Molybdenite Electro-oxidation Decomposition Process

Molybdenite from Jiangxi Dexing Copper Mine is reaserched. For disadvantages of common decomposing molybdenite technique, the good-prospect leaching technique without ejection was designed. It is hydrometallurgical process of electro-oxidation for Molybdenite.The trunk electrochemical reactor (ECR) was designed. And its operation mode is intermittent. The material of the cell body is made of polypropylene. The inert anode adopts DSA (dimension stable anode) with the coat consisting of RuO₂ and TiO₂, while cathode material uses the steel net with the low emitting hydrogen potential. Through experiment, the voltage of the electrolytic cell is calculated to be about 3.8V and the interelectrode distance is 10mm. The attended mode between each pair of electrodes is parallel connection. When at work, the electrolytic cell is put into stable temperature horizontal bath, add electric stir rods between electrodes, and put the probe of pH meter into pulp in order to keep the stable temperature of the additional electrolytic cell, strengthen mass transfer and control pH value.In the hydrometallurgical process of electro-oxidation for Molybdenite, Mo in molybdenite can be oxidized into negative ion MoO₄^2-, which is soluble in electrolyte, by Cl₂ generated in the process of NaCl solution electrolysis and HClO or NaClO transformed by Cl₂. The best process condition in the research is that under room temperature, pH of the pulp in the reaction process is about 9, NaCl concentration in the electrolyte is 4.0mol/L,liquid-to-solid ratio of pulp is 25,the mixing speed is 400rpm, the current density of electrolytic cell is 466.0A·m^-2 and cell voltage is 3.5 to 3.8V. Under this condition, 5 grams molybdenite can be completely decomposed in only 240 minutes, with leaching yield of molybdenum at 98 percent and current efficiency at 70 percent. In the process of electrolysis, there is neither Cl₂ spilled out, nor metal deposited on the cathode.Anodizing curve kinetics shows that the oxidation leaching of molybdenite mostly depends on chlorine emitted by the anode. Mixing is helpful to diffuse the mass transfer, boost ion migration speed in the electrolyte, and make it easier for molybdenite granules to get to anode surface so that electric current increases. The increase in pulp concentration is bad for anodic chlorine generation, which will decrease electric current. Leaching process kinetics indicates that in the room temperature, when pH is 3, liquid-to-solid ratio is 25, mixing speed is 400rpm, and NaCl concentration is 4.0mol/L, the data processing we get is in accord with the kinetics equation of shrinking particle model. According to the data, leaching apparent activation energy is 8.282KJ/mol, and the process is mainly controlled by fluid diffusion. When pH is 9, liquid-to-solid ratio is 25, mixing speed is 400rpm, and NaCl concentration is 4.0mol/L in the room temperature, the data processing we get conforms to the kinetics model of solid reactant generated. Through calculation, the leaching apparent activation energy is 8.56kJ/mol, and there are solid reactants generated on the reaction interface. The whole process is controlled by liquid film diffusion.According to the process oxidation mechanism analysis,it is showed that the oxidant is HClO and Cl₂ under the acidic condition,and the S element is oxidanted to SO₄^2-; but under the alkaline condition ,the oxidant is NaClO and part of S element is oxidanted to sulfur. This didn't affect leaching yield of molybdenum.