| 1. |
- Awe, Samuel Ayowole, et al.
(author)
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Formation of sulphur oxyanions and their influence on antimony electrowinning from sulphide electrolytes
- 2013
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In: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 53, s. 39-47
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Journal article (peer-reviewed)abstract
- Antimony electrowinning from synthetic alkaline sulphide electrolytes has been studied in a nondiaphragm electrolytic cell. The electrodes were constructed in such a way that the anode produces ten times higher current density than the cathodic current density to promote sulphide oxidation to sulphate at the anode; and simultaneously decreasing the tendency of hydrogen evolution at the cathode. The result revealed that at an anodic current density lower than 1500 A/m2, minute amounts of sulphate ions were formed but when the anode current density increased beyond 1500 A/m2, sulphate formation was promoted. The initial molar concentration ratio between hydroxide and free sulphide ions should be ≥ 10.3 to avoid thiosulphate formation at 2000 A/m2 anodic current density under the conditions used in these experiments. The highest anodic current efficiency obtained based on the amount of sulphate formed was 89%. An increase in the anode current density as well as NaOH concentration enhances the cathodic and anodic current efficiencies with respect to the antimony metal deposited and sulphate ions produced, respectively. Despite the high anodic current densities used, the specific energy of this process ranges from 0.6 to 2.3 kWh/kg which is significantly lower than values reported previously due to the prevention of undesirable sulphur species from being formed. The tests revealed that the concentration of thiosulphate formed during the electrolysis decreased with increasing anode current density and NaOH concentration. Addition of polysulphide from 0 to 30 g/L to the electrolyte decreases the current efficiency from 83% to 32% and correspondingly increases the specific energy from 1.7 to 4.8 kWh/kg. Results showed that a build-up of sulphite and sulphate ions in the solution does not have any detrimental effect on the current efficiency of antimony deposition.
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| 2. |
- Awe, Samuel Ayowole, et al.
(author)
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Process flowsheet development for recovering antimony from Sb-bearing copper concentrates
- 2013
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In: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 49, s. 45-53
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Journal article (peer-reviewed)abstract
- The technical feasibility, on laboratory scale, of hydro- and electrometallurgical processes of recovering metallic antimony from an antimony-bearing copper sulphide concentrate has been investigated. The influence of Na2S concentration, temperature and solid concentration was studied during the leaching test while the effect of current density, Na2S concentration, electrolyte temperature and NaOH concentration on antimony electrowinning from alkaline sulphide solutions was investigated. The leaching results showed that antimony dissolution is strongly dependent on the concentration of the leaching reagent as well as the leaching temperature. The antimony content in the concentrate was reduced from 1.7% to less than 0.1% Sb which is desirable for copper metallurgy. Cathode current efficiency is one of the important parameters to evaluate the performance of an electrolytic process. It is revealed in this study that current efficiency of antimony deposition from sulphide electrolytes is highly dependent on the concentration of sodium hydroxide and the current density used. The results illustrate that the combined effect of increasing anode current density (which was 10 times higher than the cathode current density) and NaOH concentration enhanced the current efficiency of the electrolytic process. It was demonstrated that excess free sulphide ions impacts the current efficiency of the process detrimentally. An integrated hydro-/electrometallurgical process flowsheet for antimony removal and recovery from a sulphide copper concentrate was developed.
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| 3. |
- Broman, Elias, 1985-, et al.
