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

Abstract

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)(2)SO4. 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 (similar to 70%) was higher in the CH3COONH4 and NH4NO3 solutions, but lower in the NH4Cl (32%) and (NH4)(2)SO4 solutions (5%). The Ca selectivity (similar to 98%) was higher in the CH3COONH4, NH4NO3, and NH4Cl solutions, but lower in the (NH4)(2)SO4 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. (C) 2014 Elsevier B.V. All rights reserved.