The Research Of Calcium Carbonate Doping With Al³⁺ To Rempve Phosphate And Synthesis Of CaCO₃/zeolite Composite For Simultaneous Removal Of Ammonium And Phosphate

Exceeding phosphorus（P） and ammonium（NH4+） in wastewater could trigger eutrophication, so it’s an urgency challenge to recover P and NH4+. This paper focuses on three ways as follow:（i） synthesis calcium carbonate（CaCO₃） with doping Al3+（Al-ACC-X） to improve its adsorption P capability;（ii） synthesis CaCO₃/zeolite（CCZ-X） composite to elimination P and NH4+ in solution simultaneously;（iii） in order to chose the optimum synthesis CCZ-X condition to fix P and NH4+, some synthesis and modification means have been taken.As P is one of necessary elements to lead eutrophication, it could inhibit the speed of eutrophication. Previous research has reported that CaCO₃ owns high capacity to adsorb phosphate in aqueous solution, although calcite has a lower efficiency in alkaline solution so as to restrict its application range. In order to solve this problem, an idea, doping Al3+ in synthesis CaCO₃ process, has been proposed. The result shows that Al3+doping into CaCO₃（Al-ACC） has the enormous conversion from the sphere phase crystal morphology of CaCO₃ into amorphous phases. In addition, Zeta zero potential of samples also have been decreased, insulting in the higher adsorption capacity to P in alkaline condition. The adsorption isothermals of phospahte onto Al-ACC fit well Freundlich model, and coprecipitation is dominating its removal P principle. In compare with FITR patterns, it can conclude that HAP（hydroxyapatite） and AlPO4 are the mainly chemical precipitation types. It is very significant to remove P in the wastewater.It is well known that CaCO₃ and zeolite could respectively eliminate P and NH4+capability. For the sake of inhabitation eutrophication, the paper put forward that synthesizing CaCO₃/zeolite composite（CCZ-X） remove of P and NH4+ simultaneously.According to the XRD, SEM, EDX patterns of CCZ-X, it can infer that CaCO₃ and zeolite composite a new composite that possesses sphere crystal morphology. The adsorption experiments show that CCZ-X could remove of P and NH4+ effectively in alkaline aqua so as to restrain eutrophication, meanwhile, the mass ratio of CaCO₃/zeolite in CCZ-X determine its removal of P and NH4+efficiency. The adsorption P and NH4+ isothermals of CCZ-X could fit Langmuir model, while the mechnism of CCZ-X removal NH4+ is ion-exchange property and coprecipitation is the dominate its removal P principle. In the comparison of the results, CCZ-4 has advantage to simultaneously fix P and NH4+ property at pH=9. The research revises a traditional opinion that could remove P and NH4+ with one material.Even though composite could simultaneous remove P and NH4+ in effluent, some modification means proposed so as to improve composite removal of P and NH4+capability. Base on the results, it finds that calcining composite could obviously lower adsorption P capability when improving its removal of NH4+ property because of the crystal conversion of CaCO₃ loading on the surface of zeolite in composite from vaterite to calcite. In addition, the results show that stirring time and stirring speed have fine effect on boosting composite to remove P and NH4+ capability simultaneously. Considering that CaCO₃ should uniform disperse on the surface of zeolite in synthesis composite process, it chooses 700-1100 r/min as synthesis stirring speed. In order to enhance the efficiency of composite removal of P and NH4+, some pretreatments, such as acid, base and salt, are taken, the experiments indicate that the pretreatments have subtle improvement on removal of P and NH4+ property as CaCO₃ loading on the surface of zeolite in synthesis composite. It analyzes that the optimum synthesis composite to removal of P and NH4+condition is the mass ratio of CaCO₃/zeolite is 1:4 stirring with high-speed in water bath for one hour at 75 ℃.All in all, some new adsorbents are synthesized to remove P and NH4+ in effluent.The results show that they have excellent control P and NH4+capacity in effluent. So,the studies are meaningful that inhibit eutrophication in the future.