References of "Gaydardzhiev, Stoyan"
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See detailCOPPER LEACHING FROM WASTE ELECTRIC CABLES BY BIOHYDROMETALLURGY
Lambert, Fanny ULg; Bastin, David ULg; Gaydardzhiev, Stoyan ULg et al

in Minerals Engineering (2015)

This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption ... [more ▼]

This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption. Operational parameters such as the nature of the oxidant (Fe3+, O2), the initial ferric iron concentration (0-10 g/L) and the temperature (21-50°C) were identified to have an important influence on the degree of copper solubilisation. At optimal process conditions, copper extraction above 90% was achieved in both leaching systems, with a leaching duration of 1 day. The bacterial leaching system slightly outperformed the chemical one but the positive effect of regeneration of Fe3+ was limited. It appears that the Fe2+ bio-oxidation is not sufficiently optimised. Best results in terms of copper solubilisation kinetics were obtained for the abiotic test at 50°C and for the biotic test at 35°C. Moreover, the study showed that in same operating conditions, a lower acid consumption was recorded for the biotic test than for the abiotic test. [less ▲]

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See detailSEM and EDS observations of carrollite bioleaching with a mixed culture of acidophilic bacteria
Nkulu, Guy; Gaydardzhiev, Stoyan ULg; Mwema, Edouard et al

in Minerals Engineering (2015), doi:10.1016/j.mineng.2014.12.005

Bioleaching of high purity carrollite minerals with mesophilic bacteria was carried out and monitored by observations in scanning electron microscopy (SEM) and elemental X-ray microanalysis (EDS) to ... [more ▼]

Bioleaching of high purity carrollite minerals with mesophilic bacteria was carried out and monitored by observations in scanning electron microscopy (SEM) and elemental X-ray microanalysis (EDS) to provide evidence of the interaction pattern between carrollite and microorganisms. A bacterial consortium involving three different acidophilic chemolithotrophs was adopted. The evolution of the surface topography, inside alteration effects and elemental composition of the mineral with leaching time was followed. It could be postulated that bacterial adhesion takes place on the mineral surface, resulting in the formation of dissolution pits of various shapes and continues by boring elongated channels deep inside the mineral grains. Enhanced concentration of ferric iron and sulphur could be assumed in vicinity of the zones where mineralized polymer substances are precipitated. It could be inferred that carrollite dissolution is governed by cooperative bioleaching involving oxidation induced by bacteria attached to the surface and ferric iron re-oxidized by planktonic bacteria in suspension. [less ▲]

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See detailPossibilities for Co(III) dissolution from an oxidized ore through simultaneous bioleaching of pyrite
Zeka, Leon; Lambert, Fanny ULg; Frenay, Jean ULg et al

in Minerals Engineering (2015)

Solubilisation of Co(III) from a heterogenite met in copper cobaltiferous oxide ore has been realized through reductive leaching using ferrous iron generated via bio-oxidation of pyrite. Biotic and ... [more ▼]

Solubilisation of Co(III) from a heterogenite met in copper cobaltiferous oxide ore has been realized through reductive leaching using ferrous iron generated via bio-oxidation of pyrite. Biotic and abiotic experiments at various pulp densities and redox potentials have been performed and results compared. Cobalt leaching at elevated redox potential is possible, offering cost reduction benefits due to reduced consumption of ferrous iron. At elevated potential of 625 mV, however, the initial rate of cobalt leaching has been found as 115 mg/(g ore)⋅(24 h), lower than the rate of 865 mg/(g ore)⋅(24 h) registered at 505 mV. Less stochiometric amount of ferrous iron was required when cobalt leaching was coupled to pyrite bioleaching, with 75% of cobalt recovered for 12 h at the optimally found conditions. It could be inferred that the Fe3+–Fe2+ cycle exists and is efficiently maintained through bacterial presence in the studied system. [less ▲]

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See detailPhysicochemical observations during process water reuse in flotation of oxide copper-cobalt ore
Shengo, Michel; Gaydardzhiev, Stoyan ULg; Kalenga, Pierre

in Yianatos, Juan (Ed.) Proceedings of the XXVII International Mineral Processing Congress (2014, October 20)

