| 1. |
- Kero Andertun, Jakob
(author)
-
Leaching of water-granulated iron silicate slags and their compounds : A study of synthetic and industrial slag systems
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- Copper smelter slag is a residue product of the pyrometallurgical extraction of copper. Due to its physical properties, the iron silicate type of copper smelter slag has many possible application areas, e.g., different aggregates and abrasives. During the copper-making process, some copper becomes distributed in the slag; therefore, copper recovery from the slag is commonly done through slag treatment processes. Despite treatment, copper-containing inclusions can remain in the final slag. In order to secure the environmental properties of slags containing inclusions, the leaching mechanisms needs to be understood, which is the focus of the thesis presented.Synthetic and industrial iron silicate slags have been studied with respect to the impact of the slag constituent’s oxide (glass), sulfide (matte) and metalloids (speiss) on leaching as well as the impact of chemical composition (ZnO and CaO content). The synthetic slags are melted in laboratory furnaces. The industrial slags have undergone a Zn-fuming and settling process (including CaO additions for some slags) to recycle and reduce the zinc content and further separate copper-containing inclusions such as sulfide (matte) and metalloid (speiss) species. The materials investigated in the thesis are solidified using water granulation.All materials are characterized by their chemical compositions and mineralogy. Further, industrial slag constituents are investigated regarding their leaching contribution. Syntheticiron silicate (oxide) is investigated regarding the influence of ZnO content and granulation temperature on Zn leaching. CaO-modified industrial iron silicate slags are investigated regarding the leaching of specific elements (e.g., Cu, Zn, Ni, As, Sb). The leaching tests examine the effect of pH, oxidation and time using water leaching, acid and oxidating leaching and dynamic leaching methods.Characterizing the slag constituents shows that the glass mainly contains amorphous iron silicate. The matte contains mainly copper sulfides, and speiss contains copper metalloids. The leaching results show that the glass contributes to Cu and Zn leaching at pH 8.4, and the speiss contributes to Ni and Sb leaching at pH 7.8. Further, the leaching contribution of matte and speiss increased with decreasing pH. The main leaching elements from the matte and speiss include Cu, Ni, As and Sb.Characterization of the ZnO-modified iron silicate shows that Zn is mainly distributed in glass and partly in fayalite. Further, the Zn leaching increases with granulation temperature, ZnO content in the glass and decreasing pH.Characterization of CaO-modified slags shows that up to 20 wt.% CaO dissolves into the glass phase. An increased CaO content resulted in increased Ca leaching, yielding higher pH. Leaching of Zn, Cu, Ni and Sb was on the other hand shown to decrease. Further, long-term leaching studies confirm increasing pH and Ca leaching. In contrast, the leaching of Cu, Zn and Ni showed a peak after a certain time, which was lowered with increasing CaO content in the slags. The leaching of As and Sb increased with increasing leaching time, but the increase diminished with increasing CaO content in the slags. A lower pH and an oxidating environment increased the leaching of Zn, Cu and Ni.The summarized results from this thesis indicate that the glass contributes to Zn leaching while copper-containing inclusions matte and speiss contribute to the leaching of Cu, Ni, As and Sb. The leaching of elements from the copper-containing inclusions matte and speiss can be limited by ensuring a pH buffer preventing acidification, for example, by CaO modification. CaO modifications decrease the slag leaching resistance, which contributes to increasing pH in the leachate by Ca-dissolution and hence decreased leaching of copper-containing inclusions in the slag. Also, the Zn leaching from the slag decreased with increasing pH in the leachate.
|
|
| 2. |
- Yang, Yang
(author)
-
Investigation of vanadium-containing oxide systems : CALPHAD and experiments
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Fundamental studies on thermodynamic properties of vanadium-containing oxides systems are essential to understand practical vanadium metallurgical process. The CALPHAD technique is here applied to the thermodynamic modelling of the V-O, Ca-V-O and Ti-V-O systems. The compound energy formalism is used for all the solution phases. All optimization processes and calculations are performed using the Thermo-Calc software package. The present work attempts to develop a self-consistent thermodynamic database of all phases in the studied systems. The obtained datasets can be used to calculate thermodynamic properties, stable as well as metastable phase equilibria and driving forces for oxidation etc.Steelmaking slag is an important secondary source for vanadium extraction. The phase relationships and vanadium distribution in the CaO-SiO2-MgO-V2O3-Al2O3 synthetic slags, whose compositions were chosen based on the relevance to the steel producers, are also studied. Phase equilibria in the temperature range of 1773 to 1823 K at oxygen partial pressure of 10-10 bar and 0.21 bar were characterized.An investigation of the volatilization of vanadium oxide was also carried out in the present work. Isothermal evaporation of vanadium pentoxide in the temperature range between 1723 and 1873 K was investigated by Thermogravimetric Analysis under different oxygen partial pressures, viz. oxygen, air or CO2. The Arrhenius activation energy for the evaporation reaction in various atmospheres was calculated from the experimental results. A mathematical model was developed to describe the kinetics of the evaporation process. Evaporation coefficients and enthalpies in various atmospheres were also estimated. The present results may have some implications in recovering vanadium from different vanadium-bearing sources.
