Hydrometallurgical Processing Routes Research Articles

Electrochemical Oxidation of Cobalt at a Platinum Electrode in a Chloride Medium

Cobalt is a highly important metal that is widely used in lithium-ion batteries, cemented carbide, magnetic materials, chemical, and medical industries. The current global cobalt reserves (in total around 6.9 million tons) are unevenly distributed mainly between the Democratic Republic of Congo (48%) and Australia (21%) [1]. One of the main sources of cobalt is nickel production where Co is as a byproduct. Nevertheless, research related to cobalt extraction from both primary or secondary resources must be accelerated to address the current imbalance between supply and demand, that has resulted in cobalt being classified as highly critical by the EU [2]. Currently, primary and secondary raw materials are refined using pyro-hydrometallurgical or hydrometallurgical processing routes, followed by e.g. cobalt crystallization, or electrowinning. Battery grade cobalt salts can be further subjected for calcination to form battery grade oxides. In the current study, we investigate a novel approach of electrifying metallurgy - attempting for direct electrochemical cobalt recovery as cobalt oxide from a hydrometallurgical chloride based process solution.Potentiostatic electrolysis was performed in synthetic cobalt chloride solution, mimicking the industrial concentrations. SEM and EDX were used for microstructural characterization and determination of sample compositions, respectively. Cyclic voltammetry (CV) was also carried out to understand the anodic behavior of cobalt on the Pt electrode. CV studies suggested the formation of different cobalt-containing phases and the obtained precipitates in potentiostatic experiments were identified as Co3O4 and CoOOH. However, the precipitate composition was strongly dependent on the conditions of electrolysis, such as potential, temperature, and pH. At the highest studied potential (1150 mV vs. Ag/AgCl) the precipitate obtained had a saturated black color indicating desired formation of Co3O4, while at lower potentials the brown colour indicated dominance of other phases. The microstructure of the electrodes due to different potentials was investigated by SEM, indicating also morphology changes as a function of recovery potential. EDX analysis suggested that the precipitates recovered included not only cobalt and oxygen but also traces of chloride ions.Overall, this study highlights the possibility of cobalt recovery in oxide form in a chloride medium as an alternative method for the recovery of cobalt from industrial process solutions. The proposed approach can be suggested as an alternative to the traditional process of crystallization or electrowinning. In addition, cobalt obtained in a form of oxide is an important class of materials characterized by good electrochemical, catalytic, and optical properties and can be used as a final product in a variety of applications if quality requirements can be achieved. Acknowledgment The ENICON project (https://enicon-horizon.eu/) has received funding from the European Union’s Framework Program for Research and Innovation Horizon Europe under Grant Agreement No. 101058124 References Rahimpour Golroudbary, S.; Farfan, J.; Lohrmann, A.; Kraslawski, A. Environmental Benefits of Circular Economy Approach to Use of Cobalt. Global Environmental Change (2022) 76, doi:10.1016/j.gloenvcha.2022.102568.Blengini, G.A.; EL Latunussa, C.; Eynard, U.; Torres de Matos, C.; Wittmer, D.; Georgitzikis, K.; Pavel, C.; Carrara, S.; Mancini, L.; Unguru, M.; et al. Study on the EU’s List of Critical Raw Materials (2020) Final Report., doi:10.2873/904613.

Evaluating glycine as an alternative lixiviant for copper recovery from waste printed circuit boards

