New Methods of Eliminating Free Alkali from Sodium Tungstate -3/3
We know that the traditional inorganic acid neutralization method, not only costs a lot of acid and alkali, but also increases the high salt liquid waste emissions and that causes environmental pollution. Even though we use ion exchange process, we should dilute the solution at high magnification to free alkali concentration less than 8 g/L, then it can be swapped. Some of its alkali was abandoned after entering in liquid. Single positive membrane electrolysis method which is reported to removing free alkali from coarse sodium tungstate solution made great progress. The industrial test showed that the method is basically cause no tungsten loss. The dc consumption is 2000-2500kwh/T sodium hydroxide. It is superior to the conventional crystallization. In general, electrodialysis method compares with electrochemical method, its unit of dc consumption and equipment investment are lower. The difficulty about electrodialysis method of removal of free alkali lies in the separation effect of alkali tungsten. The separation effect of ordinary negative membrane on hydroxide radical and the tungsten acid radical is poorer. Alkali process causes big tungsten loss. It should not be used. the negative ion（1）selective membrane selectively makes the negative ion（1）to pass and can realize the separation. This is the electrodialysis method of negative ion（1）selective membrane.
In the experiment, the influence of many factors cannot be ignored, such as current density. with the operating current density increases, which increase the electric drive of electrodialysis process, good free alkali selective removal. Another city to process index in the process of electrodialysis is dealkalization dc power consumption. The results show that the choice of higher current density can obtain larger dealkalization rate and better alkali tungsten separation effect, the process of information and to reduce costs, enhance the yield of tungsten. In addition to the operating current density, the material liquid alkali concentration and the concentration of recycle alkali process parameters on the process energy consumption, current efficiency and migration rate than the technology indexes such as alkali tungsten also has very big effect.Studies have shown that it is economical and feasible to eliminate the free Alkali from Sodium tungstate with electrodialysis method of negative ion（1）selective membrane. It can reduce the cost of tungsten smelting process and has high economic value and social significance.
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