Mari Lundström

Reaction product layer on chalcopyrite in cupric chloride leaching

Abstract During the leaching of chalcopyrite in cupric chloride solutions, a reaction product layer forms on the mineral surface. In the present work, the formation and the composition of the reaction product layer on solid stationary chalcopyrite was studied in a chemical environment similar to that of the HydroCopper® process. The effect of the process parameters on the reaction product layer was investigated. Electrochemical measurements, including A.C. impedance spectroscopy, were carried out and an equivalent circuit was used to estimate the surface parameters of the reaction product layer, such as resistance, capacitance and porosity. Scanning electron microscopy was used to complement the electrochemical measurements. The results suggest that at pH = 1, a fragile more resistive elemental sulphur layer forms, whereas at pH = 3, a porous less resistive FeOOH layer is formed. Lors de la lixiviation de la chalcopyrite en solutions de chlorure cuivrique, une couche de produit de reaction se forme a la surface du mineral. Dans le present travail, on a etudie la formation et la composition de la couche du produit de reaction sur de la chalcopyrite solide stationnaire dans un environnement chimique similaire a celui du procede d’HydroCopper®. On a etudie l’effet des parametres du procede sur la couche de produit de reaction. On a effectue des mesures electrochimiques, incluant la spectroscopie a impedance A.C., et l’on a utilise un circuit equivalent pour estimer les parametres de surface de la couche de produit de reaction, comme la resistance, la capacitance et la porosite. On a utilise la microscopie electronique a balayage pour completer les mesures electrochimiques. Les resultats suggerent qu’a un pH = 1, une couche fragile de soufre elementaire plus resistive se forme, alors qu’a un pH = 3, une couche poreuse moins resistive de FeOOH est formee.

Transient Surface Analysis of Dissolving Chalcopyrite in Cupric Chloride Solution

Abstract This study presents an investigation of chalcopyrite surfaces dissolving in concentrated cupric chloride solutions similar to those used in the HydroCopper® process, [NaCl] = 280 g/L, [Cu2+] = 30 g/L and T = 90 °C. The leaching of chalcopyrite and the parameters of the reaction product layer formed on the mineral surface were studied at the open circuit potential as a function of time (0.5 – 22 hours) and at pHs in the range 1 - 3. The electrochemical impedance spectroscopy (EIS) data indicated that there were two or three time constants present. These were suggested to be due to the double layer and to elemental sulphur and FeOOH. With pH 1 at OCP the reaction product layer was a single-phase layer of elemental sulphur (t = 0.5 – 9 h) or two-phase layer with elemental sulphur and FeOOH (t = 22 h). The apparent charge transfer resistance was higher (>25 Ωcm2) at the beginning of leaching (t ≤ 4 h), but decreased to about 4 Ωcm2 with increasing time to 22 hours. The reaction product layer resistance did not change markedly. It is likely that the apparent charge transfer resistance reflects the resistance of the reaction product layer at pH 1, showing apparent changes in the calculated charge transfer resistance values. At pH 2, the reaction product layer was an elemental sulphur layer at t ≤ 2 h, becoming a two-phase layer of elemental sulphur and FeOOH at t = 3 – 22 h. The apparent charge transfer resistance was <8 Ωcm2 at all times, whereas the reaction product layer resistance decreased with time from 30 Ωcm2 to about 4 Ωcm2. The two-phase layer at pH 2 was electrically less resistive than the one-phase layer at pH 1. At pH 3 the reaction product layer was a two-phase layer at all times, consisting of goethite and S8. This layer allowed more rapid dissolution at the beginning, but with time a reaction product layer grew, increasing the electrical resistance as well as decreasing the dissolution rate of chalcopyrite. The apparent charge transfer resistance at pH 3 was constant at all times.

