Sn recovery from a tin-bearing middling with a high iron content and the transformation behaviours of the associated As, Pb, and Zn

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 As_99.5, and it could act as a chemical product. In addition, As_99.5 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.

A review of glass ceramic foams prepared from solid wastes: Processing, heavy-metal solidification and volatilization, applications

The safe utilization of solid wastes containing heavy metals plays a crucial role in environmental preservation. As an efficient technology to achieve this goal, the preparation of glass ceramic foams from solid wastes can produce an excellent solidification effect on heavy metals. At present, there have been plenty of efforts made to achieve an excellent combination of such characteristics as mechanical strength, bulk density, thermal conductivity and so on, with the purpose to ensure the application in various high value-added fields. Due to the concentration on their application in the construction sector such as the use of thermal and acoustic insulation materials, some researchers seek to expand the scope of their applications. In this paper, a review is conducted into the methods used to prepare solid waste-based glass ceramic foams. Depending on the exact processing route, these methods can be categorized into two classes, which are powder sintering and inorganic gel casting. Not only heavy metals hinder the application of solid waste, they can also cause irreversible pollution to the wider environment. Solidification and volatilization represent the two routes associated with heavy-metal migration during the preparation of glass ceramic foams. Both traditional and innovative applications are indicated in this review. Furthermore, a discussion is conducted about the prospects and challenges facing different processing strategies, heavy-metal migration and applications.