Powdery Tungstic Acid Preparation

In order to improve the leaching rate of tungsten, high pressure leaching, extraction and ion exchange are generally used to improve the recovery of tungsten.

However, high pressure equipment has high technical requirements and difficult to maintain. The successful extraction and ion exchange process of the domestic tungsten smelting process reform the classical process, but before extraction, the sodium tungstate solution must remove a large amount of phosphorus, arsenic, silicon and other impurities in the solution, and the alkali is not recovered, and a large amount of acid is needed to neutralize it. In order to meet the discharge requirements, the raffinate must neutralize acid and remove organic matter with alkali. In this way, the process is elongated and the economic benefits are reduced. The exchange capacity of the ion exchange method is small, and it can not remove molybdenum and recover alkali.

In order to overcome these shortcomings, some scholars have studied a process which can produce tungstate and produce ammonium para tungstate. The process is simple and the equipment is easy to be obtained. The main contents are as follows:

1. Preparation:
The main tasks of this process are: the tungsten concentrate enriched by mineral processing will be ground in the grinding equipment, so that the particle size of the ore powder is -300 mesh > 90%;

2. Alkali boiled:
The equipment used in this process is alkali boiled tank, which is about to add the required tungsten concentrate to the alkali boiled tank, and then through the industrial caustic soda, at the temperature of 80~105 ℃, the high alkali pressure leaching is carried out, and the solid: liquid = 1: 2~3, that is to match the 1 ton concentrate with 2~3 Li rice lye. This is an effective method to improve the leaching rate. At the same time, the use of crystalline mother liquor can make full use of the alkali. The amount of alkali is 120 ~ 150% of the theoretical amount, the leaching efficiency can reach 97-99%, and the slag insoluble WO₃ is about 3%, which is obviously superior to low alkali leaching (slag insoluble WO₃ > 7%).

3. Concentrating process:
The concentration is carried out in an alkali resistant reaction tank and heated by steam. The sodium tungstate solution treated by concentrated crystallization is generally 150~250 grams / liter, and the concentration of free NaOH in the general control mother liquor is 400~430 grams / liter. After concentration, the concentration of sodium tungstate is 400~430 grams / liter, and after concentration, it is cooled to 40~60 degrees C, centrifuged and filtered to produce the mother liquor pump to the alkali boiling process, and the sodium tungstate crystal is sent to dissolve process.

4. Dissolution process:
Sodium tungstate crystals are dissolved in the dissolving tank, using deionized water as dissolving agent and operating at room temperature. The specific gravity of the solution is 1.30 ~ 1.45, and the acid precipitation mother liquid is adjusted to pH7 to 9. After stating, it is naturally filtered to separate the impurities such as SiO₂ and Fe. More than 99.5% of the WO₃ was dissolved in the solution, and most of the SiO₂ and most of the iron was removed.

5. Acid precipitation process:
Acid precipitation is the filtration of the solution into the reactor, at the same time adding acid, heating, controlling the use of acid, at 95 degrees centigrade for 1 to 2 hours after heat filtration of tungstate. Tungstic acid was washed by 0.5% hydrochloric acid and 0.5% nitric acid respectively, then centrifugally filtered to obtain tungstic acid. It is orange, loose, powdery, and does not lump after drying. The acid precipitation mother liquid contains WO₃ at about 1 g / L, and the lowest can be reduced to 0.42 g / L. One part of the solution can return to the pH of the solution, a part of which can be neutralized with lime, and the recovery of WO₃ and the production of calcium chloride. The precipitation rate of tungstate can reach more than 99%.

Compared with traditional technology, this process is simple in operation, low in alkali consumption, high in recovery and low in cost. From tungsten concentrate to powdery tungstic acid, the yield is more than 97%, and the solubility of ammonium tungstate is good. It can be sold directly in the form of powdery tungstate and ammonium para tungstate can be made down.

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