GB366971A - Improvements in treating mineral salts - Google Patents

Abstract

<PICT:0366971/III/1> Magnesium chloride, either alone or mixed with sodium chloride, potassium chloride or ammonium chloride, and also in the form of double salts such as carnallite or ammonium carnallite, is dehydrated in two stages. In the first stage, the compounds are partially dehydrated by introducing them continuously or intermittently into the upper end of a drying apparatus through which they descend while a current of hot air is passed upwardly through the mass, and the dehydrated products are continuously or intermittently removed from the lower end of the apparatus, e.g. by a mechanical grate. In the second stage, the partially dehydrated products are similarly treated by a countercurrent of hot hydrochloric acid gas to obtain the anhydrous salt, the temperatures in both stages being so regulated that the desired degree of dehydration is obtained in the lower part of the furnace and the upper portion of the mass is not heated to the fusion or sintering point. No external heating is used in either stage. For the preparation of the dihydrate, the temperature at the bottom of the mass ranges from 140-160 DEG C., and for the tetrahydrate 120-140 DEG C., while the temperature of the exit gases is 60-80 DEG C. In the preparation of the anhydrous salt, the temperatures are 450-550 DEG C. and 150-250 DEG C. respectively. A suitable apparatus is shown in the Figure, wherein the salt is fed down through the furnace a, which may have an enamel or ceramic lining, in counter-current to the drying agent which is forced in through the opening d after passing through a heater p. The dehydrated material is removed by a rotating grate b and falls into a tapping chamber g closed by valves h<1>, h<2>. Thermometers t<1>, t<2>, t<3> are used to regulate the temperature of the drying agent and of the mass. The inlet for the drying agent may be arranged above the grate, and provision may be made for evacuating the apparatus or rinsing with indifferent gases to remove the air contained in the mass before the drying commences. When preparing the anhydrous salt, the hydrogen chloride issuing from the apparatus is dried, reheated and recycled through the furnace, any losses being made up from a suitable supply.