Current hydrometallurgical processing routes for copper recovery from waste printed circuit boards (PCBs) utilise strong mineral acids, which pose environmental hazards. Glycine has been proposed as an alternate lixiviant with a lower environmental impact. This study aimed to investigate the effectiveness of glycine as lixiviant for copper dissolution from waste PCBs. Bench scale laboratory leaching tests were performed to investigate the effect of key process variables such as temperature, oxidant type and lixiviant concentration on the rate, extent and selectivity of copper leaching.In the presence of oxygen as oxidant, the glycine concentration did not have a significant effect on the rate or extent of copper leaching in the range 1 M to 2 M. Increasing the temperature from 25 °C to 60 °C increased copper dissolution after 22 h from 29.6% to 81.2% when using a glycine concentration of 1 M. When air instead of oxygen was used as oxidant, the copper dissolution achieved with 1 M glycine after 22 h at 60 °C decreased by 43.9 percentage points to 37.3%, due to the lower concentration of dissolved oxygen in the system. Using hydrogen peroxide instead of oxygen as oxidant, did not improve the overall extent of copper leaching achieved.Leaching with 1 M glycine and oxygen as oxidant at 60 °C is proposed as the most feasible operating conditions within the ranges investigated, because these conditions yielded the highest copper dissolution (81.2%) with relatively low (1.3%) gold co-extraction.

Selective precipitation of rare earth from non-purified and purified sulfate liquors using sodium sulfate and disodium hydrogen phosphate

The conventional hydrometallurgical process routes for the recovery of rare earth elements (REEs) from ores employs sulfuric acid. After being leached, the rare earth sulfate liquor presents impurities that need to be removed before they can be used in the production of marketable products. In this sense, a non-purified rare earth sulfate liquor obtained from a rare earth mineral processing and containing low rare earth oxides (REOs) concentration (∼4.6 g/L) and high Ca2+, Mg2+, Mn2+, Fe3+, Al3+, Th4+, UO22+, PO43− and SO42− content were used in this study. In order to remove all the Fe3+, Th4+ and PO4−3 ions and reduce Al3+, Ca2+, UO22+ and SO42− concentrations, the liquor was purified in two consecutive steps: first by addition of limestone to pH of 3.5 and then with a dosage of lime until it reached a pH of 5.0. Only about 7% of the REEs mass feed in the liquor was lost in the purification step. The REEs precipitation experiments were carried out with two liquors, non-purified and purified, using Na2SO4 and Na2HPO4 as reagents. The rare earth products with the highest purity were obtained with purified rare earth sulfate liquor. In the best condition, the consumption ratio was 0.31 ton of Na per ton of REEs and it resulted in the precipitation of 100% of the REEs feed in the liquor by addition of Na2HPO4. In the experiments in which Na2SO4 was used, the consumption was 0.82 ton of Na per ton of REEs and only 88% of the REEs feed was precipitated. The temperature to precipitate the REEs using Na2HPO4 ranged from 20 °C to 70 °C, whereas precipitation with Na2SO4, only occurred at 70 °C. The rare earth products obtained with Na2SO4 (sodium and rare earth double sulfate) and with Na2HPO4 (a mixture of rare earth phosphate and sodium and rare earth double sulfate), containing respectively 41.4% w/w and 42.9% w/w of REOs, seemed to have enough purity to be processed in downstream steps. As a result, a flowsheet for a process route to recover the rare earth elements from a non-purified rare earth liquor was proposed.

Improving urban mining practices for optimal recovery of resources from e-waste

In this article, current progress in urban mining related to e-waste recycling is reviewed and associated state-of-the-art recycling technologies are evaluated. As sufficient volume of e-waste is a limiting factor for its recycling economy, the need for the establishment of effective e-waste collection mechanisms, particularly for small sized End-of-Life (EoL) devices, is emphasized in terms of the need for effective government policies, increased public awareness, economic incentives, establishing industry-funded co-regulatory agreements, etc. Feasible options for e-waste recycling through pyro- and hydro-metallurgical process routes are reviewed. Deficiencies in e-waste recycling chains are highlighted, and recommendations to improve the current very low collection rate of small sized EoL devices such as mobile phones are made. Optimization of the recovery of the critical metals and energy through different processing options is discussed.

