Browsing by Author "Jokilaakso, Ari, Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland"

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  • Behaviour of trace elements in copper smelting processes - LA-ICP-MS as a tool for sample characterisation
    (2021) Klemettinen, Lassi
     School of Chemical Engineering | Doctoral dissertation (article-based)
    The rapidly increasing demand for metals used for instance in batteries, electronics and renewable energy production cannot be satisfied merely by increasing mining and primary production capacities. In order to better secure the metal supply and achieve a circular economy, metal recycling and recovery from End-of-Life (EoL) products must be significantly increased. One viable option for recycling several metals is to utilise existing primary or secondary copper smelters. Many of these smelters have been optimised for handling primary ores, which means that more research is needed in order to understand and quantify the effects of introducing secondary raw materials into the process circuits. In this thesis, the behaviour of several trace elements present in secondary raw materials (Ir, Mo, Pb, Re, Sn, Sb, Te, Ga, In, La, Nd, Li, Co, Mn) was investigated in laboratory-scale primary and secondary copper smelting experiments. The experiments were conducted in equilibrium conditions or as a function of time at 1300 °C. Different gas atmospheres were utilised for simulating the process conditions in different stages of industrial smelting operations. The phase-by-phase elemental concentrations were analysed using scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS), electron probe micro-analysis (EPMA), as well as the state-of-the-art laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) technique. A convenient way of presenting and comparing the behaviour of different trace elements is via distribution coefficients (L = wt.% metal in alloy or matte / wt.% metal in slag). Some of the obtained distribution coefficient data represents the first reported values in the literature, whereas some provide significantly more accurate results compared to earlier results. For the distributions of gallium, indium and lanthanum between copper sulphide mattes and iron silicate slags, no previous data was found in the literature. This also applies to the experimentally verified distribution coefficients of lithium and lanthanum between copper-rich alloy and high-alumina iron silicate slags. Regarding manganese, the new data indicates significantly lower distribution coefficients compared to previous data, i.e. manganese deports extremely heavily to slag. The improved accuracy and reliability in distribution data is due to the use of direct phase-by-phase analysis techniques without the need of manual phase separation, as well as the extremely low detection limits obtained with the LA-ICP-MS. The results of this thesis can be applied to industrial processes in designing, optimising, modelling and evaluating processes for industrial-scale recycling of electronic scrap and EoL batteries, for example.
  • Experimental determination of phase equilibria in CuOx-containing slag systems at 1100 - 1500 °C
    (2018) Hellstén, Niko
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Copper is vital to modern society. However, its production consumes non-renewable resources, generating waste and harmful emissions. Currently, the copper production industry is trying to optimize pyrometallurgical processing to increase resource efficiency. Good control of slag is key in achieving this goal. Prediction and optimization of the slag properties is possible using computational thermodynamics. Nevertheless, creation of reliable thermodynamic models for a multicomponent slag requires experimental phase equilibria and thermodynamic data, especially from its binary and ternary subsystems. Presently, there is a lack of experimental data concerning Al2O3, CuOx, MgO and SiO2 containing subsystems of the slag. In the present work, thermodynamic phase equilibria, and especially the liquidus, of the Cu-O-Al2O3, Cu-O-MgO, Cu-O-Al2O3-MgO and Cu-O-Al2O3-SiO2 systems were studied experimentally in the temperature range of 1100 °C – 1500 °C. The experiments were conducted using a primary-phase quenching method and a spectroscopic analysis of the chemical compositions of the resulting phases. This method produces direct phase equilibria data from the liquid and solid phases. The experimental results of this work were compared with the predicted phase equilibria calculated using MTDATA 6.0 software and Mtox database version 8.2. It was found that 0 – 2 wt% of Al2O3 and MgO dissolved in the liquid oxide phase at the studied temperatures. Moreover, the addition of SiO2 increased the solubility of Al2O3 in the liquid oxide phase by up to 18 wt%. These results indicate that Al2O3, MgO and MgAl2O4 spinel are chemically resistant to a CuOx-rich liquid oxide at the studied conditions. Discrepancies were found between this new liquidus data, previous experimental data, and calculated liquidus by MTDATA and Mtox database. These discrepancies highlight the necessity of this experimental work. These results indicate that earlier descriptions of the studied systems in Mtox database need reassessment. Furthermore, the new experimental phase equilibrium data obtained in this work is of great importance in generating reliable thermodynamic descriptions of copper-making slag, leading to resource-efficient processing. In addition, these data are useful in various other applications, such as superconductors, refractories and glass-ceramics.
