Browsing by Author "Salminen, Justin"

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Applications of Ionic Liquids for Chemical and Electrochemical Systems
(2007) Rantala, Terhi
Helsinki University of Technology | Master's thesis
Arsenic recovery and recycling in non-ferrous metal processes
(2018-02-27) Hirvinen, Juho
Kemian tekniikan korkeakoulu | Master's thesis
Arsenic is a challenging and unavoidable element in non-ferrous metal processing, however also a necessary reagent in solution purification of copper and zinc electrolytes and is safe with proper process control. Arsenic is an environmental contaminant and a known carcinogenic and toxic in every form. In metallurgical operations main concerns are exposure to arsine gas in solution purification processes of electrolytes and the environmental contamination from volatilized products. Theoretical part of this thesis aims at describing the arsenic chemistry and presence in copper and zinc processing and the methods for recovering and stabilizing arsenic in these processes. Arsenic exhibits oxyanion behavior in aqueous environment with much of the chemistry being similar with the other elements of the nitrogen group (P, Sb, Bi). Soluble aqueous compounds are arsenic acid (H3AsO4) and arsenious acid (H3AsO3) and their alkali-metal variants. Ions in aqueous solutions are hydrogen dissociated forms of these compounds. Arsenic enters copper and zinc processes as an impurity in concentrates and as additives such as pure As2O3. Arsenic can be removed from process solutions by solvent extraction, ion exchange, and precipitation. Roasting of concentrates is a known method for arsenic removal and it is also a possible treatment for arsenic-rich by-products. Experimental part of this thesis focuses on leaching of copper and arsenic from copper electrolyte purification by-product, known as liberator cell sludge, using sulfuric acid with oxygen purging. The sludge consisted mostly of copper arsenides, insoluble arsenates such as SbAsO4 and BiAsO4 and lead sulfate (PbSO4). Other minor elements are nickel and tellurium. Results indicate that arsenic can be removed from liberator cell sludge by sulfuric acid leaching with best extractions 92% for arsenic and 98% for copper with 2 M H2SO4 at 90°C with 1 L/min oxygen gas feed. Equal volume air feed produces lower extractions and significantly slower kinetics. The best results with using air as oxidant was 54% for copper and 56% for arsenic 4 hour leaching in 3 M H2SO4 at 75°C. The contrast between worst and best results show the necessity of oxygen and sufficient temperature for successful leaching. The leaching is not selective as most of the compounds present in the sludge dissolve into sulfuric acid under oxidizing conditions. Not all of arsenic can be leached due to the formation of insoluble arsenates with Sb and Bi. Sulfuric acid leaching is a logical first step in the treatment of the liberator cell sludge, however, to selectively recover copper, arsenic and other elements, further unit processes are required.
Chemical equilibrium reactions related to the buffer capacity in anaerobic digestion
(2006) Iivonen, Suvi-Maaria
Helsinki University of Technology | Master's thesis
Chemical thermodynamics of aqueous electrolyte systems for industrial and environmental applications
(2004-03-20) Salminen, Justin
Doctoral dissertation (article-based)
This thesis consists of studies of chemical thermodynamics of aqueous electrolytes for industrial and environmental applications. Calculations have been used to represent vapor-liquid-solid equilibria and chemical equilibria for aqueous systems including solubility of gases. Modern simulation methods combined with experiments provide a useful tool for the research and design of new processes as well as evaluating changes in the operational conditions of chemical processes. The Gibbs energy minimization methods ChemSage, and ChemSheet have been used along with activity coefficient models including Pitzer ion interaction model. The calculated results were compared if possible with experiments or with reference data. Further this work consists of studies on oxygen-pressurized peroxide bleaching, which is an important sequence of total chlorine free (TCF) bleaching for environmental reasons. The solution properties like pH have been measured and modelled both in pure H2O2-NaOH-H2O system and in bleaching conditions. Further, the thermodynamic multicomponent model was used with kinetic constraints for pH calculations in reactive solution. The knowledge of the pulp- and solution properties along with the results of the model calculations could be used for optimisation of the bleaching process with respect to reaction time and temperature. Thermodynamics provides a practical tool for the estimation of the chemical states of pulp and paper solutions as well as in hydrometallurgical applications. Such a fundamental approach relates to the chemical energy, chemical reactions, solubility of gases and salts, and an important online process parameter pH. The Gibbs energy approach was further applied to equilibrium and reaction dynamic studies of multiphase CO2-CaCO3-H2O system.
