Magnetic biochar combining adsorption and separation recycle for removal of chromium in aqueous solution

Effect of biochar addition on the anaerobic digestion of food waste: microbial community structure and methanogenic pathways

This study assessed the effects of the addition of biochar prepared at 700 °C with different dosages on the anaerobic digestion of food waste. The biochar addition at a concentration of 10.0 g/L increased the cumulative methane yield by 128%, and daily methane production was also significantly promoted. The addition of biochar derived from poplar sawdust significantly increased the relative abundance of dominant bacteria for anaerobic digestion by 85.54-2530% and promoted the degradation of refractory organic matter and the transfer of materials between the hydrolysis and acid production stages. Further analysis has demonstrated that Bathyarchaeia and hydrogenotrophic methanogens were enriched by the biochar addition. Meanwhile, the relative abundances of functional genes, including C5-branched dibasic acid metabolism, and pyruvate metabolism, were increased by 11.38-26.27%. The relative abundances of genes related to major amino acid metabolism, including histidine metabolism, lysine biosynthesis, and phenylalanine, tyrosine, and tryptophan biosynthesis, were increased by 11.96-15.71%. Furthermore, the relative abundances of genes involved in major replication and repair were increased by 14.76-22.76%, and the major folding, sorting, degradation, and translation were increased by 14.47-19.95%, respectively. The relative abundances of genes related to major membrane transport and cell motility were increased by 10.02 and 83.09%, respectively.

Synthesis and application of lanthanum-doped magnetic biochar composite adsorbent for removal of fluoride from water

Fluoride levels greater than 1.5 mg/L in drinking water are a global environmental issue that can seriously harm the health of humans. One of the most effective techniques for defluoridating water is adsorption. The main drawbacks of many adsorbent materials include their poor adsorption capabilities, prolonged contact times, excessively low or high pH levels, and high dosages. The biochar-based magnetic nanocomposite adsorbent was synthesized in the current study and used as an adsorbent for water defluoridation. Through slow pyrolysis, coffee husk waste was converted to biochar. The composite was created by chemically co-precipitating iron and lanthanum oxide nanoparticles onto the surface of biochar. By using X-ray diffraction analysis (XRD), Fourier transform infrared spectrometry (FTIR), Brunauer-Emmett-Teller (BET), and pHPZC values, researchers were able to describe the magnetic biochar nanocomposite material. The Central Composite Design (CCD), which uses four input variables including dosage (2-5 g/L), solution pH (4-8), contact time (30-70 min), and initial concentration (10-20 mg/L), was used to design the experiments. The quadratic model indicated that the ideal conditions for removing 98.994% of the fluoride from water (adsorbent dosage of 5 g L-1, pH 5.74, contact period of 60 min, and initial concentration of 12.245 mg/L) would be attained. The average triplicate value in ideal circumstances produced a removal effectiveness of 98.51%, demonstrating the proposed response surface's capacity for prediction. The findings of this investigation showed that the magnetic biochar nanocomposite that was created is an effective fluoride adsorbent.

Removal of hexavalent chromium via biochar-based adsorbents: State-of-the-art, challenges, and future perspectives

Chromium originates from geogenic and extensive anthropogenic activities and significantly impacts natural ecosystems and human health. Various methods have been applied to remove hexavalent chromium (Cr(VI)) from aquatic environmental matrices, including adsorption via different adsorbents, which is considered to be the most common and low-cost approach. Biochar materials have been recognized as renewable carbon sorbents, pyrolyzed from various biomass at different temperatures under limited/no oxygen conditions for heavy metals remediation. This review summarizes the sources, chemical speciation & toxicity of Cr(VI) ions, and raw and modified biochar applications for Cr(VI) remediation from various contaminated matrices. Mechanistic understanding of Cr(VI) adsorption using different biochar-based materials through batch and saturated column adsorption experiments is documented. Electrostatic interaction and ion exchange dominate the Cr(VI) adsorption onto the biochar materials in acidic pH media. Cr(VI) ions tend to break down as HCrO₄^-, CrO₄^2-, and Cr₂O₇^2- ions in aqueous solutions. At low pH (∼1-4), the availability of HCrO₄^- ions attributes the electrostatic forces of attraction due to the available functional groups such as -NH₄⁺, -COOH, and -OH₂⁺, which encourages higher adsorption of Cr(VI). Equilibrium isotherm, kinetic, and thermodynamic models help to understand Cr(VI)-biochar interactions and their adsorption mechanism. The adsorption studies of Cr(VI) are summarized through the fixed-bed saturated column experiments and Cr-contaminated real groundwater analysis using biochar-based sorbents for practical applicability. This review highlights the significant challenges in biochar-based material applications as green, renewable, and cost-effective adsorbents for the remediation of Cr(VI). Further recommendations and future scope for the implications of advanced novel biochar materials for Cr(VI) removal and other heavy metals are elegantly discussed.

