Preparation and Testing of Value-Added Sulfur Sorbent Pellets from In Situ Mined Minnesota Manganese Deposits

Abstract

The U.S. Bureau of Mines is developing an in situ leach mining process that would selectively extract manganese from low-grade oxide ores in the Cuyuna range deposits of central Minnesota. Aqueous sulfur dioxide solutions are used to leach the manganese contained in core samples, and the resulting sulfate stream contains about 28 g of Mn/L. The practical feasibility of manganese recovery by oxidation and selective precipitation of iron (major impurity) from the leach solution, followed by manganese precipitation in the form of carbonate, was established. To ensure the economic feasibility of this advanced mining process, it would be desirable to develop a manganese-based product having a potential market value of at least $1.00/lb. Such potential exists in the area of a regenerable sorbent for the desulfurization of coal-derived fuel gases at high temperatures (>500 °C). For these reasons, a number of pellet formulations consisting of the manganese carbonate product, alundum, and bentonite are prepared and subjected to screening tests in a thermogravimetric apparatus. The effectiveness (in terms of sulfur capacity, extent of reaction, and kinetics) of these pellet formulations in removing sulfur from hot H2S−H2 gas mixtures is evaluated and then compared to that of a leading Mn-based sulfur sorbent.