| Abstract:Ammonium paratungstate is an important intermediate compound during the preparation of pure compounds in the tungsten metallurgy process. Presently the main method of preparing ammonium paratungstate is the evaporation crystallization method; but the spent liquor is hard to be economically recovered. To make things worse, the sodium carbonate and the sodium hydroxide used to decompose the tungsten ores can’t be recycled, which causes the severe environmental problems.To solve these problems, this study proposed a new method to prepare the ammonium paratungstate:using CO2to adjust the pH value of sodium tungstate solution and then adding ammonium into the solution to precipitate ammonium paratungstate. The research mainly includes the purification of green sodium tungstate solution using carbon dioxide to adjust the pH value and preliminary study of the laws of thermodynamics for the WO42--CO2-NH4+-H2O system. The effect of reaction temperature, the pre-aerating carbon dioxide time, the amount of ammonium, the seeds and the additives added on the preparation of product had been studied too. The study shows that:1) Using carbon dioxide with certain pressure to adjust the pH value of green sodium tungstate and then adding magnesium salt and CuS to remove the impurities in the solution can reduce the concentrations of Si, P, As, and Mo to0.014g/L,0.046g/L,0.081g/L and0.0061g/L respectively.2) During the preparation of ammonium paratungstate in the sodium tungstate-carbon dioxide-ammonium-water system, raising reaction temperature results in lower reaction rate but bigger size of the product. Adding more seeds and ammonium improves the reaction rate.3) The prepared product contains1.2%sodium, which can’t be completely removed by pure water. Washing the product with saturated ammonium solution under75℃can reduce the sodium content to6ppm.(graph:24, chart:26, references:75.)... |
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