The Preparation of Eco-Friendly Magnetic Adsorbent from Wild Water Hyacinth (Eichhornia crassipes): The Application for Removing Lead Ions from Industrial Wastewater

Water hyacinth (Eichhornia crassipes) is a wild floating plant that can be found widely in pond or river areas. The plant grows fiercely and causes many harmful issues to the ecosystem around its covered area. This work provides a utilization method that converts wild water hyacinth to reliable magnetic biochar which can be used as a very effective adsorbent for the removal of lead ion Pb(II) in industrial wastewater. The mentioned magnetic biochar can be prepared via a modified pyrolysis process at 550°C with the support of cobalt sulfates as magnetite precursors and limited oxygen from the sweeping gas (the gas mixture ratio is 4 : 1 nitrogen/oxygen). The produced samples were hydrophobic biochar with high oxygen-containing functional groups that are suitable for the removal of inorganic contaminants. The impregnation of cobalt (II, III) oxides provided high magnetic separation performance and additional adsorption sites on the produced magnetic biochar. As indicated by the obtained result, the WHB-Co2M sample possesses a highly porous structure (0.126 cc/g), higher thermal stability (thermal durability reaches 900°C), relatively stable magnetic properties (14.74 emu/g), and a larger surface area (192 m2/g). These beneficial properties led to its suitability to serve as an adsorbent in removing lead ions in the contaminated effluent, recording 95% of removal efficiency and adsorption capacity of 67.815 mg/g. As indicated in the result, all prepared magnetic biochar samples were fitted to two-parameter (Langmuir models) and three-parameter (Sips model) isotherm models. Therefore, the adsorption process in this work could be carried out on both homogeneous and heterogeneous adsorbent surfaces. The adsorption kinetics of the removal process also was described by the pseudo-first-order, pseudo-second-order, and Elovich models to reveal the adsorption and desorption rate of the as-prepared magnetic biochar. This work indicates a successful waste refinery route of converting lignocellulosic biomass such as water hyacinth into value-added material for use as promising heavy metal adsorbents.

A comparison between the characteristics of a biochar-NPK granule and a commercial NPK granule for application in the soil

Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not return a profit to farmers due to the costs of application and the loss of NPK from soil in various ways. Thus, a combination of NPK granule with a porous biochar (termed here as BNPK) appears to offer multiple benefits resulting from the excellent properties of biochar. Given the lack of information on the properties of NPK and BNPK fertilizers, it is necessary to investigate the characteristics of both to achieve a good understanding of why BNPK granule is superior to NPK granule. Therefore, this study aims to investigate the characteristics of a maize straw biochar mixed with NPK granule, before and after application to soil, and compare them to those for a commercial NPK granule. The BNPK granule, with a greater surface area and porosity, showed a higher capacity to store and donate electrons than the NPK granule. Relatively lower concentrations of Ca, P, K, Si and Mg were dissolved from the BNPK, indicating the ability of the BNPK granule to maintain these mineral elements and reduce dissolution rate. To study the nutrient storage mechanism of the BNPK granule in the soil, short- and long-term leaching experiments were conducted. During the experiments, organo-mineral clusters, comprising C, P, K, Si, Al and Fe, were formed on the surface and inside the biochar pores. However, BNPK was not effective in reducing N leaching, in the absence of plants, in a red chromosol soil.

