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Acid mine drainage (AMD) sludge can be used to prepare adsorbent materials for the removal of heavy metals in water, which is an effective means for its resource utilization. Magnetic modified biochar (MMB), which can be recovered by magnetic separation, was prepared from sludge generated from the carbonate rock neutralization treatment of AMD and rice straw agricultural waste. Unmodified biochar (UMB) was obtained from rice straw and chemically modified and treated by ultraviolet radiation to produce MMB. The Pb2+ and Zn2+ adsorption capacities of UMB and MMB were investigated. Simultaneously, the materials were characterized by SEM, FTIR, BET, and ZETA. The results showed that the specific surface area (130.89 m2·g−1) and pore volume (0.22 m2·g−1) of MMB were significantly increased compared to those of UMB (9.10 m2·g−1 and 0.05 m2·g−1, respectively). FTIR images showed that MMB was successfully loaded with Fe3O4. The adsorption process of Pb2+ and Zn2+ onto MMB was consistent with the Langmuir adsorption isotherm and second-order kinetic models, with maximum adsorption capacities of 329.65 mg·g−1 and 103.67 mg·g−1, respectively. In a binary system of Pb2+ and Zn2+, MMB preferentially binds Pb2+. The adsorption efficiencies of MMB reached >80% for Pb2+ and Zn2+.

Acid mine drainage (AMD) has a low pH and high concentration of sulfates and heavy metals and its untreated discharge contributes to environmental pollution. Traditional bio-oxidation is less effective in...

The effect of pH is a key factor in biomineralization mediated by Acidithiobacillus ferrooxidans to promote the transformation of Fe into secondary iron minerals. This study aimed to investigate the effects of initial pH and carbonate rock dosage on bio-oxidation and secondary iron mineral synthesis. Variations in pH and the concentrations of Ca2+, Fe2+, and total Fe (TFe) in the growth medium of A. ferrooxidans were examined in the laboratory to determine how they affect the bio-oxidation process and secondary iron mineral synthesis. The results showed that in systems with an initial pH of 1.8, 2.3, and 2.8, the optimum dosages of carbonate rock were 30, 10, and 10 g, respectively, which significantly improved the removal rate of TFe and the amount of sediments. At an initial pH of 1.8 and a carbonate rock dosage of 30 g, the final removal rate of TFe reached 67.37%, which was 28.03% higher than that of the system without the addition of carbonate rock, and 36.9 g·L−1 of sediments were generated, which was higher than that of the system without the addition of carbonate rock (6.6 g·L−1). Meanwhile, the number of sediments generated by adding carbonate rock were significantly higher than those without the addition of carbonate rock. The secondary minerals were characterized by a progressive transition from low crystalline assemblages composed of calcium sulfate and subordinated jarosite, to well crystal-line assemblages composed of jarosite, calcium sulfate, and goethite. These results have important implications for comprehensively understanding the dosage of carbonate rock in mineral formation under different pH conditions. The findings help reveal the growth of secondary minerals during the treatment of AMD using carbonate rocks under low-pH conditions, which offers valuable information for combining the carbonate rocks with secondary minerals to treat AMD.

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