Extract Alkali from Crude Sodium Tungstate Solution

Scheelite is hard mining and smelting tungsten smelting raw material in the last century, when alkali pressure leaching and scouring process of popularity, production capacity and size of scheelite smelting technology has been greatly enhance, and also further mature. Due to the excessive alkali process, although the leaching process consumes a large part of the base, but after the reaction, residual alkali from crude sodium tungstate solution is very high.

Residual alkali recycle is the process of evaporation, concentration and crystallization of the solution, mainly energy consumption, but because of the rising energy price, most tungsten smelting enterprises will not consider the recycle of residual alkali. After all, the economic benefit is very small. Only when the concentration of the residual alkali in the solution is above 100 g/L, the recycle of the residual alkali is necessary. The brief process for the recycle of the residual alkali is:

From the autoclave out of sodium tungstate material solution containing tungsten trioxide 100g / L, sodium hydroxide concentration of 45 g / L, the solution volume of 5000mL, after liquid-solid filter press separation, the pump into the three effect evaporative crystallization a steam evaporator inlet efficiency steam pressure 0.4MPa, temperature 155 ℃, the second effect evaporation crystallizer and the triple effect evaporative crystallizer deliver sodium tungstate crystal to the frame filter press for solid-liquid separation, the filtrate is returned to the pressure cooking process, the residue is dissolved and sent to the ion exchange process, the condensed water is used as a main process dilution water, the filtrate sodium hydroxide concentration of 385 g / L, tungsten trioxide 25.5g / L. Tungsten straight yield of 97%, alkali recycle 96.8%.

The main point of this technique is that the crude sodium tungstate solution at low residual alkali concentration must be vaporized in a large amount of solution.

As the concentration continues, the viscosity of the solution increases. Therefore, in the design and layout of the three-effect evaporative crystallizer, the second and third effect crystals will be evacuated to effectively reduce the boiling temperature of the solution, although the effect of regenerative steam than steam temperature reduced, also can realize the purpose of further enrichment of the solution. Since the solubility of sodium tungstate decreases with increasing alkali concentration, independent crystal discharge ports are provided in the secondary and tertiary effect evaporative crystallizers to prevent fouling due to the large amount of crystals precipitating in the secondary effect crystallizers pipe problem.

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