Purification mechanism of city tail water by constructed wetland substrate with NaOH-modified corn straw biochar

The pollution of corn straw to the environment had attracted much attention. The preparation and alkali modification of corn straw biochar as the constructed wetland (CW) substrate was conducive to solving the environment pollution caused by straw and improving the purification effect of CW. The NaOH modification mechanism of corn straw biochar was analyzed by measuring the surface morphology, element content, specific surface area (SSA), pore volume, crystal structure, surface functional groups and CO₂ adsorption. Biochar prepared under relatively optimal NaOH-modified conditions was used as the vertical flow CW substrate to treat city tail water. The results showed that controlling the modification condition of NaOH (< 1.0 mol·L^-1, ≤ 24 h) was conducive to prevent the biochar structure destruction and C element reduction. The SSA and pore volume of NaOH (0.1 mol·L^-1) modified biochar are 360 m²·g^-1 and 0.109 cm³·g^-1, respectively. The biochar adsorption for CO₂ conformed to the Langmuir and Freundlich isothermal adsorption theoretical model (R² > 0.9). The maximum adsorption capacity of CO₂ by modified biochar with NaOH (0.1 mol·L^-1) was 64.516 cm³·g^-1 and increased by 10.3%. The city tail water treated by CW with plants showed that the removal rates of ammonia nitrogen, total nitrogen and nitrate nitrogen reached about 90%. The research results improved the utilization value of straw, realized straw carbon sequestration and promoted the progress of CW technology.

Phosphorus-modified biochar cross-linked Mg-Al layered double-hydroxide stabilizer reduced U and Pb uptake by Indian mustard (Brassica juncea L.) in uranium contaminated soil

The decommissioning of uranium tailings (UMT) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological security. Therefore, the remediation of uranium pollution in soil is imminent from ecological and environmental points of view. In recent years, the use of biochar stabilizers to repair uranium tailings (UMT) soil has become a research hotspot. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg-Al layered double-hydroxide composite (PBC@LDH) was prepared. The hyperaccumulator plant Indian mustard (Brassica juncea L.) was selected as the test plant for outdoor pot experiments, and the stabilizers were added to the UMT soil at the dosage ratio of 15 g kg-1, which verified the bioconcentrate and translocate of U and associated heavy metal Pb in the UMT soil by Indian mustard after stabilizer remediated. The results shown that, after 50 days of growth, compared with the untreated sample (CK), the Indian mustard in PBC@LDH treatment possessed a better growth and its biomass weight of whole plant was increased by 52.7%. Meanwhile, the bioconcentration factors (BF) of U and Pb for PBC@LDH treatment were significantly decreased by 73.4% and 34.2%, respectively; and the translocation factors (TF) were also commendable reduced by 15.1% and 2.4%, respectively. Furthermore, the Tessier available forms of U and Pb in rhizosphere soil showed a remarkably decrease compared with CK, which reached by 55.97% and 14.1% after PBC@LDH stabilization, respectively. Complexation, precipitation, and reduction of functional groups released by PBC@LDH with U and Pb described the immobilization mechanisms of biochar stabilizer preventing U and Pb enrichment in Indian mustard. As well as, the formation of U-containing vesicles was prevented by the precipitation of -OH functional groups with free U and Pb ions around the cell tissue fluids and vascular bundle structure of plant roots, thereby reducing the migration risk of toxic heavy metals to above-ground parts. In conclusion, this research demonstrates that the PBC@LDH stabilizer offers a potentially effective amendment for the remediation of U contaminated soil.

Sorption, separation and recycling of ammonium in agricultural soils: A viable application for magnetic biochar?

