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Aqueous behaviour of cobalt in the presence of copper, iron and sulphur dioxide with and without microwave processing

  • Authors: Ndalamo, John
  • Date: 2009-05-19T07:40:16Z
  • Subjects: Cobalt , Leaching
  • Type: Thesis
  • Identifier: uj:8393 , http://hdl.handle.net/10210/2558
  • Description: M.Tech. , Recent studies have explored the capabilities of sulphur dioxide (SO2), a reducing agent that shows great potential to enhance the leaching efficiency of cobalt from mixed Co-Cu oxidized ores. The research study reported in this dissertation was conducted to further explore the efficacy of SO2 as a suitable reagent to improve the cobalt yield in solution from mixed Co-Cu oxidised ores. Four mixed Co-Cu oxidised ores were used in this study; namely, high cobalt ore (34% Co), low cobalt ore with mica (4% Co), low cobalt ore without mica (3% Co) and high copper ore (0.5% Co). The mechanistic leaching pathways of cobalt from these ores with and without SO2 were investigated and monitored using Ultra-Violet/Visible spectroscopy. Mineralogical studies of these ores was carried out by X - ray diffraction (XRD), X - ray fluorescence (XRF) and flame atomic absorption spectroscopy (AAS). Microwave processing of these ores prior to leaching experiments was also investigated. The experimental work was carried out on a laboratory scale and highlights of results obtained are summarized as follows:  Although not much information pertaining to Co2+ bearing minerals in mixed Co-Cu oxidised ores was derived from XRD results, two forms of heterogenite minerals (CoOOH-2H and CoOOH-3R), which bear cobalt as Co3+ were noted in the low cobalt ores.  High percentage cobalt dissolutions (85% to 95%) were achieved when leaching mixed Co-Cu oxidised ores in the presence of SO2.  UV/Visible spectroscopy confirmed concentrations of Co3+ and Co2+ before and after SO2 treatment of mixed Co-Cu oxidised ores.  Percentage cobalt dissolutions improved by 10% to 20% in microwave irradiated mixed Co-Cu oxidised ores  The presence of iron and copper in leach solutions can limit the dissolution of cobalt from mixed Co-Cu oxidised ores to a certain extent.
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An investigation into the effect of temperature on the leaching of copper-matte

Process intensification of zinc oxide leaching process using sulphuric acid

  • Authors: Napo, P. , Ntuli, Freeman , Muzenda, Edison , Mollagee, Mansoor
  • Date: 2011
  • Subjects: Leaching , Zinc oxide ores
  • Type: Article
  • Identifier: uj:4705 , ISSN 2078-0966 , http://hdl.handle.net/10210/10948
  • Description: This study investigated methods of intensifying the leaching of zinc oxide ore using sulphuric acid for the improvement of zinc recovery. The factors that were investigated in this study were agitation speed, acid concentration and the feeding mechanism of reactants into the reactor (batch and semi-batch processes). Analysis of the elemental composition of the ore was performed using XRF prior to leaching and an Atomic Absorption Spectrometer (AAS) was used to determine the amount of zinc recovered. The results obtained, showed that increasing the acid concentration results in a significant increase zinc recovery...
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The effect of leaching time and ammonia concentration on the atmospheric leaching of copper

  • Authors: Ntuli, Freeman , Muzenda, Edison , Ramatsa, Ishmael , Belaid, Mohamed , Kabuba, John
  • Date: 2011
  • Subjects: Copper recovery , Leaching , Ammonia concentrations
  • Type: Article
  • Identifier: uj:5319 , ISSN 2010-4618 , http://hdl.handle.net/10210/8195
  • Description: The effects of ammonia concentration and leaching time were investigated to determine the optimum leaching conditions. The experiments were conducted in a leaching cell submerged in a water bath, with ammonia concentrations of 1.5 M, 2.0 M, 2.5 M and 3.0 M and varying leaching time from 0 to 300 min. Ni-Cu matte containing 23% by mass Cu was used in this experimental study. Increase in the concentration of the lixiviant was found to increase recovery when leaching for 130 minutes, with a recovery of 32.86% Cu using 3 M solution of ammonia. An increase in the leaching time resulted in more copper being leached for all lixiviant concentrations. However, leaching with 2 M ammonia solution gave a higher yield of copper compared to higher concentrations. This anomaly could be a result of cementation; Cu is displaced by Ni as Ni is a more electronegative metal than Cu .It was found that at higher concentrations more nickel was extracted.
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The effect of zinc ion concentration and pH on the leaching kinetics of calcined zinc oxide ore

