A novel method for effective solidifying chromium and preparing crude stainless steel from multi-metallic electroplating sludge.

Electroplating sludge (ES) is a globally prevalent hazardous waste that primarily contains Cr, Cu, Ni, and Fe. However, the residual Cr phases within the slag potentially poses an environmental risk in current vitrification. A novel method for effective recovering and solidifying Cr in ES is proposed in this work. ES was desulfurized and subsequently co-treated with ferrosilicon (Fe-Si) and spent carbon anode (SCA) for enhancing the recovery of Cr, Cu, Ni, and Fe to prepare crude stainless steel. Under optimal conditions, the recovery ratios of Cr, Cu, Ni, and Fe reached 96.96%, 99.45%, 99.92%, and 99.20%, respectively, signifying improvements of 21.4%, 0.2%, 1.5%, and 2.8%, respectively, compared with existing research. Meanwhile, the fluoride in SCA yielded CaF2, further progressing to the Si-Ca-F-Na-Al-O phase, with a solidification ratio of 97.87%. The Cr leaching content of the residual Cr-Cu-S phase in the slag remained below 5 mg/L across a pH range of 2-4, demonstrating enhanced stability compared to prior alloy, oxide, and chemically dissolved phases. An innovative approach for solidify Cr by forming matte holds implications for the treatment of Cr-containing solid wastes such as chromium slag, tannery sludge and stainless steel slag.

An all-in-one strategy for resource recovery and immobilization of arsenic from arsenic-bearing gypsum sludge.

Arsenic (As)-bearing gypsum sludge, one of the most prominent hazardous wastes, has created a myriad of critical problems in human health, waters, soils, and sediments at the global scale. Unfortunately, the reclamation and disposal of As-bearing gypsum sludge have been rarely investigated. This paper aims to explore a novel technology for simultaneous value-added utilization and harmless exploitation of As-bearing gypsum sludge. In the experiment, As-bearing gypsum sludge and anthracite were mixed, granulated, and then roasted in Ar atmosphere. Based on the thermodynamic analysis and experimental results, the As migration mechanism in the As-bearing gypsum sludge was determined during the roasting process. Under optimal conditions, 90% of As phase was volatilized and then recovered in the form of elemental As99.5, and it could act as a chemical product. In addition, As99.5 could be further processed into high-purity As and As2O3 using existing chlorination-rectification-reduction process and oxidation process, respectively, which can be widely used in the treatments of semiconductor material, pigment, and wood. Residual As primarily occurred as Fe-As compounds, but the leached As concentration in the toxicity characteristic leaching procedure was only 0.008 mg/L. Correspondingly, a new As immobilization method that generates Fe-As compounds (α-Fe and AsFe2) is first proposed and then verified, which may be widely used for simultaneous As-bearing solid wastes reduction and improved harmlessness. This paper is significant for development of the metallurgical, mining, acid, and thermal power industries, minimizing its environmental risk.

Co-treatment of electroplating sludge, copper slag, and spent cathode carbon for recovering and solidifying heavy metals.

Electroplating sludge, a hazardous solid waste product of the electroplating industry, presents a serious environmental pollution risk. In this study, an environmentally friendly process for solidifying and recovering heavy metals from electroplating sludge using copper slag and spent cathode carbon is proposed. Combining the results of toxicity characteristic leaching procedure tests, thermodynamic analysis, chemical analysis, X-ray diffraction analysis, and electron probe microanalysis, the Cr, Ni, Cu, Fe, and F transformation mechanisms were first probed during vitrification. Under optimal experimental conditions, the Cr, Ni, and Cu recovery ratios reached 75.56 wt%, 98.41 wt%, and 99.25 wt%, and they increased by 40%, 5%, and 5%, respectively compared with the currently utilized technique. Moreover, the toxicity leaching results of the slag indicate that the Cr, F, and Cu are stable, while Ni is easily leached from the (Fe,Ni)(Fe,Cr)2O4 and alloy phases. Under the optimal metal recovery conditions, the leaching concentrations of Cr, Cu, F, and Ni were 0.57 mg/L, 4.45 mg/L, 1.52 mg/L, and 1.85 mg/L, respectively, which can be reused in other materials, minimizing the environmental risk. The electroplating sludge, copper slag, and spent cathode carbon co-treatment process achieves waste disposal with waste and significantly reduces electroplating sludge processing costs.