Effect of Organic Acid on Crystalline Habit of α-Hemihydrate Desulfurization Gypsum and its Crystal Modification Mechanism

The adsorption characteristic of organic acid and its effect on the crystalline habit and morphology of α-hemihydrate desulfurization gypsum were investigated.The crystal modification mechanism of organic acids was analyzed by means of adsorption and crystal growth.The results show that organic acid evidently changes the crystalline habit of dihydrate,leading to a large crystal size and transformation of crystal shape from long clavate-like to short columnar-shaped.The short columnar-shaped α-hemihydrate desulfurization gypsum crystals with a length-diameter ratio of 1:1 could be prepared by controlling the dosage of organic acid.Organic acid complexes with Ca2+,and organic acid calcium complex compounds were formed on the crystal nucleus of α-hemihydrate desulfurization gypsum,which hindered Ca2+ diffusion and crystal growth,and decreased the growth rate of α-hemihydrate desulfuri-zation gypsum crystals.The crystals could thus have time enough to grow up,and as a result,the size of dihydrate crystals became coarser.Organic acid was selectively chemisorbed on the(111) face of gypsum crystal,which inhibited the growth of c axis and al-tered the relative growth rate of crystal faces in different axis directions,consequently leading to the transformation of crystalline habit and crystal morphology of dihydrate gypsum.