GB1009736A - Method for purifying salt - Google Patents

Abstract

<PICT:1009736/C1/1> <PICT:1009736/C1/2> A method for producing purified anhydrous sodium chloride from a supply of relatively impure anhydrous salt (e.g. impure solar salt) comprises (1) circulating or passing a saturated brine through the supply salt while maintaining the salt and brine mixture at a temperature between 32.2 DEG and - 6.02 DEG F. inclusive to dissolve the salt feed and form dihydrate therefrom, (2) subjecting the brine-dihydrate slurry so formed to heating in order to melt the dihydrate and to form an excess of purified anhydrous salt precipitating from the associated brine, (3) then separating the excess anhydrous salt for product delivery, (4) while returning the associated brine to the salt feed supply for repetition of the process. For example, in Fig. 4, dihydrate crystals formed in crystallizer 12 from salt feed 10 and brine cooled by refrigerating coils 14 (coils are in surrounding jacket in Fig. 5, not shown) pass as slurry in brine to melting tank 20 (or heat exchanger 34 in Fig. 5). Pure salt slurry 22 is withdrawn (or filtered by rotary vacuum pump 36 in Fig. 5), and brine mother liquor is recycled (in Fig. 5 to the impure salt feed). In Fig. 6, dihydrate crystals formed, are conveyed by screw 40, are drained and delivered by screw 42 to melting tank 44. Pure salt is conveyed by screw 46 and drained and delivered by screw 48. Brine is recycled from the melting tank.