Study On Theory And Technology About Production Of KNO₃with Evaporated Brine Of NaNO₃

In this paper, the metastable phase equilibrium in the quinary system of Na+,K+//Cl-, SO42-, NO3--H2O were studied by isothermal evaporation method. The solubilities of metastable phase equilibrium have been obtained, and dry salt phase diagram and water diagram of the quinary system also have been drawn. Based on these works, the manufacture process of potassium nitrate was studied and the raw material is brine of NaNO3evaporated. The results show that:(1)In the metastable phase diagram of Na+,K+//Cl-, SO42-, NO3--H2O system at25℃, there are three crystallization areas of NaCl; six crystallization areas of binary salt: Na2SO4+NaCl,3K2SO4·Na2SO4+NaCl, Na2SO4·KNO3+NaCl, KCl+NaCl, KNO3+NaCl, NaNO3+NaCl and fifteen co-saturated lines. The co-saturated lines of three salts are: NaCl+Na2SO4+3K2SO4·Na2SO4,NaCl+Na2SO4+Na2SO4·NaNO3·H2O,3K2SO4·Na2SO4+NaCl+Na2SO4·KNO3,NaCl+3K2SO4·Na2SO4+KCl,NaCl+KNO3+KCl,NaCl+Na2SO4·KNO3+KNO3,NaCl+KNO3+NaNO3,NaCl+NaNO3+Na2SO4·NaNO3·H2O,3K2SO4·Na2S04+KNO3; The co-saturated lines of binary salts:Na2SO4+NaCl,3K2SO4·Na2SO4+NaCl, Na2SO4·NaNO3H2O+NaCl, KCl+NaCLKNO3+NaCl, NaNO3+NaCl.In the meastable phase diagram, the crystallization fields of KCl and Na2SO4are bigger than in the stable one; the crystallization fields of3K2SO4·Na2SO4and Na2SO4·NaNO3·H2O are obviously smaller than in the stable one. In general, the meastable phase diagram is different from stable phase diagram.(2)The evaporated brine of NaNO3can be used to produce potassium nitrate by adding KC1, stirring, settling at constant temperature, separating waste salt, cooling and crystallizing. The suitable mole ratio is KC1: NaNO3=1.05:1, the temperature of settling is above75°C, and the reaction time is about20-40min. The recover ratio of potassium is low in a single process, but the circulation of raw material will help us achieve one hundred recover ratio of potassium.