Chemical thermodynamics of carbon dioxide with mixed aqueous alkanolamine solutions and metalcarbonates
(2004) Chen, Qian
Helsinki University of Technology | Master's thesis
A computational thermodynamic model for conversion of jarosite residue into an inert slag via a pyrometallurgical process
(2017-02-13) Toropainen, Antti
Kemian tekniikan korkeakoulu | Master's thesis
Millions of tons of jarosite residue is produced each year as a by-product of zinc smelting. This residue is classified as a hazardous waste because it contains heavy metals that are leached into the environment as it is stored in open-air piles. The residue also contains metal values which are not recovered due to storing. The purpose of this thesis is to create a computational thermodynamic model for conversion of jarosite residue into an inert slag via a pyrometallurgical process. Earlier studies of this topic show that pyrometallurgical processes can be used to treat jarosite residue. However, a thermodynamic model for producing an inert slag is not found in scientific literature. The thermodynamic model in this thesis was created with MTDATA computer program and Mtox database. In addition, decomposition of Boliden Kokkola’s jarosite residue was studied experimentally with thermogravimetry (TG) and differential scanning calorimetry (DSC). The results show that the thermal decomposition of the residue depends on the location of the waste in the waste pile with respect to its height. The waste in the upper half of the pile loses more mass during thermal decomposition than the waste in the lower half of the pile due to combustion of elemental sulfur. In the thermodynamic model created, jarosite smelting is defined to consist of two functional steps that are: melting and reducing. The melting step produces a melt that consists of metal oxides and flux (SiO2). The reduction step purifies the melt of trace metals and thus produces an inert slag. Only the thermodynamics of the reduction step are modelled with MTDATA. Modelling is limited to the following trace elements present in the melt: As, Cd, Cu, Sb, Pb and Zn. The thermodynamic model shows that during reduction Cd, Pb and Zn are volatilized whereas As, Cu and Sb form a liquid metal phase (speiss) together with iron. If speiss is not formed, solid iron will precipitate. Furthermore, an inert slag is only obtained when the resulting off-gas is removed from the system continuously. If the off-gas remains in the systems, the trace metal concentrations in the slag are considerably higher. In addition, the effects of silica concentration, copper concentration and temperature on trace metal recovery efficiency were tested. Adding flux (SiO2) gives rise to reduced recovery of all trace metals whereas increasing copper concentration in the feed enhances the recovery of As, Cu and Sb. Raising the process temperature increases Pb recovery and reduces arsenic recovery. The results of the modelling are promising in terms of process development and should therefore be verified experimentally.
