Review of recovery processes of palladium, platinum, gold, and silver from metallurgical wastes

Metallurgical solid waste residue derived from lead and zinc smelting, steel dust, and galvanized steel scrap that is important secondary sources of zinc and other valuable metals. In order to realize recycling utilization of zinc secondary resource, a clean zinc production process of zinc recovery from metallurgical solid waste residue in NH3–(NH4)3AC–H2O system is investigated. It was found that the addition of (NH4)3AC to a NH3–H2O system promotes the zinc extraction, and 78.59% of zinc could be leached and recovered from the metallurgical solid waste residue under the following conditions: total ammonia concentration of 5 mol/L, stirring speed of 400 rpm, ammonia/ammonium ratio ([NH3]/[NH4]+) of 1:1, solid/liquid ratio of 1:4, leaching temperature of 35 °C, and a leaching time of 30 min.

The current study outlines the electrochemical recovery of tellurium from a metallurgical plant waste fraction, namely Doré slag. In the precious metals plant, tellurium is enriched to the TROF (Tilting, Rotating Oxy Fuel) furnace slag and is therefore considered to be a lost resource—although the slag itself still contains a recoverable amount of tellurium. To recover Te, the slag is first leached in aqua regia, to produce multimetal pregnant leach solution (PLS) with 421 ppm of Te and dominating dissolved elements Na, Ba, Bi, Cu, As, B, Fe and Pb (in the range of 1.4–6.4 g dm−3), as well as trace elements at the ppb to ppm scale. The exposure of slag to chloride-rich solution enables the formation of cuprous chloride complex and consequently, a decrease in the reduction potential of elemental copper. This allows improved selectivity in electrochemical recovery of Te. The results suggest that electrowinning (EW) is a preferred Te recovery method at concentrations above 300 ppm, whereas at lower concentrations EDRR is favoured. The purity of recovered tellurium is investigated with SEM–EDS (scanning electron microscope–energy dispersion spectroscopy). Based on the study, a new, combined two-stage electrochemical recovery process of tellurium from Doré slag PLS is proposed: EW followed by EDRR.Graphic abstract

Metal mobilization from metallurgical wastes by soil organic acids

As a result of the increasing global demand for refined copper, the reserves of primary sources of copper have been decreasing at a tremendously fast rate; which thus makes secondary copper processing an ever-increasing importance within the global copper industry. Copper smelter dust (CSD) is a potential secondary source of copper that is produced during copper pyrometallurgy. The significant amount of copper value these CSDs often plays host to prompts the need to develop processes to meaningfully remove sulfur and other associated impurities from it, prior to subsequent treatment in the copper recovery process. Hence, this present work carried out a thermal analysis and kinetic study on the oxidative roasting process of copper smelter dust under non-isothermal condition in air using DSC-TGA equipment. The non-isothermal experiments were carried out at heating rates of 5, 10, 15, and 20 °C/min, from room temperature up to 1000 °C. The intermediate phases formed in each stage of the oxidative roasting of the CSD were identified. After the first weight loss step, sulfate compounds were mainly formed in the second stage, and approximately 48% of sulfur contained in the metallurgical waste was removed. In the third stage, the sulfur removal reaction was carried out; the rest of sulfur was nearly removed in this stage. Kinetics of the third stage was analyzed from the dynamic DSC-TGA data by means of Coats and Redfern equation. The nucleation and growth model yielded a satisfactory fit to these experimental data.

To meet the demands of the green transition and mitigate climate change there is an increasingly urgent need for a wide range of crucial raw materials. Global resource scarcity, criticality, and supply disruption due to material shortfalls or geopolitical instability is driving efforts towards an inclusive, multi-materials circular economy with the objective of providing a more sustainable future. Within the domain of metals production, recent focus has been on development of new technological approaches that maximize the recovery of valuable materials, whilst simultaneously aiming at the reduction of the associated environmental impacts. In addition, the shift towards the increased use of lower grade input materials - either because of reduced ore quality or inclusion of secondary raw materials sources as feedstocks - often means there is a broader range of impurities within metallurgical process streams.In the case of industrial hydrometallurgical base metals—Cu, Ni, Zn—production methods like leaching, precipitation, and electrochemical reduction (electrorefining/electrowinning) impurities can include valuable metals like silver, gold, or platinum at such limited concentrations that conventional methods of recovery are often not economically viable. Moreover, the nature of hydrometallurgy process solution is that it is often contain highly concentrated levels of base metal (10’s g/l) - relative to the impurity materials (ppm/ppb) - that excludes the selective extraction of the valuable metals by conventional separation steps like solvent extraction, precipitation, cementation, or ion exchange. Consequently, there exists a need for alternative methods that can efficiently remove such low-level elements from complex solutions for recirculation or re-use.Over the last decade, two related electrochemical approaches have emerged as possible ways not only for the recovery of metals at low concentrations, but also for the creation of surfaces with additional functionality. The Electrodeposition-Redox Replacement (EDRR) methodology [1] exploits the cathodic reduction of less noble metal ions to electrodeposit a solid layer on an electrode surface by application of a constant or pulsed potential or constant current. This ED process is then followed by a period when the system is allowed to relax to its open circuit potential (OCP), which results in the spontaneous redox replacement (RR) of the deposited metal layer with more noble ions from the solution. These two steps - which can also be considered as sequential electrowinning-cementation - can be tailored to salvage different metals or produce different surfaces depending on the predominating base metal and the type of impurity within solution. For example, EDRR has been utilized to recover metals including Ag (from Zn process solutions), Au (from Cl leach solutions) and Te (from metallurgical industrial waste) as well as create surfaces with catalytic, anti-corrosion and analytical applications [1].More recently, the related Electrochemically-assisted Aqueous Reduction (EAR) method has emerged as an alternative approach to selectively recover Au from high concentration Cu chloride-based solutions[2]. In contrast to EDRR, this method uses a current or potential that is pulsed in order to reduce the copper ions in the solution proximal to the electrode from Cu(II) to Cu(I). This generated monovalent copper can then reduce the Au(III) or Au(I) present in solution due to their nobility difference. In situ studies performed with EQCM-D have allowed the influence of solution concentration changes and applied electrochemical parameters on the overall recovery process to be determined. Additionally, through the appropriate selection of the system boundaries, electrode surfaces decorated by gold nanoparticles could be created demonstrating that EAR can be used to electrochemically prepare noble metal surfaces with the potential for additional functionalities like electrochemical ethanol oxidation from complex process solutions.Overall, both EDRR and EAR offer alternative and efficient methods that allow not only for the recovery of trace levels of valuable metals from under exploited hydrometallurgical solutions, but these approaches also provide the potential to directly create materials with a range of surface functionalized materials. Furthermore, EDRR is already being exploited on an industrial scale [3] to enhance energy efficiency, improve materials circularity and process economics in a range of applications. Acknowledgments This work was supported by the Research Council of Finland project EARMetal (#339979 and #342080). The RawMatTERS Finland Infrastructure (RAMI) also funded by the Research Council of Finland and based at Aalto University is acknowledged.

