The Book: SODIUM CHLORIDE by KAUFMANN, has ±700 pages dealing with all aspects of NaCl - Sodium Chloride.
Standard Specification for Salt defines Refined Salt as Technical Types A & B (SABS: 638-961)
The salt as produced by solar evaporation of sea water brine, mechanically harvested and stockpiled into heaps is known as CRUDE SALT.
To refine this Crude Salt to a NaCl purity of 99.8% on a dry basis, it is re-washed up to 7 times by a partially treated controlled brine plus some fresh water. It is allowed to dry for a day or two in bins. Thereafter it is conveyed to a rotary hot-air dryer fired by gas, and heated to 365 degrees F, reducing moisture content to a few hundredths of 1%, and charring all organics by flame impingement. This industrial salt emerges as a sterile product, passing into a rotary cooler, then to grinders/crushers and electric screens, to be graded into various sizes for packing and shipment.
The NaCl content varies from 97% for natural hand-harvested salt; to 99% for washed, Grade I Coarse salt, which is defined as Crude Salt by Kaufmann.
There are other ways of producing Refined Salt directly from sea brine, but not using solar energy. The manufacturers use gas or electricity and therefore have a large carbon footprint, namely, Vacuum Pan Salt and Grainer Salt, which are used in areas where solar energy is not feasible due to weather conditions.
Imported Pan-Heated Salts also have a high carbon footprint and are not eco-friendly.