Carbon Capture and Storage by mineralisation aims to reduce carbon dioxide emissions (CO2) by reacting CO2 with rocks rich in magnesium or calcium oxide and producing solid mineral carbonates, which can provide safe storage capacity. Recently, indirect mineral carbonation by pH swing mineralisation processes that use recyclable ammonium salts has shown promising results, but the process needs to be optimised. For example, the feasibility of this process in the presence of a mixture of NH3-salts has not been demonstrated. Accordingly, carbonation of rocks rich in magnesium and a mixture of NH4HCO3 and (NH4)(2)CO3 under different temperatures was investigated to reproduce a real scenario from an ammonia capture process. The highest 'carbonation efficiency' (expressed as the conversion of Mg ions to hydromagnesite) was 93.5% at 80 degrees C and 1:4:3 as Mg:NH4 salts:NH3 molar ratio, while the 'total CO2 captured' was 62.6% under the same conditions, indicating that the process in presence of ammonium salts mixture is feasible. (C) 2012 Elsevier Ltd. All rights reserved.