  • Experimental investigation on time-dependent recycling behaviour of WPCBs in copper flash smelting conditions
    (2021) Wan, Xingbang
     School of Chemical Engineering | Doctoral dissertation (article-based)
    With the rapid development of technology, the depletion of limited existing resources as well as more and more serious environmental pollution problems, increasing attention in recent years has been drawn to the responsible processing of end-of-life (EoL) Waste Electrical and Electronic Equipment (WEEE). Waste Printed Circuit Boards (WPCBs) are one of the main components of WEEE, accounting for 40% of the total metal recovery value and they have nowadays become an important part of urban mining. Feeding WPCBs into existing pyrometallurgical processes is developing as an easy-to-adapt and efficient way to recycle them. To fulfil sustainability and circular economy targets, the thermodynamics, kinetics and distribution behaviour of WPCBs during the pyrometallurgical process are the key factors. This study employed a series of experiments to investigate the dynamic behaviour of WPCBs in copper flash smelting process. The kinetic data were obtained by employing a well-developed high temperature reaction–quenching technique followed by direct phase analyses with a scanning electron microscopy-energy dispersive X-ray detector (SEM-EDS), electron microprobe (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The industrial copper flash smelting process was firstly simulated on laboratory scale and investigated in this study by smelting industrial chalcopyrite concentrate and FeOx-SiO2 slag at a typical smelting temperature of 1300 °C in both air and argon atmospheres. Then WPCBs were added to this system to track their physical and chemical time-dependent behaviour. Moreover, two groups of WPCB elements (Ag, Au, Pt, Pd, and As, Sb, Bi) were separately added into the matte-slag system, and their time-dependent behaviour in different phases and distribution coefficients were concluded and also compared in detail with those of In, Sn, Ge, Te, La and Nd, which were also treated in the same system. Moreover, the kinetic data and distribution ratios of base metals as well as minor elements (Ag, Au, Pt, Pd, As, Sb, Bi) in the flash smelting process were obtained experimentally and calculated. They can be used in process development for the WPCB precious metal recycling process and, equally, when using complex copper concentrates with high As, Sb and Bi content. Furthermore, the results are essential for complementing CFD models to simulate the flash smelting process more precisely, which is of significance to achieve industrial visualization and artificial intelligence to satisfy the future requirements of Industry 4.0 and even 5.0.
  • Phase equilibria and precious or high-tech metal distributions in copper smelting systems
    (2022) Chen, Min
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Metals have historically played an important role in modern societies and the industrial revolution. Nowadays, however, they are mainly derived from primary ore resources and secondary materials, such as waste electrical and electronic equipment (WEEE). WEEE contains a variety of products that no longer serve their initial purpose and their metal concentrations are significantly higher than that in primary ores. In the face of a strong demand for a circular economy model, the recovery of metal values from WEEE has attracted increasing attention. Base metals like copper, lead, and nickel are good collector metals for precious/high-tech metals. Therefore, the smelting technologies of base metals are potential and effective methods for recycling metals from secondary materials. To have a better understanding of the favorable conditions for the recoveries of valuable metals from secondary materials through copper smelting, it is critical to determine the behavior of various metals in copper smelting systems.  In this study, the phase equilibria of matte/copper and silica/spinel/wüstite-saturated iron silicate slags as well as the distribution equilibria of precious (Au, Ag, Pt, and Pd) and high-tech (Ni, Co, and Sn) metals in the equilibrium systems were investigated using an advanced high-temperature isothermal equilibration/quenching technique, followed by direct phase composition analyses using electron probe X-ray microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The experimental parameters and conditions were selected to simulate primary and secondary copper smelting processes. An investigation was made of the effects of pSO2, the slag modifiers Al2O3 and CaO, the temperature, and the saturation phase on the equilibrium phase relations of copper/matte and slag, as well as on the equilibrium distributions of the aforementioned precious/high-tech metals. The equilibrium compositions of matte/metal, slag, and spinel/wüstite were displayed as a function of matte grade or oxygen partial pressure. The distribution coefficients of precious/high-tech metals between matte/metal and spinel/wüstite/slag were calculated based on experimentally determined metal concentrations in matte, slag, and spinel/wüstite. The novel experimental data obtained in this study provide insights for improving the performance of copper smelters and increasing the recovery of valuable metals from primary and secondary materials by adjusting the temperature and oxygen partial pressure, and by adding fluxes like Al2O3 and CaO. Moreover, the present results are useful for thermodynamic database development and for the modeling of the phase relations of major components and precious/high-tech metals distributions in copper smelting systems.
