The influence of carboxyl number, carboxyl distance, and other auxiliary groups such as hydroxyl, double bond and its cis/trans structure of organic acid on the crystal morphology of α-hemihydrate desulfurization gypsum were studied. The crystal modification mechanism of organic acids was analyzed from the point of adsorption and crystal growth. The results showed that monoacid has no crystal modifying effect, while dibasic acid or polybasic acid with carboxyl distance of three C atoms such as succinic acid and citric acid are highly efficient crystal modifying agents. Adjacent hydroxyl groups have aid-modifying function to organic acids. Cis-structure could slightly enhance the crystal modifying effects of organic acids, while the trans-structure damages synergy reaction among carboxyl groups, leading to the ability lose of its crystal modification. Two carboxylic of organic acid complexs with Ca2+, selectively adsorbed on the (111) face of α-hemihydrate desulfurization gypsum, formating ring-shaped complex compound, which hinder Ca2+ diffusion and crystal growth, weakens the rative advantage of growth rate on (111) face in c-axis directions, and thereby changes the crystal growth habit and morphology of α-hemihydrate desulfurization gypsum.
