The calcium sulphate is removed by filtration and the citric acid solution is further purified. Crystallization of citric acid from a hot aqueous solution yields anhydrous citric acid; crystallization from a cold solution yields the monohydrate. ... The neutralized solution must then be evaporated to dryness in a strictly controlled manner to avoid undue losses. ... In the cyanide processes, the most widely used method for extracting gold and silver from the ores, the finely divided ore is contacted with a dilute solution of sodium or potassium cyanide. ... The insoluble polymer protects the...

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• Grade Level: Undergraduate