Understanding Chromium Slag Recycling with Sintering-Ironmaking Processes: Influence of CrO on the Sinter Microstructure and Mechanical Properties of the Silico-Ferrite of Calcium and Aluminum (SFCA).

Chromium slag is a solid waste of chromium salt production, which contains highly toxic Cr(VI) and significant amounts of valuable metals, such as Fe and Cr. Recycling chromium slag as a raw sintering material in sintering-ironmaking processes can simultaneously reduce toxic Cr(VI) and recover valuable metals. A micro-sintering experiment, compressive strength test, microhardness test, and first-principles calculation are performed to investigate the influence of CrO on the sintering microstructure and mechanical properties of the silico-ferrite of calcium and aluminum (SFCA) in order to understand the basis of the sintering process with chromium slag addition. The results show that the microstructure of SFCA changes from blocky to interwoven, with further increasing CrO content from 0 wt% to 3 wt%, and transforms to blocky with CrO content increasing to 5 wt%. CrO reacts with FeO to form (FeCr)O (0 ≤ ≤ 1), which participates in forming SFCA. With the increase in Cr doping concentrations, the hardness of SFCA first decreases and then increases, and the toughness increases. When CrO content increases from 0 wt% to 3 wt%, the SFCA microhardness decreases and the compressive strength of the sintered sample increases. Further increasing CrO contents to 5 wt%, the SFCA microhardness increases, and the compressive strength of sintered sample decreases.