  • Authors: Muzenda, Edison , Simate, Geoffrey S.
  • Date: 2011
  • Subjects: Dissolution kinetics , Leaching , Zinc ions , Zinc oxide
  • Type: Article
  • Identifier: uj:4701 , http://hdl.handle.net/10210/10940
  • Description: Previous studies on the dissolution of zinc oxide have concentrated on the effects of temperature, reagent concentration, particle size and agitation rate, among other factors. However, there is dearth data on the effect of a combination of product concentration and pH on leaching rates. This work examines the effects of the concentration of pH and zinc ions on the dissolution kinetics of zinc oxide. The results showed that the rate of zinc dissolution was greatest at lower pHs. This is because at lower pH, the concentration of acid (H+ ions) is also expected to be high (pH = log10[H+]), thus increasing the reaction kinetics in accordance with the kinetic molecular theory. The rate of reaction was found to increase with an increase in the concentration of zinc ions (Zn2+), which is in contrast to established theories. This observation can be explained by the fact that since heat energy produced (via an exothermic reaction) was continuously being dissipated through a constant temperature water bath it favoured zinc oxide dissolution. Zinc oxide ore at 62.5% purity also comprised of other metal oxides (e.g., iron, copper, manganese, etc) which were simultaneously leached. Since the solution was recycled, the concentration of iron, for example, could have also increased. Since zinc is more reactive than iron, two reaction mechanisms could have possibly been occurring at the same time, i.e., the dissolution of zinc oxide ore by sulfuric acid and the displacement of iron in solution by zinc in zinc oxide forming iron hydroxide.
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Recovery of aluminium oxide from flint clay through H2SO4 leaching

Roasting of sulphide concentrates and acid leaching of calcines emanating from conventional and microwave assisted roasting

  • Authors: Phiri, Thulane Raymond
  • Date: 2012-06-05
  • Subjects: Leaching , Gold - Metallurgy , Heat - Transmission , Microwave heating
  • Type: Thesis
  • Identifier: http://ujcontent.uj.ac.za8080/10210/380427 , uj:2395 , http://hdl.handle.net/10210/4849
  • Description: M.Tech. , The study presented, investigated the acid leaching behavior of calcines emanating from conventional roasting and microwave assisted roasting of sulphide ores. The aim was to investigate a possible change in the mineral composition of the calcine produced and to investigate the leaching behavior of the calcine produced by conventional and microwave assisted roasting. Two sulphide concentrates were received, pyrite concentrate from OTJIHASE concentrator and sphalerite concentrate from ZINCOR. The mineralogical study was done using the XRD (PANalytical X-PertPro X-Ray diffractometer) to determine the mineral composition of the concentrate and the head grade of each concentrate was determined with an Atomic Absorption Spectrometry (AAS) machine for copper, iron and zinc. The concentrates were wet screened at 500, 355, 212, 150, 106 and 75 μm screens for size distribution and for the purpose of the study it was required that 80% of concentrate should pass the 75 μm screen since after roasting, the calcine obtained were to be acid leached. Conventional roasting was carried out at temperatures of 500oC, 700oC, 850oC and 1000oC at durations of 5min, 10min, 20min, 30min, 1hour and 2hours, while microwave assisted roasting carried out at powers of 200W, 400W, 600W, 800W and time intervals of 3s, 10s, 30s, 30min and 1hour
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An investigation into hydrochloric acid leaching of low grade gold-bearing material and oxidized cobalt-copper ores

