Preparation Of Modified Porous Geopolymer And Its Effect On Nitrogen And Phosphorus Removal From Sewag

High nutrient content such as nitrogen and phosphorus will cause eutrophication of water.The foundry industry generates a large amount of solid waste,such as waste casting sand and foundry dust.Foundry dust is a fine dust produced during the production of castings.Currently,the recovery rate of foundry dust is very low,and most of them goes to landfills.Therefore,the development of the comprehensive utilization process of casting dust is of great significance to the green and sustainable development of the foundry industry.In this study,foundry dust was used to synthesize geopolymers to study the adsorption effect of ammonia nitrogen,and magnesium-modified geopolymers were used to improve its ability to remove nitrogen and phosphorus,and the optimal conditions for magnesium modification and its mechanism of nitrogen and phosphorus removal were explored and applied to the adsorption column of aquaculture wastewater,and the main conclusions were as follows:（1）Geopolymer（FDG）was synthesized by foundry dust,and it’s adsorption of ammonia nitrogen conformed to the pseudo-secondary kinetic model and the Langmuir model.The maximum adsorption capacity was 12.598 mg/g,and adsorption process of ammonia nitrogen by FDG is exothermic and entropic increase.The adsorption capacity of FDG on ammonia nitrogen was influenced by coexisting ions,and the order of the effect was as follows:Mg²⁺>Ca²⁺>K⁺>Na⁺.（2）The synthesis of geopolymer prepared by directly mixed foundry dust with magnesium oxide will damage the structure of geological polymer,resulting in a decrease in adsorption ammonia nitrogen.The modified geopolymer（MFDG）by impregnation and calcination magnesium oxide has a good adsorption effect on nitrogen and phosphorus.The modification conditions are shown as following:magnesium oxide concentration is 2 mol/L,pyrolysis temperature is 600°C,and pyrolysis time is 2 h.（3）In a single phosphorus solution,the adsorption of phosphorus by MFDG is more in line with the Langmuir model,the maximum adsorption capacity is 21.21 mg/g,the adsorption process conforms to the pseudo-secondary kinetics,and the endothermic reaction and chemical adsorption are the mainstay.For mixture solution of nitrogen and phosphorus,the adsorption of nitrogen and phosphorus by MFDG conformed to the Langmuir model and qseudo-secondary kinetic model,and the maximum adsorption capacity of ammonia nitrogen and phosphorus was 230.693 mg/g and 175.087 mg/g,respectively.（4）The adsorption capacity of MFDG on phosphorus was influenced by p H.With the increasing of p H,the adsorption capacity of ammonia nitrogen and phosphorus by MFDG showed a trend of first increasing（p H=3～9）and then decreasing（p H=9～13）.The ability of adsorbing nitrogen and phosphorus by MFDG was obvioulsy influenced by the coexisting Ca²⁺.The removal process of ammonia nitrogen and phosphorus by MFDG was mainly based on the struvite reaction.（5）The penetration time of ammonia nitrogen in the adsorption column filled with FDG was 54 h under the condition of a flow rate of 2 m L/min of swine wastewater;The color of the effluent decreased first and then increased,and the turbidity of the effluent fluctuated between1.46 NTU and 2.6 NTU.When the adsorption column was filled with MFDG,the penetration time of ammonia nitrogen was 210 h,and the penetration time of phosphorus was 50 h;the minimum color of effluent was 32.8 PCU,and the turbidity of effluent was 1.47NTU.After operation 150th hour,turbidity of effluent fluctuated around 2.3 NTU.Geopolymer synthesized from foundry dust in this paper can be used to remove ammonia nitrogen from water.After the magnesium oxide was used to modified geopolymer,the adsorption capacity of nitrogen and phosphorus of modifying geopolymer was substantially improved.Nitrogen and phosphorus could be effectively removed from swine wastewater.This study provides a new idea for the resourceful application of foundry dust.