Study On The Preparation Of Crystalline Aluminum Chloride By Using Ammonium Aluminum Sulfate

Crystalline aluminum chloride is widely used in catalysts,flocculants,agriculture and medicine.The raw materials for the preparation of crystalline aluminum chloride are mainly bauxite.However,in recent years,bauxite resources are scarce.In order to meet the demand of domestic aluminum products,researchers have begun to pay attention to the search for substitutes for bauxite.China's fly ash storage is increasing and a large amount of fly ash is not easy to handle,causing serious environmental problems.Therefore,the preparation of aluminum products from fly ash has caused widespread concern due to the content of alumina in fly ash is 30% to 50%.The commonly used methods of recovering aluminum include roasting method,acid method and ammonium method.The acid method can realize the separation of aluminum and silicon,and becomes a popular method for aluminum ash from aluminum ash.The acid method mainly includes hydrochloric acid method,sulfuric acid method and ammonium sulfate method.Among them,the sulfuric acid method and the hydrochloric acid method are easy to leach along with aluminum ions in the acid leaching process,which affects product quality and restricts its industrial development.Some scholars have proposed that leaching of fly ash by sulfuric acid and ammonium aluminum sulfatemonium hydrogen sulfate mixed medium.The solubility of the intermediate product ammonium aluminum sulfate is relatively large with temperature and easy to precipitate.Also,the impurities are not easily precipitated in this process.Therefore,this paper proposes two processes.One process is to prepare crystalline aluminum chloride by using ammonium hydrogen sulfate as raw material and hydrogen chloride gas crystallization.The second process is to convert ammonium aluminum sulfate to aluminum hydroxide and then crystallize the aluminum chloride by reaction crystallization with hydrochloric acid.The main research contents and conclusions are as follows:(1)Aluminum chloride crystal was prepared from solution of ammonium aluminum sulfate using HCl gas sparging with Ammonium aluminum sulfate dodecahydrate as raw material.The effects of sparging rate,sparging time of HCl gas,reaction temperature and initial concentration of aluminum ions on the morphology of aluminum chloride crystal were investigated.The ICP,XRD,SEM and other characterization methods were used to analyze the yield of aluminum,the purity of crystalline aluminum chloride and the crystal morphology under different process conditions.The results show that when the sparging rate is 60ml/min,the sparging time is 2 h and the initial concentration of aluminum ions is 20 g/L in 50 m L ammonium sulfate aqueous solution aluminum chloride products with good shape can be obtained at 30 o C reaction temperature.The yield of aluminum was 85.0%and the purity of the crystalline aluminum chloride is 88%.This study provides a technical reference for the extraction and preparation of high quality aluminum chloride hexahydrate crystals.(2)Based on the direct preparation of crystalline aluminum chloride with ammonium aluminum sulfate,there will be the presence presence of sulfate impurities in the product.We tried to convert aluminum ammonium sulfate into aluminum hydroxide first and then use aluminum hydroxide as raw material to prepare crystalline aluminum chloride.Based on this,the process of preparing crystalline aluminum chloride by aluminum hydroxide-hydrochloric acid reaction crystallization was studied.The aluminum chloride was used as raw material to prepare crystalline aluminum chloride by hydrochloric acid reaction crystallization method.The effect of hydrochloric acid concentration,reaction temperature,reaction time and solid-liquid ratio on crystallization were investigated.The ICP,XRD,SEM and other characterization methods were used to analyze the yield of aluminum,the purity of crystalline aluminum chloride and the crystal morphology under different process conditions.The results showed that when the concentration of hydrochloric acid was 12 mol/L,the reactiontemperature was 80 o C,the reaction time was 10 h and the solid-liquid ratio was 1:15,the yield of aluminum was 74.2% and the crystal purity was more than 99.99%.A block-shaped crystal of uniform overall size.(3)In order to provide certain data support for the pilotization of the process,material balance and energy balance calculation were carried out for the two processes.The advantages and disadvantages of the two processes were analyzed.It was found that the high yield of the product(9991 T/year)and low energy consumption were obtained by the “aluminum ammonium sulfate and hydrogen chloride gas aeration crystallization” process,but the product contains many impurities.The “aluminum hydroxide-hydrochloric acid reaction crystallization” process yielded aluminum chloride crystals obtaining an aluminum purity of 99.99%.