Qualitative and quantitative analysis for Cd2+ removal mechanisms by biochar composites from co-pyrolysis of corn straw and fly ash

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Efficient degradation of sulfadiazine by UV-triggered electron transfer on oxalic acid-functionalized corn straw biochar for activating peroxyacetic acid: Performance, mechanism, and theoretical calculation

A novel UV/oxalic acid functionalized corn straw biochar (OCBC)/peroxyacetic acid (PAA) system was built to degrade sulfadiazine from waters. 94.7 % of SDZ was removed within 30 min by UV/OCBC/PAA. The abundant surface functional groups and persistent free radicals (PFRs) on OCBC were responsible for these performances. Cyclic voltammetry (CV) and other characterization analysis revealed, under UV irradiation, the addition of OCBC served as electron donor, which might promote the reaction of electrons with PAA. The quenching and electron paramagnetic resonance (EPR) tests indicated that R-O•, 1O2 and •OH were generated. Theoretical calculations indicated sulfonamide bridge was vulnerable under the attacks of reactive species. In addition, high removal effect achieved by 5 reuse cycles and different real waters also suggested the sustainability of UV/OCBC/PAA. Overall, this study provided a feasible approach to remove SDZ with high mineralization efficiency, in addition to a potential strategy for resource utilization of corn straw.

Effect of biochar and iron ore tailing waste amendments on cadmium bioavailability in a soil and peanut seedling system

Biochar and iron ore tailing waste have been widely separately applied for remediation of various contaminants, but the remediation effect of their combination on cadmium (Cd) pollution is unclear. In this study, the peanut biochar (BC), thermally activated iron ore tailing waste (TS), and the products of the co-pyrolysis of peanut shell and iron ore tailing waste (TSBC) were prepared for stabilizing Cd and reducing its bio-accessibility in soil and peanut seedling system. Present amendments enhanced soil pH, cation exchange capacity, electrical conductivity, and organic carbon content. The application of BC, TS, and TSBC led to decreases in acid-extractable Cd proportion of 2.2-8.81%, 2.43-7.20%, and 7.84-11.57%, respectively, and increases in the residual Cd proportion of 3.48-8.33%, 3.27-11.50%, and 9.02-13.45%, respectively. There were no significant differences in Cd accumulation in peanut roots due to three amendments treatments, especially at low Cd concentrations (i.e., Cd concentration of 0, 1, and 2 mg·kg-1), and with a relatively small reduction (2.16-9.05%) in root Cd accumulation under the high Cd treatments of 5 and 10 mg·kg-1. The Cd concentrations in seedling roots were significantly positively related to the acid-extractable Cd fraction, with a Pearson correlation coefficient of r = 0.999. The maximum toxicity mitigating effects were found in TSBC treatment, with increases in the ranges of 9.80-17.58% for fresh weight, 5.59-14.99% for dry weight, 5.16-10.17% for plant height, 5.96-10.34% for root length, 5.43-21.67% for chlorophyll a content, 17.17-71.28% for chlorophyll b content, and 13.11-39.60% for carotenoid content in peanut seedlings. Therefore, TSBC is a promising amendment for minimizing Cd contamination in peanut crops and utilizing industrial solid waste materials efficiently.

Bismuth oxymetallate-modified biochar derived from Euryale ferox husk for efficient removal of Congo red from wastewater: adsorption behavior and mechanisms

Using Euryale ferox husk as raw material, pristine biochar (EBC), Bi2MoO6-modified biochar (BM-EBC), and BiFeO3-modified biochar (BF-EBC) were prepared and employed for decontaminating Congo red (CR) from wastewater. Compared with EBC (217.59 mg/g) and BF-EBC (359.49 mg/g), a superior adsorption capacity of 460.77 mg/g was achieved by BM-EBC. Based on the evaluation results of the Freundlich and pseudo-second-order models, multilayer chemisorption was suggested as the adsorption mechanism. The adsorption process of BM-EBC was spontaneous and endothermic, and the rate-limiting step pertained to liquid film diffusion and intraparticle diffusion. The underlying removal mechanism was explored via SEM, BET, FTIR, XPS, Raman spectra, and Zeta potential analyses. The introduction of bismuth oxymetallates with their high number of M-O (M: Bi, Mo, Fe) structural elements provided the adsorbent with enlarged surface areas and reinforced oxygen functional groups, thereby promoting pore filling, π-π interactions, hydrogen bonding, and complexation, leading to enhanced adsorption capacity. These results demonstrate that Euryale ferox husk biochar modified by bismuth oxymetallates has high prospects for valorizing biomass waste and removing CR from wastewater.