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Tungsten and Molybdenum Separation from Bismuth by Alkaline Pressure Oxidation of Bismuth Sulfide Concentrate

Author: ZhangDuChao
Tutor: YangTianZu
School: Central South University
Course: Metallurgical Engineering
Keywords: alkaline pressure oxidation leaching bismuth sulfideconcentrates tungsten and molybdenum ion-exchange reductionsmelting method
CLC: TF803.2
Type: PhD thesis
Year: 2012
Downloads: 67
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Abstract


Bismuth sulfide concentrates, often coexists with tungsten, molybdenum, silver and other valuable metals, is mainly treated by the Precipitation Process in practice. However, the scattered losses of tungsten and molybdenum during the extraction process of bismuth are not conducive to the comprehensive recovery of these metals, and this method has some disadvantages of high energy consumption, severe environment contamination and tedious subsequent recovery process. In order to solve the above problem, this research was posed out.The bismuth sulfide concentrates was leached with pressure oxidation method in alkaline medium to get the leaching solution containing tungsten and molybdenum and the oxidation residue containing bismuth, which achieves the separation of tungsten, molybdenum and bismuth, and convert the sulfide into sodium sulfate simultaneously to avoid the sulfur pollution problem. Then the ion-exchange method was used to recover tungsten and molybdenum from the leaching solution, and the research about the recovery of bismuth, silver and other valuable metals from the oxidation residue was also carried out. The main purpose is to achieve the efficient separation and recovery of valuable metals from bismuth sulfide concentrates. The main research content and conclusion are as follows.The behavior of bismuth, iron and sulfur were analyzed through the potential-pH diagram of S-H2O, Bi-S-H2O and Fe-S-H2O which are drawn under the temperature of25℃,100℃,150℃,200℃. Under the condition of higher pH value and higher potential value, sulfur exists as SO42-. Under the condition of lower pH value and oxidants existing, Bi2S3can be oxided into Bi2(SO4)3, and as the pH value increasing Bi2S3can be converted into Bi2O3. Fe3+in solution can be converted into FeO—OH under25℃through hydrolysis reaction, and under higher temperature it will be changed into Fe2O3. The increasing temperature will reduce the equilibrium potential for oxidation reaction, which is conducive to the oxidation reaction of Bi2O3and Fe2O3, as a result sulfur enter into solution in the form of SO42-while bismuth and iron exist as metal oxides in the leaching residue.By comparing several alkaline system to treat the bismuth sulfide concentrate containing tungsten and molybdenum, sodium hydroxide system was selected with the optimum leaching conditions were:liquid to solid ratio5:1, temperature150℃, sodium hydroxide concentration of130g/L, fill ratio0.6, stirring speed10000rpm, time of180min, oxygen partial pressure of0.7MPa. Under this condition, the residue ratio is basically stable around82%, sulfur leaching ratio is more than96%, the extraction ratio of tungsten and molybdenum are93%and95%respectively, the concentration of tungsten and molybdenum in leaching solution are1.31g/L and2.76g/L respectively, and in residue the content of bismuth is39.60%and that of silver is265.3g/t, the content of lead and copper are1.25%and2.48%respectively. Nearly all the sulfur, tungsten and molybdenum enter leaching solution, which achieve the preliminary separation of valuable metals and is conducive to the subsequent recovery of tungsten and molybdenum from leaching solution and that of bismuth and silver from the oxide residue.A macroporous anion resin D363was selected to make static adsorption of tungsten and molybdenum. The results show that when the pH value of solution is6.6-7.5, D363has a good adsorption property for tungsten and the adsorption capacity reaches to236.3mg/g dry resin when pH is6.66; when the pH value of solution is2.2-4.6, D363shows great adsorption property for molybdenum and the adsorption capacity reaches356.4mg/g dry resin when pH is3. The results of adsorption isotherm experiments demonstrate that the adsorption process is close to the Freundich model, and the process is endothermic, higher temperature is conducive to the adsorption of tungsten and molybdenum by D363resin. Results of the dynamic adsorption and desorption experiment for tungsten show that the penetration adsorption capacity of tungsten by D363resin can reach19.3mg/ml wet resin when the pH of solution is6.79, temperature is25℃, the resin column ratio of height to diameter is16:1, the time for adsorption is40min and the volume of raffinate is416ml(26 times the volume of wet resin). The adsorption of tungsten reaches85%and the distribution ratio of tungsten and molybdenum is7.4, which achieve the goal of effective recovery of tungsten and preliminary separation of tungsten and molybdenum. Tungsten loaded on D363resin can be effectively desorbed by10%ammonia solution with the desorption ratio of94.6%. Results of the dynamic adsorption and desorption experiment for molybdenum show that the penetration adsorption capacity of molybdenum by D363resin can reach55.2mg/ml wet resin when the pH of solution is3.02, temperature is25℃, the resin column ratio of height to diameter is16:1, the time for adsorption is40min, and the volume of raffinate is384ml(24times the volume of wet resin), which make the effective recovery of molybdenum. Molybdenum loaded on D363resin can effectively desorbed by10%ammonia solution with the desorption ratio of87.2%.Fluosilicic acid system was used to treat the oxidative residue and the optimum condition was determined according to a series of experiment. However, the problem of difficult separation of bismuth and iron during wet process cannot be effectively solved neither by changing the leaching condition to change the composition of oxide residue nor by controlling the final pH value to make hydrolysis reactions. In order to resolve this difficult, the reducing smelting method is selected to recover bismuth and other valuable metals from tne oxide residue. The ternary slag type FeO-SiO2-CaO is selected according to the the compostions of oxidative residue. The corresponding optimum condition is determined as follows:the amount of coal added is7%of the weight of leaching residue, in slag the ratio of CaO to SiO2is0.5and FeO to SiO2is1.5, temperature is1300℃and time is40min. Under this condition the recovery ratio of bismuth, silver, copper and lead are99.6%,99.8%,97.0%and97.3%respectively, which achieve the efficient recovery of bismuth, silver, lead and copper.

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