Selective reductive leaching of cobalt and lithium from industrially crushed waste Li-ion batteries in sulfuric acid system

Recycling of valuable metals from secondary resources such as waste Li-ion batteries (LIBs) has recently attracted significant attention due to the depletion of high-grade natural resources and increasing interest in the circular economy of metals. In this article, the sulfuric acid leaching of industrially produced waste LIBs scraps with 23.6% cobalt (Co), 3.6% lithium (Li) and 6.2% copper (Cu) was investigated. The industrially produced LIBs scraps were shown to provide higher Li and Co leaching extractions compared to dissolution of corresponding amount of pure LiCoO2. In addition, with the addition of ascorbic acid as reducing agent, copper extraction showed decrease, opposite to Co and Li. Based on this, we propose a new method for the selective leaching of battery metals Co and Li from the industrially crushed LIBs waste at high solid/liquid ratio (S/L) that leaves impurities like Cu in the solid residue. Using ascorbic acid (C6H8O6) as reductant, the optimum conditions for LIBs leaching were found to be T = 80 °C, t = 90 min, [H2SO4] = 2 M, [C6H8O6] = 0.11 M and S/L = 200 g/L. This resulted in leaching efficiencies of 95.7% for Li and 93.8% for Co, whereas in contrast, Cu extraction was only 0.7%. Consequently, the proposed leaching method produces a pregnant leach solution (PLS) with high Li (7.0 g/L) and Co (44.4 g/L) concentration as well as a leach residue rich in Cu (up to 12 wt%) that is suitable as a feed fraction for primary or secondary copper production.

Challenging the concept of electrochemical discharge using salt solutions for lithium-ion batteries recycling

The use of lithium-ion batteries (LIB) has grown significantly in recent years, making them a promising source of secondary raw materials due to their rich composition of valuable materials such as Co, Ni and Al. However, the high voltage and reactive components of LIBs pose safety hazards during crushing stages in recycling processes, and during storage and transportation. Electrochemical discharge by immersion of spent batteries in salt solutions has been generally accepted as a robust and straightforward discharging step to address these potential hazards. Nonetheless, there is no clear evidence in the literature to support the use of electrochemical discharge in real systems, neither are there clear indications of the real-world limitations of this practice. To that aim, this work presents a series of experiments systematically conducted to study the behavior of LIBs during electrochemical discharge in salt solutions. In the first part of this study, a LIB sample was discharged ex-situ using Pt wires connected to the battery poles and submerged into the electrolyte solution on the opposite end. The evolution of voltage in the battery was measured for solutions of NaCl, NaSO4, FeSO4, and ZnSO4. The results indicate that, among the electrolytes used in the present study, NaCl solution is the most effective for LIBs discharge. The discharge of LIB using sulfate salts is however only possible with the aid of stirring, as deposition of solid precipitated on the electrodes hinder the electrochemical discharge. Furthermore, it was found that the addition of particulates of Fe or Zn as sacrificial metal further enhances the discharging rate, likely due to an increased contact area with the electrolyte solution. While these findings support the idea of using electrochemical discharge as a pre-treatment of LIBs, severe corrosion of the battery poles was observed upon direct immersion of batteries into electrolyte solutions. Prevention of such corrosion requires further research efforts, perhaps focused on a new design-for-recycling approach of LIBs.

Lanthanide-alkali double sulfate precipitation from strong sulfuric acid NiMH battery waste leachate

In NiMH battery leaching, rare earth element (REE) precipitation from sulfate media is often reported as being a result of increasing pH of the pregnant leach solution (PLS). Here we demonstrate that this precipitation is a phenomenon that depends on both Na+ and SO42- concentrations and not solely on pH. A two-stage leaching for industrially crushed NiMH waste is performed: The first stage consists of H2SO4 leaching (2 M H2SO4, L/S = 10.4, V = 104 ml, T = 30 °C) and the second stage of H2O leaching (V = 100 ml, T = 25 °C). Moreover, precipitation experiments are separately performed as a function of added Na2SO4 and H2SO4. During the precipitation, higher than stoichiometric quantities of Na to REE are utilized and this increase in both precipitation reagent concentrations results in an improved double sulfate precipitation efficiency. The best REE precipitation efficiencies (98-99%) - achieved by increasing concentrations of H2SO4 and Na2SO4 by 1.59 M and 0.35 M, respectively - results in a 21.8 times Na (as Na2SO4) and 58.3 times SO4 change in stoichiometric ratio to REE. Results strongly indicate a straightforward approach for REE recovery from NiMH battery waste without the need to increase the pH of PLS.

