Study On The Flocculation,sedimentation And Separation Of The Ammoniated Slurry Of Wet Phosphoric Acid

Industrial wet process phosphoric acid has many impurity ions,such as Fe³⁺、Mg²⁺、Al³⁺、SO₄^2-.In the process of wet phosphoric acid in ammoniation,the impurities will be ammoniated and produced a variety of complex precipitations which will affect the subsequent process of settlement and separation.In order to achieve the purpose of increasing productivity of ammonium phosphate,adding flocculant to speed up the process of sedimentation and separation.In this paper,on the basis of some flocculating conditions,cation polyacrylamide（CPAM）can increases the sedimentation rate of ammoniated slurry with the method of gravity sedimentation.Through the vacuum filtration,CPAM and polymeric ferric sulfate（PFS）working together have the best effect on ammoniated slurry separation.The wet phosphoric acid is simulated with pure chemical reagents.The content of the other impurities in the simulating wet-process phosphoric acid were fixed while one was varied.Study the effect of impurities on the flocculation of the ammoniated slurry.Researches show that Fe³⁺and Mg²⁺have the similar effect,with the increase of the content,the sedimentation rate becomes faster first and then slow down.when the content is beyond the certain range,the slurry hardly settle.With the increase of the content of Mg²⁺in a certain range,the sedimentation rate probably has no change.With the increase of the content of SO₄^2-,the sedimentation rate becomes slower.The impurities of industrial wet phosphoric acid in a certain range have the similar effect on the flocculation and sedimentation of the ammoniated slurry.By the quadratic regression orthogonal design,it can be concluded that the impurities have the influence on the viscosity of the ammoniated slurry.Aluminum and magnesium ions are the main factors and the influence of iron and sulfur is smaller.The interaction effect of Magnesium and aluminum,iron and aluminum cannot be neglected.And the viscosity of the ammoniated slurry will be risen by the increase of all impurities together.By gravity settling experiments,the optimum experiment condition is as follows:30%of CPAM ion degrees,0.4%of CPAM concentration,flocculation temperature of90℃,rapid mixing time of 1.5 minutes.By analyzing the Zeta potential of the ammoniated slurry and characteristics of the flocculants,the flocculating mechanism of CPAM in the ammoniated slurry is charge-neutrality principle and adsorption bridging principle.