Lab-scale flotation of copper and cobalt oxidized ore from the Luiswishi deposit in the Katanga province (DRC) has been done focusing on the influence of the degree of process water recycling on metals ... [more ▼]

Lab-scale flotation of copper and cobalt oxidized ore from the Luiswishi deposit in the Katanga province (DRC) has been done focusing on the influence of the degree of process water recycling on metals recovery. Results have shown that at 20 % recycling rate, the recovery of copper and cobalt in the cleaner stage have been respectively reduced to 23 % and 45 % in comparison to 53 % Cu and 63 % Co if process water has not been recycled. At 10 % recycling rate however, the system could still tolerate the effect from recycling, since Cu and Co recovery has remained respectively at acceptable levels of 52 % and 60 %. In order to explain the reasons for the observed worsening of flotation results if process water was recycled at rate higher than 20 %, electrochemical investigation of the pulp has been performed. It has been established that the chemical compounds formed in the pulp when process water was recycled, do influence the sulfidization of malachite and heterogenite and impact further collector adsorption. To confirm these assumptions, the effect from thiosulphate ions presence during the sulfidization of high purity malachite has been studied. It has been found, that thiosulphate ions depending on their concentration in water induce variations in pulp properties such as DO content, pH, Es and contribute to formation of undesirable chemical compounds on mineral surface as identified by DRIFT spectroscopy. [less ▲]

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See detailInsights upon the adsorption mechanism of KAX on malachite
Kanda, Jean-Marie; Kongolo, Mukendi; Gaydardzhiev, Stoyan ULg et al

in Yianatos, Juan (Ed.) Proceedings of the XXVII International Mineral Processing Congress (2014, October 20)

The adsorption patterns of potassium amylxanthate on the surface of high purity malachite subjected to prior sulfidization with NaSH have been followed and elucidated. DRIFTS spectroscopy has been used to ... [more ▼]

The adsorption patterns of potassium amylxanthate on the surface of high purity malachite subjected to prior sulfidization with NaSH have been followed and elucidated. DRIFTS spectroscopy has been used to trace the associated physicochemical alterations as well as the chemical species present on the mineral surface. Varying the collector concentration from 5.10-4 to 1.10-2 mol/L has led to different degree of surface coverage of the alkyl groups in combination with formation of organometallic hydrophobic complexes of CuX and CuX – X2 type. The results reveal that the CuX complex formed on the malachite surface without sulfidizing agent is more unstable and prone to dissolution-precipitation phenomena. Based upon the constructed adsorption isotherms and upon the degree of statistical coverage, different zones of mineral-reagent interactions could be distinguished. They correspond respectively to the monolayer, bi-layer and tridimensional condensation domains. In each of the identified zones mono or double layer adsorption patterns of the collector are proposed leading respectively to formation of surface compounds with different degree of hydrophobicity. [less ▲]

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See detailAssessment of water quality effects on flotation of copper-cobalt oxide ore
Shengo, Michel; Gaydardzhiev, Stoyan ULg; Kalenga, Pierre

in Minerals Engineering (2014), 65

Results from lab scale flotation show that when process water was re-used copper and cobalt recovery from an oxidized ore decreased respectively with 25 and 30 percent at the rougher stage bringing lower ... [more ▼]

Results from lab scale flotation show that when process water was re-used copper and cobalt recovery from an oxidized ore decreased respectively with 25 and 30 percent at the rougher stage bringing lower grade concentrate as well. The presence of thiosulphate ions contributed to slow down of NaHS consumption during sulphidization of pure malachite and hindered collector adsorption. Elevated concentration of thiosulphate ions affected malachite surface properties and induced dissolution effects. DRIFT spectroscopy on activated malachite enabled to reveal the effects of thiosulphate ions presence with hydrophilic species being identified. [less ▲]

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See detailCharacterization of printed circuit boards from scrap printers
Silvas, Flávia; de Moraes, Viviane; Bortolini, Guilherme et al

in Yurko, James; Zhang, Lifeng; Allanore, Antoine (Eds.) Proceedings TMS 2014 143rd ANNUAL MEETING & EXHIBITION (2014, April)

