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The Study of a Novel Process on Extraction of Molybdenum from Ni-Mo Ores Calcine

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Tutor: XiaoLianSheng
School: Central South University
Course: Non-ferrous metallurgy
Keywords: Ni-Mo ore,Ammonium molybdate,High pressureleaching,Solvent extraction
CLC: TF841.2
Type: Master's thesis
Year:  2013
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A novel process to treat calcine of Ni-Mo ore from Zunyi (Guizhou province) with high efficiency, environmental friendlyness and low cost was developed in the paper, including caustic leaching of calcine followed by direct extraction of molybdenum from the leach solution using extractant of TOMAC to obtain pure ammonium molybdate solution. The process exhibits advantages of simple flowsheet, low consumption of reagent, low discharge of wastewater, which can be easily applied in industry.The research and results are mainly concluded as follows:1. Caustic leaching of calcineThe result of atmospheric pressure leaching of calcine showed that the leaching of molybdenum was only87.4%under the optimal conditions, leaving1%of molybdenum still in the leach residue. Thus, the high pressure leaching was employed to increase the leaching of molybdenum. The results revealed that the leaching of molybdenum reached95.8%with soda/ore mass ratio of30%and L/S ratio of2/1at170℃for90min, leaving0.296%of molybdenum in the leach residue.To restrain the leaching of impurities such as phosphorus, arsenic and silicon during the high pressure leaching, the types and amounts of additives, soda dosage and leaching temperature were investigated. The leaching of molybdenum reached95.9%with soda/ore and magnesium oxide/ore mass ratio of30%and2.5%, respectively, and L/S ratio2:1at160℃for90min, while the concentration of molybdenum, phosphorus, arsenic and silicon in the leach solution were10.69g/L,0.18g/L,0.32g/L and0.48g/L, respectively. The separation coefficient of silicon over molybdenum was25and the crude separation of molybdenum over main impurities achieved, which alleviated the burden of impurity removal in subsequent step of solvent extraction. The pro had great value in industrial application.2. Direct solvent extraction of molybdenum from the caustic leach solution The organic solution consisting of350g/L TOMAC and25%ec-caprylic acohol in sulphated kerosene has to be transformed into carbonate type before extraction. Given consideration of feed concentration and the saturated capacity of TOMAC on molybdenum, the extraction of molybdenum reached98.7%with a phase ratio1:2after five stages of counter-current extraction, leaving0.1g/L Mo,0.16g/L P,0.25g/L As and0.28g/L SiO2in the raffinate, resulting in removal of impurities of88.9%P,89.3%As and71.8%Si, respectively. The small amount of impurities entered into the organic phase can be easily scrubbed using deionized water before stripping. The mechanism of extraction of molybdenum by quaternary amine salt proved by slope ratio method can be expressed below: The stripping of molybdenum from loaded organic reached95.8%using2.84mol/L NH4HCO3at O/A=2/1and15counter-current stage, the concentration of molybdenum, phosphorus, arsenic and silicon in the strip liquor were34.5g/L,0.0066g/L,0.025g/L and0.39g/L, resulting in the concentration ratio of P/Mo, As/Mo and Si/Mo of0.00019,0.00071and0.011, respectively. The total removal of phosphorus, arsenic and silicon reached99.15%,97.97%and77.39%during the process of extraction-stripping, respectively, indicating that the main impurities of P, As and Si can be effectively removed.The stripped organic can be regenerated using NaOH solution for recycling use. The experimental results showed that the extraction effect of organic phase after regeneration was good when NaOH dosage was1~1.25times of the theoretical calculation. The increase of phase ratio in regeneration resulted in better phase separation.The raffinate can be returned to the leaching step after the supplement of soda. The results indicated that the accumulated ion of SO42-has little effect on the leaching of molybdenum, phosphorus, arsenic and silicon when its concentration below90g/L. The simulative model presented the ultimate concentration of SO42-was no more than58g/L, which made it possible for the recycling of aqueous phase.The novel process of soda high-pressure leaching of Ni-Mo ore calcine followed by direct extraction of molybdenum from the leach solution exhibited advantages of simple flowsheet, high recovery of molybdenum, low consumption of reagent and low discharge of wastewater. The raffinate can be returned to leaching step. In addition, the alkiline system means low requirement of anti-corrosion. Application of this process is expected to make an important impact on the extraction of molybdenum from the caustic leach solution and to deliver good economical benefits.
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