment is another choice, in contrast, to sample dilution with an option for retrofitting of existing treatment schemes.

Chromium adsorption on coir pith charcoal from tannery wastewater

Emission of high chrome tanning wastewater is catastrophic for the environment. In this work, the effectiveness of coir pith charcoal is stated for the removal of chromium from tannery wastewater. The charcoal yield from the coir pith was 2.4%. The prepared charcoal was characterized by Fourier transform infrared spectroscopy (FT-IR). The efficiency of coir pith charcoal for chromium removal was assessed experimenting with various parameters e.g., charcoal dose, contact time, and relative pH. The content of chromium in the raw wastewater and after treatment at filtrate was 3439.2 mg/L and 14.9 mg/L, individually. In the batch experiment at optimized condition, for 75 mL chrome wastewater at 4 g charcoal dose with 15 min contact time, the chromium removal efficiency was attained 99.6%. The level of chloride (Cl-), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) were significantly reduced by 65.7%, 93.7%, and 95.6%, respectively. The use of coir pith charcoal could be an alternative source for the removal of chromium from chrome containing wastewater.
 Bangladesh J. Sci. Ind. Res.56(1), 53-60, 2021

Remediation of As/Cr co-contaminated soil by electrokinetic coupled with permeable reactive barrier

In this study, the permeable-reactive-barrier (PRB) assisted electrokinetic (EK) was used to remediate As/Cr Co-contaminated soil, aiming to explore the optimal remediation conditions and the migration of As/Cr. The effects of PRB active substance, PRB location, voltage gradient and running time on the migration and transformation of Cr and As in simulated As/Cr contaminated kaolin were studied. The optimal parameters were as follows: PRB position was located near the anode (PRB A, the medium of PRB was hydrocalumite (CaAl-LDH)), initial voltage gradient was 1 V/cm, running time was 96 h. Under the optimal conditions, the removal efficiency of total arsenic (TAs) and total chromium (TCr) were 40.1% and 81.0%, respectively. This indicated that EK can effectively migrate As and Cr, and PRB can effectively adsorb As and Cr. The migration of As tends to both anode and cathode, while Cr tends to migrate towards the anode. The XRD patterns and FTIR spectra confirmed that the As immobilized by CaAl-LDH was mainly adsorbed on the surface, while Cr existed in CaAl-LDH by surface adsorption and intercalation.

A comparative study on the efficiency of various cathodes in reducing hexavalent chromium at low voltage

AbstractElectroreduction of Cr (VI) ions in effluents to its less toxic Cr (III) ions is a simple and efficient water treatment technique. The present study aims at using graphite as an anode to reduce the metal ion pollution that occurs due to the dissolution of the metal anode in electrochemical reduction. Also, the efficiency of aluminum, stainless steel, and copper plates as cathodes in removing chromium (VI) ions in aqueous potassium dichromate solution is compared in the low potential range. The effect of cathode surface area and solution pH on chromium removal efficiency has been studied. Stainless steel and copper are shown to have similar to no change in removal efficiency and higher than aluminum. The maximum removal efficiency of approximately 72% is obtained with the copper cathode (5.5 cm × 1 cm) and 6 volts in acidic pH. For the same voltage, with an increase in surface area, removal efficiency decreases due to a decrease in current density. The experimental data are fitted best with pseudo‐first‐order kinetics, indicating the potential flux limits the reduction rate in the lower range of current density. Thermodynamic studies concluded the feasibility, spontaneity, and endothermic nature of the electroreduction process.

Development of copper—iron bimetallic nanoparticle impregnated activated carbon derived from coconut husk and its efficacy as a novel adsorbent toward the removal of chromium (VI) from aqueous solution

AbstractThe present work demonstrates the preparation of biodegradable coconut husk derived activated carbon (CAC) impregnated with bimetallic nanoparticles consisting of zerovalent iron and copper to produce a new adsorbent (Fe0/Cu‐CAC). The new adsorbent was further employed to determine the removal efficiency of Chromium (VI) from aqueous solutions. Chromium (VI) adsorption process by Fe0/Cu‐CAC was found to be favorable at pH ~ 3, attaining 95.28% removal efficiency while its counterpart CAC attained only ~41%. Negative ΔG0 value suggests that the process was thermodynamically spontaneous and ΔH0 was observed to be 8.496 kJ/mol, further corroborating the endothermic nature of the process. Pseudo‐second order model was best suited to explain the kinetics of the process with R2 value of 0.99683 and an error of 6.73%. Equilibrium parameter (RL) derived from Langmuir isotherm was calculated to be 0.1103, indicating favorable adsorption and thus Langmuir isotherm can be used to describe the process of adsorption of Cr (VI) by Fe0/Cu‐CAC. Finally, a maximum monolayer adsorption capacity of 173.9 mg/g indicated the suitability of the prepared adsorbent in treating chromium contaminated wastewater streams.Practitioner points Facile development of novel adsorbent from biodegradable coconut husk via cost effective route. Utilization of the adsorbent towards removal of toxic pollutant like Cr (VI) from its aqueous solution. Validation of the effective adsorption mechanism by Kinetic and Thermodynamic study.