Printed circuit boards (PCB) are particularly problematic to recycle because of the heterogeneous mix of organic materials, metals, and glass fiber. PCBs are found in almost every electroelectronic ... [more ▼]

Printed circuit boards (PCB) are particularly problematic to recycle because of the heterogeneous mix of organic materials, metals, and glass fiber. PCBs are found in almost every electroelectronic equipment and their recycling process involves a pre-treatment to separate the products which contain targeted metals. In this work, a physical processing involving sequential shredding and hammer milling were used to obtain a comminuted sample from scrap printers PCBs. The thus prepared sample was analyzed for particle size distribution and by optical microscopy as well was subjected to pyrolysis, leachabilty and chemical composition determination by XRF. The metals concentration was determined by ICP and AAS. The PCBs have been also analyzed by SEM-EDS (micro-analysis and X-ray mapping). The results show that the studied PCBs are lead free, multilayer with 4 copper layers, have 45% of metals and the copper is present in significantly higher concentration than the rest of the metals. [less ▲]

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See detailBiolixiviação de cobre contido em placas de circuito impresso (pci) com micro-organismos mesófilos.
Rodrigues, M; Gaydardzhiev, Stoyan ULg; Lopes, K et al

in Silva, André Carlos; Silva, Elenice Maria Schons (Eds.) ANAIS PROCEEDINGS (2013, October)

This work investigated the bioleaching of electronic waste, specifically printed circuit boards (PCB). The bio-assisted leaching was carried out with At. ferrooxidans in shake flasks in order to evaluate ... [more ▼]

This work investigated the bioleaching of electronic waste, specifically printed circuit boards (PCB). The bio-assisted leaching was carried out with At. ferrooxidans in shake flasks in order to evaluate the influence of presence of microorganisms on the dissolution of metallic copper. The effects of the initial Fe2+ concentration and the presence of pyrite, as a source of iron, on copper dissolution were analyzed. The experiments were performed in an orbital shaker under the following conditions: 34°C, stirring speed of 150 min-1, particle size below 420μm and 0.5% solids percent (w/v). The results indicated high extraction, around 100%, and proved the feasibility of copper recovering from PCB through bioleaching. [less ▲]

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See detailThe influence of grinding media alloys on the flotation performances at Ellatsite plant (Bulgaria)
Bastin, David ULg; Gaydardzhiev, Stoyan ULg; Jacques, Simon et al

in Proceedings of the XV Balkan Mineral Processing Congress (2013, June)

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See detailOverview of technologies for mineral/metal recuperation – challenges and technological gaps
Gaydardzhiev, Stoyan ULg

Conference given outside the academic context (2013)

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See detailAmenability for processing of oolitic iron ore concentrate for phosphorus removal
Ionkov, Krassimir ULg; Gaydardzhiev, Stoyan ULg; Correa de Araujo, Armando et al

in Minerals Engineering (2013), 46-47

Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic concentrate and involving a combination of roasting, re-grinding, magnetic separation and water and acid leaching are ... [more ▼]

Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic concentrate and involving a combination of roasting, re-grinding, magnetic separation and water and acid leaching are investigated. Roasting was carried out at 900ºC for one hour without or with lime or sodium hydroxide as roasting additives. When additives were used, cement phases of Si-Al-Na-Ca-O type were detected as well as the mineral giuseppettite. During the thermal process sodium silicate is liquefied and the newly formed phases coat the oolites and penetrate inside the cracks. Energy Dispersive Spectroscopy analysis has indicated that the zone surrounding the oolites consists of Na, Al and Si phases with part of phosphorus being captured there. As a result of the alkaline roasting, goethite is partly transformed to magnetite and this reduction is reinforced with an increase in sodium hydroxide dosage. Investigation of redistribution of phosphorous shows that it could be only partly separated if leaching is not accompanied by re-grinding and physical separation. The recommended dosage of the reductive agent for the final flowsheet is 8 % mass ratio to concentrate. Grinding to a mean size of 0.040 mm, with water and acid leaching and double magnetic separation creates conditions to obtain a high-quality iron concentrate with 65.97 % Fe and recovery of 92.43 %, with simultaneous decrease in the phosphorus content from 0.71 % to 0.05 %. [less ▲]

