Accelerated carbonation of ferrous and non-ferrous slags to produce clinker-free carbonate-bonded blocks: Synergetic reduction in environmental leaching

•Clinker-free blocks by accelerated carbonation of ferrous and/or non-ferrous slags.•Decreased Cr-leaching in SSS used individually, disproportional decrease with NFMS.•Pb-slag vs P(CO2): decreased Pb-leaching, Co/Zn/Mn leaching increase then decrease.•Synergetic reduction in leaching from mixes of ferrous/non-ferrous slags.•In addition to encapsulation, a chemical synergy between sulfide/Cr is discussed. Clinker-free, carbonate-bonded monoliths are prepared by accelerated carbonation for immobilization of hazardous elements present in: a stainless-steel slag, two copper slags, and one lead slag. In addition to the studies on individual slags, mixes of copper slags and lead slags with 33 % and 66 % replacements of stainless-steel slag are also studied. Combinations of two temperatures (30 and 60 °C) and three CO2-pressures (1, 5, and 10 barg) are studied. Among the non-ferrous slags carbonated individually, lead slag carbonated at 10 barg exhibited carbonate-cementation. The carbonate-bonded monoliths containing stainless-steel slag exhibited high compressive strengths, individually or as in its mixes with other slags. In stainless-steel slag, while its individual carbonation also showed a decrease in Cr-leaching, the Cr-leaching from its mixes with non-ferrous slags are disproportionately lower: possible chemical synergy of stainless-steel slag with sulfidic non-ferrous slags is discussed. For lead slag individually, carbonation significantly decreases Pb-leaching; while Co, Zn, and Mn leaching first increase and then decrease with an increase in CO2-pressure. In mixes of lead slag with stainless-steel slag, Pb, Co, Zn, and Mn leaching are significantly decreased. Temperature does not have a significant influence on the product properties. Copper slag remained relatively insensitive towards carbonation. Comparisons are made with the Flemish legislative limits.