Leaching of residual steel slag from a mineral carbonation process

In an alternative concept for producing precipitated calcium carbonate (PCC), calcium is extracted from steelmaking slag using ammonium salt solutions, from which PCC can subsequently be precipitated using CO2. A by-product of the process is a calcium-depleted slag residue. The objective of this study was to compare the composition and solubility of residual slag generated by the process to that of raw, untreated slag. Three different stainless steel slag products were tested. Samples representing residual slag were prepared by leaching each slag in 4 M ammonium acetate solutions. The solubility in water of each raw slag and residual slag was tested using two-stage and single-stage batch leaching tests. The leaching tests with residual slag showed a high concentration of calcium and dissolved organic carbon (DOC), which was most likely a remnant of the spent ammonium acetate solvent used in preparation of the residual slag. The processing does not appear to significantly affect the solubility of other elements. The results implies that the PCC process would have to filter and wash the residual slag to remove the remnants of organic carbon, which adds some costs to the process and increases the use of water