| 21. |
- Javadi, Alireza, et al.
(author)
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Formation of hydrogen peroxide by sphalerite
- 2013
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In: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 125, s. 78-85
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Journal article (peer-reviewed)abstract
- Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by sphalerite ((Zn, Fe) S) was examined during its grinding process. It was observed that sphalerite generated H2O2 in pulp liquid during wet grinding and also when the freshly ground solids placed in water immediately after dry grinding. The generation of H2O2 in either wet or dry grinding was thought to be due to a reaction between sphalerite and water where the mineral surface is catalytically active to produce OH• free radicals by breaking down the water molecule. Effect of pH on the formation of H2O2 by sphalerite was shown that the acidic pH generated more H2O2. Mixtures of pyrite, chalcopyrite and galena with sphalerite on the formation of H2O2 were also probed. It was shown that the concentration of H2O2 increases with increasing pyrite or chalcopyrite fraction in pyrite–sphalerite, chalcopyrite–sphalerite mixtures but with an increase in galena proportion, the concentration of H2O2 decreased in galena–sphalerite mixture. The oxidation or dissolution of one mineral than the other in a mixture can be explained better with the extent of H2O2 formation in the pulp liquid than galvanic interactions. It is clear of the greater role of H2O2 in the oxidation of sulphides or aiding the extensively reported galvanic interactions since the amount of H2O2 generated with a specific mineral followed the rest potential series. This study highlights the necessity of further investigations into the role of H2O2 in electrochemical and/or galvanic interaction mechanisms between pyrite, chalcopyrite and galena with sphalerite.
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| 22. |
- Javadi, Alireza, et al.
(author)
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Formation of hydrogen peroxide by sulphide minerals
- 2014
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In: Hydrometallurgy. - : Elsevier BV. - 0304-386X .- 1879-1158. ; 141, s. 82-88
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Journal article (peer-reviewed)abstract
- Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by sulphide minerals during grinding was investigated. It was found that pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite ((Zn,Fe)S), and galena (PbS), which are the most abundant sulphide minerals on Earth, generated H2O2 in pulp liquid during wet grinding in the presence of dissolved oxygen in water and also when the solids are placed in water immediately after dry grinding. Pyrite generated more H2O2 than other minerals and the order of H2O2 production by the minerals found to be pyrite > chalcopyrite > sphalerite > galena. The pH of water influenced the extent of hydrogen peroxide formation where higher amounts of H2O2 are produced at highly acidic pH. Furthermore, the effect of mixed sulphide minerals, i.e., pyrite–chalcopyrite, pyrite–galena, chalcopyrite–galena and sphalerite–pyrite, sphalerite–chalcopyrite and sphalerite–galena on the formation of H2O2 showed increasing H2O2 formation with increasing pyrite fraction in chalcopyrite–pyrite, galena–pyrite and sphalerite–pyrite compositions. The results also corroborate the amount of H2O2 production with the rest potential of the sulphide minerals; higher the rest potential of a sulphide mineral, formation of H2O2 is more. Most likely H2O2 is responsible for the oxidation of sulphide minerals and dissolution of non-ferrous metal sulphides in the presence of ferrous sulphide in addition to galvanic interactions. This study highlights the necessity of revisiting the electrochemical and/or galvanic interactions between pyrite and other sulphide minerals in terms of their flotation and leaching behaviour in the context of inevitable H2O2 existence in the pulp liquid.
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| 23. |
- Javadi, Alireza, et al.
