Fluoride Ion Adsorption Effect And Adsorption Mechanism Of Self-supported Adsorbent Materials Based On Desulfurization Gypsum-aluminate Cement

With the rapid development of high-tech industries such as integrated circuits,semiconductors,chips and solar cells,the demand for fluorine-chemical products surges,and the treatment of fluorine-containing sludge and fluorine-containing wastewater becomes more urgent.The treatment of fluorinated wastewater by adsorption technology is not only easy to operate,but also has high efficiency and low maintenance cost.Layered bimetallic hydroxides（LDHs）have been widely studied and applied as adsorbent materials to treat polluted water due to their characteristics of tunability of main layer composition,interlayer anion interchangeability and structural memory.However,since LDHs prepared by conventional methods are mostly powders and have no gelling property,they cannot form self-supporting fluoride ion adsorption materials.In the process of defluorination,a large amount of fluorine-containing sludge will be produced,and the post-treatment is complicated,which is restricted to some degree in engineering application.AFm and AFt are the main hydration p H ases of sulfoaluminate cement.The compounds have similar layered structures and interlayer exchangeable properties to LDHs.Therefore,the preparation of self-supported adsorption materials based on the inherent hydration p H ases AFm and AFt of cement-based materials and their self-cementing properties has become a research focus for the treatment of industrial wastewater.In this paper,using flue gas desulfurization gypsum and aluminate cement as raw materials,self-supporting porous fluoride ion adsorption materials were prepared by chemical foaming technology.Firstly,the influence rule of the mass ratio of desulfurized gypsum and aluminate cement on the mineral composition and fluorine ion adsorption capacity of the adsorbed material was studied.Combined with the characterization results of self-supporting porous adsorption materials,the ratio of desulfurized gypsum and aluminate cement with the best adsorption effect on fluoride was determined.Secondly,the influence of different conditions,such as initial fluoride ion concentration,solution p H value,solid-liquid ratio,adsorption time and other factors on the effect of fluoride removal was discussed,and the adsorption isothermal model and adsorption kinetics model of PAG（Porous Aluminate cement Gypsum）for fluorine ions were established.Finally,A-PAG（Al₂（SO₄）₃-PAG）and L-PAG（La Cl₃-PAG）adsorbents were prepared,and the adsorption effect of modified PAG on fluoride ions and its influence rule were studied.The main conclusions of this study are as follows:（1）When the mass ratio of CAC and FGDG decreased from 1∶0.2 to 1∶0.7,AFm of hydration p H ase in PAG increased first and then decreased,AFt increased and AH₃decreased,and the adsorption effect of PAG on fluoride ion was gradually enhanced,and the adsorption effect of hydration relative to fluoride ion was from weak to strong in the order of AH₃,AFm and AFt.AFm,AFt,Ca SO₄·2H₂O and CAC hydration p H ase AH₃together form the complexation,precipitation and ion exchange adsorption system of fluoride ions,showing higher efficiency of fluoride removal.（2）The adsorption performance of PAG varies with the initial concentration of fluoride ion.With the increase of initial concentration of fluoride ion,the defluorination efficiency of PAG decreases gradually,while the adsorption capacity of fluoride ion increases gradually.The p H value has a significant effect on the adsorption of fluoride ions by PAG,and the optimal p H value is 7.With the increase of liquid-solid ratio,the adsorption capacity of PAG for fluorine increases rapidly,while the removal rate of fluorine decreases gradually.Considering the adsorption cost and effect,the optimal adsorption time was determined to be 8 h.The isothermal adsorption line of PAG for fluoride ion conforms to Langmuir model and has strong single-layer adsorption property.The adsorption kinetics of the adsorbent was analyzed.The results showed that the adsorbent obeys quasi-second-order kinetics,and the chemical adsorption is dominant.The adsorption mechanism includes chemical adsorption,p H ysical adsorption and ion exchange adsorption.（3）Compared with A-PAG,the adsorption effect of L-PAG was improved at low initial concentrations of 10 mg/L,20 mg/L and 40 mg/L,and L-PAG had better adsorption effect than A-PAG.The adsorption behaviors of PAG,A-PAG and L-PAG at low initial concentrations of 10 mg/L,20 mg/L and 40 mg/L followed the quasi-second-order kinetic model,which was mainly chemisorption.In F^-concentration of 100 mg/L～800 mg/L solution,Compared with A-PAG,L-PAG showed a higher defluorination effect with the increase of initial concentration.Langmuir model can more accurately describe the adsorption process of F^-in L-PAG,indicating that the adsorption process of L-PAG is monolayer adsorption.