Preparation Of Calcium Carbonate From Calcium Carbide Residue

Calcium carbide slag is the by-product of production of PVC by calcium carbide method. As its main component is calcium hydroxide with high alkaline and water-retaining property, it is belongs to the industrial solid waste. In this paper, according to the composition and content of calcium carbide slag material, the two refining process involved calcination method and extraction method of ammonium chloride were studied. The effect of process parameters on the quality and morphology of calcium carbonate were discussed.1) In the calcination process, the addition of sodium carbonate was proposed to remove the insoluble impurities in acid in the calcium carbide slag and the effects of calcination temperature, calcination time, the added quantity of the sodium carbonate, the hydration conditions and other factors on the quality and morphology of calcium carbonate was studied. The optimum technical conditions were obtained as follows: calcination temperature is 900℃, calcination time is 1 hours, the number of sodium carbonate is 1.5 times the molar amount of impurities, lime-water ratio is 1:7, The initial hydration temperature is 93 "C, the concentration of sodium hydroxide in digestive water is 20 g/L, the holding temperature time is 0.5 hours, the lime milk is sifted by 500-mesh sieve. Finally, the content of calcium carbonate reaches to 96.8%.2) In the NH4CI solution extraction method, the optimum technical conditions were as follows:The mass ratio of the reactants is calcium carbide slag:ammonium chloride: water= 1:1.5:8, reaction temperature is 85℃, reaction time is 1 hours. Finally, the conversion rate of calcium is 83.3% and the purity of calcium carbonate is 99.6%.3) In the carbonization process of calcium extract, the chlorine ion does not affect the appearance and size of calcium carbonate particles, the particle size of the calcium carbonate become small because of NH3 existing. Calcium carbonate products by extraction method of ammonium chloride are large spherical particles composed of Nano-sized calcium carbonate particles.