Study On Preparation Of Calcium Sulfate Whisker From Phosphogypsum

With the industrial development of phosphate fertilizer in China,the increasing accumulation of phosphogypsum requires the high value utilization of phosphogypsum has become a big problem.Therefore,using phosphogypsum as raw material prepare the calcium sulfate whisker as a way to make phosphogypsum high value.At the meanwhile,it can solve the problem of environmental pollution caused by phosphorus gypsum stacking.Calcium sulfate whisker is a high quality and inexpensive material.It has good toughness,high strength,high temperature resistance and corrosion resistance.It has been widely applied in plastics,ceramics and other fields.We have prepared calcium sulfate whisker by using calcium sulfate,and obtain the process conditions of stable calcium sulfate whisker.And we investigate the mechanism of whisker,and study on the process conditions of purification of phosphogypsum which is conducive to high value utilization of phosphogypsum.The purpose of this study is to provide a theoretical basis for the preparation and application of calcium sulfate whiskers.First of all,we have prepared the calcium sulfate whisker using gypsum as main raw material,and discussed the effects of different conditions including reaction temperature and reaction time on the appearance of calcium sulfate whisker.Under the optimum reaction temperature and reaction time on the preparation process,we focus on the influence of stabilizers and crystallization how to effect on the appearance of whiskers.Thus the stable hemihydrate calcium sulfate whisker is obtained.The results show that under the condition of 150?and 6h,0.3% magnesium chloride and 0.100% sodium oleate additives,the ratio of length to diameter of calcium sulfate whiskers can be 40.Secondly,we have analyzed the influence of impurities to hemihydrate calcium sulfate whisker crystallization,and added phosphoric acid and hydrofluoric acid in the raw materials of the gypsum.Soluble phosphorus in phosphogypsum and calcium ion combine to be calcium phosphate which can reduce the saturation of the solution and has an effect on the growth process of whisker.Soluble fluorine in phosphogypsum makes the whisker thicker and affects its crystallization and decrease the ratio of length to diameter.The results show that when the amount of soluble phosphorus reaches 1%(according to the raw material mass),it is difficult to form whiskers.When the amount of soluble fluorine reaches 1.2%,the whiskers are hardly formed.Finally,according to the analysis of the phosphogypsum components,the chemical treatment process was selected to treat the phosphogypsum.And ammonium bicarbonate and ammonia water were reacted with phosphogypsum to extract sulfate.The hydrochloric acid was reacted with calcium carbonate to extract calcium ions.Calcium sulfate was recovered through the metathesis reaction.The results show that this method has achieved high recovery.The sulfate conversion rate can reach 82.66% and the calcium ion conversion rate can reach 98.89%.Calcium sulfate whiskers with purified calcium phosphogypsum can be prepared.The product is measured by morphological characterization.With the measurement and calculation,a half-calcium sulfate whisker product with an average ratio of length to diameter of 50-80 was obtained,basically fulfilling the research objectives.