APT Crystallization Liquor Treatment -- Ammonia Liquid Recycle
At present, in Chinese ammonium paratungstate (APT) enterprises, the most commonly used crystallization method often requires a lot of ammonia, in the production of ammonium tungstate process there are two cases will escape ammonia.
There are two cases will escape ammonia: One is the free ammonia in the ammonium tungstate solution, which quickly escapes in the early stages of the heating ammonium tungstate solution; the other is the reaction of ammonia, it is with the loss of the ammonia concentration in the solution and the precipitation of ammonium paratungstate, and constantly to escape.
Ammonia liquid is a high energy consumption products, the current market price is about 2400 RMB / ton. If the recycle rate of ammonia is 80%, the recycle value is considerable, and the recycle cost is low, it don’t need to increase in capacity, using the cooling cover to recycle, only add a small amount of vacuum pump and water pump for electricity, thus removing the recycling cost, annual net profit is bigger; If you do not recycle ammonia, not only cause undue economic losses, more importantly, the environment is seriously polluted.
There are many liquid ammonia recycle methods, in the preparation of APT is mainly used the condensation method and hydrochloric acid leaching method.
Condensation absorption method is based on NH3 have a certain degree of solubility in the water, and in a certain NH3 partial pressure conditions, the lower the temperature, the greater the solubility, so the evaporation of the mold out of the H2O + NH3 mixed gas turn into the jacketed condenser, congeal the water, meanwhile NH3 dissolved in the condensed water into ammonia, can be returned to use. This method and the disadvantage lies in the periodic evaporation of the crystallization process, the early and late evaporation crystallization NH3 concentrations of the gas phase is different, the early stage of the gas phase NH3 high solubility, and the ammonia concentration is high, easy to return to use, and the late ammonia concentration is low, there is no value.
Hydrochloric acid leaching method is the evaporation of the mold output of H2O + NH3 mixed gas leaching with HCl, resulting in NH4Cl. NH4Cl solution can be returned to the cycle of leaching, so that the concentration increased to a certain extent, for crystallization recycle or with desorbent.
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