Experimental Study On Removal Of Ammonia Nitrogen And Phosphate From Wastewater By Kaolin Based Composites

With the rapid development of the country,a large amount of ammonia nitrogen and phosphorus wastewater is still produced in the process of development,causing significant environmental problems.In order to solve the water eutrophication caused by ammonia nitrogen and phosphorus wastewater,scholars tend to use efficient and economical adsorption materials to deal with such environmental problems,but the application of mineral-based materials as adsorbents is limited,especially kaolin.In this study,a series of modification experiments were carried out to improve the low ammonia nitrogen and phosphorus adsorption capacity of kaolin.Through hydrothermal synthesis and salt modification methods,the natural kaolin with low ammonia nitrogen and phosphorus adsorption capacity was synthesized into Kaolin based molecular sieve（Na CK）with high ammonium removal capacity and magnesium and aluminum modified kaolin based molecular sieve（Mg/Al-Na CK）with phosphorus removal capacity.Based on the optimized adsorption material,the influence of adsorption experimental parameters such as reaction p H,adsorbent dosage and coexisting ions on the adsorption process was investigated,and XRD,SEM-EDS,FT-IR,XPS and BET were used to combine with adsorption kinetics and isothermal adsorption fitting.The morphology and structural properties of adsorbent materials before and after adsorption were analyzed and the adsorption mechanism was explored.In addition,on the basis of clear adsorption mechanism,desorption-regeneration experiments were carried out to determine the practicability of the adsorbed materials.In addition to solving the problem of ammonia nitrogen and phosphorus wastewater,it provides a new idea for the application of mineral based materials.The main conclusions of the experiment are as follows:（1）Na CK was synthesized from NK by hydrothermal synthesis method.The results of Na CK preparation showed that the optimum preparation conditions of ammonium removal adsorption materials were as follows:calcination temperature of 600℃,aging temperature of 60℃,aging time of 2 h,crystallization temperature of 90℃,crystallization time of 4 h under the solid-liquid ratio of 1:14 between 3 mol/L Na OH and calcined kaolin.Na CK was prepared by salt modification method to obtain Mg/Al-Na CK.The results of Mg/Al-Na CK preparation showed that the optimum phosphorus removal Mg/Al-Na CK adsorption material could be obtained under the condition of n(Mg²⁺):n(Al³⁺)=3:1 and p H=10.（2）The results showed that at p H=6,dosage of 6 g/L and reaction time of 60 min,the removal rate of ammonia nitrogen and adsorption capacity of Na CK were 89.5%and 1.48 mg/g,respectively.The results showed that the phosphate removal rate and adsorption capacity of Mg/Al-Na CK were 93.9%and 0.67 mg/g,respectively,at p H=7,dosage of 3 g/L and reaction time of 60 min.（3）The research results of ammonia nitrogen and phosphate removal mechanism of kaolin based adsorption materials show that Na CK and Mg/Al-Na CK are more inclined to the quasi-second-order kinetic model by using the quasi-first-order and quasi-second-order kinetic equation models respectively.This indicated that the adsorption mechanism of Na CK and Mg/Al-Na CK was mainly chemical adsorption,in which Na CK reached the equilibrium state around 30min,while Mg/Al-Na CK reached the equilibrium state around 40min.It was found that the crystal structure and morphology of Na CK synthesized by NK changed greatly through different testing methods.The results of XPS and FTIR show that the main mechanism of ammonia nitrogen removal by Na CK is the ion exchange between Na⁺and NH₄⁺,and there is a small amount of electrostatic attraction.The main mechanism of Mg/Al-Na CK phosphate removal is interlayer ion exchange and coordination complexation.（4）The desorption and regeneration test results of kaolin based ammonia nitrogen and phosphate removal adsorbent showed that Na CK showed good desorption and regeneration efficiency under 1 mol/L Na Cl desorption solution,both of which were above 90%,showing a good reusable prospect.The desorption performance of Mg/Al-Na CK was slightly poor at 0.1mol/L Na OH,and the regeneration gradually decreased with the increase of desorption rate,indicating that the Mg and Al ion in Mg/Al-Na CK may dissolve out and lead to the decrease of adsorption efficiency.Mg/Al-Na CK in simultaneous ammonia nitrogen and phosphate removal applications（2 mg/L and 8 mg/L）.Under the dosage of 4 g/L,the adsorption of ammonia nitrogen and phosphate by Mg/Al-Na CK can meet the maximum allowable discharge standard of total phosphorus and the maximum allowable discharge standard of ammonia nitrogen ClassⅢ（<0.2mg/L;<1.0 mg/L）.