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See detailClean Coal Technologies and Carbon Capture and Storage in Kazakhstan – Reflections and ACCESS project results
Nesladek,, Milos; Helsen, S; Piessens, Kris et al

Book published by Royal Belgian Institute of Natural Sciences (2013)

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See detailStatistical analysis of bioleaching copper, cobalt and nickel from polymetalic concentrate originating from Kamoya deposit in the Democratic Republic of Congo
Nkulu, Guy; Gaydardzhiev, Stoyan ULg; Mwema, Edouard

in Minerals Engineering (2013), 48

The effects of five parameters, temperature, pH, leaching duration, stirring speed and pulp density on the bioleaching of copper, cobalt and nickel from a polymetallic flotation concentrate were ... [more ▼]

The effects of five parameters, temperature, pH, leaching duration, stirring speed and pulp density on the bioleaching of copper, cobalt and nickel from a polymetallic flotation concentrate were investigated. The leaching was carried out according to the L25 (55) orthogonal design. The optimal values of the parameters were determined using a Taguchi method through signal-to-noise analysis. ANOVA was applied to verify the individual contribution of each parameter and their degree of significance. It was found out that pulp density was the most influential factor on the bioleaching yield of the three metals altogether, followed by pH and temperature. For the copper bioleach, the following optimal parameters were determined: temperature - 37.5 °C, pH 1.6, leaching duration - 20 days, stirring speed - 350 rpm and pulp density - 7.5%. Verification experiments conducted according to these optimal parameters brought copper yield of 72.6%. For the cobalt bioleach, SEM observations of pure carrollite indicated a progressive bacterial colonization of mineral surface with time. [less ▲]

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See detailPotential for application of alkali roast acid leach technology for removal of phosphorus from iron ore
Ionkov, Krassimir ULg; Gaydardzhiev, Stoyan ULg; Bastin, David ULg et al

in Proceedings of 6-th International Congress on the Science and Technology of Ironmaking ICSTI (2012, October)

The present study deals with the effect of sodium hydroxide and sodium carbonate used as additives during oxidizing roasting of oolitic limonite iron concentrate and more precisely upon the change in its ... [more ▼]

The present study deals with the effect of sodium hydroxide and sodium carbonate used as additives during oxidizing roasting of oolitic limonite iron concentrate and more precisely upon the change in its magnetic susceptibility. Further, the efficiency of Alkali Roast Acid Leach (ARAL) technology for dephosphorisation of the concentrate is compared with the case when sodium hydroxide was added in alkali leach after roasting. The treatment without additives in roasting resulted in obtaining iron concentrate with 58 % iron and 0.21 % phosphorus, while the ARAL approach yielded concentrate with 63 % iron and 0.09 % phosphorus. The influence of combination of coke as reducing agent and sodium hydroxide in roasting at 900°C is also investigated and results displayed in 3D form. The combination of ARAL with reductive roasting, grinding of the clinker to 80 % - 0,075 mm, flotation of the non-reacted coke and magnetic separation before and after the acid leach resulted in iron concentrate with 66 % iron and 0.05 % phosphorus. The study has shown that the application of the ARAL approach with low addition of alkalis followed by 10 to 15 minute acid leaching at ambient temperature could substantially reduce phosphorus, thus offering the possibility for efficient treatment of high phosphorus iron ores. [less ▲]

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See detailRemoval of phosphorous through roasting of oolitic iron ore with alkaline earth additives
Ionkov, Krassimir ULg; Gaydardzhiev, Stoyan ULg; Bastin, David ULg et al

in Proceedings of the XXVI International Mineral Processing Congress (2012, September)

The present study is devoted to improvement of the leaching efficiency during phosphorous removal from high phosphorous gravity-magnetic concentrate. Before leaching the concentrate has been subjected to ... [more ▼]