(author)
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Sulphide mineral flotation : a new insight into oxidation mechanisms
- 2013
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In: XIII International Seminar on Mineral Processing Technology. - Madras : Indian Institute of Technology Madras. - 9788192855202 ; , s. 169-182
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Conference paper (peer-reviewed)abstract
- The formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by sulphide minerals during grinding was investigated. It was found that pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite (ZnS), and galena (PbS), which are the most abundant sulphide minerals on Earth, generated H2O2 in pulp liquid during wet grinding in the presence and absence of dissolved oxygen in water and also when the freshly ground solids were placed in water immediately after dry grinding. Pyrite generated more H2O2 than the other sulphide minerals and the order of H2O2 production by the minerals was found to be pyrite > chalcopyrite >sphalerite> galena. The pH of water influenced the extent of hydrogen peroxide formation where higher amounts of H2O2 were produced at highly acidic pH. The amount of H2O2 formed also increased with increasing sulphide mineral loading and grinding time due to increased surface area and its interaction with water.The sulphide surfaces are highly catalytically active due to surface defect sites and unsaturation because of broken bonds and capable of breaking down the water molecule leading to hydroxyl free radicals. The type of grinding medium on formation of hydrogen peroxide by pyrite revealed that the mild steel produced more H2O2 than stainless steel grinding medium, where Fe2+ and/or Fe3+ ions played a key role in producing higher amounts of H2O2.Furthermore, the effect of mixed sulphide minerals, i.e., pyrite–chalcopyrite, pyrite–galena, chalcopyrite–galena and sphalerite–pyrite, sphalerite–chalcopyrite and sphalerite–galena on the formation of H2O2 showed increasing H2O2 formation with increasing pyrite fraction in chalcopyrite–pyrite composition. In pyrite–sphalerite, chalcopyrite–sphalerite or galena– sphalerite mixed compositions, with the increase in pyrite or chalcopyrite proportion, the concentration of H2O2 increased but with increase in galena proportion, the concentration of H2O2 decreased. By increasing the pyrite proportion in pyrite–galena mixture, the concentration of H2O2 increased. Similarly, in the mixture of chalcopyrite–galena, the concentration of H2O2 increased with increasing chalcopyrite fraction. The results of H2O2formation in pulp liquid of individual sulphide minerals and in combination at different experimental conditions have been explained by Eh–pH diagrams of these minerals and the existence of free metal ions that are equally responsible for H2O2 formation besides the catalytic activity of surfaces. The results of the amount of H2O2 production also corroborate with the rest potential of the sulphide minerals; higher the rest potential more is the formation of H2O2. Most likely H2O2 is responsible for the oxidation of sulphide minerals and dissolution of non-ferrous metal sulphides in the presence of ferrous sulphide besides the galvanic interactions.This study highlights the necessity of revisiting the electrochemical and/or galvanic interactions between the grinding medium and sulphide minerals, and interaction mechanisms between pyrite and other sulphide minerals in terms of their flotation behaviour in the context of the inevitable existence of H2O2 in the pulp liquid.
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| 24. |
- Javadi Nooshabadi, Alireza, et al.
(author)
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Formation of hydrogen peroxide by pyrite and its influence on flotation
- 2013
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In: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 49, s. 128-134
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Journal article (peer-reviewed)abstract
- Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by pyrite (FeS2), the most abundant metal sulphide on Earth, during grinding was investigated. It was found that pyrite generated H2O2 in pulp liquid during wet grinding and also the solids when placed in water immediately after dry grinding. Type of grinding medium on formation of hydrogen peroxide revealed that the mild steel produced more H2O2 than stainless steel grinding medium, where Fe2+ and/or Fe3+ ions played a key role in producing higher amounts of H2O2. The effect of grinding atmosphere of air and N2 gas showed that nitrogen environment free from oxygen generated more H2O2 than air atmosphere suggesting that the oxygen in hydrogen peroxide is derived from water molecules. In addition, the solids after dry grinding producing more H2O2 than wet grinding indicate the role of pyrite surface or its catalytic activity in producing H2O2 from water. This study highlights the necessity of relooking into the electrochemical and/or galvanic interaction mechanisms between the grinding medium and pyrite in terms of its flotation behaviour.
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| 25. |
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| 26. |
- Karlkvist, Tommy, et al.
