| Calcium carbide reside (CCR) leaching solution with Ca2+ was prepared from CCR using ammonium chloride solution as leaching reagent to remove unsoluble impurities in CCR, and the optimized leaching conditions were confirmed as well. Using NH4HCO3 and CO2 as carbonation reagent respectively, calcium carbonate was synthesized from CCR leaching solution, D and sodium polyphosphate were selected as the more appropriate additives for the above carbonation methods and the carbonation conditions were confirmed after that. The main results are obtained as follow:(1) Taking the leaching ratio of Ca2+ as the main index, leaching conditions were investigated and optimized via single-factor and orthogonal experiments. The optimized leaching conditions were as follow:leaching temperature 20 ℃, leaching time 70min, stirring rate 300rpm, mole ratio of n(2NH4Cl)/n(Ca(OH)2) 1.2:1 and ratio of liquid to solid 10:1. The leaching ratio of Ca2+ under the optimized conditions can reach 94.55%.(2) Taking the particle size of calcium carbonate synthesized by different additives as the main index, D was selected as the more appropriate additive when preparing nano calcium carbonate using NH4HCO3 as carbonation reagent while sodium polyphosphate as the more appropriate additive when using CO2 as carbonation reagent.(3) Nano calcium carbonate was synthesized from CCR leaching solution reacting with NH4HCO3 solution, taking the particle size of calcium carbonate as the main index, the reaction conditions were optimized via single-factor experiments. The optimized reaction conditions were as follow:adding CCR leaching solution with Ca2+ concentration of 1.5mol/L to 0.5mol/L NH4HCO3 solution, dose of additive (D) 3%, reaction temperature 20℃. Particle size of calcium carbonate under the optimized condition is 40-60nm with good dispersion.(4) Nano calcium carbonate was prepared from CCR leaching solution reacting with ammonium bicarbonate reacting with CO2, taking the particle size of calcium carbonate as the main index, the reaction conditions were optimized via single-factor experiments. The optimized reaction conditions were as follow:Ca2+ concentration in CCR leaching solution lmol/L, dose of additive (sodium polyphosphate) 3%, initial carbonation temperature is 20℃. Particle size of calcium carbonate under the optimized condition is about 40nm with good dispersibility. |