  • Authors: Apua, Momboyo Clotilde
  • Date: 2012-06-07
  • Subjects: Leaching , Hydrochloric acid , Reduction (Chemistry)
  • Type: Thesis
  • Identifier: uj:8652 , http://hdl.handle.net/10210/5008
  • Description: M.Tech. , The efficiency of hydrochloric acid leaching of gold from low grade gold-bearing material has been investigated in the presence of sodium hypochlorite (NaOCl) to produce in situ chlorine gas which is an oxidizing agent able to oxidize gold metal to gold soluble forms: Au+ and Au3+. The effect of concentrations of HCl, NaOCl, and mixtures HCl + NaOCl was sought. An investigation on chlorine species was conducted to predict their stability areas. The reactions involved and their mechanisms were established. Prior to leaching, the feed was subjected to fire assay, Atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR) analyses, to quantify the various elements, and to find out the chemical composition and the different mineralogical phases which are present. The main minerals found in the feed were: quartz, pyrite, muscovite-2M1, (M); and clinochlore. The grade was found to be 0.62 g/t. It was found from the hydrochloric acid leaching process that most of metals constituents (iron and potassium) of the feed were leached and consumed all the hydrochloric acid. Therefore, leaching of gold from low grade gold-bearing materials in aqueous chlorine solution is not an effective process for now. Hydrochloric acid leaching of cobalt and copper from four oxidized cobalt-bearing ores was studied in the presence of FeCl2 to produce in situ Fe2+ that is a reducing agent able to reduce Co3+ to Co2+ which is the soluble form of cobalt. The effects of the concentrations of HCl, FeCl2, mixture HCl + FeCl2, leaching time, particle size, and the dissolution kinetics were investigated. Prior to leaching the feeds were characterized with XRD, XRF, FTIR, AAS, Scanning electron microscopy (SEM), and gravimetric analysis. Cobalt contents were found to be between 2.59% and 39.76% in the four ores namely, high Cu ore, high Co ore, low Co ore, and high Co ore with mica. Effect of FeCl2 concentrations in HCl solutions involving 35.06 g; 70.13 g; and 105.18 g corresponding to 0.25 M; 0.5 M; and 0.75 M respectively, were studied and the reactions mechanism established. It was found that an increase in FeCl2 concentration increases the Co dissolution due to the reduction of Co3+ into Co2+ which is soluble. High Co extractions of 99%, 99%, 99%, and 95% were obtained when mixtures 1 M HCl + 105.18 g FeCl2 were used as lixiviants for high Cu ore, high Co ore, low Co ore, and high cobalt ore with mica, respectively. Copper recoveries of 88%, 77%, 75%, and 86% were obtained for high Cu ore, high Co ore, low Co ore, and high Co ore with mica, respectively. The increase in FeCl2 concentration did not have any important effect on the Cu extraction. Mechanisms of involved reactions were established. The order of cobalt leaching reaction was found to be 2 with respect to cobalt concentration. Optimum leaching conditions were found to be: leaching time: 30 minutes, reagent concentrations: mixture 1 M HCl + 105.18 g FeCl2, S/L ratio = 1:20, stirring speed avoiding the vortex, room temperature, pH values from 2.28 to 0.03, and ORP values from 0.402 to 0.322 V.
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An investigation into the leaching behaviour of nickel-copper bearing matte

  • Authors: Ramatsa, Ishmael Matala
  • Date: 2012-10-24
  • Subjects: Leaching , Sulfides , Smelting , Copper-nickel alloys
  • Type: Thesis
  • Identifier: uj:10420 , http://hdl.handle.net/10210/7886
  • Description: M.Tech. , The Bushveld complex of South Africa contains the world`s largest resources of platinum-group elements and it occurs over an area of ~ 65,000 km2, and it includes the largest known terrestrial layered mafic intrusion. A broad group of deposits containing nickel, copper and platinum group elements (PGE) occur as sulphide concentrations associated with a variety of mafic and ultramafic magmatic rocks. In the current study the leaching behaviour of Ni-Cu was studied in an ammoniacal solution using the matte that was provided by Impala Platinum. To understand the leaching behavior of Ni – Cu matte the effect of the key leaching parameters were studied, i.e. temperature, solvent concentration, effect of oxygen as an oxidant and effect of stirring speed, and the end the kinetic model was used. Leaching is basically making use of a hydrometallurgical process, that is chemical dissolution or leaching, metals can efficiently be extracted from sulphide concentrate/matte, leaving behind a residue of inert minerals originally present as well as insoluble decomposition products of the reacted minerals. Effect of the temperature was tested and it was found that Ni and Cu extraction increased when the temperature increased from 50- 60oC, and beyond 60oC no significant increment was observed. Ni was found to increase with the increase in solvent concentration, as concentration increased from 1.5 – 3 M, Ni increased from 3.93 – 32.88%. And with Cu the opposite was observed, 2 M NH3 solution and beyond 250 min the extraction of Cu metal began to decline. It was observed that between 10.43 – 10.37 pH more of the Ni and Cu were extracted, and below 10.37 the metal extraction started to decrease with decrease in the pH. The stirring speed was investigated between the range 320 – 560 rpm and it was observed that 45.5% of Cu and 34.7% of Ni were leached out from the Ni-Cu matte and as the speed increase beyond 410 rpm the percentage extraction of Ni and Cu started to decline, this behavior could be attributed to the disintegrate of the soft hydrated iron oxide residue particles and this determines the practical limit of agitation, XRD results after leaching showed that the Ni3S2 phase transformed to NiS2 phase after 270 min of leaching, while Cu2S phase transformed to Cu1.8S phase. The results of using oxygen as an oxidant showed an increment in Ni and Cu extraction even though the increment was not that significant. After leaching the data obtained was modeled to determine whether the kinetic model follows diffusion controlled process, chemical controlled process or mixed controlled process and it was found that diffusion controlled process best describes the kinetic model at all temperatures.
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Leaching of Nickel from a Jarosite Precipitate with Hydrochloric Acid

