Study On Preparation Of MgAl-LDH From Waste Slurry Of Aluminum-air Battery And Its Adsorption Properties

Hydrotalcite material has been widely used in wastewater treatment because of its unique layered structure and good adsorption performance.In recent years,there have been studies on the synthesis of hydrotalcite from solid waste,and high value added utilization is one of the eternal research directions of waste treatment.In this paper,magnesium-aluminum hydrotalcite（MgAl-LDH）was prepared based on waste electrolyte slurry of aluminum-air battery,and the synthesis process,structure and adsorption performance were systematically studied.The following research results were obtained:（1）The basic physichemical properties of the waste slurry were analyzed,including p H value,solid content,Al and Mg element content,etc.Aluminum and magnesium components and high alkaline in the waste electrolyte slurry were explored to synthesize MgAl-LDH using hydrothermal method for the first time.The insufficient Mg resources were supplemented by adding Mg O.The lamellar structure of MgAl-LDH was studied by X-ray diffraction（XRD）,infrared spectroscopy（FTIR）and transmission electron microscopy（TEM）.The optimum process parameters including the reaction temperature60℃,the reaction time 30 min,the crystallization temperature 150℃,and the crystallization time 15 h were acquired.（2）Based on the above studies,MgAl-LDH was prepared from the simulated slurry from pure chemical reagents,in order to compare with MgAl-LDH synthesized from waste slurry and filtrate of the waste slurry.The results showed that morphologies of the three samples were almost similar,representing spherical structures by accumulation of lamellar grains.However,the MgAl-LDH by simulated potassium aluminate solution has a cross-supported structure between the lamellae with good dispersion,the specific surface area is 53.69 m²/g,the largest among the three samples.（3）According to adjustability of the chemical compositions and the structures of MgAl-LDH can be regulated,Ca²⁺or Zn²⁺doped MgAl-LDH was prepared in this paper.Results indicated that with the increase of Ca²⁺doping,crystallinity decreases gradually,absorption peaks of some functional groups move to the lower bands by FTIR investigation,the lamellar structure tends to agglomerate,the lamellar layer accumulates closely,and presents polygonal morphology.Elemental surface scanning analysis suggests that only a small amount of Ca²⁺doping enters into the Mg AL-LDH structure.Meanwhile,with the increase of the amount of Zn²⁺doping,the crystallinity first increased and then decreased,while the absorption peak of the functional group did not significantly change.The lamellae structure was lamellae with polygonal lamellae and reduced lamellae agglomeration.Elemental surface scanning analysis suggested that a small amount of Zn²⁺doping entered the MgAl-LDH structure.（4）According to the special properties of MgAl-LDH,the application of MgAl-LDH as adsorbent in wastewater was studied for the first time.According to the phosphorus static adsorption experiment,the prepared MgAl-LDH has a high adsorption capacity of phosphorus ion.The optimal conditions for phosphorus adsorption by Mg AL-LDH were as follows:the additive amount of MgAl-LDH synthesized by adding ethanol was 0.5 g/L,the adsorption time was 12 h,the initial concentration of phosphorus was 20 mg/L,and the solution p H was 6.At this time,the phosphorus removal rate can reach 99%.By adding ethanol as the template agent,the hydroxyl density on the surface of the adsorbent was increased,the surface charge was increased,and the adsorption capacity was improved.The kinetics of MgAl-LDH adsorption was in accordance with the quasi-second-order kinetic model,and the isotherm data of MgAl-LDH was in good agreement with the Freundlich model,indicating that chemical adsorption and multi-molecular layer adsorption were the main factors in the adsorption process.