Method for industrial manufacture of pure MgCO3 from an olivine containing species of rock

Method for industrial manufacture of purified MgCO3 comprising the steps of:

• providing an olivine containing species of rock,
• comminuting the olivine containing species of rock to increase surface area thereof,
• contacting the comminuted olivine containing species of rock with water and CO2, said contacting comprising at least first and second separate steps:
• a first step under pressure and at a first pH in which a reaction dissolving the comminuted olivine containing rock in water containing CO2 takes place generally according to a reaction equation:
• Mg2SiO4(s)+4H+=2Mg2++SiO2(aq)+2H2O,
• producing thereby a solution and non-reacted solid components and precipitated materials which are separated from the solution, and
• a second step in which purified MgCO3 is precipitated from the solution from the first step, conducted at a second pH which is higher than the first pH, with silicate remaining in the solution from which purified MgCO3 has been precipitated, the second step being represented generally by reaction equations:
• Mg2++HCO3−=MgCO3(s)+H+, and
• Mg2++CO32−=MgCO3(s),
• the presence of HCO3− and H+ ions in the contacting steps being due mainly to a reaction between the CO2 and the water with which the comminuted olivine containing rock is contacted.