Towards viable CO2 sequestration: Production of high specific surface area silica by olivine dissolution in concentrated acidic solutions

Abstract

CO2 sequestration by reaction with ultramafic minerals such as olivine has been considered for decades. However, the moderate leaching yield of olivine by CO2 even at high temperature and pressure, led to consider an alternative. For this purpose, indirect sequestration process has been investigated with acidic dissolution of olivine for the formation of valuable silica. The remaining concentrated solutions of magnesium, iron and nickel salts could be used for production of the separate carbonates. Numerous dissolution tests of industry-grade 120 μm olivine were carried out in a 250 mL stirred reactor under non-oxidant atmosphere with concentrated acidic solutions. Two solid fractions (“Upper” and “Bottom”) and a metal-rich liquor were recovered, then thoroughly characterized. Results are discussed in terms of quality of the silica nanoparticles produced (BET specific area, pore size distribution, purity) as well as of dissolution yields, depending on operating conditions. BET surface area of the silica over 500 m2/g and nearly complete dissolution could be obtained for 3 h at 80 °C, however with appreciable excess of acid. A final test was conducted with an acid excess fixed at 12%, a solid/liquid ratio at 180 g/L, for 2 h at 95 °C: olivine was converted at 72% to silica. The “Upper” solid fraction recovered consisted of regular 15–20 nm particles in agglomerates with an overall BET area near 400 m2/g.