(author)
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Low temperature, autotrophic microbial denitrification using thiosulfate or thiocyanate as electron donor
- 2017
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In: Biodegradation. - : Springer. - 0923-9820 .- 1572-9729. ; 28:4, s. 287-301
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Journal article (peer-reviewed)abstract
- Wastewaters generated during mining and processing of metal sulfide ores are often acidic (pH < 3) and can contain significant concentrations of nitrate, nitrite, and ammonium from nitrogen based explosives. In addition, wastewaters from sulfide ore treatment plants and tailings ponds typically contain large amounts of inorganic sulfur compounds, such as thiosulfate and tetrathionate. Release of these wastewaters can lead to environmental acidification as well as an increase in nutrients (eutrophication) and compounds that are potentially toxic to humans and animals. Waters from cyanidation plants for gold extraction will often conjointly include toxic, sulfur containing thiocyanate. More stringent regulatory limits on the release of mining wastes containing compounds such as inorganic sulfur compounds, nitrate, and thiocyanate, along the need to increase production from sulfide mineral mining calls for low cost techniques to remove these pollutants under ambient temperatures (approximately 8 °C). In this study, we used both aerobic and anaerobic continuous cultures to successfully couple inorganic sulfur compound (i.e. thiosulfate and thiocyanate) oxidation for the removal of nitrogenous compounds under neutral to acidic pH at the low temperatures typical for boreal climates. Furthermore, the development of the respective microbial communities was identified over time by DNA sequencing, and found to contain a consortium including populations aligning within Flavobacterium, Thiobacillus, and Comamonadaceae lineages. This is the first study to remediate mining waste waters by coupling autotrophic thiocyanate oxidation to nitrate reduction at low temperatures and acidic pH by means of an identified microbial community.
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| 4. |
- Dopson, Mark, et al.
(author)
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Silicate mineral dissolution during heap bioleaching
- 2008
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In: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 99:4, s. 811-820
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Journal article (peer-reviewed)abstract
- Silicate minerals are present in association with metal sulfides in ores and their dissolution occurs when the sulfide minerals are bioleached in heaps for metal recovery. It has previously been suggested that silicate mineral dissolution can affect mineral bioleaching by acid consumption, release of trace elements, and increasing the viscosity of the teach solution. In this study, the effect of silicates present in three separate samples in conjunction with chalcopyrite and a complex multi-metal sulfide ore on heap bioleaching was evaluated in column bioreactors. Fe2+ oxidation was inhibited in columns containing chalcopyrite samples A and C that leached 1.79 and 1.11 mM fluoride, respectively but not in sample B that contained 0.14 mM fluoride. Microbial Fe2+ oxidation inhibition experiments containing elevated fluoride concentrations and measurements of fluoride release from the chalcopyrite ores supported that inhibition of Fe2+ oxidation during column leaching of two of the chalcopyrite ores was due to fluoride toxicity. Column bioleaching of the complex sulfide ore was carried out at various temperatures (7-50 degrees C) and pH values (1.5-3.0). Column leaching at pH 1.5 and 2.0 resulted in increased acid consumption rates and silicate dissolution such that it became difficult to filter the leach solutions and for the leach liquor to percolate through the column. However, column temperature (at pH 2.5) only had a minor effect on the acid consumption and silicate dissolution rates. This study demonstrates the potential negative impact of silicate mineral dissolution on heap bioleaching by microbial inhibition and liquid flow.
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| 5. |
- Dopson, Mark, et al.
(author)
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Toxicity of metal extraction and flotation chemicals to Sulfolobus metallicus and chalcopyrite bioleaching
- 2006
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In: Hydrometallurgy. - : Elsevier BV. - 0304-386X .- 1879-1158. ; 81:3-4, s. 205-213
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Journal article (peer-reviewed)abstract
- The effect of chemicals used in preparation of mineral concentrates and subsequent extraction of metals to the thermophilic, acidophilic microorganism Sulfolobus metallicus has been tested. The chemicals tested included collectors and frothers employed during flotation of the oreto produce a mineral concentrate, solvent extraction reagents used to remove metals after leaching, and thiocyanate produced as a decomposition product during cyanidation for gold recovery. The effect of these chemicals to S. metallicus depends on the conditions and time frame that the experiments were carried out due to their mode of toxicity and stability in acid pH. The metal extraction chemical that had the least effect on bioleaching was potassium amyl xanthate that increased the leaching rate, possibly due to solubilization of sulfur that can form passivation layers on the surface of minerals. The frother Flotanol C-7 decreased the chalcopyrite leaching rate, despite having no effect on Fe2+ oxidation by S. metallicus resting cells. This is probably due to inhibition of oxygen transfer during bioleaching that had little effect on Fe2+ oxidation over 20 min. Solvent extraction chemicals inhibited both Fe2+ oxidation and bioleaching suggesting their mode of inhibition is due toFe2+ oxidation. The results suggest that relevant concentrations of metal extraction and flotation chemicals can be toxic to chalcopyritebioleaching by S. metallicus.
