Study On The Preparation Of Nano-CaCO₃ From Phosphogypsum

In this dissertation, the preparation conditions of nanometer CaCO3 from phosphogypsum were studied via "phase transfer precipitation" and "two-step metathetical reaction" methods. The main research work includes:(1) Preparation of nano-CaCO3 from phosphogypsum via "phase transfer precipitation" method.Using MY as phase transfer agent, anhydrous Na2CO3 as precipitant, taking the morphology of calcium carbonate sample preparation and particle size as the main index, STP was screened and determined as the more suitable additive and the precipitation conditions were optimized as follow: reaction temperature was 25?, the precipitation reaction feeding method was dropping CaY2 solution into sodium carbonate solution (containing STP) and STP addition amount was 3%wt. Under this condition, the as-prepared samples were calcite-type nano-CaCO3 with uniform particle size of about 30nm. At the same time, the effect of initial concentration of Na2SO4 on the phase transfer rate of Ca2+ ions was investigated through the circulation experiments of the precipitated mother liquor, and concluded that the enrichment of SO42- ions in the mother liquor was the main factor for the decrease of the phase transfer rate of Ca2+ ions.The mechanism of controlling by additives and process conditions on the growth of CaCO3 grains was studied preliminarily and the conclusion was obtained as follow:The additive STP changed the surface energy of CaCO3 mainly through ionization to produce P3O105-, adsorption and implantation into the lattice of CaCO3 to change the surface energy of CaCO3, thus reduced the active spots in the growth of CaCO3 crystal, so as to prepare the nanometer calcium carbonate with uniform particle size.(2) Preparation of nanometer calcium carbonate from phosphogypsum via"two-step metathetical reaction" method.Taking the conversion rate of Ca2+ ions in phosphogypsum as the main index,the preparation conditions were investigated via single-factor experiments and orthogonal experiments, and the optimized conditions were as follows: reaction time 120min,reaction temperature 40? the molar ratio of CaSO4-2H2O in phosphogypsum to ammonium bicarbonate and ammonia 1:1:1.4. The average conversion rate of calcium reached 95.45% under the optimized condition.Taking the particle size of calcium carbonate as the main index, the STP-was-screened and determined as the more suitable additive; And the CO2 carbonization precipitation conditions was obtained as follows: Ca2+ concentration in calcium chloride solution 0.5mol·L-1, dose of dispersant STP 3%, reaction temperature 25?.Under the optimized condition, the crystal type of the as-obtained nano-CaCO3 was vaterite, and performed good dispersibility with the particle size of about 20?30nn.