Valorization of acid mine drainage (AMD): A simplified approach to reclaim drinking water and synthesize valuable minerals – Pilot study

Abstract

In this pilot study, acid mine drainage (AMD) was valorized to drinking water and valuable minerals. Clarifiers with a capacity of 3.5 kl were used to achieve the goals of this study and for the synthesis of valuable minerals. Reverse osmosis (RO) was further integrated into the system to reclaim drinking water. By adopting optimized conditions attained from previous batch laboratory experiments, AMD was interacted with pre-treated magnesite at 25 kg:3.5 kl S/L ratios. Lime and soda ash were mixed with treated water at 15 kg:3.5 kl S/L and 10:3.5 kl S/L ratios, respectively. Various steps in the treatment chain produced Fe-rich sludge (step 1), gypsum-rich sludge with brucite (step 2) and calcium carbonate sludge (step 3) from the treatment process in a stage-wise fashion. This was further confirmed by the X-ray diffraction (XRD) and SEM-EDS analysis. Drinking water that meets the South African National Standard (SANS 241) and specifications was reclaimed from the product water using an RO system. The findings of this pilot study proved that the developed process can reclaim, recover, and synthesize valuable minerals from AMD. Techno-economic evaluation processes revealed that, the direct field cost (DFC) to treat the AMD is 65.60 South African Rands per kl (R65.60/kl). However, 14% of this cost can be recuperated from the sale of valorized products, thus reducing the AMD DFC treatment cost to R56.60/kl. With reference to its capacity, this plant can treat 20,000 LPD at its optimum operations.