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| 6. |
- Gahan, Chandra Sekhar, et al.
(author)
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A study on the toxic effects of chloride on the biooxidation efficiency of pyrite
- 2009
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In: Journal of Hazardous Materials. - : Elsevier BV. - 0304-3894 .- 1873-3336. ; 172:2-3, s. 1273-1281
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Journal article (peer-reviewed)abstract
- Bioleaching operations in areas with limited chloride-free water and use of ashes and dust as neutralizing agents have motivated to study the chloride toxicity and tolerance level of the microorganisms. Biooxidation of pyrite using chloride containing waste ash compared with Ca(OH)2 + NaCl as neutralizing agent was investigated to evaluate the causes of low pyrite oxidation. Both precipitation of jarosite as well as the toxic effect of chloride on the microorganisms were responsible for lower pyrite recoveries. Another study with sudden exposure of chloride during pyrite biooxidation, addition of 4 g/L was lethal for the microorganisms. Addition of 2 g/L chloride resulted in precipitation of jarosite with slightly lower pyrite recovery whereas the addition of 3 g/L chloride temporarily chocked the microorganisms but activity was regained after a short period of adaptation. Population dynamics study conducted on the experiment with 3 g/L chloride surprisingly showed that Leptospirillum ferriphilum, which was dominating in the inoculum, completely disappeared from the culture already before chloride was added. Sulphobacillus sp. was responsible for iron oxidation in the experiment. Both Acidithiobacillus caldus and Sulphobacillus sp. were adaptive and robust in nature and their numbers were slightly affected after chloride addition. Therefore, it was concluded that the microbial species involved in the biooxidation of pyrite vary in population during the different stages of biooxidation.
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| 7. |
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| 8. |
- Gahan, Chandra Sekhar, et al.
(author)
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Comparative assesment of Industrial oxidic by-products as neutralising agents in biooxidation and their influence on gold recovery in subsequent cyanidation
- 2011
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In: Proceedings of the XI International Seminar onMineral Processing Technology (MPT-2010). ; , s. 1293-1302
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Conference paper (peer-reviewed)abstract
- The neutralisation cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralising agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S° in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulphur oxidation would be more complete, thereby possibly decreasing cyanide consumption.
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| 9. |
- Gahan, Chandra Sekhar, et al.
(author)
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Evaluation of oxidic by-products as neutralizing agents in biooxidation of a refractory gold concentrate and their influence on gold extraction through cyanidation
- 2013
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In: Research Journal of Recent Sciences. - : International Science Congress Association. - 2277-2502. ; 2:11, s. 41-47
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Journal article (peer-reviewed)abstract
- The neutralization cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralizing agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulfur oxidation would be more complete, thereby possibly decreasing cyanide consumption.
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| 10. |
- Gahan, Chandra Sekhar, et al.
(author)
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Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation
- 2010
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In: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 23:9, s. 731-738
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Journal article (peer-reviewed)abstract
- The cost of lime/limestone for neutralisation is the second largest operating cost in bioleaching. Therefore, these studies have been conducted with the aim to investigate the possibilities for use of by-products such as mesalime and electric arc furnace (EAF) dust for neutralisation during biooxidation of a refractory gold concentrate. Experiments were carried out using a retention time of 57 h in a one-stage reactor and the influence of two industrial by-products on the biooxidation performance was evaluated. The neutralising capacity of EAF dust was lower, while the mesalime was similar to the Ca(OH)2 reference. The arsenopyrite oxidation in experiments ranged from 85% to 90%, whereas the pyrite oxidation was 63-74%. In subsequent cyanidation, final gold recoveries of 90% were achieved in bioresidues from mesalime and Ca(OH)2, while the EAF dust bioresidue had a recovery of 85%. A comparatively high elemental sulphur content in EAF dust probably encapsulates part of the gold, which explains the lower recovery for the EAF dust bioresidue despite a longer residence time. Cyanide consumption was relatively high and ranged from 8.1 to 9.2 kg/ton feed after 24 h of cyanidation. Overall, the by-products tested here have proved to be feasible options as neutralising agents in bioleaching operations.
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