Removal of Pyrrhotite from High-Sulphur Tailings Utilising Non-Oxidative H2SO4 Leaching

Tailings are a residual material stream produced in the mineral processing of ores. They may contain a major sulphide content that increases the risk of acid rock drainage (ARD) but may also host valuable metals. Tank bioleaching is a technically viable method to treat sulphide tailings. However, a significant pyrrhotite content may cause increased acid and oxidant consumption and result in longer retention times in a bioleaching process. In this work, non-oxidative H2SO4 leaching of pyrrhotite is studied for high-sulphur tailings, both as a pre-treatment method and to consider the recovery possibilities of Fe and S. Continuous mode validation tests, conducted at 90 °C, pH 1.0 and 106 min retention time, resulted in a complete pyrrhotite dissolution with 427 kg/t acid consumption (as 95% H2SO4). Unwanted dissolution of Ni and Zn was taking place with a leaching yield of 21.5% and 13.5%, respectively, while Co and Cu dissolution was negligible. The continuous mode tests signalled that by shortening the retention time, Ni dissolution could be dramatically decreased. The non-oxidative pyrrhotite leaching produced a H2S-rich gas stream, which could be utilised in later metals’ recovery processes after bioleaching to precipitate (CoNi)S, ZnS and CuS products. The non-oxidative pyrrhotite leaching also produced a FeSO4 solution, with approximately 20 g/L of Fe

Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems

Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process due to its simplicity and relatively low capital investment requirement. As a result, the technology appears to be an attractive process option for treatment of low-grade chalcopyrite ores as well. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional heaps: its dissolution is slow and it halts on a low level of copper extraction usually unacceptable for a commercial practice. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its oxidative dissolution, often termed “passivation”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation.In this thesis, dissolution of a pyritic and a pure chalcopyrite concentrate was studied in stirred tank reactors in the absence and presence of moderately thermophilic microorganisms. The abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. The results showed that the microorganisms did not have any effect in the copper leaching efficiency other than oxidation of ferrous ions to ferric ions. Comparing the copper dissolution rates in the experiments where bulk elemental sulphur was formed with those experiments where the elemental sulphur was oxidised to sulphate due to microbial activity showed that the bulk elemental sulphur did not hinder the dissolution. The same phenomenon was observed in case of bulk jarosite. Under otherwise identical leaching conditions, the presence of bulk jarosite did not decrease the leaching efficiency compared to those experiments were bulk jarosite was not formed. It was also shown that surface spectroscopic methodologies such as X-ray photoelectron spectroscopy (XPS) cannot be applied on powder leached samples due to interfering data from the bulk precipitated species. As a result, massive natural chalcopyrite samples were II prepared and used in the leaching experiments for XPS measurements. Different samples in different stages of leaching were extracted from the biotic and abiotic experiments and analysed by XPS. Results indicated that the surface elemental sulphur was not oxidised by bacterial activity. The data revealed that the common phases on the surface of the samples leached biotically and abiotically for different durations were elemental sulphur and iron-(oxy)hydroxides. The surface elemental sulphur was rigidly bound to the surface and did not volatise in the room temperature XPS measurements. Jarosite was observed in only one sample from the abiotic experiment, but no correlation between its presence and the slow dissolution could be made. Other minor surface compounds such as iron-sulphate was also observed in some samples with no contribution to the leaching behaviour. It was concluded that a multi-component surface phase consisting of mainly sulphur and iron-hydroxides were responsible for the slow chalcopyrite dissolution.Godkänd; 2014; 20140410 (seykos); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Mohammad Khoshkhoo Ämne: Processmetallurgi/Process Metallurgy Uppsats: Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems Examinator: Professor Åke Sandström, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Professor Wolfgang Sand, Fakultät für Chemie – Biofilm Centre, Universität Duisburg-Essen, Tyskland Tid: Måndag den 16 juni 2014 kl 09.30 Plats: E632, Luleå tekniska universitet</p

Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems

Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process due to its simplicity and relatively low capital investment requirement. As a result, the technology appears to be an attractive process option for treatment of low-grade chalcopyrite ores as well. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional heaps: its dissolution is slow and it halts on a low level of copper extraction usually unacceptable for a commercial practice. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its oxidative dissolution, often termed “passivation”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation.In this thesis, dissolution of a pyritic and a pure chalcopyrite concentrate was studied in stirred tank reactors in the absence and presence of moderately thermophilic microorganisms. The abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. The results showed that the microorganisms did not have any effect in the copper leaching efficiency other than oxidation of ferrous ions to ferric ions. Comparing the copper dissolution rates in the experiments where bulk elemental sulphur was formed with those experiments where the elemental sulphur was oxidised to sulphate due to microbial activity showed that the bulk elemental sulphur did not hinder the dissolution. The same phenomenon was observed in case of bulk jarosite. Under otherwise identical leaching conditions, the presence of bulk jarosite did not decrease the leaching efficiency compared to those experiments were bulk jarosite was not formed. It was also shown that surface spectroscopic methodologies such as X-ray photoelectron spectroscopy (XPS) cannot be applied on powder leached samples due to interfering data from the bulk precipitated species. As a result, massive natural chalcopyrite samples were II prepared and used in the leaching experiments for XPS measurements. Different samples in different stages of leaching were extracted from the biotic and abiotic experiments and analysed by XPS. Results indicated that the surface elemental sulphur was not oxidised by bacterial activity. The data revealed that the common phases on the surface of the samples leached biotically and abiotically for different durations were elemental sulphur and iron-(oxy)hydroxides. The surface elemental sulphur was rigidly bound to the surface and did not volatise in the room temperature XPS measurements. Jarosite was observed in only one sample from the abiotic experiment, but no correlation between its presence and the slow dissolution could be made. Other minor surface compounds such as iron-sulphate was also observed in some samples with no contribution to the leaching behaviour. It was concluded that a multi-component surface phase consisting of mainly sulphur and iron-hydroxides were responsible for the slow chalcopyrite dissolution.Godkänd; 2014; 20140410 (seykos); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Mohammad Khoshkhoo Ämne: Processmetallurgi/Process Metallurgy Uppsats: Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems Examinator: Professor Åke Sandström, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Professor Wolfgang Sand, Fakultät für Chemie – Biofilm Centre, Universität Duisburg-Essen, Tyskland Tid: Måndag den 16 juni 2014 kl 09.30 Plats: E632, Luleå tekniska universitet</p

Chalcopyrite (Bio)leaching in Sulphate Solutions : An Investigation into Hindered Dissolution with a Focus on Solution Redox Potential

Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process nowadays. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional leaching systems in sulphate media. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its dissolution and is often termed “passivation” or “hindered dissolution”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation under strictly controlled redox potential conditions. The leaching experiments of the aged and fresh chalcopyrite concentrate under identical conditions showed that copper dissolution was significantly lower from the aged concentrate. The common understanding of reductive leaching mechanism (i.e. higher recoveries at lower redox potentials) was not valid for aged concentrates. Aged concentrates gave steadily increasing recoveries with increased redox potential. The hindering effect exerted from the atmospheric oxidation products on the surface of the aged concentrates was found to be responsible for this behaviour. It was also shown that the reductive leaching mechanism would be beneficial in the presence of an active galvanic interaction. Experiments using a pyritic concentrate resulted in higher recoveries at low redox potential while the dissolution rates were similar at low and high redox potentials using a relatively pure concentrate. In addition, the effect of initial copper concentration had no influential effect on the leaching rates for possible industrial processes. Redox potential development during moderately thermophilic bioleaching experiments of a pyritic chalcopyrite concentrate and a relatively pure chalcopyrite concentrate were chemically/electrochemically mimicked in the absence of microorganisms. The copper recoveries in absence and presence of microorganisms were similar. In some of the abiotic experiments, jarosite precipitated due to a loss of control of the redox potential. However, presence of bulk jarosite did not hamper the copper recovery compared to the bioleaching experiments where there was no bulk jarosite formation. Bio-oxidation of elemental sulphur did not have a positive effect on the leaching behaviour compared to the abiotic experiments where bulk elemental sulphur accumulated. Isotopic fractionations of copper and iron during the bioleaching and abiotic experiments showed that regardless of presence or absence of microorganisms the copper and iron isotopes fractionation followed a similar trend and that such analyses could be used in natural systems as an indicator of the oxidation extent. Surface analyses using X-ray photoelectron spectroscopy (XPS) measurements revealed that common phases on the surface of the samples leached for different durations were iron-oxyhydroxides and elemental sulphur. The elemental sulphur on the surface of the samples was bound to the surface rigidly in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature measurements. Surface jarosite was observed in only one sample but no correlation between its presence and the hindered leaching could be made. It is proposed that iron-oxyhydroxides are the main precursor of chalcopyrite hindered dissolution in sulphate media where their inevitable formation entraps surface elemental sulphur resulting in a consolidated phase on the surface. It was shown that when suitable conditions are met, high copper recoveries can be obtained before the surface is finally hindered.Godkänd; 2016; 20151215 (seykos); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Mohammad Khoshkhoo Ämne: Processmetallurgi /Process Metallurgy Avhandling: Chalcopyrite (Bio)leachning in Sulphate Solutions An Investigation into Hindered Dissolution with a Focus on Solution Redox Potential Opponent: Professor Joachim Petersen, Department of Chemical Engineering, University of Cape Town, Rondebosch, Sydafrika. Ordförande: Professor Åke Sandström, Avd för mineralteknik och metallurgi, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet, Luleå. Tid: Fredag 26 februari, 2016 kl 09.30 Plats: E632, Luleå tekniska universite