(author)
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Flotation selectivity of novel alkyl dicarboxylate reagents for apatite-calcite separation
- 2015
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 445, s. 40-47
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Journal article (peer-reviewed)abstract
- The investigation aims to demonstrate the conceptual thoughts behind developing mineral specific reagents for use in flotation of calcium containing ores. For this purpose, a series of dicarboxylate-based surfactants with varying distance between the carboxylate groups (one, two or three methylene groups) was synthesized. A surfactant with the same alkyl chain length but with only one carboxylate group was also synthesized and evaluated. The adsorption behavior of these new reagents on pure apatite and pure calcite surfaces was studied using Hallimond tube flotation, FTIR and zeta potential measurements. The relation between the adsorption behavior of a given surfactant at a specific mineral surface and its molecular structure over a range of concentrations and pH values, as well as the region of maximum recovery, was established. It was found that one of the reagents, with a specific distance between the carboxylate groups, was much more selective for a particular mineral surface than the other homologues. For example, out of the four compounds synthesized, only the one where the carboxylate groups were separated by a single methylene group floated apatite but not calcite, whereas calcite was efficiently floated with the monocarboxylic reagent, but not with the other reagents synthesized. This selective adsorption of a given surfactant to a particular mineral surface relative to other mineral surfaces as evidenced in the flotation studies was substantiated by zeta potential and infra-red spectroscopy data.
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| 27. |
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| 28. |
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| 29. |
- Kota, Hanumantha Rao, et al.
(author)
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Atomistic simulations on the adsorption of water, methanoic acid and methylamine on pure and hydroxylated quartz
- 2006
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In: Proceedings of the XXIII International Mineral Processing Congress. - Istanbul : IMPC. ; , s. 1729-1735
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Conference paper (peer-reviewed)abstract
- The atomistic simulation code METADISE was used to construct and describe the predominant quartz surfaces at atomic level by static energy minimisation procedure. The surface energies were calculated and unsaturated surface sites are identified. Hydroxylation of quartz surfaces was performed in order to satisfy full coordination of surface sites. The surfaces became most stabilised when they adsorb water in dissociated form justifying hydroxylated quartz surface prevalence in nature. Water, methanoic acid, and methylamine adsorption calculations were carried out on both pure and hydroxylated quartz surfaces. Relative adsorption energies suggest that both methanoic acid and methylamine adsorb preferably than water on pure quartz surface. On hydroxylated quartz surfaces, methylamine adsorption is preferred than water and methanoic acid, which match quartz flotation practice with cationic amine collectors. These simulations have given an insight into interactions at the atomic level which indicate that modelling techniques should be capable of predicting adsorption behaviour and designing mineral specific collector molecules.
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| 30. |
- Kota, Hanumantha Rao, et al.
(author)
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Challenges in sulphide mineral processing
- 2011
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In: Open Mineral Processing Journal. - : Bentham Science Publishers Ltd.. - 1874-8414. ; 4, s. 7-13
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Journal article (peer-reviewed)abstract
- Scientists and technologists in world over are making large efforts to streamline the conventional technological schemes of ore processing, in particular froth flotation towards reducing overall costs, limiting the use of dangerous substances, decreasing waste streams and improving waste disposal. Hitherto, search for such innovations has been performed mainly empirically and there is an urgent need to shift these technologies to be more innovative and effective. Understanding of the fundamental concepts of aquatic chemistry of minerals-selective adsorption and selective redox reactions at mineral-solution interfaces would impact innovating conventional flotation process. Molecular-level knowledge and coherent understanding of minerals contacted with aqueous solutions is required which underlie great opportunities in controlling mineral-solution interfaces towards the grand challenge of tomorrow's science and mineral processing technology.Aqueous redox chemistry of sulphides and adsorption mechanisms, the problems of metal sulphides selectivity against pyrite and fine particle flotation have been highlighted and discussed in the light of literature. The requisite knowledge and research needs to address these issues have also been briefly presented.
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