Study On Fluoride Removal Behavior Of Lanthanum Modified Geopolymer Microspheres

Fluorine pollution in water bodies has brought negative impacts on human beings,animals and plants,as well as ecology.The main removal methods include sedimentation flocculation,membrane treatment,ion exchange,and adsorption.Among them,adsorption method is easy to operate and widely used,but in engineering applications,the deep purification performance of fluoride in acidic wastewater still needs to be improved.This study used nano lanthanum oxide（La₂O₃）to modify geological polymer microspheres（GP）and prepared two types of GP-La composite adsorbents,characterized their microstructure and studied their defluorination behavior.Firstly,a new type of lanthanum-loaded geopolymer microsphere composite adsorbent（MK-GP-La）was synthesized using metakaolin（MK）as raw material to adsorb and separate fluoride ions（F^–）from water.The adsorption kinetics,adsorption isotherms,p H,coexisting ions,acidic water quality,dynamic adsorption and regeneration ability of MK-GP-La were studied,and the adsorption mechanism of MK-GP-La for F^–was analyzed.The results showed that the adsorption kinetics of MK-GP-La for F^–conformed to a pseudo second order kinetic model,and the adsorption amount reached 91%of the final adsorption amount within 3 minutes.Temperature has a small impact on the adsorption process of MK-GP-La.The maximum adsorption amount of F^–by MK-GP-La has 152 mg/g,which conformed to the Langmuir isotherm adsorption model.The adsorption process of MK-GP-La for F^–was highly dependent on p H,and the adsorption efficiency reached over 90%at p H 2.0～5.0.Except for HCO₃^–,HA,Cl^–,NO₃^–,PO₄^3–,and SO₄^2–do not exhibit significant competitive effects on the defluorination process of MK-GP-La.Using oxalic acid solution to soak and calcine to achieve desorption and regeneration of MK-GP-La,the desorption and regeneration ratios for the first three times were 1:0.99,1:0.93,and 1:0.87,respectively.MK-GP-La showed good fluoride removal performance in the acidic water and column adsorption test,maintaining a removal efficiency of 98%at p H=2,and having a treatment capacity of 1100 kilograms of water per kilogram of composite adsorbent,which has practical application prospects.Based on MK-GP-La defluorination data,a coal ash and slag（CFA）defluorination agent was designed for the recycling of bulk solid waste from coal-fired power plants.Using CFA as the precursor of geopolymer,a partial factorial design was used to screen the main factors affecting the efficiency of fluoride removal during the preparation process,and a response surface analysis was conducted using a Box-Behnken design to analyze the main factors.The optimized CFA-based lanthanum loaded geopolymer microspheres composite adsorbent（CFA-GP-La）was prepared,its fluoride removal performance was evaluated,and a saturated adsorbent resource utilization scheme was proposed.The results showed that the main factors affecting the fluorine adsorption capacity were the amount of CFA added,the curing temperature,and the burning temperature of lanthanum.The optimal condition was 6.1 g,65℃,and 470℃.The difference between the actual adsorption capacity of CFA-GP-La prepared with the optimal condition and the predicted adsorption capacity given by the model fitting was less than 10%.The selectivity and dynamic adsorption capacity for fluorine treatment were comparable to MK-GP-La.This indicates that CFA-GP-La was a reasonable way to recycle bulk solid waste from coal-fired power plants,and has good application value in the field of fluoride removal.The above results indicate that the preparation of CFA-GP-La from CFA and its application in the field of fluoride removal is an effective way to recycle bulk solid waste from coal-fired power plants.