Hydro–pyro integration in the processing of nickel laterites

Hydrometallurgical process routes are seen to be the future of treatment of the lower grade nickel laterites ores. Hydrometallurgical projects of recent years have focused on HPAL and have been largely unsuccessful economically so far, with huge capital cost overruns.The simplest and least capital intensive of the possible alternatives to HPAL is atmospheric heap leaching. Development work is also underway by several companies into atmospheric tank leaching which is also a potentially viable alternative.The natural product for a leaching process is a high grade nickel intermediate either from a direct precipitation process (containing approx. 36% Ni) or via ion exchange (>50% Ni).There are many existing pyrometallurgical facilities which could easily be adapted to take this nickel intermediate giving them significant potential benefits especially as nickel laterite ore grades diminish. The nickel production from these plants could also be increased and for new plants large capital and operating cost savings achieved by using suitable intermediates.There are also potential environmental benefits with much less energy consumed and lower greenhouse gases emitted per tonne of nickel produced.In the future an integrated hydrometallurgical plant with attached existing smelter or a more advanced pyrometallurgical smelting process (e.g. a DC arc furnace) could well be the way forward for new projects.

Hydrometallurgical processing of Platreef flotation concentrate

Platinum producers are evaluating hydrometallurgical process routes to extract platinum group metals (PGM) and base metals (BM) from flotation concentrate that are alternative to conventional pyrometallurgical matte smelting treatment of flotation concentrates. This approach would attract several potential benefits to the cost-effective processing of lower-grade and high-chromium concentrates. Ivanhoe Nickel and Platinum Ltd. wished to investigate this option on samples arising from their Platreef project in the northern limb of the Bushveld Complex in South Africa, from concentrate containing 1.5 g/t Pt, 2.5 g/t Pd and 0.5 g/t Au, as well as 1.5% Ni and 1.2% Cu. Other PGMs assayed rather low grades in the concentrate (Rh 128 ppb; Ru 153 ppb; Os 18 ppb; Ir 31 ppb) so the focus was on Pt, Pd and Au in this study. Some twenty-two hydrometallurgical process flowsheet variants were considered for evaluation in a testwork programme combining several conventional and proprietary unit process technologies. The testwork outcomes suggested that a hydrometallurgical flowsheet alternative to smelting (the patented Kell Process) is potentially a practical, environmentally benign and energy-efficient approach for treating low-grade Platreef concentrate with relatively low risk. This process broadly comprises selective leaching of base metals by pressure oxidation, followed by leaching of PGMs after a roasting pretreatment step shown to render PGMs and particularly Pt amenable to leaching. The process embodies separation of the value metals (PGM and base metals) into separate chloride and sulfate solution streams, respectively, and impurity elements (Fe, Al and gangue) into a tailings product. Key elemental deportments from the un-optimized process were Ni 96%, Co 94%, Cu 94%, Pt 96%, Pd 94% and Au 87%. Preliminary work indicated that further improvements in value metal recoveries, impurity separations and reagent consumptions may be gained from further optimization of the individual unit processes. Moreover, the recycle of key reagents uses existing proven technologies, rendering the process more economically and environmentally favourable. Initial assessment suggests that the Kell Process should offer both economic and environmental benefits over conventional pyrometallurgical matte smelting treatment of Platreef flotation concentrate.

Determination of the relative leaching kinetics of Cu, Rh, Ru and Ir during the sulphuric acid pressure leaching of leach residue derived from Ni–Cu converter matte enriched in platinum group metals

Hydrometallurgical process routes are typically used for separation of platinum group metals (PGMs) from base metals in Ni–Cu converter matte. Nickel dissolution is primarily achieved in the first stage leach (high pressure or atmospheric leaching, or a combination of the two), which is followed by second stage high pressure sulphuric acid/oxygen leaching to dissolve copper and the remaining nickel. PGMs are recovered from the leaching residue, and their dissolution must hence be limited. The leaching of base metals in the first stage has been characterised, but there is a limited understanding of the behaviour of metals, and more specifically PGMs, in the second stage pressure leach. This research presents the results of laboratory work performed to investigate the kinetics of leaching in the second stage pressure leach. The influence of key operating parameters such as the temperature, pressure, and initial acid concentration on PGM dissolution was investigated.

