Revealing the role of calcium alginate-biochar composite for simultaneous removing SO42− and Fe3+ in AMD: Adsorption mechanisms and application effects

The remediation of acid mine drainage (AMD) is particularly challenging because it contains a large amount of Fe3+ and a high concentration of SO42-. To reduce the pollution caused by SO42- and Fe3+ in AMD and realize the recycling of solid waste, this study used distillers grains as raw materials to prepare biochar at different pyrolysis temperatures. Calcium alginate-biochar composite (CA-MB) was further synthesized via the entrapment method and used to simultaneously remove SO42- and Fe3+ from AMD. The effects of different influencing factors on the sorption process of SO42- and Fe3+ were studied through batch adsorption experiments. The adsorption behaviors and mechanisms of SO42- and Fe3+ were investigated with different adsorption models and characterizations. The results showed that the adsorption process of CA-MDB600 on SO42- and Fe3+ could be well described by Elovich and Langmuir-Freundlich models. It was further proved by the site energy analysis that the adsorption mechanisms of SO42- onto CA-MDB600 were mainly surface precipitation and electrostatic attraction, while that of Fe3+ removal was attributed to ion exchange, precipitation, and complexation. The applications of CA-MDB600 in actual AMD proved its good application potential. This study indicates that CA-MDB600 could be applied as a promising eco-friendly adsorbent for the remediation of AMD.