Thermodynamic Behavior Of Typical Impurity Elements During Roasting Of Molybdenum Concentrate

Many impurity elements in molybdenum concentrate have great harm to product quality.In recent years,molybdenum processing enterprises have been forbidden to remove impurities by pickling in the production process,and the impurity elements are mainly removed by washing molybdenum calcine,so it is necessary to study the soluble transformation mechanism of impurity elements in the roasting process.In this paper,by studying the change of the occurrence form of impurity elements in the roasting process,the specific chemical reaction of impurity minerals into soluble ions and the influence of molybdenum concentrate particle size on the removal of impurity elements in the whole production process were explored.The industrial process of producing ammonium molybdate from molybdenum concentrate involves four solid samples:molybdenum concentrate,molybdenum calcine,molybdenum calcine after washing and ammonia leaching residue.The impurity minerals in four samples were quantitatively analyzed by mineral dissociation analyzer（MLA）,and the reaction process of impurity minerals in molybdenum concentrate roasting was thermodynamic analyzed by Fact Sage 7.0 software.Molybdenum concentrate was divided into coarse molybdenum concentrate of 75～106μm and fine molybdenum concentrate of 48～75μm.Molybdenum concentrate of different particle size was treated by simulating the industrial production steps of ammonium molybdate to obtain the corresponding two groups of products.The contents of main impurity elements in different products were analyzed by X-ray fluorescence spectrometer（XRF）and inductively coupled plasma spectrometer（ICP）.The results show that:（1）the particle size of molybdenum concentrate ranges from1 to 300μm,and the particle size is mainly concentrated in about 100μm.（2）The reaction rate of the roasting process at 500℃,550℃and 600℃is mainly affected by the internal diffusion process,and the reaction rate increases first and then decreases.Increasing the temperature can accelerate the oxidation rate of molybdenum concentrate,and it is also conducive to promoting the internal diffusion rate of gas.（3）Grinding molybdenum calcine can increase the contact area between the leachable component and the leaching solution,which is conducive to the removal of impurity elements in the washing process and the formation of ammonium molybdate in the ammonia leaching process.（4）Typical impurity elements in molybdenum concentrate are mainly in the form of large molecular weight potassium-containing minerals and other minerals,such as FeS₂,CaSO₄,SiO₂,etc.These impurity minerals form sintered blocks during the roasting process and affect the leaching of Mo and K.（5）Potassium in molybdenum concentrate mainly comes from Muscovite and feldspar,during the roasting process,the H₂SO₄ formed by the water formed by mineral dehydration and the baking gas product SO₂ can promote the conversion of potassium minerals into soluble ions,and the humidification of the atmosphere during the roasting process is conducive to promoting the soluble conversion of potassium-containing minerals and other alkaline minerals.（6）The particle size of molybdenum concentrate affects the behavior of impurity minerals in the roasting process,and has a negative effect on the leaching of soluble components in the ammonia leaching process.Compared with the crude molybdenum concentrate,the fine molybdenum concentrate is easier to form a dense sintered block with impurities such as FeS₂,CaSO₄and SiO₂,and the MoO₃ inside the particles cannot be in contact with ammonia,thus reducing the leaching of Mo.Therefore,reasonable control of molybdenum concentrate particle size and roasting conditions can not only increase the conversion of impurity silicate minerals to soluble ions,but also increase the leaching rate of Mo in the ammonia leaching process.