A clean approach for detoxification of industrial chromium-bearing stainless steel slag: Selective crystallization...

The complete detoxification and resource utilization of stainless steel slag are still facing challenges. In this paper, the harmless treatment of industrial stainless steel slag was realized by using a high temperature modification-crystallization control approach, and the influence of binary basicity (B) on selective enrichment of Cr-containing spinel in the slag and corresponding detoxification effect were systematically explored. Results demonstrated that the enrichment degree of Cr and the amount of Cr-bearing spinel separately reached 98.62 wt% and 13.32 wt% when B= 1.2. The reason was that low alkalinity promoted the reaction of Cr in slag to form Cr-containing spinel, thus improving the enrichment of Cr in the spinel and reducing the occurrence probability of Cr in the matrix phase. Furthermore, the toxicity test of modified slag powder was proceeded according to Chinese standard HJ/T 299-2007 and American standard EPA (Toxicity Characteristic Leaching Procedure, TCLP), and the feasibility of using modified slags as admixture for producing cement was discussed. Even if TCLP was adopted, the Cr leaching concentration in modified slag powder with B= 1.2 was only 1.59 mg/L, which was far lower than the national limit of heavy metal leaching concentration (15 mg/L) of solid waste. Remarkably, when the powder was formed as cement, the Cr leaching concentration was even lower than ICP-OES detection line. Meanwhile, its mechanical property was better than that of cement prepared without powder, indicating the detoxified slag powder met the requirements of concrete admixture. This paper provides a new way with certain economic value for detoxification and large-scale utilization of stainless steel slag.