Washing of Raw Salt - Washing Principle
The essence of washing raw salt is the process of removing both soluble and insoluble impurities.
1. Removal of Soluble Impurities:
The principle for removing soluble impurities from raw salt is based on the fact that the washing solution is saturated with NaCl but unsaturated with soluble salts such as MgCl₂ and MgSO₄.
Therefore, during the washing process, NaCl does not dissolve, while soluble salts like MgCl₂ and MgSO₄ are removed through dissolution.
2. Removal of Insoluble Impurities:
The principle for removing insoluble impurities relies on the different settling velocities of insoluble substances with varying densities in the brine.
Insoluble substances such as grass, wood chips, and soil, which have a lower density than raw salt, settle more slowly in the washing process. These impurities often remain suspended in the washing solution and are separated from the salt through overflow. The more insoluble impurities carried away by the overflow, the higher the washing efficiency for insoluble substances.
(Linear Vibrating Seive)
However, larger particles like sand cannot be removed by the overflow brine, so raw salt is usually screened before entering the washing machine to improve the efficiency of removing insoluble impurities during washing.
3. Exchange Process:
The washing process also involves the exchange of the mother liquor attached to the surface of the salt crystals with the washing solution.
By washing, the composition of the mother liquor attached to the crystal surface is updated, and the mother liquor from salt production is replaced with saturated brine containing fewer impurities.
This exchange enhances the quality of the salt. The more thorough this exchange, the higher the washing efficiency of the raw salt.
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