US Patent 7682589 Method for industrial manufacture of pure MgCO

Method for industrial manufacture of pure MgCO3 comprising providing an olivine containing species of rock, to comminute the olivine containing species of rock to increase its surface, to contact the comminuted olivine containing species of rock with water and CO2. The process is conducted in at least two steps, namely a first step (R1) at a first pH where a dissolving reacting as represented the equation: Mg2SiO4(S)+4H+=2Mg2++SiO2(aq)+2H2O, takes place. Then a precipitation takes place in the second step (R2) at a higher pH as represented by the equations: Mg2++HCO3−=MgCO3(S)+H+, and Mg2++CO32−=MgCO3(S), the presence of HCO3− and H+ ions mainly provided by the reaction between CO2 and water.