The Use of Limestone, Lime and MnO2 in the Removal of Soluble Manganese from Acid Mine Drainage

Acid mine drainage (AMD) is one of the main environmental issues faced by the mining industry, as it often contains elevated levels of metals, including manganese, which is challenging to remove due to its high solubility across a broad pH range. This study aimed to optimize manganese removal from AMD by utilizing laboratory-prepared acid solutions and effluents from the Poços de Caldas uranium mine in Brazil, striving to reach manganese discharge levels below the permissible threshold of 1 mg/L while minimizing sludge production. The experimental methodology involved the precipitation of manganese using lime, limestone, and a non-conventional catalyst/adsorbent—MnO2 residue. Results indicated that both lime and limestone effectively removed manganese at pH levels exceeding 10, with lime demonstrating superior performance by yielding 50% less precipitate than limestone. Furthermore, the innovative application of the MnO2 residue facilitated nearly complete manganese removal, reducing concentrations from 140 mg/L to below 1 mg/L at near-neutral pH levels (6.8 to 7.2). The final effluent met regulatory standards for manganese discharge, confirming the efficacy of the proposed methods.