Hydrogen peroxide coordination-calcium salt precipitation for deep phosphorus removal from crude sodium tungstate solution

Abstract

In the traditional alkali smelting process of tungsten ore，a small amount of the associated phosphorus will enter the sodium tungstate solution. In order to produce a qualified tungsten product, phosphorus must be removed in depth. Conventional methods for removing phosphorus, such as magnesium salt precipitation, ion exchange, etc., are difficult to efficiently remove high concentrations of phosphorus from sodium tungstate solution. In this paper, a method for deep phosphorus removal from crude sodium tungstate solution by hydrogen peroxide coordination‑calcium salt precipitation is proposed due to the coordination ability of hydrogen peroxide with tungstate to form peroxytungstate which is difficult to be precipitated by calcium. The paper mainly explores the theoretical feasibility of this method, the influence of time, calcium addition, pH value, initial phosphorus concentration and other factors on P removal. The best phosphorus removal condition has been obtained: under the condition of adding hydrogen peroxide, when the reaction time is 10 min; the molar ratio of calcium to phosphorus added is 3; the pH value is 9.5, and the phosphorus concentration is higher than 1 g/L, the phosphorus removal effect has been basically stable. The phosphorus removal ratio can reach 99.9% which means that phosphorus concentration in solution is <10 ppm after phosphorus removal, and the tungsten loss is as low as 0.1%. This method can remove phosphorus deeply from sodium tungstate solution containing different initial phosphorus concentration.