ST09 Separation of homogeneous solid - liquid mixtures

Aim: To show two crystallisation processes: one in the laboratory and one in industry.

On the left-hand side of illustration ST 09 the crystallization of a solution of aqueous copper sulphate can be seen.

If the water evaporates slowly beautiful blue crystals of copper sulphate are formed. Copper sulphate is thus separated from the solvent in a homogeneous solution.

On the right of the illustration the extraction of salt from seawater is shown. This is a technique that is used frequently in many Southern European countries. The seawater is transferred via sluice gates into the first settlement basin (A). Here the sand and mud sink to the bottom. The clarified seawater then passes through sluice gates into the first crystallisation basin (B). Here, the less soluble calcium salts precipitate out (among others, the calcium halides).

Some evaporation takes place in this basin and so the concentration of the sodium chloride increases. When the original volume has been reduced by a factor of 10, the almost saturated salt solution is transferred via sluice gates into the shallow salt basins (C). Common salt (NaCl) crystallises out as the water evaporates. The crystallised salt is gatheredinto heaps (D).