An investigation into the dissolution of pyroxene : a precursor to mineral carbonation of PGM tailings in South Africa

Abstract

Carbon sequestration through mineral carbonation is becoming an increasingly attractive alternative for mitigating excess CO₂ in the atmosphere. Mineral carbonation is a natural process whereby CO₂ is fixed to CaFeMg-silicates to form Ca-, Fe-, and Mg-carbonates. This process is thermodynamically favourable and the products are benign and stable over millions of years. Pyroxene-rich tailings generated from the processing of PGM ores in South Africa have the potential to sequester significant amounts of CO₂ (~14 Mt per annum). In the indirect pH swing method, silicate minerals are initially leached at low pH and then carbonated at high pH. A previous study on these tailings highlighted the slow extraction of cations from orthopyroxene, the major Mg-host. The low reactivity of the orthopyroxene resulted in an overall low conversion of tailings to carbonates with only 30 % for Ca, 3 % for Mg and 9 % for Fe. Under similar experimental leach conditions, ~100 % dissolution of olivine and serpentine can be achieved.