The Processing of Salt For its main bulk usage, road de-icing, rock salt with a purity of 95 to 100 per cent is merely crushed, screened and sized, but it must be purified for almost all other uses. In the production of fine salt, a vacuum pan process is used to evaporate salt brine. Impurities are removed and the brine is fed into a series of three or four large cylindrical steel vessels. They are designed to operate under vacuum so the brine will boil at lower temperatures. The result is a product called fine salt, which can be further refined to make commercial salt products.
Final processing involves screening and the removal of metallic impurities.
The salt is then prepared and packaged for as many as 100 different end uses. It may be treated to 'iodize' it or to make it free flowing, or it may be pressed into blocks, briquettes or tablets. In processing, the salt may also be fused at temperatures of 815 degrees Celsius, when it becomes a clear liquid that looks and flows like water. The fused salt is piped from the furnaces into metal molds to make salt slabs which, in turn, are crushed and screened. Products from this process are used in refrigerator cars, water softeners and for hide curing.