Leaching of nickel from a jarosite precipitate with hydrochloric acid

  • Authors: Nheta, Willie , Makhatha, Mamookho E.
  • Date: 2013
  • Subjects: Hydrochloric acid , Leaching , Nickel , Jarosite precipitates
  • Type: Article
  • Identifier: uj:4969 , http://hdl.handle.net/10210/13070
  • Description: Jarosite precipitates produced at Impala’s Base Metal Refineries contain substantial amounts of nickel. Laboratory-scale experiments were carried out in an attempt to recover nickel by leaching with hydrochloric acid. The leaching efficiency of nickel was 60% at 25oC. The acid concentration of 0.5 – 1 molar, pulp density of 10% and leaching time of 90 min was found to be optimum under the present conditions. High pH could break the jarosite structure and release more iron into the solution which will adversely affect the following precipitation process to recover nickel. 27% of the nickel lost is by entrainment. The reaction is diffusion independent.
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Quantitative leaching of nickel from jarosite using sulphuric acid

The effect of leaching time and ammonia concentration on the atmospheric leaching of copper

Acidified ferric chloride leaching behaviour of a complex Ni – Cu matte at atmospheric pressure

An attempt into identification of suitable recovery process for nickel value from nickel sulfide ore and tailings

  • Authors: Madiba, Mapilane S.
  • Date: 2013-11-25
  • Subjects: Nickel - Metallurgy , Nickel sulfide , Tailings (Metallurgy) , Leaching
  • Type: Thesis
  • Identifier: uj:7796 , http://hdl.handle.net/10210/8691
  • Description: M.Tech (Metallurgy) , Nickel in South Africa is scarce. Other than as a by-product from platinum mining, its only source is the Uitkomst Complex, a satelite of the Bushveld Igneous Complex, located between Machadodorp and Barberton and mined by Nkomati Nickel. Pentlandite occurs as the main nickel-bearing mineral, disseminated within a sulfide matrix of pyrrhotite, pyrite and chalcopyrite. Accessories are of chromite and platinum in solid solution with the sulfides. The sulfides are hosted in mainly ultramafic rocks. The presence of talc is of particular nuisance. Head grade is in the decline, from earlier 0.7 to more recently 0.3% or even lower. Standard froth flotation yields a concentrate of 7 – 9% nickel at a recovery of up to 70%. A higher nickel recovery from such low – grade feed stock would be desirable. To achieve these two methods were investigated and reported in the following:  Non-oxidative leaching as an alternative to flotation, using strong hydrochloric and sulfuric acid and also aqueous ammonia solutions at various liquid-to-solid ratios. Only the degree of nickel dissolution over time at room temperature was studied and no attempt was made to recover the dissolved metal from solution.  Froth flotation after pre-treatment with microwaves at various power levels and over various periods of time of irradiation. It was surmised that a certain amount of inter-granular cracking could thus be achieved that would improve the flotation behavior in respect of grade and recovery. An extensive literature study, in particular, of the nature of microwaves, their interaction with matter and possible metallurgical benefits derived as a consequence of such interaction, forms part of the investigation and is reported in detail. A lot of theoretical and experimental work has been done in this respect, although the obtained results were not conclusive.
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Application of microwaves in leaching

