Charcoal ash leachate and its sparingly soluble residue for acid mine drainage treatment: Waste for pollution remediation and dual resource recovery

Abstract

Acid mine drainage (AMD) is one of the serious environmental pollutants due to its high acidity, toxic metals and sulfate concentration. In this study, Namibian hardwood charcoal ash leachate, sparingly soluble charcoal ash residue in deionized water and 25% NH4OH (aq.) solution were used for AMD treatment. The ICP-OES analysis results of treated AMD filtrate revealed that almost complete removal of Al, Co, Fe, Mn, Ni, Sb and Zn, and partial removal of Ca, Mg, and Na. The sulfate removal of charcoal ash leachate, residue and 25% NH4OH (aq.) was 66, 56 and 46%, respectively. The removal capacity of charcoal ash leachate and residue were almost better than 25% NH4OH (aq.). About 81% sludge composition recovered at pH 3.7 composed of Fe and O, while the sulfate recovered from the finally treated filtrate of AMD was with above 99% purity. This reveals the possibility of selective resource recovery with high purity from AMD using charcoal ash leachate. Furthermore, the formation of industrially important magnetic nanoparticles such as Fe3O4, Mg0.2Mn0.8Fe2O4 and Mg(Al, Fe)2O4 makes the sludge an eye-catching for future use. Indeed, waste for waste treatment for AMD pollution remediation and simultaneous double resource recovery are interesting findings of this study.