  • Phase relations and thermodynamic properties of slag and metal systems related to the processing of copper anode slime
    (2018) Santoso, Imam
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Due to the sustainability related issues, metallurgical industries in the world have to improve and optimize their metal production processes. These efforts require many tasks including the collection of vital thermodynamic data related to the processed materials. However, in the processing of copper anode slime, for example, there are still lack of data of the melting point for the slag phase and the thermodynamic properties of some precious metals in the metal phase. Therefore, an extensive research is required. To obtain accurate experimental data in a slag phase containing Na2O, PbO, SiO2 and TeO2 and a metal phase carrying Pt, Ag, Au and Pd, two experimental approaches were adopted in the present study. By using these developed techniques, some difficulties and errors occurred in the previous studies were resolved. To study phase equilibria in the Na2O-PbO-SiO2-TeO2 system, advanced technique involving equilibration of mixtures at high temperature, rapid quenching of equilibrated samples into ice cold water, and compositional measurement of the phases using electron probe micro analyzer (EPMA), has been employed. To obtain silver activity data, solid-state electromotive force (EMF) method incorporating equilibration of silver alloys in a galvanic cell was used. Darken method was employed to calculate integral thermodynamic properties in the ternary system. In the present investigation, liquidus data of binaries Na2O-SiO2 and Na2O-TeO2, as well as ternaries Na2O-SiO2-PbO and Na2O-SiO2 TeO2 systems were determined at several crystal saturations. Activity of silver in the Ag-Pt and Ag-Au Pd alloys were measured. Results for the Na2O-TeO2-SiO2 system obtained in the present investigation are the first data published in the literature. Effect of Na2O and TeO2 on the liquidus is outlined. Data for the phase relations in the Na2O-SiO2, Na2O-TeO2 and Na2O-SiO2-PbO systems were compared with previous investigations. Notable differences between liquidus data measured in the present study and those reported by previous investigations were observed and evaluated. It indicated that, in general, the systems were more sensitive to Na2O than to TeO2 or PbO2. The effects of the results on the processing of the materials were outlined. Results for the Ag-Au-Pd and Ag-Pt systems are also the first thermodynamic data published in the literature. Deviation of silver activity from ideal was discussed. The results indicated that in the Ag-Pt system silver activity has a positive deviation from ideal. In the Au-Ag-Pd system, silver activity, on the other hand, has a negative deviation from Raoult's law in almost entire range of the composition. Thermodynamic data such as Gibbs energy, enthalpy and entropy were calculated. Validation of the calculated data in the Ag Au-Pd system was also performed to evaluate the calculation approach. It was shown that the method was powerful.
  • Thermodynamic properties of WEEE-based minor elements in copper smelting processes
    (2019) Avarmaa, Katri
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Today, primary and secondary copper smelters are used as recycling facilities for different wastes, such as Waste Electric and Electronic Equipment (WEEE) -based copper scrap and industrial nonferrous waste. Consequently, multiple precious and rare metals, many of them not typical in primary concentrates, are entering the copper-making circuits with increasing concentrations. Thermodynamic properties of these WEEE-based minor elements are not known well enough or at all in copper smelting processes. In this study, the distribution equilibria of precious (Ag, Au, Pd and Pt) and high-tech (Ga, Ge, In and Sn) metals were investigated experimentally under primary and secondary copper smelting, as well as converting conditions. The experiments were executed employing a well-developed equilibration – quenching technique followed by direct phase analyses with electron microprobe (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). This study applied these experimental and analytical techniques to study minor element behaviour in copper/matte-slag systems for the first time. Especially, the use of the latter analytical technique was a great leap forward and enabled minor element concentration analyses even below 1 ppbw in metallurgical slags. The main thermodynamic parameter examined was the distribution coefficient, L = wt% of metal in matte or copper / wt% of metal in slag, which describes the behaviour of a minor element in smelting conditions. This research was implemented with a multi-disciplinary approach providing results for different fields of sciences and industries. The results present influences of different smelting conditions (especially pO2), primary saturation phase and slag composition on minor element equilibria. Moreover, the slag chemistry and copper losses in slags were examined. Precious metals – Au, Pd, Pt – were distributed and recovered efficiently in copper matte (L (m/s) > 10^2) and metal (L (Cu/s) > 10^4) in all conditions, much greater than previously considered in metallurgical literature. The results for high-tech metals Ga and Ge in the investigated copper-slag systems are novel and present the first data published in the literature. The distribution results for Ag, Sn and In were close to the distribution data found in literature. The thermodynamic data acquired is useful for industry in multiple purposes, such as process development, improving resource efficiencies and recoveries of the minor elements. To attain reliable simulation and modelling data of processes and metals behaviour, the presented properties need to be added into the thermodynamic databases of calculation programs.
