Experimental Study On Removal Of Phosphorus From Moiecular Sieve Wastewater By Metal Salt Precipitation

SAPO-34 zeolite molecular sieve is a microporous crystal structure composed of[Si O₂]、[PO²⁺]and[Al O₂^-]tetrahedral structure,which uses Si,Al and P as synthetic raw materials and organic ammonia as a template.SAPO-34 zeolite molecular sieve is mainly synthesized by hydrothermal method.In the production process of molecular sieve,a large amount of ultra-high phosphorus industrial wastewater is synthesized,and the organic matter content is high,and it is difficult to directly carry out biochemical treatment.The chemical precipitation method has the advantages of good phosphorus removal effect,simple operation,stable effect and low cost of chemical reagents.In this paper,a chemical precipitation method is used to use metal ions to react with phosphate in wastewater to generate insoluble particulate matter,and precipitation filtration is used to remove phosphorus in wastewater,creating favorable conditions for subsequent biochemical treatment.The research results of this paper are as follows:（1）The phosphorus removal effects of precipitation agents such as Fe₂（SO₄）₃,Fe SO₄,Al Cl₃,Al₂（SO₄）₃,KAl（SO₄）₂,Ca Cl₂ and MgCl₂·6H₂O were compared.Without adjusting the p H value,adding 20 g/L precipitant separately,reacting for 30 minutes,and standing for 30 minutes,Ca Cl₂and MgCl₂·6H₂O have the best phosphorus removal effect on molecular sieve wastewater,and the removal rate of TP can reach more than 50%.For the single factor variable method of Ca Cl₂,it was determined that under the conditions of adding 40 g/L and 0.04 g/L PAM,initial p H value of10.5,reaction time of 20 minutes,and standing for 30 minutes,the removal effect of TP was the best,and the removal rate was 98.75%,the residual concentration of TP is 175.97 mg/L.（2）Comparing the removal effect of calcium salt and magnesium salt on TP under their respective optimal conditions,the results show that the removal effect of magnesium salt on TP is better than calcium salt,and Mg²⁺and the phosphate in the wastewater will generate Mg NH₄PO₄·6H₂O（stuvite）precipitation,as a good slow-release fertilizer,struvite has high purity and has good recycling value.（3）Comparing the removal effects of MgCl₂·6H₂O,Mg SO₄·7H₂O,Mg O and Mg（OH）₂ on TP in wastewater,it is found that MgCl₂·6H₂O has the best phosphorus removal effect.MgCl₂·6H₂O has the best dephosphorization effect under the conditions of initial p H value of 11.0,Mg:P molar ratio of 1.1:1,rotation speed of 900 r/min,reaction for 20 minutes,and standing for 30 minutes.The removal rate of TP is 99.57%,the residual amount of TP is 58.31 mg/L.（4）There are obvious characteristic absorption peaks of PO₄^3-and NH₄⁺in the infrared spectrum,indicating the presence of struvite in the precipitated product.Through SEM electron microscopy analysis,it is found that there is agglomeration in the precipitated product,and there is adhesion on the surface.At larger magnifications,it is observed that the precipitates are closely arranged in small spherical particles.In the XRD pattern,There are still a small amount of miscellaneous peaks in the spectrum,indicating that the precipitate is an amorphous magnesium ammonium phosphate precipitate.（5）The response surface model determined that the initial p H value has the greatest influence on the phosphorus removal effect.The optimal process conditions calculated by the model are:Mg:P molar ratio 1.1:1,initial p H value 10.00,stirring rate 900 r/min,and the highest TP removal rate can reach 99.65%.In addition,the relative error between the experiment and the model is low,and the accuracy of the model is high.（6）In the experiment of removing phosphorus by metal salt compound precipitation method,the molar ratio of Mg:P is controlled to be 1.1:1 without adjusting the initial p H value.It is found that the[Mg O+MgCl₂·6H₂O]compound precipitation agent has the best TP removal effect when the molar ratio of Mg O/MgCl₂·6H₂O is 1:1,reacts for 20 minutes and stands for 30 minutes,and the removal rate of TP is 99.60%,the residual concentration is 53.60 mg/L,and the cost of the[Mg O+MgCl₂·6H₂O]compound precipitation agent is the lowest.