Effect of Calcium Oxide on Solidification Properties of Soluble Phosphorus and Soluble Fluorine in Phosphogypsum
Phosphogypsum is a large-scale solid waste produced in wet-process production of phosphoric acid,which is mainly composed of CaSO4·2H2O.The migration of soluble phosphorus and fluorine in the phosphogypsum stack will cause environmental pollution.In this paper,calcium oxide was used to solidify soluble phosphorus and fluorine in phosphogypsum.Response surface analysis shows that the solidification efficiency of soluble phosphorus and soluble fluorine is positively correlated with CaO mass fraction and reaction time,the influence of various factors on the solidification efficiency is in the order of CaO mass fraction>liquid-solid ratio>reaction time.The optimized parameters are CaO mass fraction of 3.30%,liquid-solid ratio of 1.90 and reaction time of 110 min.And the solidification efficiencies of soluble phosphorus and soluble fluorine are 98.6%and 99.7%,respectively.The results of solution chemical calculation show that soluble fluorine is precipitated prior to soluble phosphorus in the solidification process.The results of X-ray diffraction and scanning electron microscopy show that soluble phosphorus is mainly precipitated in the form of CaHPO4∙2H2O,while soluble fluorine in the form of amorphous CaF2.
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