Comparing Chemical Coagulation and Electrocoagulation on removal efficiency of Chromium (VI) from Galvanic Effluents

Comparing Chemical Coagulation and Electrocoagulation on removal efficiency of Chromium (VI) from Galvanic Effluents

Adsorptive Mechanism of Chromium Adsorption on Siltstone–Nanomagnetite–Biochar Composite

In this work, the potential of a novel and highly efficient composite of Eleocharis dulcis biochar with magnetite nanoparticles and siltstone was explored for removing chromium from water. Characterization of the prepared biochar composite was carried out using thermal gravimetric analysis (TGA), X-ray photon spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy, point of zero charge and BET. XRD confirmed magnetite and quartz to be the main phases in biochar composite. TGA results showed higher thermal stability of the composite after the addition of siltstone. Batch adsorption mode was employed for studying the adsorption capacity of sample for the decontamination of chromium as a function of concentrations, time, temperatures and pHs. Kinetic modelling confirmed pseudo second order to fit best to the kinetic data for chromium adsorption on the composite biochar. An increase of adsorption was observed with the rise in temperature from 303 to 318 K showing the endothermic nature of the process whereas pH study showed higher removal efficiency of chromium in the acidic pH range. Langmuir model was applicable to the data with higher value of correlation. The thermodynamic parameter ΔH° (40.46 kJ mol−1) and negative but higher values of (ΔG°) shows the endothermic and spontaneous nature of the adsorption process respectively. Higher value of activation energy (15.08 kJ mol−1) confirmed the chemical nature of the process. Post adsorption FTIR and XPS confirmed the adsorption of chromium on the surface of the composite. The adsorption capacity obtained in the present study was found to be higher as compared to many other reported adsorbents used for chromium removal.

Chromium VI Detoxification by <i>P. fluorescens </i>Adopted from Tannery Effluent under Optimal Condition

The present study is aimed to isolate and evaluate chromium reduction by the indigenous bacterium Pseudomonas fluorescens in tannery effluents collected from airport, Tiruchirappalli. Chromium resistant pattern was studied by plate method and reduction was studied by shake flask method. Isolate Pseudomonas fluorescens biochemically characterized as Gram negative siderophore producing bacteria and found to tolerate 1000 ppm Cr VI. Among the pH best growth was found at pH 6 showed Lag Growth phase was observed on 4 h at nonchromium condition and 6 h for chromium supplemented medium at 100 ppm and 7 h at 1000ppm. The growth was retreated by chromium but not arrested. The yield of the bio-surfactant was relatively higher in pH 8. Medium with yeast extract, pH 8 comparatively better than other nitrogen in chromium reduction. Maximum Chromium removal efficiency was 82% under chitosan and 78% by EDTA supplemented medium. Other nitrogen sources were less significant. In pH 8 under yeast extract and glucose with EDTA and 68% chromium reduction was noted without EDTA. Medium with chitosan showed enhanced reduction from 55 % to 88%. Other nitrogen sources like peptone, casein, ammonium nitrate showed 60-70% reduction in the presence of EDTA and reduction was reduced to 50% without EDTA. The increase of dextrose strength does not influence the reduction of chromium and maximum activity was found at 2% same as 10%.

Reusable magnetite nanoparticles\u2013biochar composites for the efficient removal of chromate from water

Biochar (BC) and magnetite (Fe3O4) nanoparticles (MNP) have both received considerable recent attention in part due to their potential use in water treatment. While both are effective independently in the removal of a range of anionic metals from aqueous solution, the efficacy of these materials is reduced considerably at neutral pH due to decreased metal adsorption and MNP aggregation. In addition to synthetic metal oxide–biochar composites for use in treatment and remediation technologies, aggregates may also occur in nature when pyrolytic carbon is deposited in soils. In this study, we tested whether magnetite synthesized in the presence of biochar leads to increased removal efficiency of hexavalent chromium, Cr(VI), at the mildly acidic to neutral pH values characteristic of most natural and contaminated aqueous environments. To do so, magnetite nanoparticles and biochar produced from ground willow were synthesized to form composites (MNP–BC). Batch studies showed that MNP–BC markedly enhanced both adsorption and reduction of Cr(VI) from aqueous solution at acidic to neutral pH as compared to MNP and BC separately, suggesting a strong synergetic effect of hybridizing Fe3O4 with BC. Mechanistically, the Cr(VI) removal processes occurred through both adsorption and intraparticle diffusion followed by reduction to Cr(III). Synchrotron-based X-ray absorption spectroscopy analyses confirmed that Cr(VI) was reduced at the surface of MNP–BC, with electrons derived directly from both biochar and magnetite at low pH, while at near-neutral pH, biochar increased Cr(VI) reduction by inhibiting MNP aggregation. Extended X-ray absorption fine structure fitting results confirmed that the Cr(III) precipitates consist of Cr(OH)3 and chromite (Cr2FeO4) nanoparticles. Our results demonstrate that MNP–BC composites have great potential as a material for the treatment of chromate-containing aqueous solutions across a wide range of pH values, and provide information valuable broadly relevant to soils and sediments that contain biochar.