Experimental study on the extraction of calcium, magnesium, vanadium and silicon from steelmaking slags for improved mineral carbonation of CO2

Abstract

In this paper X2PCC (Calcium containing material X to Precipitated Calcium Carbonate) process wherein a steelmaking slag is used as a source of Ca for mineral carbonation of CO2 was studied. Mineral carbonation refers to binding of CO2 into mineral carbonates, here CaCO3. In the process, we first dissolve Ca selectively from the slag, then separate the solid phase and finally, bubble CO2 into the solution to make precipitated calcium carbonate CaCO3. Based on our current understanding, the extraction step limits the process feasibility. In the experiments, ammonium chloride (NH4Cl) water solution was used as an extracting solvent with varying concentrations of 0, 0.5, 1 and 2 mol/L using slag to solvent ratio of 100 g/L. The main objective of this study was to determine the optimal concentrations of solvent and particle size for leaching out calcium from the slag. Tests were performed at room temperature with varying particle size and solvent concentration. The extraction behaviors of different size fractions of the slag, 0–50 μm, 50–74 μm and 74–125 μm were studied. Dissolution results showed that with high solvent concentrations calcium extraction efficiency increases but at the same time, other elements are leached, such as vanadium, silicon and magnesium that act as impurities in the subsequent carbonation stage. It was found that with the largest particles, Ca extraction becomes limited by mass transfer and the availability of Ca from the particle. Our hypothesis is that the surface layer of the particles gets blocked by reaction products and stops the reaction. With the smallest particle size, before the surface gets blocked, more calcium could be extracted and the maximum extraction efficiency was not reached.