Arsenic sequestration by granular coal gangue functionalized with magnesium: Effects of magnesium and insight of arsenic sorption mechanisms

Leveraging natural waste materials for inorganic contaminant removal in solution offers a novel approach to boost resource recycling and foster sustainable development by enhancing waste use. This research advanced the modest arsenite (As[III]) removal capacity of raw coal gangue through a magnesium-soaking and calcination-based surface modification. Batch experiments showed As(III) removal efficiency was improved from 39.8% to 89.9% after modification, independent of initial pH levels. The Langmuir model estimated the maximum sorption capacity of 0.979 mg/g for the modified coal gangue. Physicochemical analyses confirmed that the modification increased the surface area, pore volume and size of the coal gangue. Furthermore, SEM, and subsequent TEM and SAED analyses identified acicular arsenic trioxide (As₂O₃) on the modified gangue, enhancing As(III) removal. Variations in sorption kinetics hinted at precipitation, likely due to AsO₃ polymer chains formed by As(III)'s sorption onto Mg(OH)₂, created from MgO hydration in aqueous conditions. Our findings show that coal gangue has potential applications in the development of sustainable methods for waste recycling.