A shortcut approach for cooperative disposal of flue dust and waste acid from copper smelting: Decontamination of arsenic-bearing waste and recovery of metals

Recycling and reutilization of smelting dust as a secondary resource: A review

Smelting dust is a toxic waste produced in metal-mineral pyrometallurgical processes. To eliminate or reduce the adverse environmental impacts of smelting dust, valuable components need to be selectively separated from the toxic components present in the waste. This paper reviews the chemical composition, phase composition and particle size distribution characteristics of smelting dust, and the results show that smelting dust has excellent physicochemical characteristics for recovering valuable metals. The process flow, critical factors, development status, advantages and disadvantages of traditional technologies such as pyrometallurgy, hydrometallurgy and biometallurgy were discussed in depth. Conventional treatment methods typically prioritize separating and reclaiming specific elements with high concentrations. However, these methods face challenges such as excessive chemical usage and limited selectivity, which can hinder the sustainable utilization of smelting dust. With the increasing scarcity of resources and strict environmental requirements, a single treatment process can hardly fulfil the demand, and a physical field-enhanced technology for releasing and separating valuable metals is proposed. Through analysing the effect of electric field, microwave and ultrasound on recovering valuable metals from smelting dust, the enhancement mechanism of physical field on the extraction process was clarified. This paper aimed to provide reference for the resource utilization of smelting dust.

Co-treatment of copper electrolytic sludges and copper scraps for the recycled utilization of copper and arsenic

The Cu electrolytic sludge is a hazardous waste because of its high Cu and As contents. In contrast, As content in Cu scraps is low but causes massive floating slime to be formed during its electrolytic refining, thus decreasing quality of the obtained cathode Cu. In this study, an innovative process was developed to transfer As from the electrolytic Cu sludge into Cu scraps, realizing the recycled utilization of As and Cu from them. The Cu electrolytic sludge was firstly subjected to oxidization roasting in the presence of Ca(OH)2, where the As2O3, Cu3As, and elemental As from the sludge were oxidized and immobilized into Cu3(AsO4)2 and Ca3(AsO4)2. The Cu3(AsO4)2 and Ca3(AsO4)2 retained in the roasted residue. The As volatilization efficiency was only 3.7% under the optimized roasting condition. In the next co-fire-refining of the roasted residue and Cu scraps, the As in Cu3(AsO4)2 and Ca3(AsO4)2 was reduced and transferred into the refined Cu at a content of 0.17 wt%. Although a volatile As2O3 could be generated in this co-fire-refining, the molten Cu scraps restricted As volatilization by forming a Cu-As alloy. With the obtained As-containing refined Cu used in electrolytic refining, the formation of floating slime could be decreased and consequently the quality of the cathode Cu would be increased. This research provided an alternative technology for Cu and As recycling by co-treating Cu electrolytic sludges and Cu scraps.

Strong binding of heavy metals in fayalite of copper smelting slags: Lattice site substitution

A deep understanding of the binding relationship between Fe₂SiO₄ and heavy metals from the perspective of lattice site substitution is essential to improve the theoretical knowledge regarding heavy metals binding in copper smelting slags (CSS). Here, we proposed the lattice site substitution behavior of heavy metals in Fe₂SiO₄ by preparing M-Fe₂SiO₄ (M = Cu, Pb, and As). X-ray diffraction refinement, scanning electron microscopy, and Fourier transform-infrared spectroscopy analysis showed that heavy metals were involved in the formation of Fe₂SiO₄ during the smelting process. Compared with pure Fe₂SiO₄, the fine structure of M-Fe₂SiO₄ was significantly changed by the lattice substitution of heavy metals. X-ray photoelectron spectroscopy and Raman and Mossbauer spectra combined with Density Functional Theory calculation confirmed that the divalent metal elements including Cu and Pb were bound to the Fe₂SiO₄ lattice by replacing M2 site. However, the trivalent As element could substitute both the positions of M2 site and part of the central Si atom through a charge compensation mechanism. Overall, the proposed lattice site substitution behavior of heavy metals in Fe₂SiO₄ could enrich the theory of the lattice substitution of heavy metals in CSS, also further provide guidance for the comprehensive disposal of CSS.

Synergy of directional oxidation and vacuum gasification for green recovery of As2O3 from arsenic-containing hazardous secondary resources

Arsenic, a hazardous material that is toxic for humans, enters the human body through soil, water, and air. Furthermore, metal smelting is known to produce arsenic-containing hazardous secondary resources (AHSRs), which cause irreversible damage to the total environment. Therefore, a novel, clean, and efficient arsenic fixation technology has been developed in this study for arsenic removal, which involves directional oxidation and vacuum gasification of AHSRs. Oxidation results revealed that physical phases containing arsenic (As, As₂O₃, As₂Te₃ and Cu₃As) are selectively oxidized to As₂O₃ completely and thus classified as oxidative modulation products (OMPs). Meanwhile, approximately 98.82% As₂O₃ of OMPs convert into volatiles in the following gasification. Characterization results showed that As₂O₃ with 96.72% purity and uniform microscopic distribution was obtained in the form of monoclinic crystalline needle-like crystals. The proposed approach organically combines oxidation and volatilization properties of each element to facilitate clean and efficient separation as well as recovery of As₂O₃. No hazardous gas or wastewater is discharged during the entire process, thereby ensuring that arsenic is recycled in a sustainable and clean manner. Overall, this study provides a clean and low-carbon approach for recycling secondary resources containing arsenic.