Recent research on the magnetisation of biochar, a carbon-based material that can be used as a sorbent, has opened novel opportunities in the field of environmental remediation, as incorporating magnetic particles into biochar can simplify subsequent separation. This could offer a sustainable circular economy-based solution in two areas of waste management; firstly, pyrolysis of agricultural waste for magnetic biochar synthesis could reduce greenhouse gas emissions derived from traditional agricultural waste processing, such as landfill and incineration, while secondly, application of magnetic biochar to remove excess nitrogen from soils (made possible through magnetic separation) could provide opportunities for this pollutant to be used as a recycled fertiliser. While sorption of pollutants by magnetic biochar has been researched in wastewater, few studies have investigated magnetic biochar use in polluted soils. Nitrogen pollution (e.g. NH₄⁺), stemming from agricultural fertiliser management, is a major environmental and economic issue that could be significantly reduced before losses from soils occur. This review demonstrates that the use of magnetic biochar tailored to NH₄⁺ adsorption has potential to remove (and recycle for reuse) excess nitrogen from soils. Analysis of research into recovery of NH₄⁺ by sorption/desorption, biochar magnetisation and biochar-soil interactions, suggests that this is a promising application, but a more cohesive, interdisciplinary approach is called for to elucidate its feasibility. Furthermore, research shows variable impacts of biochar upon soil chemistry and biology, such as pH and microbial diversity. Considering wide concerns surrounding global biodiversity depletion, a more comprehensive understanding of biochar-soil dynamics is required to protect and support soil ecosystems. Finally, addressing research gaps, such as optimisation and scaling-up of magnetic biochar synthesis, would benefit from systems thinking approaches, ensuring the many complex considerations across science, industry, policy and economics are connected by circular-economy principles.

Characterization of amphoteric bentonite-loaded magnetic biochar and its adsorption properties for Cu2+ and tetracycline

To realize simultaneous adsorption of heavy metal and antibiotic pollutants by a BC-based recyclable material, Fe₃O₄ magnetic biochar (MBC) was prepared by co-precipitation method. Then different ratios of dodecyl dimethyl betaine (BS-12)-modified bentonite (BS-B) were loaded on the surfaces of biochar (BC) and MBC to prepare BS-B-loaded BC and MBC composites, called BS-B/BC and BS-B/MBC, respectively. The physicochemical and structural properties of the composites were characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, specific surface area (S_BET) analysis, and vibrating sample magnetometry, and the adsorption efficiencies of BS-B/BC and BS-B/MBC to Cu²⁺ and tetracycline (TC) were studied. The following results were obtained. (1) Compared with BS-B/BC, BS-B/MBC had decreased pH and cation exchange capacity (CEC) and increased S_BET. The pH, CEC, and S_BET of BS-B/BC and BS-B/MBC decreased with the increase in the BS-12 proportion of BS-B. The surface of BS-B/MBC became rough after Fe₃O₄ loading. (2) The residual rate of BS-B/MBC was higher than that of BS-B/BC after high-temperature combustion, and the residual rate decreased with the increase in the BS-12 proportion of BS-B. The 2D infrared spectra showed that Fe₃O₄ and BS-12 were modified on the surface of BS-B/MBC. MBC and BS-B/MBC had splendid magnetism and could be separated by external magnetic field. (3) Compared with unmagnetized ones, the adsorption effects of Cu²⁺ and TC on different BS-B/MBCs improved, and the average adsorption rate reached the largest value of 91.92% and 97.76%, respectively. Cu²⁺ and TC adsorptions were spontaneous, endothermic, and entropy-increasing processes. The pH and S_BET of the material had a great influence on Cu²⁺ and TC adsorptions, respectively, than CEC.

Adsorption of metolachlor by a novel magnetic illite-biochar and recovery from soil

In this study, we investigated a highly efficient adsorbent that can be recycled from the soil. Walnut shells were used as raw materials to prepare original ecological biochar (OBC), illite modified biochar (IBC), FeCl₃ modified biochar (magnetic biochar; MBC), and illite and FeCl₃ modified biochar (IMBC), which were tested as low-cost adsorbents. The agents were used to remove metolachlor (MET) from soil. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, magnetic sensitivity curve analysis, and a series of adsorption experiments were conducted to study the interaction between illite and MBC, and the effect on MET adsorption. Compared with OBC, IMBC had more adsorption sites on the surface. IMBC improved the hole filling effect during the adsorption process. IMBC had more oxygen-containing functional groups and it performed better at removing organic matter through π-π interactions. According to the Langmuir model, the Q₀ values for IBC, MBC, and IMBC were 91.74 mg g^-1, 107.53 mg g^-1, and 129.87 mg g^-1, respectively, which were significantly higher than that for OBC (72.99 mg g^-1). The response surface model was used to explore the optimal adsorption conditions for IMBC. After three regeneration cycles, the MET adsorption rate with IMBC was still 81.38% and the MET recovery rate was 98.12%. Therefore, IMBC was characterized as an adsorbent with high efficiency, low cost, and good recyclability. In addition, we propose a suitable agricultural system for recovering MBC on site in the field.

