Inorganic Chemicals Industry ›› 2024, Vol. 56 ›› Issue (12): 127-133.doi: 10.19964/j.issn.1006-4990.2024-0133

• Environment·Health·Safety • Previous Articles     Next Articles

Study on crystallization and filtration properties of calcium sulfate for treating industrial waste sulfuric acid with calcium carbonate

LUO Ya1(), ZHOU Rong2, LÜ Li1(), YANG Jie1, TANG Shengwei1, ZHANG Tao1   

  1. 1.School of Chemical Engineering,Sichuan University,Chengdu 610065,China
    2.Sichuan Sanlian New Materials Co.,Ltd.,Chengdu 610101,China
  • Received:2024-03-07 Online:2024-12-10 Published:2024-04-11
  • Contact: Lü Li E-mail:2717214639@qq.com;lily@scu.edu.cn

Abstract:

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 industrial 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 precipitants 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 concentration of H+ and the amount of CaCO3 added.At the conditions of sulfuric acid of 5%,reaction temperature of 30 ℃,stirring 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 content 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 carbonate slowly at low temperature.SDS could regulate the morphology of gypsum,promote the crystal growth,and improve the filtration performance of gypsum.

Key words: industrial gypsum, crystallization, filtration quality, moisture content

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