Study On Preparation Of Polyaluminum Chlorine From Aluminum Dross

Aluminum dross is a kind of solid waste produced in aluminum industry.China is a big aluminum producer,there are a lot of aluminum dross produced every year,which directly discharged without treatment is harmful to soil,atmosphere and water.Aluminum dross was included in the national hazardous waste list in 2016,attracting more and more attention from all sectors of society.At the same time,aluminum dross is also an important secondary resource of aluminum,and recycling valuable elements in aluminum dross is of great significance to the construction of environment-friendly and resource-conserving society.The types and contents of elements in aluminum dross from different sources vary greatly.According to the characteristics of high content of aluminum,magnesium and nitrogen in aluminum dross produced in the production of magnesium aluminum alloy,the method of washing removal of nitrogen,fluorine,chlorine,alkali leaching and acid leaching of aluminum,acid leaching plus calcium aluminate polymerization and acid leaching plus alkali leaching were studied.The possibility of preparing magnesium-aluminum spinel by acid leaching slag sintering was also explored experimentally,aiming to obtain a method of efficient utilization of aluminum dross.The main research contents and results are as follows:（1）Thermodynamics of the washing process was calculated.At 273～413K,the standard gibbs free energy of the hydrolysis reaction of aluminum nitride turned negative,and the reaction could proceed spontaneously.The results showed that under the experimental conditions of 80℃,the liquid-solid ratio was 3:1 mL/g,the reaction time was 2 h,and the stirring speed was 400 r/min,the removal rate of N was 62.8%,the removal rate of F was 77.6%,and the Cl was completely removed.The phase of washed aluminum dross consists of magnesium-aluminum spinel,corundum,aluminum nitride,aluminum metal and aluminum hydroxide.（2）NaOH solution was used for alkaline leaching of aluminum dross.Under the conditions of NaOH concentration of 240 g/L,liquid-solid ratio of 8:1 mL/g,reaction time of 2 h,and temperature of 40～200℃,the leaching ratio of aluminum was about 60%.When the temperature rose to 260℃,the leaching ratio of aluminum was 77.5%.The alkali leaching experiment of aluminum dross was conducted at low temperature（60℃）.Under the conditions of temperature of 60℃,NaOH concentration of 300 g/L,liquid-solid ratio of 4:1 mL/g and reaction time of 2 h,the leaching ratio of aluminum was 58.08%and the molecular ratio of filtrate was 2.26.The phase in alkali leaching slag at high temperature（240℃）was magnesium-aluminum spinel and magnesium hydroxide,while the phase in alkali leaching slag at low temperature（60℃）was corundum and magnesium-aluminum spinel.（3）Hydrochloric acid solution was used to conduct acid leaching experiment on aluminum dross.The experimental results showed that when the initial concentration of hydrochloric acid was 6 mol/L,the temperature was 85℃,the reaction time was 2 h,the stirring speed was 200 r/min,and when the ratio of hydrochloric acid solution to aluminum dross was 4:1 mL/g,the leaching ratio of aluminum was 48.1%,the concentration of aluminum filtrate was 73.7 g/L.When the experimental conditions were changed,the leaching ratio of aluminum was not significantly increased,and the maximum was only 53.8%.The phase of acid leaching slag is corundum and magnesium-aluminum spinel.The sintering experiments of acid leaching slag were conducted at 1100℃,1300℃ and 1500℃.The sintering products of leaching slag contained 81.51%～83.75% Al₂O₃ wt.%and 13.79%～15.38%MgO wt.%.The impurities of CaO,SiO₂,Na₂O and Fe₂O₃ were relatively low.（4）The method of adding calcium aluminate was used to conduct the polymerization experiment on the aluminate leaching solution.The experimental results showed that under the conditions of adding 12 g/80 mL calcium aluminate leaching solution,the temperature was 85℃,the reaction time was 1.5 h,and the stirring speed was 200 r/min.The utilization rate of calcium aluminate was 69.58%,the pH of the filtrate at the end of the reaction was 2.83,the content of alumina in the product was 14.21%,the salt base was 55.29%,the density was 1.33 g/cm³,and the pH of 1%aqueous solution was 4.31,meeting the requirements of liquid poly aluminum chloride products in GB15 892-2009.There are Al—OH and Al—OH—Al functional groups in the product,and the product has purification effect on simulated waste humic acid.After evaporation and concentration of liquid products and drying,the solid products are composed of AlCl₃·6H₂O and Al₂,Al₅,Al₆,Al₉,Al₁₀ and Al₁₁,and the resulting polymer is flake structure.（5）Used to join in aluminum dross acid dipping aluminum dross alkaline immersion method and preparation of polymeric aluminium chloride of experimental research,the experimental results show that the temperature is 85℃,the reaction time of 2 h,stirring speed of 200 r/min,the product ratio of alkali leaching liquid to acid leaching liquid is（4～20）:80.The alumina content of the product is between 9.17%and 9.56%,which is relatively low and fails to meet the requirement of≥10%of alumina content in GB15892-2009.The process of neutralization is longer and the equipment investment is larger.For the aluminum dross in this paper,the method of acid leaching plus calcium aluminate polymerization is more suitable.