Experimental investigation of jarosite residue thermal processing
(2017-12-12) Rämä, Minna
Kemian tekniikan korkeakoulu | Master's thesis
In hydrometallurgical production of zinc, the leaching stage produces 0.5‒0.9 tons of jarosite leach residue for every ton of zinc produced. Jarosite leach residue contains several potentially recoverable metals that can be critical (In, Ga, Ge, and Sb), precious and valuable (Ag and Au), heavy metals of concern (Cd, As, Pb, and Hg), or unrecovered Zn. The residues are classified as hazardous waste due to the aforementioned heavy metals. Currently, the metals present in the jarosite leach residue are not recovered or utilized, but disposed into the ponds. Therefore, metallurgical treatment of these residues has become more attractive. The purpose of this thesis was to investigate experimentally the thermal processing of jarosite residue. The treatment is divided into two steps (oxidizing and reducing). In the oxidizing step, jarosite is decomposed, sulfates and OH-groups are released, metals are oxidized into their highest oxidation states and an oxide melt is formed. In the reduction step, the melt is reduced, volatile elements are removed to gas phase and a clean slag and a metal phase (speiss) are formed. The aim was to determine the optimal processing times for these steps and study the distribution of elements between the phases. The experiments were carried out in a vertical tube furnace at 1350 °C. Two sets of oxidation experiments were carried out. The first set was conducted under air atmosphere with 65 ml/min air flow rate. The chemical analyses showed that the material had not been efficiently oxidized as even after the longest experiment (256 min), the sulfur content was 21.3 wt.-% when the target is below 1 wt.-%. The air flow rate was quadrupled for the second set to oxidize the material more efficiently. However, this did not show any significant improvement. It was observed that the material was not completely melted during the experiments. SEM backscattered images showed that there were large sulfur precipitates left in the material. The XRD analyses showed that the material consisted mainly of wurtzite (ZnS) and troilite (FeS). In addition, there were magnetite (Fe2+Fe3+2O4), galena (PbS) and sulfur. As the material was not efficiently oxidized in the experimental set up, only one reduction experiment was carried out. The material was first oxidized under O2 atmosphere (65 ml/min, 120 min) and then reduced (CO-CO2, 50:50, 260 ml/min in total, 120 min). The chemical analyses showed that the oxidation was significantly more efficient as O2 was used instead of air, as the sulfur content of the resulting material was 11.7 wt.-%. The removal of Zn and Pb into the gas phase was not sufficient enough as there were 4.6 wt.-% of Zn and 2.1 wt.-% of Pb when the targets are Zn < 1 wt.-% and Pb < 0.3 wt.-%. In further research, it is essential to figure out how the oxidation should be carried out so that the material would be melted completely and, thus, the sulfur content to be decreased to < 1 wt.-%. By adding an oxygen lance to the experimental arrangement the oxidizing gas could be blown directly into the material and, hereby, the oxidation is believed to be more efficient. By adding silica to the material the melting of the material could be promoted. After these problems are solved the optimal processing times for both oxidation and reduction can be investigated more closely.
Experimental Investigation of Pyrometallurgical Treatment of Zinc Residue
(2018) Rämä, Minna; Jokilaakso, Ari; Klemettinen, Lassi; Salminen, Justin; Taskinen, Pekka
A4 Artikkeli konferenssijulkaisussa
Iron containing leach residues like jarosite and goethite from electrolytic zinc production contain many valuable metals and harmful substances. These metals and substances should be removed in order to obtain an acceptable, stable and reusable product, and maximize economic feasibility as well as minimize environmental footprint. In this work, the processing of jarosite leach residue was studied in laboratory scale experiments under oxidizing and reducing conditions at high temperatures. First, the pretreated material was melted and oxidized to produce a melt of metal oxides. Second, the oxide melt was reduced in CO –CO2 atmosphere. Target after the reduction step was to obtain a clean slag and a liquid metal or speiss phase that collects the valuable metals , such as silver . The kinetics of the thermal processing were studied for determining optimal times and conditions for the aforementioned process steps. The preliminary results show that the process is thermodynamically feasible, and the desired phases can be obtained in the experimental conditions investigated.
Experimental study of speiss formation in reductive thermal treatment of jarosite residue
(2018-07-31) Nurmi, Samu
Kemian tekniikan korkeakoulu | Master's thesis
Hydrogen as Carbon-Free Reducing Agent in Non-ferrous Slag Fuming
(2022-12) Attah-Kyei, Desmond; Klemettinen, Lassi; Michallik, Radoslaw; Salminen, Justin; Taskinen, Pekka; Lindberg, Daniel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this work, pyrometallurgical treatment of non-ferrous iron residue was studied. This approach aimed to recover the valuable metals and convert the residue into reusable benign slag using hydrogen as a non-fossil reducing agent. The pyrometallurgical treatment for this type of residue involves pretreatment prior to two stages, oxidation and reduction. Hydrogen was employed as a reducing agent in slag cleaning. The reduction tests were performed at temperatures of 1200 °C, 1250 °C, and 1300 °C using H2 and N2 gases to form the reducing gas atmosphere. The results show that H2 is an effective reductant because reduction proceeded rapidly, forming speiss droplets within the slag already after 10 minutes. The laboratory-scale experiments suggest that slags or other residues obtained from metallurgical processes can be further cleaned in a fuming process using hydrogen and its mixtures to obtain environmentally friendly cleaner slag with respect of volatile metals. The results also show that one can tune the reduction and control the formation of metallic iron during the process. Thermodynamic modeling was also performed to simulate the fuming stage, i.e., reduction of the slag. Metal alloy formation as well as elemental distributions between metal and slag were studied, and results from thermodynamic modeling agree well with experimental results.