A novel synthesis of sulfurized magnetic biochar for aqueous Hg(II) capture as a potential method for environmental remediation in water

Due to public health threats resulting from mercury (Hg) and its distribution in the food chain, global restrictions have been placed on Hg use and emissions. Biochar is a porous, carbonaceous adsorbent typically derived from waste biomass or organic matter, making it an eco-friendly material for aqueous mercury (Hg(II)) control. Functionalization of biochar can improve performance in pollution control applications. In this work, carbonization, magnetization, and sulfurization of biochar were combined into a single heating step to prepare sulfurized magnetic biochar (SMBC) for Hg(II) removal from water. Results indicate that SMBC prepared at 600 °C adsorbed 8.93 mg/g Hg(II), more than materials prepared at 400, 500, 700, 800, and 900 °C. Additionally, Hg(II) adsorption onto SMBC was 53.0% and 11.5% greater than onto magnetic biochar (MBC) and biochar (BC), respectively. Hg(II) adsorption is shown to be favorable in acidic conditions (pH 3.5-5), thermodynamically spontaneous, and endothermic. Adsorption results fit the pseudo-second-order (R² = 0.990 and the sum of squared error (SSE) = 5.382) and external mass transfer (R² = 0.971 and SSE = 9.422) models. The partitioning coefficients were 4.964 mg/g/μM in freshwater, 0.176 mg/g/μM in estuary water, and 0.275 mg/g/μM in seawater, highlighting the importance of salinity in environmental remediation applications. In summary, SMBC can be readily prepared with minimal processing steps. The product is a robust adsorbent for Hg(II), and it can potentially be applied to remediate contaminated water/sediment/soil in the future.

Removal of Cd from aqueous solution by chitosan coated MgO-biochar and its in-situ remediation of Cd-contaminated soil

In this study, magnesium oxide biochar-chitosan composite (MgO-BCR-W) prepared through modification with MgCl₂ and chitosan was investigated as an adsorbent for the removal of Cd from the aquatic and soil environment. Kinetic and thermodynamics revealed that the Cd(II) adsorption onto MgO-BCR-W was well fitted by pseudo-second-order and the Langmuir adsorption isotherm. The adsorption capacities of rice husk biochar (BCR) and MgO-BCR-W for Cd(II) reached 11.09 mg/g and 59.66 mg/g, respectively. Attractively, the computed values of R_L ranged between 0 and 1, suggesting that the adsorption of Cd(II) onto MgO-BCR-W is favourable. Characterisations of the adsorbents revealed that the synergistic effect of surface complexation and precipitation mechanisms played a major role in the removal of Cd. In soil incubation experiment, the addition of MgO-BCR-W at the level of 2% was most effective in Cd stabilization compared to the control, which reduced the content of bioavailable Cd by 22.32%. Furthermore, it reduced the acid extractable Cd by 24.77%, while increased the residual Cd content by 22.24%. The results demonstrated that MgO-BCR-W could be used as an effective and eco-friendly adsorbent for Cd remediation in both water and soil environment.

Surface characterization of maize-straw-derived biochar and their sorption mechanism for Pb2+ and methylene blue

Biochar derived from straw is a potential low-cost adsorbent for metal ions and organic pollutants, but its practical application is still limited by the adsorption capacity. In this study, the correlation between the biochar’s properties and pyrolysis temperature was explored. The adsorption mechanism was studied by monitoring the changes of biochar properties before and after adsorption using BET, SEM, XPS and FT-IR spectroscopy. The adsorption mechanism was revealed following the adsorption kinetics and the changes in biochar’s properties before and after adsorption. The methylene blue (MB) and Pb²⁺ adsorption removal efficiency reached 95% at the initial concentration of 125 and 500 mg/L, respectively. Physisorption, chemisorption, and pore filling mechanisms determined the adsorption process of MB and Pb²⁺ on biochar. The Pb²⁺ adsorption process was highly affected by chemical co-precipitation at higher pyrolysis temperatures. The appearance of tar particles increased the adsorption rate of Pb²⁺. The biochar obtained at the pyrolysis temperature at 500, 800 and 900°C proved to be applicable for Pb²⁺ removal. Chemisorption and porosity dominated the MB adsorption, and biochars produced at pyrolysis temperatures of 200, 800 and 900°C are potential materials for MB removal. This study provides optimal pyrolysis conditions for transforming maize straw into valuable, low-cost materials for the removal of different pollutants.

