Optimum conditions for extracting Ca from CKD to store CO2 through indirect mineral carbonation

Abstract

Cement Kiln Dust (CKD), a by-product of the cement industry, was used as the raw material to determine the optimum conditions of Ca extraction, which could ultimately be used for indirect mineral carbonation. CKD was a suitable raw material for mineral carbonation due to its high CaO content (42.7%) and fine particle size (23.08 μm), not requiring a pretreatment such as grinding and pH adjustment. Extractions were conducted by varying the factors such as the solvent type, reaction time, temperature, solid-liquid ratio, solvent concentration, and stirring speed, which could affect the Ca extraction. The solvents used (hydrochloric acid, acetic acid, ammonium chloride, ammonium acetate, and sodium citrate) resulted in high Ca extraction efficiencies, and the resultant Ca extract (except for hydrochloric acid) had sufficiently high pH for the carbonation reaction. The optimum conditions set for extracting Ca from the CKD were: 30 min reaction time, 25°C reaction temperature, 1:10 solid-liquid ratio, 1.74 M solvent concentration, and 250 rpm stirring speed. Under these conditions, Ca extraction efficiencies were very high and depended on the solvent used: hydrochloric acid (94.3%), acetic acid (93.7%), ammonium chloride (86.9%), ammonium acetate (85.3%), and sodium citrate (70%). Calcium carbonate was produced by reacting CO2 with Ca extracted with ammonium chloride and ammonium acetate.