Hydrometallurgy of Sn and other impurities present in industrial Zn bearing solutions
(2020-12-15) Karppinen, Anssi
Kemian tekniikan korkeakoulu | Master's thesis
During the past 40 years, worldwide zinc consumption has doubled which increases need for secondary raw materials in zinc refining. Secondary zinc-containing raw materials that originate from waste electric equipment (WEEE) or coating materials increasingly contain tin and other impurities that are not typically found from primary zinc concentrates. Consequently, zinc refineries that utilize these types of secondaries must evaluate their suitability for the current unit processes used for treatment. If ended up in zinc electrolysis, tin, bismuth, and tellurium could co-deposit on the zinc cathodes, reduce current efficiency and modify the morphology of the deposit. For this reason, the impurity metal concentrations must be minimized in zinc electrolyte by selection of suitable leaching parameters and solution purification methods beforehand. In this thesis, chemistries and hydrometallurgy of tin, bismuth, and tellurium is studied in sulfuric acid media with secondary zinc-containing dusts. Leaching parameters were chosen to cover a wide range of variable conditions in order to determine the hydrometallurgical behavior of these selected impurities. Leaching experiments, where the acidity of the solution was increased step by step, were conducted to ascertain at which acidity the metals start to dissolve in a sulfate solution. Leaching behavior could be predicted based the experiments performed and Pourbaix diagrams constructed by HSC Chemistry modelling. The results of the work indicate that tin has a low solubility in sulfuric acid media, which is in line with the findings from literature. Under higher acidity conditions (Hot acid leaching) less than 1% of tin is leached into solution and although further increase in acidity increases tin recovery, the recovery remains below 10% with a 120 g/l sulfuric acid concentration. An increase in leaching time and inclusion of air purging was found to slightly increase tin recovery, whereas divalent tin sulfate (SnSO4) showed a marginally higher solubility than the quadrivalent tin oxide (SnO2). Based on this work, it can be determined that almost all the tin would end up within the high lead containing leaching residue. In addition, bismuth and tellurium were shown to be insoluble under weak acid leaching conditions but dissolved significantly with hot acid leaching. Closer inspection indicates that bismuth and tellurium start to dissolve within pH < 1 and pH < 0.5, respectively. Air purging and resulting higher oxidation potential in the solution decreased bismuth leaching and increased tellurium leaching. This research strongly indicates that tin can be recovered in lead containing leaching residue, hence minimizing the possible detrimental effects at later process stages of zinc refining.