|
|
| 3. |
- Andersson, Anton
(author)
-
Recycling of Blast Furnace Sludge within the Integrated Steel Plant : Potential for Complete Recycling and Influence on Operation
- 2019
-
Doctoral thesis (other academic/artistic)abstract
- Ore-based steelmaking generates various residues including dust, sludges, scales and slags. Internal and external recycling has allowed for 68-90 % of the dust, sludges and scales to be recycled. However, several residues are landfilled despite containing elements valuable as raw material in the production of steel. One such residue is the blast furnace (BF) sludge which has a chemical composition dominated by iron and carbon. In 2008, the annual worldwide landfilling of BF sludge was estimated to 8 million metric tons in dry weight. Furthermore, as the iron production via the BF route has increased significantly since 2008, the landfilling of BF sludge could be even higher as of today. Thus, the potential to reclaim valuable iron and carbon while improving the raw material efficiency is substantial.Traditionally, in-plant recycling of residues generated in the integrated steel plant is conducted via the sinter or, in the case of pellet-based BFs, via cold-bonded briquettes and injection in the BF tuyeres. The challenges in recycling BF sludge via these routes are the fine particle size distribution, the high water content and the zinc content. Of these challenges, the latter is the main concern as too high zinc loads in the BF lead to increased reductant rates, reduced lining life of carbon-based bricks and scaffold formation, which may disturb the process. The challenge regarding zinc has previously been addressed by pretreating the sludge, generating a low-zinc and high-zinc fraction where the former has been recycled to the BF via the sinter or cold-bonded pellets. Although pretreatment and recycling of the low-zinc fraction have been achieved in industrial scale, the reported sludges are generally coarse in size and high in zinc. Furthermore, recycling of pretreated BF sludge to the BF utilizing cold-bonded briquettes has not been reported and the internal recycling of the high-zinc fraction has not been considered.In the present thesis, newly produced BF sludge with a fine particle size distribution and low zinc content was characterized finding that a majority of the zinc was present in weak acid soluble phases and that the finest fraction of the sludge carried most of the zinc. Based on these findings, the BF sludge was pretreated using sulfuric acid leaching, hydrocycloning and tornado treatment, respectively. Sulfuric acid leaching was the most effective method in selectively separating zinc from the iron, carbon and solids. However, both hydrocycloning and tornado treatment were successful in generating a fraction low in zinc.The low-zinc fraction of the tornado-treated BF sludge was incorporated in cold-bonded briquettes and tested for strength, swelling and intrinsic reducibility. Furthermore, the briquettes were charged as basket samples in the LKAB Experimental Blast Furnace (EBF) in order to study the behavior in actual BF conditions. The results suggested that the low-zinc fraction of the BF sludge could be added to the briquettes without negatively affecting the performance of the briquettes in the BF. The results were confirmed in industrial-scale trials where non-treated BF sludge was added to cold-bonded briquettes in an amount that would facilitate complete recycling of the low-zinc fraction. Charging these briquettes to the BF did not induce any negative effects on the process or the hot metal (HM) quality.The high-zinc fraction of the tornado-treated BF sludge was added in self-reducing cold-bonded agglomerates and studied in technical-scale smelting reduction experiments aiming at recycling to the HM desulfurization plant. The experiments suggested that melt-in problems could be expected when using either briquettes or pellets. Nonetheless, industrial-scale trials were performed aiming to study the feasibility of recycling cold-bonded briquettes to both the HM desulfurization plant and basic oxygen furnace (BOF). These trials suggested that a substantial amount could be recycled without affecting the final quality of the steel. However, additional experiments were identified to be required in order to enable 100 % recycling of the high-zinc fraction of the tornado-treated BF sludge.Based on the results from the experimental work, a holistic concept to completely recycle the BF sludge within the integrated steel plant was suggested.