Chalcopyrite Dissolution in Sulphate-Based Leaching and Bioleaching Systems [Elektronisk resurs]

Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process due to its simplicity and relatively low capital investment requirement. As a result, the technology appears to be an attractive process option for treatment of low-grade chalcopyrite ores as well. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional heaps: its dissolution is slow and it halts on a low level of copper extraction usually unacceptable for a commercial practice. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its oxidative dissolution, often termed “passivation”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation.In this thesis, dissolution of a pyritic and a pure chalcopyrite concentrate was studied in stirred tank reactors in the absence and presence of moderately thermophilic microorganisms. The abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. The results showed that the microorganisms did not have any effect in the copper leaching efficiency other than oxidation of ferrous ions to ferric ions. Comparing the copper dissolution rates in the experiments where bulk elemental sulphur was formed with those experiments where the elemental sulphur was oxidised to sulphate due to microbial activity showed that the bulk elemental sulphur did not hinder the dissolution. The same phenomenon was observed in case of bulk jarosite. Under otherwise identical leaching conditions, the presence of bulk jarosite did not decrease the leaching efficiency compared to those experiments were bulk jarosite was not formed. It was also shown that surface spectroscopic methodologies such as X-ray photoelectron spectroscopy (XPS) cannot be applied on powder leached samples due to interfering data from the bulk precipitated species. As a result, massive natural chalcopyrite samples were II prepared and used in the leaching experiments for XPS measurements. Different samples in different stages of leaching were extracted from the biotic and abiotic experiments and analysed by XPS. Results indicated that the surface elemental sulphur was not oxidised by bacterial activity. The data revealed that the common phases on the surface of the samples leached biotically and abiotically for different durations were elemental sulphur and iron-(oxy)hydroxides. The surface elemental sulphur was rigidly bound to the surface and did not volatise in the room temperature XPS measurements. Jarosite was observed in only one sample from the abiotic experiment, but no correlation between its presence and the slow dissolution could be made. Other minor surface compounds such as iron-sulphate was also observed in some samples with no contribution to the leaching behaviour. It was concluded that a multi-component surface phase consisting of mainly sulphur and iron-hydroxides were responsible for the slow chalcopyrite dissolution.</p

Chalcopyrite (Bio)leaching in Sulphate Solutions [Elektronisk resurs] : An Investigation into Hindered Dissolution with a Focus on Solution Redox Potential