Recovery of precious metals from electronic scrap by hydrometallurgical processing routes

Although copper is the principal metal in most electronic scrap, printed circuit boards in mobile phones also contain a significant amount of silver, gold and palladium. A bench-scale extraction study was carried out on the applicability of economically feasible hydrometallurgical processing routes to recover these precious metals. The starting material contained 27.37% copper, 0.52% silver, 0.06% gold and 0.04% palladium. In a first step, the following leaching solutions were applied: an oxidative sulfuric acid leach to dissolve copper and part of the silver; an oxidative chloride leach to dissolve palladium and copper; and cyanidation to recover the gold, silver, palladium and a small amount of the copper. A thiourea leach, as an alternative to cyanidation, was also investigated but did not give a sufficiently high yield. To recover the metals from each leaching solution, the following methods were evaluated: cementation, precipitation, liquid/solid ion exchange and adsorption on activated carbon. Precipitation with NaCl was preferred to recuperate silver from the sulfate medium; palladium was extracted from the chloride solution by cementation on aluminum; and gold, silver and palladium were recovered from the cyanide solution by adsorption on activated carbon. The optimized flowsheet pe united the recovery of 93% of the silver, 95% of the gold and 99% of the palladium.

Potential for bulk mining of oxidized platinum-group element deposits

The market for platinum-group elements (PGE) is profitable, but difficult to enter for newcomers. The main difficulties are in extraction technology, economics and marketing. Novel metallurgical processing technology may offer a route for the development of currently sub-economic PGE deposits that are amenable to surface mining. The merits of various pyro- and hydrometallurgical process routes are discussed. Before more detailed process development work can proceed it is necessary to understand the mineralogical balance of the PGE in oxidized mineralization. An example is presented from the Main Sulphide Zone (MSZ) mineralization of the Great Dyke, Zimbabwe. The PGE in the sulphide zone occur dominantly in the form of discrete bismuthotelluride, arsenide and sulphide minerals, whereas in the oxidized zone they occur as oxide or hydroxide minerals and aggregates as well as relics of the primary minerals. Such mineralogical contrasts have important implications for potential open-pit mining and processing.

Sequential differential thermal analyses (S-DTA) of autoclave reactions

The main message of this paper is the description of an analyzing technique about the measuring of the energy budget in pressure vessels on a laboratory scale. To demonstrate this technique two cases are presented. The first series deals with the oxidation of cellulose and the second series with the co-treatment of jarosite and sludge. Jarosite is a waste product of zinc refining factories using hydrometallurgical processing routes. The energy budget is always a parameter in process design. A common way to obtain the net energy transfer of reactions occurring at atmospheric pressure is to obtain the differential thermal analyses (DTA) signal by using a ‘joule measuring device’. Obtaining the reaction energy at higher pressures is more complicated. Indirect information was obtained by measuring the temperature rise produced by the ongoing reaction in an autoclave during heating, compared to the temperature profile of the same autoclave during a blank experiment. This method is called here ‘Sequential Differential Thermal Analyses’, (S-DTA). The disadvantage of such a system is the energy loss to the environment, since the autoclave is not perfectly isolated. It has been shown that for limited energy increases this effect is negligible, and for stronger exothermic reactions the autoclave should be used with smaller quantities of reagents. The wet oxidation of cellulose with varying amounts of oxygen has been used to demonstrate the possibilities and the accuracy of this method.