The present study is devoted to improvement of the leaching efficiency during phosphorous removal from high phosphorous gravity-magnetic concentrate. Before leaching the concentrate has been subjected to roasting with the addition of either Ca(OH)2 or CaO. The oolitic iron ore is roasted at 900°C for one hour. This reflects in reaction between alkaline earth additive and quartz, aluminosilicates, phosphorus, and some other minor components of the gangue minerals. The application of leaching, physical separation, and wash out of salts has resulted in the decrease of phosphorus from 0.7 to 0.15 % and it is established that the major influencing factor is the concentration of acid and to a less extent duration of the leaching process. About two third of the phosphorus can be removed by roasting with 3 % CaO to hematite, coarse grinding to d50 0.3 mm, dry high intensity magnetic separation and leaching of the magnetic fraction with hydro-chloric or nitric acid. [less ▲]

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See detailInfluence of selected parameters on the flotation of Cu-Mo ore from Ellatzite deposit in Bulgaria
Gaydardzhiev, Stoyan ULg; Bouchat, Harold ULg; Dedelyanova, K et al

in Proceedings of the XXVI International Mineral Processing Congress (2012, September)

Laboratory batch tests having preliminary and orientation character aiming at improvement of the molybdenum flotation at Ellatzite copper processing plant in Bulgaria have been conducted. The following ... [more ▼]

Laboratory batch tests having preliminary and orientation character aiming at improvement of the molybdenum flotation at Ellatzite copper processing plant in Bulgaria have been conducted. The following technological parameters have been screened to study their influence on the grade and recovery of copper and molybdenum during the rougher flotation stage: flotation pulp density, pH, addition of secondary collector and replacement of MIBC by pine oil as a frother. The results have shown that slightly better grade/recovery figures could be obtained for both copper and molybdenum at lower flotation pulp densities. The addition of kerosene has improved the recovery of molybdenum however on the expense of that of copper. The effects from pH variation and the replacement of MIBC by pine oil as a frother have been almost negligible. [less ▲]

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See detailBio hydrometallurgical recovery of metals from Fine Shredder Residues
Lewis, Grégory ULg; Gaydardzhiev, Stoyan ULg; Bareel, Pierre-François et al

in Minerals Engineering (2011), Vol 24, Issue 11

The leaching step of an integrated hydrometallurgical process for the selective recovery of metals from polymetallic concentrates has been investigated. The concentrate has been produced by physical ... [more ▼]

The leaching step of an integrated hydrometallurgical process for the selective recovery of metals from polymetallic concentrates has been investigated. The concentrate has been produced by physical treatment of Fine Shredder Residues derived from a shredding plant processing a mixed feed. Bacterially assisted leaching experiments using a copper-adapted consortium of mesophilic bacterial strains have been carried out. Various technological parameters have been studied. Under optimal conditions about 95 % extraction levels for copper and zinc have been obtained. Bacterial presence has been found beneficial in view catalysing copper dissolution. [less ▲]

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See detailDEPHOSPHORIZATION OF LIMONITIC CONCENTRATE BY ROASTING, ACID LEACHING AND MAGNETIC SEPARATION
Ionkov, Krassimir ULg; Gaydardzhiev, Stoyan ULg; Corea de Araujo, Armando et al

in Holmes, M. (Ed.) Proceedings of the Iron Ore 2011 International Conference (2011, July)

The oolitic iron ore reserves in Lisakovsky, Northwest Kazakhstan represent a quite challenging deposit both from technological and from resource point of view. The difficulties in processing such type of ... [more ▼]

The oolitic iron ore reserves in Lisakovsky, Northwest Kazakhstan represent a quite challenging deposit both from technological and from resource point of view. The difficulties in processing such type of ore are connected with the extremely fine dissemination of phosphorus and gangue minerals inside the oolitic formations. The goethite crystals are cemented in their structure by aluminosilicates with quartz and other gangue minerals and dissemination is so fine that they are not separable by physical methods. The laboratory tests performed in direction of dephosphorisation have shown that the combination of alkaline roasting followed by low intensity magnetic separation and acid leaching enables the obtaining of high grade iron concentrate. The magnetic separation performed ahead of leaching has been efficient by means of buffering the high pH via washing out the soluble salts and the excess of bases and applied after leaching has facilitated the removal of secondary liberated gangue minerals in the non-magnetic fraction. As a consequence, phosphorous content has been dropped to a more acceptable for the ferrous metallurgy levels while iron grade and recovery have reached respectively 61.6 and 80.8 percent. [less ▲]

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