Complex sentence: The sodium hydroxide reacts with the aluminous minerals of bauxite to form a saturated solution of sodium aluminate; insoluble impurities, called red mud, are suspended and separated in the clarification step.
Split into simpler sentences: The sodium hydroxide reacts with the aluminous minerals of bauxite to form a saturated solution of sodium aluminate. The resulting insoluble impurities, red mud, are suspended and separated during clarification step.