Fluorescence regional integration combined with parallel factor analysis to quantify fluorescencent spectra for dissolved organic matter released from manure biochars

Dissolved Organic Matter (DOM) in biochars is important to carbon dynamics and contaminant transport in soils. Fluorescence excitation-emission matrices (EEMs) have been widely used to characterize dissolved organic matter (DOM). In this study, fluorescence regional integration (FRI) and parallel factor analysis (PARAFAC) applied to EEM allows good quantitative assessment of the composition of DOM derived from manure biochars. Manure biochars were produced using four types of manure, chicken, pig, cow, and sheep manure under various pyrolysis temperatures (300–600 °C) and holding times (0–120 min). The results from the determination of dissolved organic carbon (DOC), SUVA₂₅₄, and humification index (HIX) reflected that high pyrolysis temperature and long holding time led to a significant decrease in DOM quantity, aromaticity and humification. The FRI result showed that the pyrolysis process of DOM released from manure biochars included three changes, aromatic protein-like substance and microbial by-product-like substance generation (300–600 °C), fulvic-acid like substance decomposition (300–500 °C) and humic acid-like substance decomposition (600 °C). The PARAFAC modeling result showed that the pyrolysis process of DOM released from manure biochars contained two changes: three high molecular-weight humic-like substances decomposition and a low molecular-weight humic-like substance generation. The effect of the holding time on biochar-DOM is more significant at higher pyrolysis temperatures than lower pyrolysis temperatures. The correlation analysis result revealed that the generation of aromatic proteins, microbial by-products and fulvic acid came from the decomposition of humic-like substances including marine humic-like, UVA humic-like, and UVC + UVA humic-like substances. The results obtained in this study would be beneficial to guide the rational production and application of manure biochars.

Dissolved Organic Matter (DOM) in biochars is important to carbon dynamics and contaminant transport in soils

Enhanced removal of hexavalent chromium by engineered biochar composite fabricated from phosphogypsum and distillers grains

Two kinds of industrial wastes (distillers grains and phosphogypsum) were used as raw materials to produce a new biochar composite for Cr(VI) removal in water. The influencing factors including pyrolysis temperature, dosage, initial solution pH as well as contacting time were explored. The adsorption kinetics, isotherms, and thermodynamics of two biochars were conducted. The results show that the adsorption of Cr(VI) by biochar is related to pH. The ideal pH was 3.0 and the adsorbed Cr(VI) decreases as the pH increases. The Cr(VI) adsorption process conformed to the pseudo-second-order equation. Phosphogypsum modified (PM)-biochar is well described by the Freundlich model. The maximum adsorption capacities of distillers grains (DG)-biochar and PM-biochar on Cr(VI) were 63.1 and 157.9 mg g^-1, respectively. The thermodynamic analysis indicates that the Cr(VI) adsorption occurs spontaneously which is an endothermic process. This study provided an alternative way for Cr(VI) removal from water.

Magnetic palm kernel biochar potential route for phenol removal from wastewater

The pollution of water resources due to the disposal of industrial wastes that have organic material like phenol is causing worldwide concern because of their toxicity towards aquatic life, human beings and the environment. Phenol causes nervous system damage, renal kidney disease, mental retardation, cancer and anaemia. In this study, magnetic palm kernel biochar is used for removal of phenol from wastewater. The effect of parameters such as pH, agitation speed, contact time and magnetic biochar dosage are validated using design of experiments. The statistical analysis reveals that the optimum conditions for the highest removal (93.39%) of phenol are obtained at pH of 8, magnetic biochar dosage of 0.6 g, agitation speed at 180 rpm and time of 60 min with the initial concentration of 10 mg/L. The maximum adsorption capacities of phenol were found to be 10.84 mg/g and Langmuir and Freundlich isotherm models match the experimental data very well and adsorption kinetic obeys a pseudo-second order. Hence, magnetic palm kernel can be a potential candidate for phenol removal from wastewater.