Structural distinction due to deposition method in ultrathin films of cellulose nanofibres

This research explores fundamental, structural differences of ultrathin films, prepared with three distinct deposition methods using 2,2,6,6-tetramethyl-piperidin-1-oxyl radical oxidized cellulose nanofibres (TEMPO-CNFs) derived from never dried bleached birch pulp. There is standard characterization by atomic force microscopy (morphology, roughness) and ellipsometry (thickness) and important structural data is gained by exposing the films to water vapor and monitoring the vapor uptake with quartz crystal microbalance (QCM). Significant distinctions were found from QCM data that could be linked to the structure of the films, originating from the three deposition methods: adsorption, spin coating and electrophoretic deposition. Moreover, the results shown here have potential implications for various types of films that comprise of amphiphilic nanomaterials that have a distinct response to moisture or aqueous based solutions.

Modelling the physico-chemical effect of silver electrorefining as effect of temperature, free acid, silver, copper and lead concentrations

The study of electrolyte bath properties is essential for the improvement of silver electrolysis based processes. The paper outlines investigations into suitable models for the calculation of physico-chemical properties with the emphasis placed on conductivity, density and viscosity. Measurements were conducted within the industrial operation parameters used for silver electrolytes and the results indicate that these type of industrial electrolytes have an operating conductivity within the range of 60–140 mS/cm, density of 1.05–1.14 g/cm3 and a viscosity of 0.75–0.91 mm2/s. A representative model for each of these properties was proposed in order to calculate the conductivity, density and viscosity of silver electrolyte. From the evaluation of models, it was determined that all models have R2 (accuracy of fit) and Q2 (accuracy of prediction) values above 0.9 and thus can be regarded as excellent models.The study of electrolyte bath properties is essential for the improvement of silver electrolysis based processes. The paper outlines investigations into suitable models for the calculation of physico-chemical properties with the emphasis placed on conductivity, density and viscosity. Measurements were conducted within the industrial operation parameters used for silver electrolytes and the results indicate that these type of industrial electrolytes have an operating conductivity within the range of 60–140 mS/cm, density of 1.05–1.14 g/cm3 and a viscosity of 0.75–0.91 mm2/s. A representative model for each of these properties was proposed in order to calculate the conductivity, density and viscosity of silver electrolyte. From the evaluation of models, it was determined that all models have R2 (accuracy of fit) and Q2 (accuracy of prediction) values above 0.9 and thus can be regarded as excellent models.

From metal-containing industrial waste towards circular economy of metals: European Training Network SOCRATES

