Selective precipitation of manganese from magnesium-containing solutions

Abstract

A process is provided for selectively precipitating and removing manganese relative to magnesium from an acidic solution, preferably barren of one or more of cobalt, nickel, copper and zinc, but containing appreciable amounts of manganese, magnesium, and aluminum. The process comprises a) adding a first alkaline reagent, for example lime and/or limestone, to neutralize the acidic solutions and to precipitate a majority of the aluminum as aluminum-containing solids, without precipitating a substantial amount of the magnesium; b) removing the precipitated aluminum-containing solids to create an aluminum-depleted solution; c) adding a second alkaline reagent, for example lime, to the aluminum-depleted solution and aerating for a sufficient retention time to preferentially precipitate a majority of the manganese as manganese-containing solids; and d) removing the precipitated manganese-containing solids. By first precipitating and removing aluminum, the process allows for selective precipitation of manganese relative to magnesium without significant co-precipitation of magnesium, thus resulting in a savings of the total amount of the first and second alkaline reagents needed to precipitate the majority of the manganese (compared to that needed without first precipitating and removing the majority of the aluminum).