Modelling of aquenous phase thermodynamics of metal carbonates in concentrated electrolyte solutions with the presence of carbon dioxide
(2005) Kivekäs, Niku
Helsinki University of Technology | Master's thesis
Tässä työssä on tutkittu metallikarbonaatti-elektrolyyttiliuosten ominaisuuksia hiilidioksidin läsnä ollessa sekä kokeellisesti että elektrolyyttiliuosmallien avulla. Aktiivisuuskerroinmallien soveltuvuutta monifaasisysteemien laskentaan tutkittiin väkevissä natriumkloridiliuoksissa. Työssä käydään läpi liuostermodynaamiikan ja faasitasapainojen teoria, sekä esitetään Debye-Hückelin yhtälö ja Pitzerin viriaaliyhtälö monifaasisysteemien mallittamiseksi soveltamalla Gibbsin energian minimointimenetelmää. Lisäksi perehdytään pH-mittauksen ongelmiin väkevissä suolaliuoksissa. Myös metallikarbonaattien kemiallinen käyttäytyminen sekä keskeiset metallikarbonaatit on esitelty. Työssä mitattiin sinkkikarbonaatin ZnCO3 saostumista 4,278 molaalisessa natriumkloridin NaCl vesiliuoksessa kolmessa eri systeemissä. Liuoksen pH:ta säädettiin lisäämällä siihen systeemistä riippuen natriumkarbonaattia Na2CO3 tai natriumhydroksidia NaOH. Osassa kokeista kuplitettiin hiilidioksidia CO2 liuoksen läpi. Sinkin liukoisuustasapainoa tutkittiin pH-alueella 5,5 - 8,5 lämpötilan ollessa 25 °C. Myös lämpötilan vaikutusta sinkkikarbonaatin saostumiseen systeemissä ZnCl2-NaCl-Na2CO3-H2O-CO2 tutkittiin lämpötila-alueella 283-323 K. Sakkojen koostumus tutkittiin kationien osalta, ja havaittiin, että sinkkikarbonaatin lisäksi saostui jokaisessa systeemissä myös natriumkarbonaattia Na2CO3 tai natriumbikarbonaattia NaHCO3. Vastaavat systeemit mallitettiin Debye-Hückelin yhtälöllä ja Pitzerin yhtälön avulla. Havaittiin että Debye-Hückelin yhtälö mallittaa sinkin saostumisen kohtuullisen hyvin. Ilman riittäviä parametreja Pitzerin yhtälöllä mallitetut tulokset eivät poikkea merkittävästi Debye-Hückelin yhtälöllä mallitetuista tuloksista.
Processing of a Zinc Leach Residue by a Non-Fossil Reductant
(2023-06-20) Rämä, Minna; Klemettinen, Lassi; Rinne, Marja; Taskinen, Pekka; Michallik, Radosław Markus; Salminen, Justin; Jokilaakso, Ari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The suitability of a non-fossil reductant in high-temperature treatment of a zinc leach residue was studied in laboratory-scale experiments. The pyrometallurgical experiments carried out at temperatures of 1200-1350 °C consisted of melting the residue under an oxidizing atmosphere to produce an intermediate, desulfurized slag, which was further cleaned of metals such as Zn, Pb, Cu, and Ag, using renewable biochar as a reductant. The aim was to recover valuable metals and produce a clean, stable slag for use as construction material, for example. The first experiments indicated that biochar is a viable alternative to fossil-based metallurgical coke. The capabilities of biochar as a reductant were studied in more detail after optimizing the processing temperature at 1300 °C and modifying the experimental arrangement by adding rapid quenching of the sample (to a solid state in less than 5 s) to the procedure. Modifying the slag viscosity by adding 5-10 wt % MgO was found to enhance the slag cleaning significantly. With an addition of 10 wt % MgO, the target Zn concentration in slag (Zn < 1 wt %) was reached after as little as 10 min of reduction, and the Pb concentration was also decreased relatively close to the target value (Pb < 0.03 wt %). With an addition of 0-5 wt % MgO, the target Zn and Pb levels were not reached within 10 min, but with longer treatment times of 30-60 min, 5 wt % of MgO was enough to decrease the Zn content in slag sufficiently. The lowest Pb concentration achieved with an addition of 5 wt % MgO was 0.09 wt % after a 60 min reduction time.
