DENG Licong, ZHANG Yifei, CHEN Fangfang, CAO Shaotao, YOU Shaowei, LIU Yan, ZHANG Yi. Reactive Crystallization of Calcium Sulfate Dihydrate from Acidic Wastewater and Lime[J]. Chin.J.Chem.Eng., 2013, 21(11): 1303-1312.
DOI:
DENG Licong, ZHANG Yifei, CHEN Fangfang, CAO Shaotao, YOU Shaowei, LIU Yan, ZHANG Yi. Reactive Crystallization of Calcium Sulfate Dihydrate from Acidic Wastewater and Lime[J]. Chin.J.Chem.Eng., 2013, 21(11): 1303-1312.DOI: 10.1016/S1004-9541(13)60626-6.
Reactive Crystallization of Calcium Sulfate Dihydrate from Acidic Wastewater and Lime
The present work focused on the recycle of the sulfate and the metal ions from acidic wastewater discharged by nonferrous metallurgical industry. The effects of the temperature
the reactant concentration
the stirring speed and the metal ions on the reactive crystallization process of calcium sulfate between sulfuric acid and lime were systematically investigated. The morphology of the precipitated crystals evolved from platelet-like and needle-like shape to rod-like shape when the temperature was increased from 25 to 70 ℃. An increase in the agglomeration of calcium sulfate was found with increasing lime concentration. Metal ions markedly retard the rate of crystallization of calcium sulfate dihydrate. The crystallization of gypsum was slowed with the existence of Mg
2+
in the solution
and the morphology of gypsum was transformed from platelet-like shape to rod-like shape when Mg
2+
concentration reached 0.08 mol·L
-1
. The amorphous ferric hydroxide was coated on the calcium sulfate after the co-precipitation process while Zn
2+
and Al
3+
ions in the solution enhanced the agglomeration of the calcium sulfate by absorbing on the surface of the crystals. Comprehensive acidic wastewater containing hea
vy metals was efficiently purified by the two stage lime neutralization technology
and highly agglomerated gypsum precipitates with needle-like shape were obtained. The precipitates could be purified by sulfuric acid washing
and the metal ions were effectively separated from the calcium sulfate by-products.
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