Recovery Of Vanadium From Alumina Production Process

Vandium is an important alloy element, but its resource which can be extracted economically is relatively scarce. It is estimated that the quantities of vanadium brought into alumina process per year are about 10-50 thousand tons, which is an important vanadium resource. Furthermore, the existence of vanadium in alumina process has large influence on the quality of alumina product. Therefore it is quite necessary to extract vanadium from alumina process.The unique method which has been applied in industry to extract vanadium from alumina process is crystallization method though there are many methods. Unfortunately, this method has the defect of very low recovery rate. Moreover, it only fits to treat liquors with high vanadium concentration and can't be able to treat liquors from domestic factories, in which the vanadium concentration is low. It is imperative to develop new technique to extract vanadium from alumina process efficiently.The influence rules of vanadium on digestion and precipitation, which are the two key procedures of alumina process, were investigated firstly. The results showed that the vanadium in alumina process basically had no effect on digestion but influenced precipitation greatly, resulting in the decrease of purity and the thinning of particle size of product. Conclusion can be made that vanadium is an impurity with great harm for the alumina process.On the basis of confirming the spent liquor of Bayer process as the material for extraction of vanadium, the technical route of this dissertation was proposed after analysis and discussion. The route included the following procedures:precipitation of vanadium from spent liquor, leaching of vanadium-containing residue, ion exchange, secondary precipitation of vanadium and roasting of ammonium metavanadate. All of the procedures were investigated systematically and completely.The thermodynamics ruls of the reactions between vanadium ion and other ions in spent liquor were discovered by the thermodynamics analysis of the reactions during the precipitation of vanadium. On this basis, according to the problem that the V2O5 content in the vanadium-bearing residue is low after precipitation of vanadium by using traditional method, a new method, that the vanadium-bearing residue was used to precipitaite vanadium circularly, was proposed. By using this method, the V2O5 content in vanadium-bearing residue could be improved to more than 2%, showing that vanadium was precipitated from spent liquor efficiently.The thermodynamics analysis results of the leaching of vanadium-bearing residue showed that the residue was fit for being leached by Na2CO3 solution at low temperature. By the kinetics investigation of this procedure, its kinetics control step, which is the diffusion rate of reacting reagents in a porous solid layer, was found. On the basis of thermodynamics and kinetics results, according to the problem of low leaching rate by using Na2CO3 solution directly, a improved method, which adds the ventilation of CO2 during leaching, was proposed. By using this method, the leaching rate could be improved from 80% to more than 90%. Suitable leaching conditions were selected by investigating the influence of leaching solution concentration, CO2 ventilation, temperature, liqid-solid ratio and leaching time on leaching.The kinetics investigation results of the adsorption of vanadium anion by resin showed that 201x7 resin had good adsorption effect on vanadium ion and the adsorption rate could be more than 87%. Moreover, the adsorption process was accordance with moving boundary model and its dominant procedure was ion diffusion through particles. Experiments investigation of adsorption showed that good adsorption effects could be obtained by using 201x7 resin to adsorb the vanadium ion in leaching solution and the adsorption rate was about 95%. Experiments investigation of desorption showed that by using the desorption system of lmol/LNaCl+lmol/L NH4Cl, good desorption effects could be obtained and the desorption rate was more than 97%. The influence of flow rate, temperature and pH on adsorption, and the influence of desorption system, desorption agent concentration, temperature and flow rate on desorption were investigated. The suitable condtions for ion exchange were found.Experiments investigation of secondary precipitation of vanadium showed that good precipitation effects could be obtained by adding NH4Cl into the desorption solution and the precipitation rate of vanadium could be 98%. According to the characteristics of the reaction for secondary precipitation of vanadium, the kinetics equation for this procedure was deduced. At the basis of the experiments results for the investigation on the influence rules of desorption solution concentration, pH, KNH4Cl and temperature the parameters of the kinetics equation were calculated that its reaction rate constant was 9.16×10-5 mol/L·s and its reaction order was 0.932. Meanwhile, the suitable conditions for secondary precipitation of vanadium were found. During the investigation on the roasting of ammonium metavanadate the suitable conditions were found by investigating the influence of roasting temperature and roasting time. More importantly, V2O5 product which meets the requirements of GB3283-1987 standard for metallurgy 99 grade was prepared. The recovery of vanadium from alumina process was realized.Through the research of this dissertation, for the first time the recovery of vanadium from alumina process comes true by using another method except for the crystallization method. And this method has the advantage of high efficiency and being able to treat liquor with low vanadium concentration. On the basis of the technical route discovered by this dissertation for recovery of vanadium from spent liquor of Bayer process, it is possible to develop industrial technique for recovering vanadium from spent liquor of Bayer process. If the industrial technique can be applied widely in alumina factories, not only the negative effect of vanadium on alumina process can be eliminated, resulting in the improvement of product quality but also good economic benefit can be achieved because of the form of new product. Therefore, the pressure of simple product and low ability of countering market risk of alumina factories can be effectively relieved.