  • The use of alternative reductants in pyrometallurgical operations
    (2024) Attah-Kyei, Desmond
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Due to the rising concern about climate change in the last few decades, the metallurgical industry is moving toward greener practices. This move is driven by pressing concerns about the reduction of greenhouse gas emissions and environmental footprints of industrial activities. One of the main strategies in this transition is to employ alternative reductants in high temperature processes. Substituting traditional reductants like coal or coke with sustainable alternatives such as hydrogen or biochar minimizes the carbon emission and provides economic benefits in addition. In this thesis work, several non-fossil reductants were applied in high temperature processes for metal recovery from secondary sources. Leach residue of printed circuit board (PCB) was employed as reductant for solid-state reduction of hematite in DSC-TGA coupled with QMS. Hydrogen was utilized in the reduction of zinc leach residue while nickel and copper smelting slag reduction were treated with biochar on laboratory scale in a vertical fur-nace. The feasibility of adopting alternative reductants in ironmaking and pyrometallurgical treatment of secondary resources were determined in this study. The effect of the amount of reducing agent, reduction time, and temperature on the extent of reduction was investigated. The studies revealed that although PCB leach residue can be applied in reduction processes, it can only partially replace conventional reductants. PCB was also found to be effective at lower temperatures (< 1000 oC). Leach residue from zinc processing were reduced with hydrogen at temperatures of 1200 oC, 1250 oC, and 1300 oC using H2 and N2 gases to form the reducing gas atmosphere. The results showed that H2 is an effective reductant because reduction proceeded rapidly, forming speiss droplets within the slag already after 10 minutes. Nickel and copper smelting slags were reacted with biochar which were produced from hydrolysis lignin and black pellet biomass by pyrolysis at 600 and 1200 °C, and with metallurgical coke for comparison. Nickel reduction experiments were done at 1400 °C for 15, 30, and 60 min under inert gas atmosphere. The samples were quickly quenched and analyzed with Electron Probe X-ray Microanalysis. The results showed that the use of biochar resulted in faster reaction kinetics in the reduction process compared to coke. Copper slag reduction experiments were performed at 1250, 1300 and 1350 °C for 60 min in order to investigate the effect of temperature and the effect of time on reduction progress was studied at 1250 °C for 15, 30 and 60 min. The results revealed that reduction rapidly progresses to the formation of metal alloy within 10 min. Valuable metals like copper and nickel were reduced to the metal phase.Thermodynamic simulations were performed with FactSageTM at the experimental conditions and compared with results from the lab scale experiments. FactSageTM predictions were in agreement with the experiments.
  • Utilization of Ti-containing microparticles on improved steel properties – Basic studies on inclusions control and interfacial phenomena
    (2020) Kiviö, Miia
     School of Chemical Engineering | Doctoral dissertation (article-based)
    Inclusions in steel are mostly regarded as harmful. However, if the size and chemistry of the inclusions are controlled, they can act as functional particles in improving the mechanical properties of the steel. Titanium as oxides or carbides can be used to control the microstructure and mechanical properties of steel. The composition, shape and size of the inclusions can vary depending on the conditions. Reactions and wetting between titanium inclusions and steel with different alloying elements are key phenomena in developing steel production processes. In this thesis the interfacial phenomena between liquid steel and titanium-containing inclusions were studied. The aim was to determine the inclusion types after additions of titanium and TiO2, the effect and role of aluminium and manganese on the inclusions, the wetting between titanium carbide and steel and the effect of chromium, nickel and molybdenum on wetting and interfacial reactions. The experiments in a vacuum furnace consisted of adding Ti and TiO2 into liquid steel before and during casting. The inclusions formed after the additions of Ti/TiO2 were comprehensively studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) and electron backscatter diffraction (EBSD), focusing on titanium oxide inclusions. The study examined inclusion types, and the composition and size of the inclusions existing in the cast ingots. Another experimental method used was wetting experiments between TiO2/TiC and steel or iron alloys. The wetting experiments were performed using two different methods: conventional sessile drop technique and separate heating of the TiC substrate and metal droplet. During the wetting experiments the contact angles were recorded and evaluated. The samples from these experiments were investigated by SEM-EDS. The interface, particles and new phases were studied. Thermodynamic calculations (FactSage) of the formation of inclusions in low-alloyed steel in the melt and during solidification as well as carbide formation in stainless steel were performed to support the experimental part. The results of the inclusion study after the addition of TiO2 into liquid steel were novel at the time of publication of the articles. The extensive study on the effect of alloying elements on the wetting and interfacial reactions between stainless steel and TiC were unique and remains pioneering work. The results showed the complexity of the titanium-containing inclusions in steel. Mastering of the inclusions demands profound knowledge of the dominating phenomena. This thesis provides valuable information for developing the production processes of steels that have improved mechanical properties by using titanium-containing functional particles.