Kinetic evaluation of mineral carbonation of natural silicate samples

Abstract

Carbon sequestration by mineral carbonation of basic silicate minerals is an important technique for climate change mitigation, because of the formation of stable mineral carbonate products and the abundant resources of amenable minerals in nature. In practice, direct aqueous mineral carbonation may need to treat natural multiple-mineral mixtures including partially serpentinized ultramafic silicates, as potentially combined with mineral processing operations and enhanced metal recovery. This work investigated the kinetics of direct mineral carbonation of multiple-minerals natural silicate samples under conditions of 34.5 bar CO2 partial pressure, 175 ℃ and concentration of 1.5 m NaHCO3, with corresponding carbonation efficiency more than 85% in 3 h. It was found that the carbonation of a natural mixture of minerals was kinetically controlled by chemical reaction of the olivine dissolution under moderate CO2 partial pressure and aqueous ionic strength, regardless of olivine content and associated mineral compositions. It was important for kinetics analysis to calculate the effective mineral carbonation capacity based on the magnesium and iron contents in olivine. If the carbonation capacity was calculated based on the total content of magnesium, calcium and iron as is conventional, the mineral carbonation efficiency was proportional to the olivine content in natural silicate samples. The carbonation process of the natural mixtures could be completely attributed to the reaction of olivine while the other silicate minerals including serpentine and diopside, as well as iron sulfides and magnetite, did not significantly participate.