Bone-derived biochar and magnetic biochar for effective removal of fluoride in groundwater: Effects of synthesis method and coexisting chromium

The presence of fluoride in groundwater in excess of 1.5 mg L^-1 is a major environmental health concern, and biochar is a promising low-cost adsorbent for the treatment of such water. In the present study, pristine and magnetic biochars were synthesized by peanut hull and bovine bone for the adsorption of fluoride. The biochars were systematically characterized by SEM-EDS, BET, XRD, VSM, FT-IR, and XPS. The experiment results showed that the magnetic biochar prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") had a higher adsorption capacity than that prepared by mixing pristine biochar with Fe²⁺ /Fe³⁺ solution and then treating with NaOH ("postpyrolysis"). The bone-derived biochar and magnetic biochar exhibited high adsorption capacity of fluoride (>5 mg g^-1 ) due to the presence of hydroxyapatite (HAP) and γ-Fe₂ O₃ . The 0.1 M NaOH solution could be optimal desorption agent, and the adsorption-desorption experiments indicated the bone biochars maintained the reasonable adsorption capacity after several cycles. Moreover, the coexisting Cr(VI) and fluoride could be removed simultaneously by bone-derived biochars. It is suggested that bovine bone-derived pristine and magnetic biochars can be used as preferential adsorbents for fluoride removal from contaminated groundwater. PRACTITIONER POINTS: Bone-derived pristine and magnetic biochars exhibit high adsorption capacity for fluoride in weakly alkaline solution. The presence of hydroxyapatite and γ-Fe₂ O₃ in bone-derived biochars plays an important role for fluoride adsorption. Magnetic biochars prepared by soaking biomass in FeCl₃ solution and then pyrolyzing ("prepyrolysis") perform better. The coexisting Cr(VI) and fluoride can be simultaneously removed in groundwater by bone biochars.

Efficient Removal of Hexavalent Chromium from Wastewater with Electro-Reduction

Removal of hexavalent chromium had attracted much attention as it is a hazardous contaminant. An electrocoagulation-like technology electro-reduction was applied. The chromium (VI) in the wastewater was reduced to chromium (III) by the electron supplied by electricity power and Fe2+, formed from corrosion of steel electrodes in acidic conditions. The mechanism and parameters affecting the reaction were investigated. The results optimized by response surface methodology indicated that the influence of single factor on the reduction efficiency followed the order: A: dosage of H2SO4 > C: reaction time > D: reaction temperature > B: current intensity. The reduction efficiency was hardly affected by current intensity, while it was increased with the increasing of reaction time and acid concentration. The reducing agent, Fe2+ an and extra free electron, acted as a reducing agent and could easily reduce hexavalent chromium to trivalent chromium at high temperatures in an acidic medium.

Synthesis of MgO-coated corncob biochar and its application in lead stabilization in a soil washing residue

In this study, a magnesium oxide (MgO) coated corncob biochar (MCB) was synthesized by pyrolyzing MgCl₂ pretreated corncob, for a better performance in lead immobilization in a contaminated soil compared with corncob biochar (CB). The properties and microstructures of CB and MCB were investigated. It was observed that MgO particles ranging from 1 to 2 μm were well coated on MCB, and the MgO content in MCB was calculated at 29.90% in w/w. The surface area of the biochar was significantly enhanced from 0.07 to 26.56 m²/g after the MgO coating. The MgO coating also significantly facilitated the lead removal percentage from 23% to 74% in aqueous solution by biochar. CB failed to immobilize lead in a soil washing residue and could not reduce its environmental risks in a laboratory incubation study. In contrast, MCB was applied to the soil and resulted in a significant reduction in TCLP leached lead from 10.63 to 5.24 mg/L (reduced by 50.71%). The comparison between MCB and other amendments suggests that the biochar component of MCB adsorbed lead onto its surface through cation-π interaction and increased surface adsorption due to higher surface area, and then the MgO coated on MCB's surface further enhanced the adsorption through precipitation. The synergistic roles of biochar-mineral composites make them a promising candidate for soil remediation.