Modeling and simulation of heat transfer between microwaves and a leachate

Kinetic and thermodynamic parameters of silica leaching from Camden power station fly ash

  • Authors: Falayi, Thabo , Ntuli, Freeman , Okonta, Felix Ndubisi
  • Date: 2015
  • Subjects: Fly ash , Leaching , Potassium silicate , Silicate leaching
  • Type: Article
  • Identifier: uj:5142 , ISBN 978-1-61804-270-5 , http://hdl.handle.net/10210/14120
  • Description: Fly ash from a South African power station ash dam was used. The fly ash approximated Class F fly ash but had a loss on ignition greater than 6%. The leaching parameters investigated were leaching time, KOH concentration, agitation speed, fly ash particle size, leaching temperature and liquid solid ratio (L/S). It was found that the optimum leaching conditions were leaching time of 6 h, 3M KOH, 500 rpm agitation speed, 25 L/S ratio, leaching temperature of 100˚C. Silica leaching followed a modified Jander equation kinetics with an N value of 1.48 and an activation energy of 5.9 kJ/mol.
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Characterization of South African waste foundry molding sand : metallic contaminants

  • Authors: Nyembwe, J. K. , Makhatha, Mamookho E. , Madzivhandila, T . , Nyembwe, K. D.
  • Date: 2015-07-20
  • Subjects: Foundry waste , Leaching , Hazardous wastes
  • Type: Article
  • Identifier: uj:5173 , http://hdl.handle.net/10210/14414
  • Description: Waste foundry sands are invariably contaminated to some extent during the manufacturing of cast alloys. As such the sand is regarded as a hazardous material that requires exceptional precautions for its disposal. Therefore, the study is initiated to identify, quantify and to classify metallic contaminants present in these sands. To achieve these objectives in conjunction with the South African Waste Management Act which plays as the guideline for industrial waste disposal, samples were collected from various South African foundries. In the present study, ten waste sand samples were characterised using XRF, XRD, SEM-EDS and Sulphur analyser. It was found after comparison with a virgin sand used as control or reference sand, that the cast alloy and the moulding additives are the main pollutants present in the waste foundry sand. The additional sulphur and acid potential characterisation, showed that the waste foundry sand has a low potential for sulphuric acid and acid sulphate soil formation when submerged in aquatic medium. The leaching behaviour and the total metallic concentration of the waste was similar to the virgin soil thus their similar classification in the same waste class category.
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Recovery of PGMS from mine sludge by leaching

  • Authors: Nheta, Willie , Mapotsane, Kutullo
  • Date: 2017
  • Subjects: Mine sludge , Leaching , Oxidizing agents
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/239288 , uj:24580 , Citation: Nheta, W. & Mapotsane, K. 2017. Recovery of PGMS from mine sludge by leaching.
  • Description: Abstract: South Africa host massive deposits of Platinum Group Metals (PGMs) in the Igneous Bushveld Complex. These deposits have been mined for a long time and in the process Mine sludge has been produced. It has been piled up and there is need to recover PGMs locked in it. The conventional way of processing PGMs has proved to be very difficult due to ultra-fines in the sludge that causes major loses during flotation. An alternative hydrometallurgical process for recovery of PGMs from a mine sludge by leaching using a mixture of hydrochloric acid and different oxidizing agents was investigated. It was found that the mine sludge contained 8.93 g/t Pt, 6.99 g/t Pd, 2.79 g/t Ru and minor percentages of Rh, Ir, and Au. It had a particle size distribution (PSD) of 84.64% passing 38 microns. Major mineral phases present are sphalerite, chalcopyrite, pentlandite, covellite, bornite, chromite, and silica as the main gangue. HCL + H2O2 (1:1) combination managed to leach all the PGMs and gold. HCL + Ferric Chloride (1:1) combination managed to leach Pt, Rh and Ru very well but it could not leach Pd. Further investigation on the optimization of the leaching conditions is being done.
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