The crystalization method of evaporation and extraction method in the preparation of APT crystallization liquor treatment.
Leaving about 5% -10% of the WO3 and part of the S, P, As, Mo, K, Na and other impurities, resulting in it can not directly return to the process, in order to improve the recycle of metal, it is necessary to set up auxiliary processes to recycle WO3 in the liquor.
The residual alkali decomposition method is characterized by the use of tungsten concentrate decomposition of sodium tungstate in the process of recycle of residual NaOH solution with the liquor reaction, turn the WO3 directly into Na2WO4 solution, after remove the molybdenum solution into the main purification process and deal with Na2WO4, and also remove the phosphorus, arsenic, tin and other impurities, the transformation equation is:
2NaOH +(NH4）2WO4===Na2WO4+ 2NH4OH
The solution recycled by the residual alkali decomposition method is only applicable to the classical precipitation process, which can directly recycle the WO3 in the crystallization liquor, metal yield can be increased by 0.52%, and the use of residual alkali molybdenum acid solution can replace by some of the hydrochloric acid, APT alkali consumption, acid consumption were reduced by 8% and 7%, but the residual alkali decomposition method is only used in the precipitation process.
Some scholars use residual alkali method and ion exchange method to test, and the result shows that the recycle of liquor has an effect on the adsorption capacity of S2- ion exchange resin, and lead to the entire ion exchange waste water ammonia nitrogen seriously exceeded, and the arsenic in the liquor can also lead to ion exchange resin poisoning, so the alkali can only be docked with the classic precipitation method. Unfortunately, the classic precipitation method of the old process is gradually being eliminated, so there is no place for residual alkali decomposition method.