Chalcopyrite (CuFeS2) is the most abundant and the most economically important copper mineral. Increasing worldwide demand for copper accompanied by exhaustion of copper resources necessitate the development of new processes for treating lower-grade copper ores. Heap (bio)leaching of copper oxides and secondary sulphides (covellite (CuS) and chalcocite (Cu2S)) is a proven technology and a convenient process nowadays. However, chalcopyrite is recalcitrant to leaching and bioleaching in conventional leaching systems in sulphate media. Slow dissolution of chalcopyrite is attributed to the formation of compounds on the surface of the mineral during its dissolution and is often termed “passivation” or “hindered dissolution”. There is still no consensus about the nature of the passivation layer. There are, however, four proposed candidates suggested in the literature: metal deficient sulphides, polysulphides, jarosite and elemental sulphur. This project was aimed to further investigate the chalcopyrite dissolution and its passivation under strictly controlled redox potential conditions. The leaching experiments of the aged and fresh chalcopyrite concentrate under identical conditions showed that copper dissolution was significantly lower from the aged concentrate. The common understanding of reductive leaching mechanism (i.e. higher recoveries at lower redox potentials) was not valid for aged concentrates. Aged concentrates gave steadily increasing recoveries with increased redox potential. The hindering effect exerted from the atmospheric oxidation products on the surface of the aged concentrates was found to be responsible for this behaviour. It was also shown that the reductive leaching mechanism would be beneficial in the presence of an active galvanic interaction. Experiments using a pyritic concentrate resulted in higher recoveries at low redox potential while the dissolution rates were similar at low and high redox potentials using a relatively pure concentrate. In addition, the effect of initial copper concentration had no influential effect on the leaching rates for possible industrial processes. Redox potential development during moderately thermophilic bioleaching experiments of a pyritic chalcopyrite concentrate and a relatively pure chalcopyrite concentrate were chemically/electrochemically mimicked in the absence of microorganisms. The copper recoveries in absence and presence of microorganisms were similar. In some of the abiotic experiments, jarosite precipitated due to a loss of control of the redox potential. However, presence of bulk jarosite did not hamper the copper recovery compared to the bioleaching experiments where there was no bulk jarosite formation. Bio-oxidation of elemental sulphur did not have a positive effect on the leaching behaviour compared to the abiotic experiments where bulk elemental sulphur accumulated. Isotopic fractionations of copper and iron during the bioleaching and abiotic experiments showed that regardless of presence or absence of microorganisms the copper and iron isotopes fractionation followed a similar trend and that such analyses could be used in natural systems as an indicator of the oxidation extent. Surface analyses using X-ray photoelectron spectroscopy (XPS) measurements revealed that common phases on the surface of the samples leached for different durations were iron-oxyhydroxides and elemental sulphur. The elemental sulphur on the surface of the samples was bound to the surface rigidly in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature measurements. Surface jarosite was observed in only one sample but no correlation between its presence and the hindered leaching could be made. It is proposed that iron-oxyhydroxides are the main precursor of chalcopyrite hindered dissolution in sulphate media where their inevitable formation entraps surface elemental sulphur resulting in a consolidated phase on the surface. It was shown that when suitable conditions are met, high copper recoveries can be obtained before the surface is finally hindered.</p

Study of Short Videos Uploaded on the Instagram platform Related to Sustainable Cross-Cultural Communication Management Cases of Iran and Oman

Technological development, especially over the past few years has influenced the quality of human lives considerably. According to the World Tourism Organization, the internet plays a crucial role in tourism, since it provides an opportunity for access to tourists across the world and it has the most audience compared to conventional media. Therefore, the main objective of this research is to study the short videos created on the Instagram platform for sustainable cross-cultural communication management in the cases of Iran and Oman. Among 50 Instagram pages related to Iran and Oman, only 10 pages were selected based on defined criteria and were studied using the thematic analysis method. The main discovered themes were commercial tourism (which includes sub-themes of company registration, exports, imports, skilled workers immigration); cultural tourism (which includes sub-themes of cultural similarities, cultural differences, and diplomatic relations between two countries); medical tourism (including sub-themes of Shiraz medical centers, Tehran medical centers, Ramsar health tourism, and the unknown destinations of health tourism in Iran); recreational tourism (which includes sub-themes of cruise ships, recreational Islands, desert tours, culinary tourism and restaurants, the unknown sights of Oman, and recreational tourism in Iran) and lastly ecotourism (including sub-themes of ecotourism in Iran and Oman). In general, all the discovered themes were about the sustainable cross-cultural communication between Iran and Oman