Research progress of chlorination roasting of heavy metals in solid waste

The historical industrial waste deposit Gater was used to dispose of different metallurgy wastes from lead and zinc production. The metallurgical waste deposit was situated in the open space, between the tailing waste deposit Žitkovac and river Ibar flow. Large amounts of lead-containing wastes are produced in the non-ferrous metallurgical industry, such as lead ash and lead slag generated in Pb smelting, lead anode slime, and lead sludge produced in the raw lead refining process. In addition to the lead concentration, numerous valuable components are found in the lead refinery waste from the group of Critical Raw Materials, such as antimony, arsenic, bismuth, copper, nickel, magnesium, scandium, as well as Rare-Earth Elements. Samples with eight characteristic points were taken to obtain relevant data indicating a possible recycling method. The chemical composition analysis was conducted using ICP; the scanning was completed using SEM-EDS. The mineralogical composition was determined by using XRD. The chemical analysis showed a wide range of valuable metal concentrations, from Ag (in the range from 14.2 to 214.6, with an average 86.25 mg/kg) to heavy metals such as Cu (in the range from 282.7 to 28,298, with an average 10,683.7 mg/kg or 1.0683% that corresponds to some active mines), Ni and Zn (in the range from 1.259 to 69,853.4, with an average 14,304.81 mg/kg), Sc (in the range from 2.4 to 75.3, with an average 33.61 mg/kg), Pb (in the range from 862.6 to 154,027.5, with an average 45,046 mg/kg), Sb (in the range from 51.7 to 18,514.7, with an average 2267.8 mg/kg), Ca (in the range from 167.5 to 63,963, with an average 19,880 mg/kg), Mg (in the range from 668.3 to 76,824.5, with an average 31,670 mg/kg), and As (in the range from 62.9 to 24,328.1, with an average 5829.53 mg/kg). The mineralogy analysis shows that all metals are in the form of oxides, but in the case of As and Fe, SEM-EDS shows some portion of elemental lead, pyrite, and silica-magnesium-calcium oxides as slag and tailing waste residues. The proposed recovery process should start with leaching, and further investigation should decide on the type of leaching procedure and agents, considering the waste’s heterogeneous nature and acidity and toxicity.

In this work, a technological scheme for the coprocessing of dissimilar zinc-containing wastes, namely, slags obtained from the autogenous smelting of copper-zinc concentrates and dusts (sludges) from gas purification during blast furnace and steelmaking production, was developed. The proposed technology was confirmed to achieve the efficient utilization of metallurgical wastes and produce the desired products (e.g., zinc sublimates, copper cast iron, and impoverished slag) for use as building materials through thermodynamic modeling, microstructural studies, and recovery process modeling. The extraction rates of copper into the alloy and zinc into sublimates by the proposed technology reached 90% and 95%, respectively. The significance of the oxide–sulfide melt as an ion-exchange medium providing high mass transfer rates and the necessary indicators for metal extraction was revealed in this study.

Extraction and separation of Fe and Ti from extracted vanadium residue by enhanced ammonium sulfate leaching and synthesis of LiFePO4/C for lithium-ion batteries

We have developed the process that enables receiving pellets from zinc-containing dust and recovering them in a Waelz kiln with practically total zinc distillation and its capture in bag filters. As this takes place, metallic iron, still present in the pellets, can be used in metallurgical treatment. We have elaborated the process instructions to obtain pellets from zinc-containing dust with an addition of solid fuel, magnesite, and bentonite. To simulate recovery of the carbon-containing pellets in production, bench tests have been performed. These allowed us to determine principal operating conditions of the technological procedure of metallurgical zinc-containing dust recovery and validate the unit for recovery of this dust. The data obtained from the production tests prove feasibility of implementation of this process and allow assessing economic efficiency of zinc-containing dust recovery.