Selective Extraction Purifying Ammonium Tungstate Solution

Alkaline sodium tungstate solution is widely used in industry to extract tungsten from tungsten containing materials by sodium hydroxide leaching or soda high-pressure leaching. Sodium tungstate solution contains sodium hydroxide or sodium carbonate, or sodium hydroxide and sodium carbonate, in addition to sodium tungstate. In addition, coarse sodium tungstate solution also contains a small amount of harmful impurities such as phosphorus, arsenic, silicon and tin.

An important method for preparing pure ammonium tungstate solution from alkaline sodium tungstate solution is solvent extraction. The extraction method used in current industry is extraction of tungsten with weak alkali amines such as high polymer TERT amine, secondary amines and primary amines in acid (pH value 2~4), and ammonium tungstate solution is obtained by reverse extraction of ammonia water in organic phase. The organic phase after reverse extraction is returned to extraction after regenerated by sulfuric acid. This method is called acid extraction.

The acid extraction process of tungsten in the existing technology needs to consume a large amount of acid in the process of regeneration, not only the free alkali (sodium carbonate and sodium hydroxide) of the crude sodium tungstate solution can not be recycled, and the inorganic salts produced by the neutralization of the acids and bases are contaminated with the ion exchange tailing or the extractive solution, and the environment is polluted. To this end, some scholars have proposed a short, low cost and low cost regenerative system for the direct extraction of tungsten acid from sodium tungstate solution from alkaline crude tungstate solution for the preparation of pure ammonium tungstate. The main contents are as follows:

Feed solution: the material is sodium hydroxide leaching solution, WO₃300.0g/L, P1.50g/L, As 0.70g/L, Si0.75g/L, NaOH70g/L.

Organic phase: organic phase is 25%N₂63+20% octanol +55% aviation kerosene (volume percentage). N₂63 is the commodity code for the domestic quaternary ammonium salt extractant. It is a methyl three alkyl ammonium chloride, of which 3 alkyl carbon atoms are 8~10 respectively. The organic phase is in contact with 1.0mol/L NH₄HCO₃ -0.5mol/L (NH4) ₂CO₃ mixed ammonium solution before extraction to convert methyl three alkyl ammonium chloride into methyl three alkyl ammonium bicarbonate and carbonate mixture, in which the molar ratio of bicarbonate to carbonate is about 6:1.

Operation: 15 stage countercurrent extraction was carried out under the condition of flow ratio 10/1. The negative tungsten organic phase used deionized water at the flow ratio of 6/1 to carry out 5 stage countercurrent washing with 1.0mol/L NH₄HCO^3-0.5mol/L (NH₄) ₂CO₃ mixed ammonium solution for 15 stage countercurrent extraction, the reverse flow ratio was 3/1, and the reverse organic phase returned directly to the extraction.

After the extraction - washing - back extraction is stable, the following results are obtained: the extraction rate of WO₃ is 97.2%, the reverse extraction rate of WO₃ is 98%, the reverse extraction is high purity ammonium tungstate solution, and the WO₃ 86.0g/L, the mass ratio of impurities and tungsten is P/WO₃<0.2 * 10-4, as/ WO₃<0.3 x 10-4, Si/ WO₃<0.6 x 10-4, respectively. The content of P, As and Si in the stripping solution is in line with the requirement of zero grade ammonium partrammonium tungstate.

The new selective extraction method reduces the process flow and the low cost and non regenerative cycle extraction system from the alkaline crude sodium tungstate solution to produce pure ammonium tungstate from sodium tungstate solution in alkaline crude sodium tungstate solution. This method realizes the direct repetition of the extractant without regeneration and reduces the consumption of chemical reagents and environmental protection. It also reduces production costs and is conducive to industrial production.

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