Separation and Extraction of NH4Br and (K,NH4)2SO4 from 1-Bromooctane Production Wastewater by Crystallization Method

This work provides a method for the separation and extraction of bromine salts from bromine-containing wastewater by crystallization. Wastewater from the production of 1-Bromooctane is rich in potassium and bromine salts. This will allow for the recycling of chemical resources in this aqueous salt system. Based on the need for the process design of the new method, the solubility phase equilibrium of the quaternary K+,NH4+//SO42-,Br-–H2O system at 298.15 K and 323.15 K was investigated in this paper by using the isothermal dissolution equilibrium method, and the dry basis phase diagrams were plotted using the experimental data. And the equilibrium solid phase composition was determined by X-ray diffraction. At 298.15 K, the dry phase diagram of the quaternary system K+,NH4+//SO42-,Br-–H2O consists of three invariant points and five crystalline regions (K2SO4, (NH4)2SO4, (K,NH4)2SO4, (K,NH4)Br, (NH4,K)Br). At 323.15 K, there is one invariant point in the phase diagram of this quaternary system and three crystalline regions((K,NH4)2SO4, (K,NH4)Br, (NH4,K)Br). The (K,NH4)Br crystallization zone grows while the (NH4,K)Br crystallization zone decreases with increasing temperature, according to comparisons of the dry basis phase diagrams of this quaternary system at different temperatures. Crystallization zones of solid solution (K,NH4)2SO4 replaced the K2SO4 and (NH4)2SO4 single salt crystallization zones at the same time. The Pitzer model was used to calculate the solubility of this quaternary system at 298.15 K. The results showed that the experimental values were in good agreement with the calculated values. Based on the theoretical analysis of the dry phase diagram of the quaternary system K+,NH4+//SO42-,Br-–H2O, a process route for salt extraction using bromine-containing wastewater generated from the production of 1-Bromooctane was proposed and designed. The new process was experimentally verified to be technically feasible to obtain NH4Br with 99.01 % purity and (K,NH4)2SO4. The process has significant advantages, such as production safety, low input costs and no three-waste emissions.