Sodium Hydroxide Recycle Process from Tungsten Smelting

With the continuous exploitation of tungsten resources, scheelite and medium ores with high impurity content become the main sources of tungsten smelting raw materials. In the existing technology, the smelting of Scheelite Concentrate and medium ore generally adopts the high alkali pressure boiling technology, and the alkali input is generally 2.8-4 times of the theoretical amount. The quality ratio of excess NaOH and WO₃ in the coarse sodium tungstate solution obtained after the alkali pressure boiling slurry is 0.7-1.2. If not recovered, it will not only bring adverse effects on the subsequent process, but also consume sulfuric acid to neutralize it before discharging.

The first step is to mix the raw material of tungsten ore and water at a volume ratio of 10:3 and add them to the ball mill to obtain tungsten ore slurry, and then add sodium hydroxide solution to the tungsten ore slurry. The added amount of sodium hydroxide solution is 1.0-1.4 times of the content of tungsten trioxide in the sodium hydroxide solution, and then pump the tungsten ore slurry added to the sodium hydroxide solution into the medium pressure reactor with agitation. After two times of pressure filtration, the coarse sodium tungstate solution was obtained.

Step 2: feed the crude sodium tungstate solution into the feeding preheating device of the three effect evaporation crystallizer through the feed pump. When the preheating temperature of the crude sodium tungstate solution reaches the boiling temperature of the three effect evaporation unit heater, the crude sodium tungstate solution is pumped into the evaporation device of the three effect evaporation unit. After the evaporation and concentration, the crude sodium tungstate solution is separated by the three effect separation crystallizer, and the residual steam from the separation enters the condensation device. The separated primary concentrate enters the evaporation device of the primary effect evaporation unit, and after evaporation and concentration, the primary effect separation crystallization device performs gas-liquid separation;

Step 3: after gas-liquid separation of the primary concentrate through the primary separation crystallization device, the primary steam obtained from the separation enters the evaporation device of the secondary effect evaporation unit as the heating source, and the secondary concentrate obtained from the separation enters the evaporation device of the secondary effect evaporation unit. After the concentration crystallization, the gas-liquid separation is carried out through the secondary effect separation crystallization device.

Step 4: the secondary concentrated solution passes through the secondary effect separation crystallization device, the secondary steam obtained from the separation enters the evaporation device of the third effect evaporation unit as the heating heat source, the sodium tungstate crystal slurry obtained from the separation enters the plate and frame pressure filtration, the filtrate is the concentrated sodium hydroxide solution and returns to the production process of ammonium paratungstate, the filter residue is the sodium tungstate crystal dissolution pressure filtration, and then enters the solution preparation process before the ion exchange of tungsten smelting.

The method is highly automatic and easy to operate. The sodium tungstate is crystallized in the secondary effect evaporation unit, so that the recovery efficiency of sodium tungstate is high. After recovering the surplus sodium hydroxide in the crude sodium tungstate solution, the cost of the subsequent solution treatment after ion exchange of tungsten smelting can be reduced, the amount of sulfuric acid used to adjust the pH value in the treatment process of tungsten smelting wastewater can be reduced, and the resource consumption and cost expenditure can be greatly reduced.

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