Occurrence, leaching behavior, and detoxification of heavy metal Cr in coal gasification slag

Abstract

Coal gasification slag (CGS) is a type of solid waste produced during coal gasification, in which heavy metals severely restrict its resource utilization. In this work, the mineral occurrence and distribution of typical heavy metal Cr in CGS is investigated. The leaching behavior of Cr under different conditions is studied in detail. Acid leaching–selective oxidation–coprecipitation method is proposed based on the characteristics of Cr in CGS. The detoxification of Cr in CGS is realized, and the detoxification mechanism is clarified. Results show that Cr is highly enriched in CGS. The speciation of Cr is mainly residual fraction (74.47%–86.12%), which is combined with amorphous aluminosilicate. Cr3+ and Cr6+ account for 90.93%–94.82% and 5.18%–9.07% of total Cr, respectively. High acid concentration and high liquid–solid ratio are beneficial to destroy the lattice structure of amorphous aluminosilicate, thus improving the leaching efficiency of Cr, which can reach 97.93% under the optimal conditions. Acid leaching–selective oxidation–coprecipitation method can realize the detoxification of Cr in CGS. Under the optimal conditions, the removal rates of Fe3+ and Cr3+ in the leaching solution are 80.99%–84.79% and 70.58%–71.69%, respectively, while the loss rate of Al3+ is only 1.10%–3.35%. Detoxification slag exists in the form of Fe–Cr coprecipitation (Fe1-xCrxOOH), which can be used for smelting. The detoxification acid leaching solution can be used to prepare inorganic polymer composite coagulant poly-aluminum chloride (PAC). This study can provide theoretical and data guidance for detoxification of heavy metal Cr in CGS and achieve resource utilization of coal gasification solid waste.