Novel Process Of Molybdenum Extraction From Ni-Mo Ore Based On Jiont Of Flotation And Smelting

Ni-Mo ore is a polymetallic mineral resource which is uniquely in China. Ni-Mo ore contains huge amounts of molybdenum and nickel with high economic value. Since the grades of Ni and Mo in the ore are relatively low, it causes higher costs of present metallurgical processes.In Central South University, scholars focused on the combined process of beneficiation and hydrometallurgy of Ni-Mo ore and realized the flotation of the ore successfully. After flotation, the grade of Mo and Ni was enriched and reached3times raw Ni-Mo ore. Besides, molybdenum oxide and molybdenum sulfide can be separated smoothly. In the Ni-Mo ore, about80%molybdenum entered into the molybdenum concentrate in the form molybdenum sulfide, while the rest of molybdenum went into talling being as molybdenum oxide. In this study, with the molybdenum concentrate as a raw material, a novel hydrometallurgical process was developed to prepare ammonium molybdate tetrahydrate.The research mainly focused on joint leaching of molybdenum concentrate, molybdenum extraction from the leaching solution with solvent extraction, arsenic removal from ammonium molybdate solution by chemical precipitation with magnesium salt, magnesium removal from the ammonium molybdate solution by ion exchange and crystallization of ammonium tetramolybdate by acidification. The final product meets the standard of GB/T3460-2007(ammonium polymolybdate). Compared with current treatment processes of Ni-Mo ore, this technology has lots of advantages such as higher valuable metal recovery, environmental-friendliness and lower production cost. Main results are as follows:Kinetics of atmospheric leaching molybdenum from the concentrate by air oxidation was studied. The results show that the leaching process consists of the following two stages. Within the initial20minutes, the leaching ratio of molybdenum reached to20%quickly. The leaching rate was not influenced obviously by temperature and the concentration of sodium hydroxide. At the second stage, the leaching rate of Molybdenum increased gradually with the increase of temperature and sodium hydroxide concentration. Moreover, different kinetic charcateristics of the leaching process was presented at different temperature ranges. When the temperature was below60℃, the leaching process was controlled by chemical reaction with the apparent activation energy of62.22kJ/mol and apparent reaction order of0.73. While the temperature was above60℃, the leaching process belongs to hybrid control with apparent activation energy of62.22kJ/mol and apparent reaction order of0.73.Based on the kinetic of leaching process, different condition experiments were carried out. The results show that the leaching rate of molybdenum was accelerated by means of high distribution of air to intensify dissolution of oxygen and diffusion of the leaching system, and most of molybdenum in the ore entered into the leaching solution. The results show that the increase of alkali dosage, temperature, time, gas flow rate and liquid-solid ratio is beneficial to the leaching of molybdenum and selenium in the process. As the molybdenum concentrate contains parts of high crystallized molybdenum sulfide, which is difficult to be oxidized by air, the content of molybdenum in leaching residue will exceed1%even though excessive dosage of sodium hydroxide was provided. In order to improve molybdenum recovery, the leaching residue was leached in the sulphuric solution by adding sodium chlorate to extract molybdenum and nickel simultaneously. Under optimum experimental conditions, the total leaching ratio of Mo, Ni and Se were98.3%,96.7%and50%, respectively.In the leaching solution of molybdenum concentrate, the content of Mo is low while it contains much low valence sulfur oxides (SO32-, S2O32-) as well as As and P. When extract molybdenum from the leaching solution with basic resin or extractant, competitive adsorption of MoO42-and impurities result in low operating exchange capacity. According to the chemical characteristic of molybdenum, by acidizing the leaching solution,Mo042-can transform into heptamolybdateand which has high affinity to organic phaseand can bereduced to molybdenum by low valence sulfur oxides. When tertiary amine N-235was used the extractant of molybdenum, molybdenum blue was extracted preferentially and other impurities remained in the raffinate, so selective separation of molybdenum was achieved. In the process of solvent extraction, the extraction efficiency of Mo was99.43%on the condition of molybdenum concentration of5.72g/L, pH3, time2min and O/A ratio1:4with15v%N-235. The loaded organic phase was stripped with15m%ammonia solution. The concentration of Mo in the strip liquor was125.82g/L. In addition, SeO32-was apt to be reduced by low valence sulphur oxide to element selenium in the acidification process of leaching solution. Under the optimum conditions:pH2.5, temperature297K, time30min, the reduction ratio of selenium reached79.6%.In solvent extraction process, hteropoly-molybdenum blue formed by arsenic and molybdenum entered into the organic phase, which was stripped with ammonia solution. Thus, arsenic concentration in the strip liquor was high. It was apt to remove arsenic from the ammonium molybdate solution by chemical precipitation with magnesium due to high ammonium concentration. Experimental results show that when molybdenum concentration and arsenic concentration in the ammonium molybdate solution were96.8g/L and8.75g/L, respectively, the dosage of magnesium chloride was1.2times of stoichiometric quantity, the reaction temperature was297K and time was30min, the residual arsenic concentration and magnesium concentration were0.046g/L and0.52g/L respectively, and the lost ratio of Mo was0.34%.Since the residual magnesium in the ammonium molybdate solution can result in magnesium content over standard in the ammonium tetramolybdate product, the excess magnesium was removed by ion exchange with cationic resin724. Experimental results show that the operating adsorption capacity of the resin was6.58mg/ml (wet resin) until the volume ratio of effluent/resin was around13.2when magnesium concentration was0.5g/L, pH value was9.2and contact time was30min. The loaded resin can be stripped with2mol/L HC1with5times the volume of loaded resin.Ammonium molybdate tetrahydrate was obtained by acidic precipitation and crystallization after remove impurities from ammonium molybdate solution. Its crystallization ratio is95.6%. The final product conforms to the standard of GB/T3460-2007-MSA-2. The Mo concentration in the mother liquor after acidic precipitation and crystallization is around3g/L, and the mother liquor can be return to the process of solvent extraction for Mo recovery.