Evaluation and microanalytical study of ZVI/scoria zeolite mixtures for treating acid mine drainage using reactive barriers – Removal mechanisms

• Published in: Journal of environmental chemical engineering 2018-10, Vol.6 (5), p.6184-6193
• Main Authors: Limper, D., Fellinger, G.P., Ekolu, S.O.
• Format: Article
• Language: English
• Subjects: Acid mine drainage; Batch and column tests; Heavy metals removal; Permeable reactive barriers; Volcanic scoria zeolite; Zero-valent iron
• ISSN: 2213-3437; 2213-3437
• DOI: 10.1016/j.jece.2018.08.064

•ZVI – zero valent iron, VS – volcanic scoria zeolite, AMD – acid mine drainage.•VS removes heavy metals from AMD even at relatively a low pH not exceeding 5.5.•50% ZVI and 50% VS mixture removes most inorganic contaminants from AMD except Mg and Mn.•Upon reacting with AMD, ZVI forms Hematite and Goethite while VS forms Forsterite and Ferroan.•Removal mechanisms are chemical precipitation for ZVI; adsorption and cation exchange for VS. Batch and column experiments were performed to evaluate contaminant removal from acid mine drainage (AMD) using volcanic scoria zeolite (VS) with or without zero-valent iron (ZVI). Two sources of AMD were used, comprising WZ from a gold mine and TDB from a coal mine. Both the WZ and TDB were acidic mine water with pH values of 2.43 and 2.93, respectively. It was found that VS was effective in removing heavy metals from AMD despite attaining a relatively lower maximum pH of 5.5, compared to the pH values of 7.0–8.5 attained using ZVI. The reactive media VS, ZVI, and 50:50 ZVI-VS all achieved effective removal of Al, Fe, Zn metals. The mixture 50:50 ZVI-VS gave the best contaminant removal performance, relative to the other reactive media used in the investigation. Hematite and Goethite minerals were formed in ZVI upon its exposure to AMD during the mine water treatment. The VS that was exposed to AMD showed enhancement of Diopside and Augite along with the formation of two new phases comprising Forsterite and Ferroan. Geochemical changes and microanalytical investigations altogether showed pH-dependent chemical precipitation to be the main mechanism of heavy metal removal by ZVI, while adsorption and cation exchange processes were found to be responsible for pollutant removal by VS.