Theoretical and experimental study on the recovery of bromide by crystallization from pesticide production wastewater

Brominated wastewater from the propyl bromide pesticide production rich in ammonium, sodium and bromine salts at a high concentration of 11 %. For the recycling of chemical resources of this mixed brine salt system, this paper proposes a method for the separation of bromide from bromine-containing chemical wastewater by crystallization. According to the process design needs of the new method, and because 298 K and 323 K are two common temperatures in industrial practice, in this paper, the solubility data of the NaCl-NH4Cl-NaBr-NH4Br-H2O quaternary system at 298 K and 323 K, as well as its ternary subsystems, NaBr-NH4Br-H2O and NH4Cl-NH4Br-H2O at 323 K were determined by the isothermal solubilization method, and the corresponding phase diagrams were drawn. The solubility of the NaCl-NH4Cl-NaBr-NH4Br-H2O quaternary system at 298 K was also calculated using the Pitzer model, and the calculated results were in good agreement with the experimental measurements. Finally, based on the theoretical analysis of the phase diagrams of the 298 K and 323 K NaCl-NH4Cl-NaBr-NH4Br-H2O quaternary systems and combined with the phase diagrams of the 298 K NaBr-NaCl-CH3OH system, this paper proposes and designs a salt extraction process route for the brominated wastewater of the propyl bromide pesticide production. Through the separation experiment, the new process proved to be technically feasible and produced NaCl with 100 % purity, Na(Br,Cl) with 98.23 % NaBr, and NH4(Cl,Br) with 99.18 % and 97.57 % NH4Cl, respectively. The new process realizes the resourceful utilization of bromine-containing wastewater, and has the significant advantages of production safety and no emission of three wastes.