Study on crystallization and filtration properties of calcium sulfate for treating industrial waste sulfuric acid with calcium carbonate
The output of industrial waste sulfuric acid with low concentration is huge in China.Due to the difficulty and high cost of recovery,it is usually neutralized by calcium salt and converted into industrial gypsum.However,the high content of soluble impurities in gypsum and the high cost of treatment and utilization are caused by the high moisture content of indus-trial gypsum.The main reason for the high moisture content of gypsum is the fine grain of calcium sulfate and poor filtration quality.In this paper,the nucleation mechanism and crystal morphology of calcium sulfate with different calcium salt pre-cipitants were investigated,and the effect of the nucleation rate,grain size and moisture content of calcium sulfate crystals by the precipitant of CaCO3 at the different reaction conditions were studied.The results showed that the crystal nucleus of calcium sulfate formed in situ on the surface of calcium carbonate particles,and the nucleation rate was affected by the con-centration of H+and the amount of CaCO3 added.At the conditions of sulfuric acid of 5％,reaction temperature of 30℃,stir-ring rate of 300 r/min,adding rate of CaCO3 of 0.45 g/min,pH=2 and reaction time of 30 min,the calcium sulfate crystals were acicular structure with an average particle size of 20 μm,which moisture content was 36.3％.Adding w(SDS)=0.04％,the calcium sulfate crystals showed a flake structure,the average particle size was increased to 50 μm and the moisture con-tent was decreased to 26.4％.The key to reduce the moisture content of gypsum was to avoid the rapid formation of calcium sulfate crystal nuclei in large quantities.The nucleation rate of calcium sulfate could be reduced by adding calcium carbon-ate slowly at low temperature.SDS could regulate the morphology of gypsum,promote the crystal growth,and improve the fil-tration performance of gypsum.
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维普
