Dissolution of natural serpentinite in mineral and organic acids

Abundant resources of magnesium silicates make an interesting prospect for long-term storage of CO₂ by mineral carbonation. Several carbonation processes proposed in literature for CO₂ storage employ extraction of silicate minerals using a liquid solvent. In this study, the dissolution of natural serpentinite in respective solutions of acids, bases and ammonium salts has been investigated. Experiments performed at room temperature showed that H₂SO₄ was most efficient at extracting magnesium from serpentinite, followed by HCl, HNO₃, HCOOH and CH₃COOH. Experiments for determining the dissolution kinetics was performed at temperatures of 30, 50 and 70 °C in 2 M solutions of H₂SO₄, HCl, and HNO₃. At 70 °C temperatures all magnesium was extracted from serpentinite in each of the three acid solutions tested during 1-2 h. Also a large part of iron in serpentinite was extracted, while very little silicon dissolved (< 4%). The dissolution rate seemed to be limited by product layer diffusion for serpentinite particles with a size distribution of 74-125 μm. The apparent activation energies were 68 kJ mol^{- 1} for dissolution in H₂SO₄, 70 kJ mol^{- 1} for dissolution in HCl, and 74 kJ mol^{- 1} for dissolution in HNO₃.