|
|
| 4. |
- Engström, Andreas
(author)
-
Reduction Annealing Synthesis of Nanostructured Carbide and Nitride Particulate Composites
- 2014
-
Licentiate thesis (other academic/artistic)abstract
- This thesis covers reduction-annealing synthesis of nanostructured SiC-TiCN and SiC-TiC particulate composite powders. These were characterized by X-ray diffraction and electron microscopy. In the SiC-TiC powder it was found that TiC could be added in certain amounts by reducing controlled amounts of titanium chloride source followed by a suitable annealing. A transmission electron microscopy showed that TiC formed polyhedrons and SiC formed rods. This was in agreement with a trend towards these crystal shapes, regardless of synthesis method, as found in the literature. In the SiC-TiCN particulate powder, nitration was achieved at low nitrogen concentration. In a scanning electron microscopy study it was seen that SiC formed elongated crystals, while TiCN formed polyhedrons. A gradual nitration of TiC into TiCN was proposed. Nitration was promoted by a high reactivity of TiC and an integrated nitrogen surplus over titanium and carbon amount during annealing.
|
|
| 5. |
- Isaksson, Jenny
(author)
-
Settling Mechanisms of Valuable Metal Droplets in Iron Silicate Slag
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- A significant source of copper losses from pyrometallurgical copper extraction is attributed to dissolved and entrained copper in discarded slag. Entrained copper can be recovered via pyrometallurgical slag cleaning in a settling furnace where the droplets settle under gravity. Reduced copper losses suggest improved raw material efficiency, and the slag becomes a more environmentally safe byproduct as it contains less copper and its associated elements. The copper content in the discarded slag often equals or is higher than in the copper ore, implying that the copper slag is a valuable secondary resource for copper.The settling velocity of droplets and, thus, the metal recovery depends on the slag viscosity, copper droplet size distribution, dissolved copper content, and density difference between the slag phase and the copper droplets. The process parameters, temperature and settling time, theoretically affect the copper recovery, where an extended settling time means that droplets have a longer time to settle, and the temperature affects the viscosity, where a higher temperature means a lower viscosity and thus a higher settling rate. However, the temperature also affects the copper solubility; therefore, the overall effect of temperature on the copper recovery during industrial settling processes is unknown. Modifying the slag composition is another option to alter the viscosity and copper solubility. CaO has experimentally been shown to affect both factors in iron silicate slag positively and is thus a potential modifier for increased copper recovery in a settling process. However, there is a knowledge gap regarding the industrial CaO slag modification in a settling process and the effect on copper droplet size distribution, dissolved copper content, copper recovery, and the relationship between recovery and viscosity. Further research is necessary to bridge the knowledge gap and explore the potential benefits of CaO slag modification for improved copper recovery.Within the scope of this thesis, an industrial trial was conducted with the identified factors, temperature, settling time, and CaO slag modification to gain knowledge of the effect on the industrial settling process. The trial was evaluated by performing a slag characterization focusing on the appearance of copper and its associated elements and phases, copper droplet size distribution, slag matrix copper content, and investigating the slag copper content, copper recovery, and slag viscosity. The results showed that the copper droplets were mainly copper matte and speiss and were primarily associated with the slag phase and occasionally with a chromium-rich spinel and bubbles, which can hinder the settling. The results suggested that the viscosity and slag matrix copper content decreased when the slag was modified with CaO, and the copper droplet size distribution shifted to contain larger droplets. The CaO modification resulted in a higher copper recovery, revealing a linear relationship between the overall recovery and the viscosity.A crucible and spindle material with minimum interaction and influence on viscosity had to be identified to perform the viscosity measurement. Iron silicate slags are the dominating slag used during pyrometallurgical copper extraction of Cu-Fe-S concentrates. The dissolution of the crucible and spindle material into the melt is often analyzed and reported. However, the influence on viscosity is rarely investigated and reported. Three crucibles were studied, Mo, Ni, and Fe, concluding that Mo was preferable for viscosity measurements as it interacted the least with the melt and gave the most stable measurements with the highest reproducibility. Mo was thus the crucible choice for viscosity measurements of the industrial slag with and without CaO modifications. Based on the results from the industrial trial and the experimental evaluation, it was concluded that it is difficult to see an effect of regulating the temperature and settling time in the settling furnace process. It was, however, possible to increase the copper recovery by industrial CaO slag modification, which contributes to an increased raw material efficiency and, thus, a more sustainable pyrometallurgical copper extraction.
