Separation and recovery of valuable metals extracted from serpentinite during the production of Mg(OH)2 for CO2 sequestration

Abstract

Amongst the several options for CO2 storage, mineral carbonation presents the highest capacity for CO2 fixation. Besides providing for a permanent (CO2 leakage free) storage option, it is also directly applied to flue gases avoiding the expensive CO2 capture processes. This paper focuses on the Åbo Akademi (ÅA) University route where suitable Mg rich silicate rocks are reacted with recoverable/recyclable ammonium salts (at ∼400–450°C) to produce mainly MgSO4. This is converted to Mg(OH)2 which reacts with a flue gas in a pressurised fluidized bed, at 20bar CO2 partial pressure and 500°C to produce MgCO3. At some extent, a lot of the metals that compose the rock (Fe, Ni, Cr, Cu, etc.) will be co-extracted along with the Mg. Being so, this work aims to recover those (valuable) metals through a combination of selective precipitation and ion-exchange technology. It was found that 1ton of the Portuguese serpentinite used in this work has the potential of capturing 270kg of CO2 while producing 517kg of MgCO3, 75kg of Fe(OH)3, 24kg of Ca(OH)2 and 1.6kg of Ni. This is equivalent to 1/3 of the nickel production per ton of nickel ore at the Hitura nickel mine in Finland.