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

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zincrich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account

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

Assessment of Alkali Activation Potential of a Polish Ferronickel Slag

In this study, the alkali activation potential of a Polish ferronickel slag (PS), for the production of inorganic polymers (IPs), is investigated. The effect of the main synthesis parameters, i.e., strength of the activating solution, consisting of NaOH and Na2SiO3 solutions and affecting (SiO2 + Al2O3)/Na2O and other important molar ratios in the reactive paste, pre-curing period, curing temperature and time and ageing period was investigated. The structural integrity of the produced specimens was tested after their (i) immersion in distilled water and acidic solutions for a period of 7–30 days, and (ii) firing at temperatures between 200 °C and 1000 °C. Several analytical techniques including X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, Differential scanning analysis-Thermogravimetry and Scanning Electron Microscopy were used for the characterization of the produced IPs. Results show that under the optimum synthesis conditions the IPs obtain compressive strength that exceeds 65 MPa. An innovative aspect of this study is that after heating at 400 °C, the specimens acquire compressive strength of 115 MPa and this indicates that they can be also used as fire resistant materials. This study highlights the potential of alkali activation for the valorization of a ferronickel slag and the production of IPs that can be used as binders or in several construction applications, thus improving the sustainability of the metallurgical sector

Assessment of alkali activation potential of a Polish ferronickel slag

Research paperSummarization: In this study, the alkali activation potential of a Polish ferronickel slag (PS), for the production of inorganic polymers (IPs), is investigated. The effect of the main synthesis parameters, i.e., strength of the activating solution, consisting of NaOH and Na2SiO3 solutions and affecting (SiO2 + Al2O3)/Na2O and other important molar ratios in the reactive paste, pre-curing period, curing temperature and time and ageing period was investigated. The structural integrity of the produced specimens was tested after their (i) immersion in distilled water and acidic solutions for a period of 7–30 days, and (ii) firing at temperatures between 200 C and 1000 C. Several analytical techniques including X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, Differential scanning analysis-Thermogravimetry and Scanning Electron Microscopy were used for the characterization of the produced IPs. Results show that under the optimum synthesis conditions the IPs obtain compressive strength that exceeds 65 MPa. An innovative aspect of this study is that after heating at 400 C, the specimens acquire compressive strength of 115 MPa and this indicates that they can be also used as fire resistant materials. This study highlights the potential of alkali activation for the valorization of a ferronickel slag and the production of IPs that can be used as binders or in several construction applications, thus improving the sustainability of the metallurgical sector.Presented on: Sustainabilit

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

status: publishe

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

Summarization: With an increasing number of low-grade primary ores starting to be cost-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zinc rich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account.Presented on