|
|
| 6. |
- Isaksson, Jenny
(author)
-
Slag Cleaning of a Reduced Iron Silicate Slag by Settling : Influence of Process Parameters and Slag Modification on Copper Content
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- During the pyrometallurgical extraction of copper, a significant part of the copper is lost with discard slag, which decreases profits, overall copper recovery, and efficiency of raw material usage. Smelting furnace slag usually has a copper content that is close to or higher than that of copper ores. The investigation of copper losses to slag is thus a task of practical significance, as the ore grades are depleting. Slag cleaning, e.g., a settling furnace, can reduce copper losses to slag as the mechanically suspended copper-containing droplets separate from slag under the action of gravity and can hence be recovered. An industrial trial was conducted in an electric settling furnace with slag originating from an electric smelting furnace and processed in a zinc fuming furnace. The trial was conducted to increase the understanding of copper losses to slag and how the process parameters temperature and settling time influence the slag copper content. The obtained slag samples were also evaluated to gain better insights as to the settling mechanism and, if any, factors that hinder the copper phases from settling. Slag modification with CaO was also evaluated to investigate how the modification influences the settling of copper phases and, thus, the final slag copper content. Samples collected during the industrial trial were the basis for the evaluation in the current work. The samples came from batches with varying temperatures, settling times, and CaO content collected at four different sample positions. Instrumental techniques, including XRF, FAAS, ICP-SFMS, and SEM-EDS, were used to analyze the chemical compositions of the samples and the appearance of copper and associated phases. The results indicated that the copper content of outgoing slag increased with increasing temperature in the evaluated interval. The copper content was also concluded to be more strongly affected by the temperature compared to the settling time. Regulating the temperature to the lower temperature interval in the settling furnace could thus decrease the final slag copper content. During the slag characterization, it was found that suspended copper-containing phases were hindered from settling, due to the attachment to solid phases and gas bubbles in the slag. By controlling and minimizing the presence of the bottom buildup and thus solid phases in the slag, the copper content can be decreased. The results indicated that the CaO slag modification decreased the final slag copper content, and can thus be used as a modifier for increased settling.
|
|
| 7. |
|
|
| 8. |
- Prasad, Pande Nishant
(author)
-
Roasting of Cu-rich complex concentrates - A mineralogical investigation
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Copper has assumed importance as a metal which is essential for realization of a sustainable modern society. Demand for copper is sharply increasing, and a supply shortfall is shortly anticipated. Such a scenario could adversely affect some of the major transformations directed toward reversal of climate change. Consequently, it is crucial to efficiently utilize all the resources available for copper extraction. This thesis investigates the challenges associated with Cu-rich complex concentrates, which are scantily used in the mainstream pyrometallurgical route of Cu-extraction. The roasting step, at the start of the pyrometallurgical-route is expected to resolve certain complexities in the incoming concentrate feed, for instance, through partial volatilization of the minor deleterious elements – As, Sb. Therefore, evaluation of the behavior of Cu-rich complex concentrates during roasting is the focus of the current study.Cu-rich complex concentrates are generally polymetallic, containing numerous major, minor and trace elements. In reality, these numerous elements in a complex concentrate occur as multiple sulphide and sometimes also as non-sulphide minerals. In this work, four Cu-rich complex concentrates are investigated for their initial mineralogy, followed by their evaluation in laboratory-scale roasting experiments between 200-700oC in inert atmosphere. These complex concentrates were produced from the Rockliden, Garpenberg and Maurliden deposits of Boliden Mineral AB in Sweden. Though industrial roasting involves a partially oxidative environment, the roasting experiments in this work were performed in an inert atmosphere which could be collectively used as a reference for future roasting experiments at higher oxidation potential. The main objective of the roasting experiments in inert atmosphere was to determine various features of the mineralogical interactions which could occur up to 700oC.The selected concentrates were found to comprise the: (1) major minerals – chalcopyrite, sphalerite, pyrite and galena; (2) minor minerals – sulfosalt and sulfarsenide minerals of As and Sb, also including a non-sulphur bearing mineral – silver antimonide, and; (3) trace elements – Cd, Mn, Hg (hosted by sphalerite) and Tl (hosted by galena). The high-temperature physicochemical interaction between the different minerals mainly involved – (1) solid-state assimilation of Cu-, Fe- and Zn-bearing minerals to form the ‘iss-phase’ existing in CuS-FeS-ZnS ternary system b) low-melting liquid formation through interactions between galena and the As/Sb-bearing minor minerals, starting from 400-500oC.The Sb- and As-volatilizations were relatively higher from sulfarsenide minerals (such as arsenopyrite (FeAsS) and gudmundite (FeSbS)) compared to the As/Sb-bearing sulfosalt minerals.Evaluation of condensates produced during the roasting experiments provided an indirect assertion of the previous findings regarding the formation of heteronuclear compounds, As4-nSbnS6(g) during simultaneous Sb- and As-volatilizations. Microstructural evaluations of the solidified melts suggested existence of multiple immiscible liquids at the roasting temperature. Liquid formation and subsequent cooling facilitated redistribution of the minor and trace elements. Most of the trace elements segregated in the phase which was the last liquid to solidify during cooling. These fundamental insights about the involved complexities could help in developing newer processes enabling increased usage of complex concentrates in Cu-extraction.
|
|