Comparative column elution of jarosite waste and its autoclaved product-evidence for the immobilization of deleterious elements in jarosite

Jarosite waste, originating from the zinc industry using hydrometallurgical processing routes, is considered hazardous. Metals such as zinc, cadmium and copper are present in an environmentally mobile form, thus the jarosite waste is usually stored in lined ponds. Autoclaving of this material with a cellulose type waste material, such as sewage sludge, with the addition of a neutralizing agent will transform most of the metals into oxides, which are immobile under neutral conditions. Jarosite waste and its treated product were tested in standard column tests, as prescribed by Dutch legislation if the material is to be used as construction material. In three weeks time an amount of simulated rainwater, equal to ten times the weight of the solid, was percolated through the samples. The moisture content of jarosite waste is about 40 wt%, reflecting the leach liquor from the zinc refining process; its solutes are easily leached out. This leach liquor initially contained high concentrations of Zn, Cu and Cd, but when a liquid/solid ratio of two (L/S=2) was reached, most of these metals were removed from the jarosite waste. Co-treatment of jarosite with sewage sludge yields a product which is far more acceptable. Even so, the leached amounts of zinc and cadmium do not match the Dutch criteria for second-grade construction material. Counter current washing of the residue improves its properties as a construction material, although the best environmental option for the solid residue is further (thermal) treatment (Rage et al., 1996).

Reduction of copper with cellulose in an autoclave; an alternative to electrolysis?

Copper is widely used in electricity wire and electronic devices, which makes it one of the most important base metals. Hydrometallurgical processing routes are typical for ores with low copper content. The low-grade copper ores are stacked in large heaps and sprinkled with dilute sulfuric acid, this is called heap leaching. The collected leach liquor is concentrated and purified in a solvent extraction step, and subsequently processed by electrowinning. Copper plates out and the generated acid is recycled to the heap leach. This paper deals with an alternative for the electrolytic processing step by autoclaving a mixture of cellulose and copper sulfate solution. In the laboratory a 600 ml. Parr autoclave was used. First the exact ratio of cellulose and copper ions was determined. Cellulose was suspended in a copper sulfate solution and heated in an autoclave till 250°C. After a retention time of 60 minutes at this temperature the pressure vessel was quenched with water. The liquid was analyzed by ICP and the solids by ICP and XRD. The copper ions were precipitated as elemental copper with a particle size around 80 pm. A solid byproduct was an easily separable, black organic phase, probably carbon. The generated dilute sulfuric acid contained dissolved organic carbon. The low pH of this acid restricts the choice of construction materials for the autoclave. Kinetic results indicate a retention time of 30 minutes, after reaching 250°C. The process is selective for copper with respect to nickel and iron, but arsenic partly precipitates with the copper. This technology might have its potential as an alternative for electrowinning or can be used for small waste streams containing copper in relatively high concentrations.

Hydrometallurgical Processing Routes in the Synthesis of Advanced Materials

Hydrometallurgical processing routes show outstanding potential for synthesizing a wide range of advanced ceramic and metallic materials, in which the composition, purity and structure are closely controlled to produce- materials with the properties needed for specific applications. The characteristics of "advanced materials'* are first discussed in general terms. Those classes of materials most likely to be amenable to hydrometallurgical processing are then considered, and the economic, technical and environmental benefits that might be derived from adopting hydrometallurgical processing routes are discussed. The thermodynamic, surface chemical, kinetic, and transport principles that could be used to control the materials characteristics are then reviewed. Finally, selected examples of aqueous processing techniques for preparing both oxide ceramics and metallic materials, as powders, films or coatings, are provided.

Aqueous processing in materials science and engineering

Reviews of aqueous processing in JOM have traditionally focused on hydrometallurgical process routes. This article, however, addresses the application of aqueous processing in materials engineering and presents some promising developments that employ aqueous-based routes for the manufacture of high-tech components and specialty products. Such applications include producing metallic and ceramic powders; etching; surface modification by electroplating and electroless plating; manufacturing jewelry and intricate components by electroforming; and producing advanced ceramics, composites, and nanophase materials by sol-gel and biomimetic processing.