Formation of X-ray amorphous and crystalline aluminium hydroxides

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Abstract
Summary: Various crystalline and X-ray amorphous forms of aluminium hydroxide prepared from sulphate and chloride solutions by varying the mole ratio of NaOH to Al3+ have been characterized by chemical analysis and X-ray diffraction. When the NaOH/Al ratio is 3 or 3·3, crystalline Al(OH)3 in the form of bayerite, nordstrandite, gibbsite, or mixtures is obtained in several hours. When the ratio is 2·75 or below, no Al(OH)3 is evident and the products are X-ray amorphous and remain so even after ageing for six months. Chemical analysis indicates that the amorphous precipitates are basic aluminium sulphates or chlorides. In the 0 to 2·1 range of NaOH/Al, the composition of the products is constant, being approximately Al(OH)2·2X0·8. In the 2·1 to 2·75 range, a continuous series of basic salts, of composition ranging from Al(OH)2·2X0·8 to Al(OH)2·75X0·25, is obtained.

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