In-situ Removal of Arsenic from Groundwaters by Using Permeable Reactive Barriers of Organic Matter/limestone Mixtures

In this study, two different mixtures of municipal compost, limestone and zero-valent iron were assessed in two column experiments on acid rock treatment. The effluent solution was systematically analysed throughout the experiments and precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffractometry were analyzed. Results showed that waters were cleaned of metals, arsenic and acidity, but chemical and morphology analyses suggest that metal removal was not due predominantly to biogenic sulphide generation, unless simple organic carbon compounds were supplemented. Instead, metal removal can be attributed to pH increase, i.e. metal (oxy)hydroxides and carbonates precipitation and sorption onto organic matter could also contribute to metal removal to some extent. Arsenic removal was typically associated to co-precipitation and/or adsorption with iron and aluminium (oxy)hydroxides. When zero-valent iron was present, cementation of copper also occurred.