Study On Foundation Of Copper-Molybdenum Separation From Refroactory Ore And The Novel Extraction Process Of Molybdenum

Molybdenum is an important metal and strategic resource, which plays a promoting role for the development of national economy. Molybdenum mainly produces from copper-molybdenum deposits, molybdenite closely coexists with chalcopyrite and it is a worldwide problem for the separation of chalcopyrite and molybdenite. In recent years, the refractory copper-molybdenum ore with the characteristic of "poor","fine" and "complicated" gradually becomes the major raw material for the extraction of molybdenum due to the excessive consumption of rich ore resources. Under this background, this work studed the separation flotation of chalcopyrite and molybdenite based on the studies on the technological mineralogy of the ore; meanwhile, the work also studed the electrochemical oxidation process of chalcopyrite in the flotation system as well as a novel extraction process of molybdenum from the low grade molybdenum concentrates.Based on the study on the technological mineralogy of the ore, the main metallic mineral are chalcopyrite, molybdenite, sphalerite, galena and bornite; the main gangue mineral are garnet, diopside, dolomite, amphibole and epidote. Chalcopyrite closely coexists with molybdenite and it makes difficult in the separation of these two ores. Additionally, chalcopyrite exhibits fine, scale shape in nature and embeds in the gangue mineral, which also makes difficult in the separation of chalcopyrite and the gangue mineral.Optimum grinding fineness and reagent system were determined according to the conditional experiment results of the separation of chalcopyrite and molybdenite. During the coarse separation stage, the content of the particle with the diameter lower than42μm is60.49wt.%; pulp concentration is20wt.%, the dosages of sodium sulphide, sodium silicate and kerosene are40kg·t-1,1kg·t-1and0.5kg·t-1, respectively. During the cleaning stage, the content of the particle with the diameter lower than42μm is82.50wt.%; pulp concentration is15wt.%, the dosages of natrium silicate dosage and kerosene are10kg·t-1and1kg·t-1, respectively. The field adjustment scheme of the separation of chalcopyrite and molybdenite was fixed according to the field flowsheet inspection and the verification test. The filed production practice suggested that the separation of chalcopyrite and molybdenite achieved good results. In the last two years, the content of copper in the molybdenum concentrate was reduced to0.10wt.%～0.20wt.%; the content of molybdenum in copper concentrate was reduced to0.50wt.%～0.80wt.%; the grade of molybdenum concentrate increased from20wt.%to33wt.%.The electrochemical oxidation process of chalcopyrite in the flotation system was studied using cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and infrared spectrum.In the collector-free flotation system, two electrochemical oxidation processes occur on the surface of chalcopyrite. The oxidations of Fe and S in the surface lattice of chalcopyrite occur in the potential range from-0.07V (vs.SCE) to0.22V (vs.SCE). The surface of the substrate exhibits S-rich characteristics due to the oxidation of iron. The electrochemical process is controlled by the growth of the hydrophobic S-rich species in this potential range. The hydrophobic S-rich species starts to dissolve to form the high valence sulfur products (S2O32/SO42-) in the potential range from-0.22V (vs.SCE) to0.46V (vs.SCE); meanwhile, the hydroxylation of iron to Fe(OH)3and the oxidation of Cu also occur in this potential range. As a result, plenty of hydrophilic Fe(OH)3as well as S2O32/SO42-species are formed on the electrode. The electrochemical process is controlled by the dissolution process of the hydrophobic S-rich species and the hydroxylation of Fe in this potential range.In the collector-induced flotation system, the hydrophobic film formed on the surface of chalcopyrite by the reaction of chalcopyrite with xanthate is mainly of dixanthogen. In the weak alkaline solution containing5×10-4mol·L-1xanthate, the oxidation of xanthate to dixanthogen occurs on the surface of chalcopyrite electrode in the potential range from-0.11(vs.SCE) to0.26V (vs.SCE). The content of xanthate on the electrode is relatively low at open circuit potential.The dixanthogen film has the maximum thickness and highest coverage at the potential of0.1V (vs. SCE). At the potential of0.1V (vs. SCE), the dixanthogen film exhibits flake-like characteristics and it partial covers the chalcopyrite electrode. At the potential of0.30V (vs.SCE), the self-activation of chalcopyrite is the mainly oxidation process on the electrode, the film of X2transformed to plenty of Cu(Ⅱ) and Fe(Ⅲ) oxygen-containing species which have the porous and loose characteristics. In the depressant flotation system, the effect of sodium sulfide on the passiviation film on the surface of chalcopyrite is complicated. Sodium sulfide promotes the passiviation of chalcopyrite when the concentration of sodium sulfide is lower than10-3mol·L-1; sodium sulfide inhibits the formation of the passiviation film on chalcopyrite when the concentration of sodium sulfide is higher than1×10-3mol·L-1.This work also studed a novel leaching process of molybdenum from low-grade molybdenum concentrates by the technologies of roasting-ammonia leaching-alkaline leaching of slag. The recovery rate of molybdenum could be reach96.80wt.%by this method and the optimum conditions are listed as follows:roasting temperature is600℃, roasting time is1h; during the ammonia leaching stage, the temperature is80℃, time is1h, the excess coefficient of aqueous ammonia is1.4, the dosage of the sodium carbonate is467kg·t-1and the liquid to solid ratio is4:1; during the alkaline leaching of slag, the temperature is95 ℃, time is2h, the liquid to solid ratio is4:1, the dosage of the sodium carbonate is533kg·t-1, and the dosage of the sodium hydroxide is433kg·t-1. The recovery rate of molybdenum could be reach98.50wt.%by the soda roasting-water leaching method and the optimum conditions are listed as follows:the ratio of molybdenum concentrates to sodium carbonate is1:1.4during the soda roasting stage and the roasting temperature is700℃; during the water leaching stage, the temperature is75℃, leaching time is2h and the liquid to solid ratio is4:1. Mesophilic bacterium was used to leaching Mo from the low grade molybdenum concentrates. The leaching rate could be reached30.23wt.%under the condition listed as follows:initial pH value is1.5, temperature is44℃, the addition of FeS2equivalenting to0.5times of iron content in9K medium.The study on the crystallization of ammonium molybdate indicated that the products are mainly of ammonium quartmolybdate. These crystals exhibit bulk and cube shape, and have uniform size.