Study On Extracting Aluminum From Fly Ash And Synthesizing Hydrotalcite And Its Application

Fly ash is one of solid waste discharged in coal-fired power plants,which is a kind of industrial waste residue with large discharge capacity in our country.Because of its rich aluminum and silicon resources,its research and application fields have become more and more extensive in recent years.The discharge of fly ash makes a large amount of aluminum resources unused and causes serious pollution to the environment.Hydrotalcite?LDHs?,also known as anionic clay?HT?,is a functional material with a tunable composition and unique structure and properties.Hydrotalcite has been widely used in ion exchange and adsorption,catalysis,flame retardant and other aspects,and has potential utilization prospects.To extract the large amount of alumina in fly ash as a source for preparing magnesia-aluminum hydrotalcite can tune it into treasure,thereby achieving the regeneration of available resources and reducing environmental pollution will be an important research direction in the fields of environmental protection and sustainable development of resources.This article takes the factory-processed fly ash as the research object,and adopts the calcination-acid leaching-precipitation process to convert the alumina in the fly ash to prepare aluminum hydroxide.The aluminum hydroxide is used as the aluminum source and magnesium oxide,sodium carbonate hydrothermal are added to synthesize magnesium aluminum hydrotalcite.The effects of Mg-Al molar ratio,hydrothermal temperature and hydrothermal time on phase composition,grain structure and morphology were discussed.In addition,this article also preliminarily studies the effects of amount of sdsorbent,adsorption time,temperature and p H on phosphorus removal based on the synthesized samples,the adsorption kinetics and isotherm adsorption line are also discussed.The main research results are summarized as follows:?1?The effect of the material ratio of sodium carbonate and fly ash,roasting temperature and time,sulfuric acid concentration,acid leaching temperature and the experimental factors of time on the alumina extraction ratio were studied by the process of mixed roasting with fly ash using sodium carbonate as a co-solvent and leaching the roasted clinker with sulfuric acid.The optimal process parameters are determined as follows:roasting temperature 850?,roasting time 2 h,alkali-ash ratio 0.8:1,sulfuric acid concentration 25%,acid leaching temperature 75?,acid leaching time 1 h,the extraction rate can reach 72.6%.?2?The product aluminum hydroxide?RA-AH?obtained during the roasting and acid leaching experiment was used as the raw material for the preparation of magnesia-aluminum hydrotalcite?RA-AH-LDHs?.The effects of different experimental factors such as the molar ratio of magnesia-aluminum,hydrothermal reaction time,and hydrothermal temperature on the synthesized samples were investigated.In the molar ratio n?Mg O?:n?RA-AH?:n?Na₂CO₃?=2:1:1,the hydrothermal time is 14 h,and the hydrothermal temperature is above 160?.The structural integrity of Mg/Al-LDHs was verified by FT-IR,XRD,SEM&EDS and other characterization methods.?3?Using the prepared RA-AH-LDHs samples to perform adsorption experiments on phosphorus solutions,the effects of different addition amounts,p H values and other factors on their adsorption performance were initially studied,and some studies on adsorption kinetics and isothermal adsorption were conducted.Progress has been made,and experiments have shown that at room temperature,p H=6,when the amount of hydrotalcite is 0.5 g,the maximum saturated amount of phosphorus adsorption can reach 24.99 mg·g^-1,and the removal rate of phosphorus is95.4%.Kinetic model,isothermal adsorption satisfies Langmuir model.