Alkali circulating leaching of arsenic from copper smelter dust based on arsenic-alkali efficient separation

Eco-friendly treatment of copper smelting flue dust for recovering multiple heavy metals with economic and environmental benefits

Handling flue dust in an environmentally friendly manner has become an urgent task for pollution prevention in the copper industry. Here, driven by the low-carbon notion, we report a process that enables the selective retrieval of multiple metals (As, Cu, Pb, Zn, and Bi) from copper smelting flue dust (CSFD). This process employed low-temperature roasting to separate arsenic from heavy metals, thereby eliminating the tedious separation steps required by existing processes. Subsequently, Zn and Cu were dissolved in water, while Pb and Bi were left as a solid residue. We achieved 98.23% extraction of Cu via Zn cementation at a micro-voltage of 0.50 V. Utilizing the difference in solubility, Bi was selectively dissolved from the residue using a NaCl-HCl medium, which enabled the subsequent production of metallic Bi through electrowinning. Finally, more than 99% of Pb in the solid was reduced to elemental Pb by mechanochemical reduction. Through optimized process conditions, high-purity As2O3 (99.04%), lead ingot (99.95%), metallic copper (94.16%), and bismuth (99.20%) were obtained. Our economic assessment revealed significant advantages, demonstrating the industrial feasibility of this process. Consequently, this study presents an effective and cost-efficient system for CSFD disposal while minimizing the environmental impact and fostering a circular economy.

Mineralogical transformation of arsenic at different copper smelting workshops: The impact on arsenic bioaccessibility

Soil arsenic (As) contamination associated with the demolition of smelting plants has received increasing attention. Soil As can source from different industrial processes, and also participate in soil weathering, making its speciation rather complex. This study combined the usage of chemical sequential extraction and advanced spectroscopic techniques, e.g., time of flight secondary ion mass spectrometry (ToF-SIMS), to investigate the mineralogical transformation of soil As at different processing sites from a typical copper smelting plant in China. Results showed that the stability of arsenic species decreased following the processes of storage, smelting, and flue gas treatment. Arsenic in the warehouse area was incorporated into pyrite (FeS2) as well as its secondary minerals such as jarosite (KFe3(SO4)2(OH)6). At the smelting area, a large proportion of As was adsorbed by iron oxides from smelting slags, while some As existed in stable forms like orpiment (As2S3). At the acid-making area, more than half of As was adsorbed on amorphous iron oxides, and some were adsorbed on the flue gas desulfurization gypsum. More importantly, over 86% of the As belonged to non-specifically and specifically adsorbed fractions was found to be bioaccessible, highlighting the gypsum-adsorbed As one of the most hazardous species in smelting plant soils. Our findings indicated the importance of iron oxides in As retention and suggested the potential health risk of gypsum-adsorbed As. Such detailed knowledge of As speciation and bioaccessibility is vital for the management and remediation of As-contaminated soils in smelting plants.

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.

Selective separation of metals from wastewater using sulfide precipitation: A critical review in agents, operational factors and particle aggregation

Extensive research has been conducted on the separation and recovery of heavy metals from wastewater through the targeted precipitation of metal sulfides. It is necessary to integrate various factors to establish the internal correlation between sulfide precipitation and selective separation. This study provides a comprehensive review of the selective precipitation of metal sulfides, considering sulfur source types, operating factors, and particle aggregation. The controllable release of H2S from insoluble metal sulfides has garnered research interest due to its potential for development. The pH value and sulfide ion supersaturation are identified as key operational factors influencing selectivity precipitation. Effective adjustment of sulfide concentration and feeding rate can reduce local supersaturation and improve separation accuracy. The particle surface potential and hydrophilic/hydrophobic properties are crucial factors affecting particle aggregation, and methods to enhance particle settling and filtration performance are summarized. The regulation of pH and sulfur ion saturation also controls the zeta potential and hydrophilic/hydrophobic properties on the particles surface, thereby affecting particle aggregation. Insoluble sulfides can decrease sulfur ion supersaturation and improve separation accuracy, but they can also promote particle nucleation and growth by acting as growth platforms and reducing energy barriers. The combined influence of sulfur source and regulation factors is vital for achieving precise separation of metal ions and particle aggregation. Finally, suggestions and prospects are proposed for the development of agents, kinetic optimization, and product utilization to promote the industrial application of selective precipitation of metal sulfides in a better, safer, and more efficient way.

