Abstract
We identified the hydrates formed from mother liquor on surface of salt on drying, measured the transition temperatures of those hydrates, and investigated the drying temperature condition for measuring of loss of mass on drying of salt.
The results were as follows:
1) For salt manufactured by the ion-exchange membrane method, the hydrates of carnallite (KMgCl3·6H2O), tachyhydrite (CaMg2Cl6·12H2O) and bischofite (MgCl2·6H2O) were formed from the mother liquor on the surface of common salt on drying, and these affected the measurement of loss of mass on drying. For solar salt, carnallite, bischofite and gypsum (CaSO4·2H2O) affected this measurement.
2) The transition temperatures of carnallite were about 95°C and about 145°C. Tachyhydrite was about 135°C, bischofite, about 110°C and 160°C, and gypsum (CaSO4·2H2O), about 105°C.
3) 110°C prescribed by ISO 2483 was near the transition temperatures of bischofite and gypsum. 140°C prescribed by “Methods for salt analysis” in Japan was near that of carnallite and tachyhydrite.
4) The loss of mass by the transition of tachyhydrite at about 135°C and that by thermal decomposition of bischofite were factors causing differences between the loss of mass at 110°C and at 140°C.
5) In the range of 120°C to 130°C, there was no transition temperature of these hydrates, so temperatures in this range were considered to be a suitable temperature condition for measuring loss of mass on drying.
