Content uploaded by Ata Akcil
Author content
All content in this area was uploaded by Ata Akcil on May 26, 2014
Content may be subject to copyright.
A preview of the PDF is not available
The Effect of Different Additives and Medium on the Bioleaching of Molybdenite for Cu and Mo Extraction Using Mix Mesophilic Microorganism
Abstract and Figures
Bioleaching processes for extraction of Cu and Mo from molybdenite cons. are more environmentally friendly and consume less energy than conventional technologies, yet less economically efficient. One necessary step towards arriving at a cost-effective bioleaching process is using appropriate methodology to optimize pertinent factors in such processes. To this end, the present study employed Response Surface Methodology to optimize important factors in a molybdenite bioleaching process by mix mesophilic microorganism using shake flasks. The effect of change in the levels of molybdenite concentration, pyrite and silver ion concentration as additives - in the range 3-9%, 1-5%, and 0-1.2gr/l, respectively - on the rate of Cu and Mo bioleaching was studied using a Central Composite Design. The results showed a statistically significant effect of silver ion and molybdenite concentration, and to a lesser pyrite concentration, on the rate of bioleaching of Cu and Mo. Further, different mediums and additives were evaluated for copper and molybdenum extraction from molybdenite concentrate in bioleaching process. Small amounts of silver (100mgr/l AgSO4) dramatically accelerated the copper dissolution process. Addition of FeS2 and sulfur with ferrous sulfate accelerated the acidification and raised the oxidation-reduction potential of solution (medium) with an inoculation of 15% (v/v) of active and adapted indigenous mesophilic bacteria, thus resulting in an overall increase in Mo dissolution efficiency.
Figures - uploaded by Ata Akcil
Author content
All figure content in this area was uploaded by Ata Akcil
Content may be subject to copyright.
... Recently, several bioleaching experiments have been carried out to evaluate the extraction of copper, molybdenum and rhenium from molybdenite concentrate. The results have indicated the successful removal of copper from Mo-concentrate within a short period of bioleaching using mesophilic and thermophilic (moderate and extreme) microorganisms; however, difficulties with low dissolution kinetics were observed for molybdenum and rhenium (Abdollahi et al., 2013a(Abdollahi et al., , 2013b(Abdollahi et al., , 2014(Abdollahi et al., , 2015. These experiments are essential in terms of expanding our knowledge and understanding such complex systems. ...
... Rhenium bearing minerals were neither detected by optical mineralogy nor instrumental techniques (XRD and SEM). Studies have shown that rhenium as elemental form is located within the molybdenite crystalline lattice (Abdollahi et al., 2013a(Abdollahi et al., , 2013b(Abdollahi et al., , 2014(Abdollahi et al., , 2015. ...
This paper presents the application of an artificial neural network (ANN) in order to predict the effects of operational parameters on the dissolution of Cu, Mo and Re from molybdenite concentrate through meso-acidophilic bioleaching. The initial pH, solid concentration, inoculum percent and time (days) were used as inputs to the network. The outputs of the models included the percent of Cu, Mo and Re recovered. The development and training of a feed-forward back-propagation artificial neural network (BPNN) was used to model and predict their recoveries. 105 sets of data were used to develop the neural network architecture and train it. To reach the network with highest generalizability, the space of neural networks with different hidden layers (one up to three hidden layers) and with the varying number of neurons each layer were searched. As a result, it was found that (4-5-5-2-1); (4-7-5-2-1) and (4-7-1-1-1) arrangements could give the most accurate prediction for Cu, Mo and Re extraction respectively. The regression analysis of the models tested gave a good correlation coefficient of 0.99968, 0.99617 and 0.99768 respectively for Cu, Mo and Re recoveries. The results demonstrated that ANN has a good potential to predict Cu, Mo and Re recoveries. Also, genetic algorithm (GA) was used to find out the optimum levels of parameters in the best models defined by ANN. The maximum recovery of Cu, Mo and Re on the 30th day were nearly 73%, 2.8% and 27.17% respectively.
The supply of metals is increasingly challenged by high demand for raw materials and the depletion of high-grade ore deposits. In addition, the management of tailings from metal processing remains a persistent problem in the mining sector. This study aims to characterize stibnite tailings and develop a hydrometallurgical process for the recovery of antimony, arsenic, and iron and the removal of sulfide minerals from these tailings. The main minerals identified were stibnite, pyrite, and a small amount of arsenopyrite, together with associated gangue minerals such as quartz and muscovite. Optimum conditions were set as follows: 4.4 M HCl, 0.5 M NaNO3, 25 % pulp density, 70 °C temperature, and 1-hour leach time. Under these conditions, flask leaching tests achieved remarkable leaching efficiencies of 99.88 % for Sb, 99.90 % for As, and 99.95 % for Fe. Bench scale experiments (1L reactor) showed high leaching efficiencies of 99.70 % for Sb, 97.50 % for As, and 97.00 % for Fe. Finally, leaching efficiencies of 98.30 % for Sb, 92.00 % for As, and 98.00 % for Fe were successfully achieved in semi-pilot tests (10 L reactor).
In this research, purification of molybdenite concentrate (MoS2) using a nitric acid leaching process was employed for the improvement of molybdenum trioxide morphology during oxidative roasting in an air atmosphere. These experiments were performed using 19 trials designed with response surface methodology and three effective parameters being temperature, time, and acid molarity. It was found that the leaching process reduced the chalcopyrite content in the concentrate by more than 95%. The influence of chalcopyrite elimination and roasting temperature on the morphology and fiber growth of the MoO3 was also investigated by SEM images. Copper plays an important role in controlling the morphology of MoO3 and its decrease led to enhancing the length of quasi-rectangular microfibers from less than 30 μm for impure MoO3 up to several centimeters for purified MoO3.