Arsenic release pathway and the interaction principle among major species in vacuum sulfide reduction roasting of copper smelting flue dust

The efficient release of arsenic in copper smelting flue dust (CSFD) with complicated production conditions and composition under the premise of environmental safety is difficult for the copper smelting industry. The vacuum environment is conducive to the volatilization of low-boiling arsenic compounds, which is beneficial to the physical process and chemical reaction of increasing the volume. In the present study, combined with thermodynamic calculations, the roasting process of pyrite and CSFD mixed in proportion in vacuum was simulated. Additionally, the release process of arsenic and the interaction mechanism of the main phases were performed in detail. The addition of pyrite facilitated the decomposition of stable arsenate in CSFD into volatile arsenic oxides. The results indicated that exceeding 98% of arsenic in CSFD volatilized into the condenser, while the arsenic content in the residue was reduced to 0.32% under optimal conditions. Pyrite could reduce the oxygen potential during the chemical reaction with CSFD, reacting with sulfates in CSFD to convert into sulfides and magnetic iron oxide (Fe₃O₄) simultaneously, and Bi₂O₃ would be transformed into metallic Bi. These findings are significant for developing arsenic-containing hazardous waste treatment routes and the application of innovative technical approaches.

Eco-friendly extraction of arsenic and tungsten from hazardous tungsten residue waste by pressure oxidation leaching in alkaline solutions: Mechanism and kinetic model

Tungsten residue waste (TRW), considered an environmental burden due to high content and excessive leaching toxicity of arsenic (As), are also secondary tungsten (W) resources. A novel method for simultaneous extraction of arsenic and tungsten from TRW via alkaline pressure oxidative leaching was proposed. The results show that As in the TRW mainly exists in the form of As coprecipitated with Mn(Ⅱ) oxides and FeAsS. In addition, As coprecipitated with Mn(Ⅱ) oxides and W are encapsulated in Fe, Mn oxides. The structure of Fe, Mn oxides with dense surface can be destroyed and the chemically stable arsenopyrite can be efficiently oxidized by oxygen in alkaline solutions. The leaching efficiency of As and S reached 97% and 99% at 80 min, respectively, while that of W reached 82% at 10 min. The leaching rate of As and S is controlled by diffusion with the apparent activation energies of 16.67 kJ/mol and 15.66 kJ/mol, respectively. Compared with TRW, the leaching toxicity of As in the leach residue decreased from 10.2 mg/L to only 0.071 mg/L. The new process suggests new possibilities for removal and recovery of As and W from TRW that will contribute to circular economy and environmental protection.

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

Recovering harmful elements (As, Pb) and metals (Cu, Bi, Zn) from copper smelting flue dust (CSFD) is a critical subject and task for arsenic contamination control and resource sustainability. In this work, a two-step pyrometallurgical process was developed to preferentially separate arsenic and recover metals from CSFD. During the low-temperature roasting, arsenic-bearing waste acid (AWA) from copper industry was used as an additive and effective removal of arsenic (97.8 %) was obtained at 350 °C, which follows the idea of "treating waste with waste". Subsequently, the recovery and separation of metals were well-achieved based on the affinity between metals and sulfur in the second stage of roasting, by which 91.28 % of Pb and 95.65 % of Bi were recovered as an alloy (Pb 86.48 %, Bi 13.21 %), while 82.62 % of Cu was enriched in the matte. The migration rules of metal elements and phase transformation in the whole process were studied in-depth from theory and experiments. This process can realize the efficient removal of arsenic as well as effective recovery of metals via cooperative disposal of CSFD and AWA, and minimize the environmental impacts.