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Study on Leaching of Nickel-molybdenum Sulfide Ore with Thermophilic Sulfolobus Metallicus

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Tutor: GaoCong
School: Central South University
Course: Non-ferrous metallurgy
Keywords: sulfolobus metallics,nickel-molybdnum sulfide ore,molybdenite,bioleaching,membra
Type: PhD thesis
Year:  2012
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The traditional metallurgical methods for nickel-molybdenum sulfide ore (jordisite) with several metal and various mineral components including carbon was roasting at high temperature. However, roasting not only is energy intensive,, but also brings serious pollution. Futhermore, traditional roasting results in huge waste of natural resource. Great effort has been made in the application chemical method, but with limited achievement-It is also found to be a high-cost approach. In past decade, application of bio-metallurgical technology in the extraction of sulphide ore raises much attention. It has been successfully employed in the metallurgy of many metallic sulphide (e.g. copper sulfide) and mass production has been actualized in some fields. Regarding bioleahcing of molybdenum mineral, a lot of exploratory researches have been conducted. Nevertheless,most of them focused on ordinary bacterias such as Thiobacillus ferrooxidans.Investigation demonstrated that the toxic inhibition of Molybdenum toward ordinary bacterias result in very low bioleaching efficiency. In view of this situation, sulfolobus metallicus, a type of acidophilic thermophile microorganins that can tolerate the toxicity of molybdenum to some degree. Bioleaching in shaking flasks and in membrane reactor combined with ion-exchange was studied. The following results were obtainedThe experimental results showed that sulfolobus metallicus, as the leaching bacteria, has strong ability to oxidize the ferrous component as well as convert S0into sulphuric acid (H2SO4). After cultivation, this type of microorganism could endure up to400mg/L of molybdenum and950mg/L of nickel. Therefore, sulfolobus metallicus was a good candidate for leaching nickel-molybdenum ore known as Mo-S-C composite.There was marked difference in the leaching rate of Ni and Mo between the leaching with and without sulfolobus metallicus;the latter was91.78%and65.98%respectively,while the former was just77.64%and50.19%. The microorganism existing on the partical surface played an important role in the bioleaching process, which was proved by other experiments including the scanning electron microscope (SEM)analysis of the surface of particles subjected to the leaching process. For the leaching with sulfolobus metallics, a lot of corroded holes were observed on the surface of the mineral particles; while especially smooth surface was observed with the particles in the leaching as control.Furthermore, there were a lot of microorganisms absorbed on the surface of the mineral particle in the former group. The bioleaching rate of Ni and Mo was distinctly improved after the strain was acclimated and induced.In addition, the leaching comparision showed that the leaching rate of Ni and Mo with sulfolobus metallicus was higher than the Thiobacillus ferrooxidans.when dialysis bag was put between the mineral and microorganism, the leaching rate of Ni and Mo was75.86%and54.69%,which were low than that of the control group without dialysis bag(95.30%and63.46%in this group). The possible reason is that S0on the surface of the mineral particle was continuously oxidized into H2SO4by sulfolobus metallicus and the S0membrane as the barrier between the mineral particle and leaching liquid was removed. Another important role of sulfolobus metallicus was to oxidize Fe2+into Fe3+that act as lixiviant for the solubilization of nickel andmolybdenum from sulfide ore.Inspite of its critical role, higher Fe3+concentration does not necessarily lead to more efficient leaching of Ni and Mo. The leaching rate did not increase when Fe3+concentration reached4.0g/L. It is concluded that the leahcing rate of Ni and Mo is influenced not only by the concentration of Fe3+but also by other factors including electric potential and primary battery effect of the metal ion in nickel-molybdenum sulfide ore. Due to its low electric potential and battery effect compared with the other metal ions such as copper in nickel-molybdenum sulfide ore molybdenum at negative pole is protected and its leaching rate was low.The impact of mineral density, pH, mineral particle and inoculation on the bioleaching rate of Ni and Mo were obviously. Mineral density was inverse relation to the leaching rate, and there was the best leaching rate of Ni and Mo,which reached99.97%and85.29%respectively under the condition of5g·L-1mineral density and initial pH=2. In addition, the less mineral particle,the more the leaching rate of Ni and Mo at the same mineral density. The experiment also revealed that the10%inoculation was the best favorable bioleaching among several group of the different inoculation.The bad result of the bioleaching on MoS2with sulfolobus metallicus reflected that there was different structure and component between nickel-molybdenum sulfide ore and MoS2so that the Mo was leached out in different leaching rate,in which the special structure of ore of C-Ni-Mo-S was further revealed.The bioleaching of nickel-molybdenum sulfide ore in MBR showed that ultra-filter could put the concentration of Mo under control by filter at regular intervals. When the concentration of Mo in MBR with sulfolobus metallicus was controlled near and under395mg/L,the leaching rate of Ni and Mo was79.57%and56.23%respectively,which reached the best among all group and exceeded the group of column leaching. The leaching rate of Ni and Mo in others group including the group of Mo<160mg/L,<250mg/L,<300mg/L,<350mg/L were all less than the group of Mo<395mg/L since a lot of Fe3+was carried away when the leaching liquid was filtered out.Therefore, Both the concentration of Mo and loss of Fe3+in the leaching liquid should be considered in MBR with sulfolobus metallicus.While the membrane was necessary in order to reach such a tuation.Otherwise,the concentration of Mo in leaching liquid will be rise till restrain the growth of micorganism.This paper used MBR conbined ion-exchange in order both to control Mo and to avoid the loss of Fe3+and retrieve the leaching liquid being exchanged.But Fe3+in leaching liquid was still partly absorbed and exchanged by resin so that the leaching rate of Ni and Mo was decreased by the loss of Fe3+when the excessive leaching liquid was filtered and exchanged. The leaching rate of Ni and Mo in the group which10%of the leaching liquid was filtered and exchanged was79.53%and56.52%which was the climax among all group including 35%and18%of leaching liquid being filtered and exchanged.lt will be favorable to MBR conbined ion-exchanged for the bioleachng of nickel-molybdenum sulfide ore especially with ordinary microorganism if a resin could be made for exclussive Mo absorption.At last, dynamics was studied according to the change of Fe3+/Fe2+and the concentration change of Ni and Mo in process of bioleaching.At the same time, themodynamics analyse was made through the drawing of Ni,Mo-S-H2O pH-E.The study mentioned above will play an important role in sustainable development of metallurgical industry at low degree mineral resource.
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