Pyrometallurgical treatment of jarosite leach residue by non-fossil reductant
(2019-12-17) Rinne, Marja
Kemian tekniikan korkeakoulu | Master's thesis
Slag Cleaning Equilibria in Iron Silicate Slag–Copper Systems
(2019) Hellsten, Niko; Klemettinen, Lassi; Sukhomlinov, Dmitry; O’Brien, Hugh; Taskinen, Pekka; Jokilaakso, Ari; Salminen, Justin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this study, the equilibrium distributions of selected trace elements between molten iron-saturated copper alloy and selected iron silicate slags were measured, and the effects of silica fluxing on them. In addition to the copper and iron main components of the system, trace elements like antimony, gallium, germanium, gold, indium, and silver were added in experiments that spanned the temperature range of 1473–1573 K (1200–1300 °C). Experimental charges were quenched and prepared in polished mounts. In situ analyses of the resulting phases were made directly on the mounts without the need of phase separation prior to analysis. Electron probe X-ray microanalysis was used for concentrations at or above approximately 100 ppmw, and laser ablation-inductively coupled plasma-mass spectrometry for the lower concentrations in the slags. The very low slag concentrations of germanium, antimony, and indium obtained indicate that these elements can be removed from the slag by reduction, whereas gallium concentrations in the slag were high. Consequently, gallium removal from iron residues, such as zinc smelting jarosite, is difficult without volatilization. Based on the present observations, the industrial reduction processes for the treatment of smelting and refining slags as well as for the processing of iron residues, and extracting the reducible metal oxides and their metal values can be optimized. The target in fluxing should be to maintain the slag compositions with a silica concentration higher than about 28 wt%.
Solubilities of gases in water solutions
(1997) Salminen, Justin
Helsinki University of Technology | Master's thesis
Some industrial applications of thermodynamics and kinetics with NaOH - H₂O₂ - H₂O - O₂ - system
(1998) Salminen, Justin
Helsinki University of Technology | Licentiate thesis
Thermal processing of jarosite leach residue for a safe disposable slag and valuable metals recovery
(2018-10-01) Rämä, Minna; Nurmi, Samu; Jokilaakso, Ari; Klemettinen, Lassi; Taskinen, Pekka; Salminen, Justin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In electrolytic production of zinc, the iron levels in the solutions are controlled by precipitation of jarosite or goethite. These precipitates also co-precipitate unrecovered valuable metals (Zn, Pb, Cu, Ag) as well as elements of concern (As, Cd, Hg). After stabilization, the residues are traditionally landfilled. This work investigates pyrometallurgical treatment of jarosite residue to convert the material into reusable clean slag and to recover the valuable metals within the residue. The pyrometallurgical treatment is divided into two functional steps. First, the material is melted in an oxidizing atmosphere, after which the oxide melt is reduced to produce an inert, clean slag. Then, a liquid metal or speiss phase collects the valuable metals, such as silver. The aim was to examine the optimal process conditions for reaching the target values for remaining metals in the slag; Pb < 0.03 wt %, Zn < 1 wt %. As a conclusion, the limiting factor in sulfur, lead, and zinc removal is the contact between the oxidizing or reducing gas and the molten sample. The mass transfer and volatile metals removal were significantly improved with a gas lance installation. The improved gas-liquid interaction enabled the first steps of gas flow rate optimization and ensured the sufficiently low end-concentrations of the aforementioned elements.
Thermodynamic modeling of elemental distribution of non-ferrous iron residue with non-fossil reducing agents
(2022-01-18) Pankka, Iida
Kemian tekniikan korkeakoulu | Master's thesis
Thermodynamic Modeling of Elemental Distributions of Trace Elements in Non-ferrous Iron Residue Hydrogen Reduction
(2023-06) Pankka, Iida; Salminen, Justin; Taskinen, Pekka; Lindberg, Daniel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Every year millions of tons of iron residue are generated as a by-product of zinc production. Stabilized landfilled iron residue contains recoverable metals that could be valorized with further processing. Pyrometallurgical processing allows the recovery of valuable metals while simultaneously producing a clean slag that can then be further utilized. A thermodynamic model was developed with FactSage version 8.0. The focus was on minor element behavior and distribution of elements between phases. Calculations were performed at 1200–1400°C and pressure of 1 atm with both pure H2 and H2-Ar mixtures used as a reductant. Also, the concentrations of Pb and Zn in the input were varied. The results showed that a liquid alloy phase forms consisting mostly of either Cu, As and Pb or Fe, As and Cu. It was noted that a higher Ar total gas amount in reduction decreased the mass fraction of the liquid alloy and increased the evaporation of elements into fume dust. S, Bi, Pb, Ge and Zn were observed to evaporate fully, while As, In, Sb and Ag evaporated only partially. The results need to be verified experimentally.