Recovery of antimony and bismuth from copper metallurgical industry process streams
(English) The pyrometallurgical industry faces challenges in maintaining copper purity due to increasing impurities in the primary resources (Sb, Bi, and As) that can reach the electrorefining unit forming insoluble minerals, compromising copper purity. To address this, the copper industry is develo...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/454068 |
| Acceso en línea: | https://hdl.handle.net/2117/454068 https://dx.doi.org/10.5821/dissertation-2117-454068 |
| Access Level: | acceso abierto |
| Palabra clave: | 66 - Enginyeria, tecnologia i indústria química. Metal·lúrgia Àrees temàtiques de la UPC::Enginyeria química |
| Sumario: | (English) The pyrometallurgical industry faces challenges in maintaining copper purity due to increasing impurities in the primary resources (Sb, Bi, and As) that can reach the electrorefining unit forming insoluble minerals, compromising copper purity. To address this, the copper industry is developing actions to reduce the presence of such impurities along different stages of the process flow sheet acting at: i) the final stages of the electrorefining process or ii) the mineral concentration stages (e.g. flotation). The main target objective of this PhD thesis has been centred in the evaluation of technological solutions to reduce such impurities (Sb, Bi and As) by introducing a sustainability concept, where elements considered as critics for the European Union (i.e. Sb and Bi) are recovered. In the case of acting in the final stage of electrorefining, ion-exchange (IX) technology is employed at industrial scale to continually treat the copper electrolyte of the electrorefining stage, removing Sb and Bi and ensuring a high copper purity. Upon IX resin saturation, regeneration with 6 M HCl produces a concentrated eluate containing Sb, Bi (7–14 g/L each), and As (1–4 g/L). Currently, lime treatment removes these impurities producing large volumes of waste containing As, Sb and Bi. Therefore, two valoriaztion routes of the eluate were evaluated based on solvent extraction (SX) and selective precipitation. SX route was based on the use of a solvated mixture of alkylphosphine oxides (commercialized as Cyanex 923) dissolved in kerosene and 1-decyl alcohol (10%) as a phase modifier. The separation factors of Sb, Biand As were evaluated and optimized as a function of extractant concentration and aqueous to organic (A/O) phase ratio. The results showed that 39% Bi and 78% Sb could be extracted with low co-extraction of As (<2.5%) working at the lowest Cyanex 923 concentration (0.15 mol/L) and A/O ratio of 1/3. Using 8M HNO3 as a stripping agent, both Sb and Bi were easily recovered (>90%). During the direct precipitation of eluate, As(V) forms an insoluble antimony arsenate (SbAsO4(s)). Therefore, it is necessary to pre-treat the eluent with SO2(g) or NaHSO3(s) to reduce As(V) to the (+III) state valence state. In this case, antimony oxychloride (Sb4O5Cl2, purity >93%) and bismuth oxychloride (BiOCl, purity >95%) can be obtained sequentially using NaOH, NaHCO3 and/or Na2CO3 under appropriate pH control. The recovered high purity Sb4O5Cl2(s) and BiOCl(s), still containing a low content of As, could be converted into oxides in alkaline media, improving the final purity making them suitable for commercial use. The techno-economic implications of Sb and Bi showed that the recovery of BiOCl(s)/Sb4O5Cl2(s) and BiOCl(s)/Sb2O3(s) is economically feasible in copper metallurgy facilities, especially when Sb and Bi prices are higher than 8.5 and 9.5 €/kg, respectively. Overall, the results highlighted the economic and technical potential of implementing Sb and Bi recovery routes in copper metallurgy plants, in line with the ambitious circular economy targets set by the European Union. In the case of approaching the reduction of the presence of impurities in the mineral copper concentrates, tetrahedrite (Cu12Sb4S13(s)) was selected as case study. Selective leaching of antimony using microwave-assisted technology in a laboratory scale was investigated at different concentrations of Na2S and NaOH, solid/liquid ratio, temperature, and microwave power. Results indicated that Sb dissolution is highly dependent on the concentrations of leaching reagents (Na2S/NaOH) and the temperature. The Sb content in the copper concentrate was successfully reduced from 1.1% to less than 0.2%, making it suitable for copper concentrate metallurgy processing. A proposal of potential integration of both alkaline leaching and selective precipitation of the Sb could provide a sustainable solution, promoting the recovery of a critical raw material for the European industry |
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