The copper extraction in shaking bioreactors was modeled and optimized using response surface methodology (RSM). Influential parameters in the mesophilic bioleaching process of a low-grade copper ore including pH value, pulp density, and initial concentration of ferrous ions were comprehensively studied. The effect of leaching time on the response (copper extraction) at the 1st, 4th, 9th, 14th and 22nd days of treatment was modeled and examined. The central composite design methodology (CCD) was used as the design matrix to predict the optimal level of these parameters. Then, the model equation at the 22nd day was optimized using the quadratic programming (QP) to maximize the total copper extraction within the studied experimental range. Under the optimal condition (initial pH value of 2.0, pulp density of 1.59%, and initial concentration of ferrous ions of 0 g/L), the total copper extraction predicted by the model is 85.98% which is significantly close to that obtained from the experiment (84.57%). The results show that RSM could be useful to predict the maximum copper extraction from a low-grade ore and investigate the effects of variables on the final response. Besides, a couple of statistically significant interactions are derived between pH value and pulp density as well as pH value and initial ferrous ion concentration which are precisely interpreted. However, there is no statistically significant interaction between the initial ferrous ion concentration and the pulp density. Additionally, the response at optimal levels of pH value and pulp density is found to be independent on the level of initial ferrous concentration.
Bioleaching of the copper flue dust emanating from smelters at Sarcheshmeh Copper Complex (Iran) has been studied. At present, the dust is recycled to the smelters which reduces their efficiency and increases the required energy for their smelting. In this study, a continuous system including a feed tank and two-stage aerated stirred tank bioreactors, each with a worked volume of 2.1 L was established. Mixed mesophile bacteria with different amounts of the dust containing 35% (w/w) of copper mainly in the form of sulfide minerals were used. The effects of pulp densities and residence times on the final copper recovery and redox potential were experienced. Despite of the oxidation of sulfide minerals (especially pyrite) in copper concentrates that produces acid, the process of dust bio-treating was net acid consuming. Lower pulp densities (2% w/v and 4% w/v) resulted in a stable redox potential in both reactors. However, increasing the pulp density to 7% (w/v) created an unstable redox potential in the first bioreactor. Final copper recoveries were calculated for pulp densities of 2%, 4% and 7% (w/v), were 89.7%, 90.3% and 86.8% with residence times of 2.7, 4 and 6 days, respectively. The promising results indicated that bioleaching is a feasible process that can be applied to copper flue dusts.
While various robust and general empirical hydrocyclone models have been developed, the modelling of a specific hydrocyclone operation is often required. This paper reviews and compares various experimental design techniques for process modelling on the basis of their rigour, amount of testwork required and ease of implementation. This investigation aims to present a direct, objective comparison of practical experimental design techniques for process modelling.
A number of techniques may be used to find, or the interaction between, and the magnitudes of, the effect of variables. Three experimental design techniques are commonly used for process analysis and modelling, namely, the full factorial, partial factorial and centrally composite rotatable (CCRD) designs. These are described and compared.
It is concluded that the use of the CCRD technique can lead to significant savings in experimental effort. The method is simple to use and yields results in a form that is directly implementable as a quadratic model.
A practical example of the technique is given, as applied to an experimental programme for the evaluation of the effect of three hydrocyclone variables, namely vortex finder diameter, spigot diameter and feed pressure on underflow recovery, % solids and feed rate.
It is known that silver ions accelerate the dissolution of copper in the bacterial leaching of chalcopyrite. The enhancement effect of silver ions is attributed to the formation of silver sulfide on the surface of chalcopyrite. The presence of chloride ions would affect the enhancement effect of silver ions because silver ions precipitate as silver chloride with chloride ions. The purpose of this work was to study the effect of chloride ions on the bacterial leaching of flotation concentrates of chalcopyrite and sphalerite using Thiobacillus ferrooxidans with the addition of silver ions. Results obtained are summarized as follow, (1) The addition of up to 100mg/l chloride ions enhanced the bacterial leaching of copper from a chalcopyrite flotation concentrate at the initial silver concentration of 50mg/l. The copper dissolution was accelerated with the addition of silver chloride powder.(2) The yield of zinc from a sphalerite flotation concentrate after the bacterial leaching of 20 days decreased with increase in the initial silver concentration. The addition of silver ions hindered the oxidation of sphalerite with ferric ions. Chloride ions weakened the negative effect of silver ions on the bacterial leaching of sphalerite.
“Cats is dogs and dogs is dogs and rabbits is dogs, and squirrels in cages is parrots ….”
Mixed mesophilic and extreme thermophilic bioleaching were evaluated to remove copper from the molybdenite concentrate. Bioleaching tests were carried out in shake flasks and in a 50-L bioreactor. The shake flask tests were performed with different inoculum size, solids density, pH, and temperature in order to identify optimum conditions. The highest amount of copper elimination, 75% was obtained with extreme thermophilic microorganisms (at 12% inoculation, 10% solids, 65 °C and a pH of 1.5). The highest copper elimination by mesophilic microorganisms was 55% (at 12% inoculation, 5% solids, 30 °C at pH 2). The optimum conditions in shake flask tests were applied to 7 days batch tests in a 50-L bioreactor. Extreme thermophilic experiment gave the best copper elimination of 60% (at 12% inoculation, 10% solids, 65 °C and pH 1.5). Mesophilic test removed 50% of the copper (at 12% inoculation, 10% solids, 35 °C at pH 2).