A Study On The Efficiency Of Sulfoaluminate Cement For Phosphorus Removal In Lake/Reservoir Sources

Lake/reservoir water sources are prone to eutrophication due to long water exchange cycles,which pose risks to human health and aquatic ecosystems.Phosphorus is a key factor to control the eutrophication of the water body.When its concentration is low,it can lead to the eutrophication of the water body.Many phosphorus removal methods are not effective in removing low concentration phosphorus.In the traditional method,the biological method is susceptible to environmental temperature and process,and has a strong dependence on the ratio of nutrients.The chemical method has a strong dependence on acidity and alkalinity,and there is a risk of secondary pollution.In comparison,the adsorption method is environmentally friendly,safer and more economical.The study was based on clay minerals,some pozzolanic materials and hydraulic materials,and based on its removal effect and removal rate of low-concentration phosphorus and the performance retention performance,a cost-effective phosphorous removal agent,sulfoaluminate cement,was screened.The phosphorus removal mechanism,the impact of environmental factors on desorption and the feasibility of using it in actual lakes and reservoirs are analyzed.The main results are as follows:（1）From 22 kinds of clay minerals,pozzolanic materials and hydraulic materials,sulfoaluminate cement is selected to effectively remove low-concentration phosphorus.The material is in a flocculent state in a neutral to slightly acidic solution.In this state,the phosphorus removal effect is the best.The addition of 0.03 g·L^-1can remove 0.10 mg·L^-1phosphate to the class III water.（2）Adsorption kinetics shows that sulfoaluminate cement flocs adsorb phosphate very quickly and can complete adsorption within half a minute.The results of adsorption isotherms show that the instantaneous adsorption equilibrium concentration is high,up to 500 mg P·L^-1,the equilibrium curve fits the Langmuir isotherm model,and the maximum adsorption capacity is 334.67 mg·g^-1;the adsorption curve of slow sedimentation changes with the oscillation time,When the oscillation time is 0,the curve can reach equilibrium within the initial concentration range of 0～5.0 mg·L^-1.The model fits the Langmuir equation,the maximum adsorption capacity is 25.03 mg·g^-1,and the oscillation time is 30 min and 60 min.The equilibrium curve in the range of initial concentration 0～5.0 mg·L^-1fits the linear model.（3）SEM and XRD characterization results show that sulfoaluminate cement flocs are more porous than raw materials and hydrates,which is more conducive to phosphate adsorption.The changes in XRD and Zeta potential values??reflect that PO₄^3-is mainly adsorbed on the surface of 3Ca O·Si O₂electric double layer,and forms Ca₂Si O₄-Ca₃（PO₄）₂system with 3Ca O·Si O₂.In addition,the sulfoaluminate cement flocs capture,adsorb,compress,and settle the ions in the solution,increasing the possibility of PO₄^3-being adsorbed.（4）The experiment of desorption of phosphate by environmental factors shows that the phosphate removal rate reaches over 90%in the p H range of 5.0 to 8.0.Light,temperature,dissolved oxygen and low-intensity hydraulic disturbance(<100 r·min^-1)hardly affect the phosphorus removal of sulfoaluminate cement flocs,while when the hydraulic disturbance is greater than 100 r·min^-1,the film formed by the precipitation was destroyed and part of the phosphate was desorbed and released into the overlying water,but the phosphate concentration remained within the range of Lake/reservoir class III water.（5）The experiment of dephosphorization of the actual micro-polluted lake water showed that the actual water dephosphorization requires more sulfoaluminate cement flocs,and the raw water dosage should be increased to 0.10～0.50 g·L^-1.After filtration,the dosage can be reduced to 0.03 g·L^-1to make the water reach the standard.In addition,the addition amount of 0.50 g·L^-1can reduce the permanganate index by about 50%,so that it reaches within the water limit of Lake III,and as the addition amount increases,the transparency of the water body increases,but the TN and NH₃-N have little effect.（6）From the safety analysis,sulfoaluminate cement is an environmentally friendly material and does not pose a threat to the ecosystem;for economic considerations,the cost of removing one ton of water from lakes or reservoirs is 0.024～0.08 yuan.Compared with the commonly used phosphorus removal agents,its economy is better,and it has a better utilization prospect.