Study On The Control Effect Of Phosphate On The Morphology Of Ultrafine Calcium Carbonate

Ultrafine calcium carbonate with special crystal morphology and particle size distribution is widely used in rubber, plastic, paper, ink, sealant, paint and other fields. By adding crystal controlling agents, and changing the carbonation reaction conditions, can realize the morphology of calcium carbonate to be specific and regular, and the particle size to be ultrafine, which will further improve the application performance.In this paper, a kind of soluble inorganic phosphate is used as crystal controlling agent, its controlling effect on morphology of calcium carbonate is discussed, and needle, spindle shaped and spherical ultrafine calcium carbonate are prepared. The carbonation temperature, crystal controlling agent adding time and amounts, CO2 ventilation rate, Ca(OH)2 suspension initial concentration and other process conditions’effects on the morphology and particle size distribution of ultrafine calcium carbonate are studied. The results as follows:Phosphate realizes its controlling functions on the morphology of ultrafine calcium carbonate includes three aspects:one is to react with Ca2+ in the system to produce insoluble hydroxyapatite, reduces CaCO3 supersaturation, so as to promote CaCO3 crystal nucleation rate; the two is to react with Ca2+ on the CaCO3 crystal surface to produce hydroxyapatite and form a steric hindrance, thereby inhibiting the growth of calcium carbonate crystal face, and improving the CaCO3 particles dispersion; the three is to react with Ca2+ on the Ca(OH) 2 particles surface to produce hydroxyapatite, coating on the surface, inhibiting the dissolution of Ca(OH)2 particles.When the carbonation starting temperature is less than 30℃, adding 4% phosphate at 60 minutes can gain acicular superfine calcium carbonate with average particle size about 0.6μm by the constant temperature carbonation reaction. When the carbonation starting temperature is 25℃, adding 1%-2% phosphate at 60 minutes can prepare 0.5～0.7μm, length to diameter ratio 8～10, narrow particle size distribution and dispersed acicular ultrafine carbonate calcium.When the carbonation reaction starting temperature is 40℃, adding 1.5%-2% phosphate at 10～20 minutes, can gain particles size of 0.7-1.0μm, length to diameter ratio of 4-5, single scattered spindle superfine calcium carbonate.When the carbonation reaction starting temperature is 40℃, adding 6% phosphate before the carbonation reaction start, can prepare spherical ultrafine calcium carbonate with average particle size of 60 nm, narrow particle size distribution, regular morphology and good dispersion. Phosphate realizes the preparation of spherical calcium carbonate by forming hydroxyapatite to form core-shell structure.