It is becoming ever more clear that the natural resources – especially metals – are gradually being depleted from the Earth’s crust. Therefore, secondary sources such as industrial residues, waste and side-streams could potentially act as a more sustainable critical metal supply. This approach is at the very heart of the circular economy principles and, actually, fromthatpointofview, European countries have ‘inherited’ a large quantity of industrial waste (e.g. tailings, sludges, slags and ashes), i.e. a potential raw material ‘mines’ for metals, since the early days of industrialisation. With this motivation, the European Training Network for the sustainable, zero-waste valorisation of critical metal-containing industrial process residues ‘SOCRATES’ has been launched in January 2017 in the framework of the Marie SkłodowskaCurie Action (MSCA-ETN). The objective of the project is twofold: (1) to provide new scientific insights into recycling and sustainable processing of materials and (2) to train new experts of metal recycling and processing when 15 early-stage researchers (ESRs) pursue their doctoral degrees within the scope of the project (Figure 1). The outcomes of the SOCRATES project will offer comprehension to the process residues valorisation, with a focus on critical metals recovery, production of catalysts and inorganic polymers and integrated assessment of process sustainability. Whether we discuss catalyst production or metal recovery from sludges, it is obvious that electrochemistry, surface science and process engineering play critical roles and it can be seen also in the training of ESRs. SOCRATES brings together organisations from academia, industry and the research sector (Table 1) and, actually, the unique combination of SOCRATES partners spans through the entire metal supply chain. The universities within the SOCRATES consortium are among Europe’s leaders in extractive metallurgy research and transfer of knowledge to new generations of scientists is the main goal of this programme. Each of the four scientific work packages (WPs, Figure 2) of SOCRATES is dedicated to one step in the value chain – namely, metal extraction from industrial residues (WP1), metal recovery from process solutions (WP2), residual matrix valorisation into high value-added products (WP3) and integrated assessment of newly developed technologies (WP4). WP1 focuses on advanced metal extraction technology combinations, ranging from plasma-, hydroto solvometallurgical unit operations. The development of plasma-driven metal extraction methods has great potential to effectively separate metals that will lead to minimising costs, emissions mitigation, safer and cleaner byproducts. Solvo-metallurgy is based on organic solvents instead of aqueous solvents; here the surface chemistry and physics play a critical role in the organic– aqueous interface. With the development of new biocompatible solvo-metallurgical leaching methods, efficient recovery of targeted elements is envisaged. The development of deep eutectic solvents is a novel approach in extractive metallurgy, still industrially not widely applied. Searching for novel methods of metals removal from aqueous solutions is one of the priorities for WP2. Emerging interest for extraction of minor quantities of valuable metals from complex impure hydrometallurgical solutions is drawn to electrochemical methods as no additional chemical reagents are required and the recovery can be precisely controlled by applying favourable process conditions. The fundamental electrochemistry knowledge of very

A future application of pulse plating – silver recovery from hydrometallurgical bottom ash leachant

ABSTRACT In the current study, electrodeposition-redox replacement was applied to a hydrometallurgical solution with the main elements of Ca (13.8 g L−1), Al (4.7 g L−1), Cu (2.5 g L−1), Zn (1.2 g L−1), Fe (1.2 g L−1), S (1 g L−1), Mg (0.8 g L−1), P (0.5 g L−1) and Ag (3.5 ppm). The solution originated from the leaching experiment of incinerator plant bottom ash, which was dissolved into 2 M HCl media at T = 30 °C. The resulting deposit on the electrode surface was analysed with SEM-EDS and the observed Ag/(Cu + Zn) ratio (0.3) indicated remarkable enrichment of silver on the surface, when compared to the ratio of these elements (Ag/(Cu + Zn)) in the solution (6.8 × 10−5). The enrichment of Ag vs. (Cu + Zn) could be demonstrated to increase ca. 4500 fold compared to the ratio of the elements in solution.

Jarogain Process—A Hydrometallurgical Option to Recover Metal Values from RLE Zinc Residue and Steel Dust

The novel Jarogain process combines treatment of the jarosite residue of zinc manufacturing and processing of arc furnace dust from steelmaking to a holistic recovery technology. The new hydrometallurgical approach is targeted to recover the major constituents (Fe, Zn, Pb) as well as valuable components such as Ag, Au, In and Ga from the jarosite-dust mixture as reusable concentrates. The fractionation process proposed by VTT and Aalto University takes advantage of jarosite being readily fine powder and directly available for wet chemical processing. Jarogain process provides an energy efficient opportunity for jarosite utilization as value added products. The experimental proof-of-concept of key stages of the process will be outlined with a comparison of available pyrometallurgical treatments of jarosite waste. The techno-economical assessment is based on estimated investment and variable production cost using the discounted cash flow (DCF) analysis.