The production of pure NaCl by the antisolvent crystallisation of NaCl · 2H₂O and a consecutive recrystallisation step

NaCl · 2H₂O crystals formed by antisolvent crystallisation with N,N-dimethylisopropylamine (DMiPA), were recrystallised batchwise into NaCl at 0.2°C and 0.5°C in pure brines and in brines containing 5 wt% DMiPA. In all experiments the recrystallisation brought about a strong purification of the solid phase. The average DMiPA concentration in the NaCl · 2H₂O crystals was approximately 1000 ppm, whereas the DMiPA concentration in the NaCl product was between 1 and 6 ppm. Both the DMiPA concentration in the mother liquor and the recrystallisation temperature influenced the average NaCl crystal size and the rate at which the recrystallisation took place significantly.