Metal extraction and indirect mineral carbonation of waste cement material using ammonium salt solutions

• The type of ammonium salt solution affects the Ca extraction from waste cement.
• A direct relationship between Ca extraction and carbonation is observed.
• NH4NO3 solution is an efficient solvent for mineral carbonation of waste cement.
• High purity vaterite is obtained, regardless of the type of ammonium salt.

The effects of different ammonium salts on the cation extraction and mineral carbonation of waste cement were evaluated using four different ammonium salt solutions: CH3COONH4, NH4Cl, NH4NO3, and (NH4)2SO4. Extraction and carbonation tests were conducted using waste cement powder as the raw material under ambient temperature and pressure conditions at a solid to liquid ratio of 50 g/L with two different concentrations of ammonium salt solution (0.5 M and 1.0 M). At higher concentration (1 M), the Ca extraction efficiency (∼70%) was higher in the CH3COONH4 and NH4NO3 solutions, but lower in the NH4Cl (32%) and (NH4)2SO4 solutions (5%). The Ca selectivity (∼98%) was higher in the CH3COONH4, NH4NO3, and NH4Cl solutions, but lower in the (NH4)2SO4 solution (90%). The carbonation efficiency was comparable to the extraction efficiency. The carbonation efficiency with the CH3COONH4 and NH4NO3 solutions was higher. Regardless of the type of ammonium salt, high purity vaterite was precipitated after CO2 injection.