| Over the past ten years,China’s aluminum industry has developed rapidly,and the output of metal aluminum and aluminum profiles has been increasing continuously.Now China has become the world’s largest aluminum production and processing country.However,in the process of aluminum production,a large amount of hazardous industrial waste secondary aluminum ash will also be produced.Secondary aluminum ash contains a large number of fluorine,chloride and AlN impurities,which are easy to react with water and seriously harm human health and ecological environment.At present,the main treatment methods for secondary aluminum ash in the world are wet treatment,in which Al2O3 is recovered by washing,alkaline leaching and acid leaching.However,the wet treatment generally has problems such as long treatment process,low treatment efficiency and large amount of waste liquid.In this experiment,a high-temperature fire treatment method is proposed.Firstly,high-temperature vacuum distillation is carried out on the secondary aluminum ash to remove the fluorine and chloride.Then the pretreatment raw materials were processed by oxidizing roasting or high temperature alkali conversion to remove and transform the AlN impurities.The main experimental results are as follows:(1)Firstly,the composition,element content,particle size distribution,morphology and element distribution of secondary aluminum ash were analyzed.The pretreatment operation of high temperature vacuum distillation was carried out for the raw materials of secondary aluminum ash,and the fluoride content was reduced to 0.004%and the chloride content to 0.018%,thus harmless treatment of the first class dangerous substances in the secondary aluminum ash was completed.(2)In the experiment of oxidizing roasting of secondary aluminum ash after pretreatment,the content of AlN in the product will gradually decrease with the increase of the experimental temperature.The product’s division rate of N can reach 62.9%at 1400℃,and it has been proved that temperature is the most important factor affecting the division rate.During the heating process of oxidizing roasting,Al2O3 crystal generated on the surface of secondary aluminum ash particles will go through the change process of growth-thinning and fusion,and eventually become very dense,which will hinder the continuous oxidation reaction.Moreover,the dense oxide film generated at high temperature also tightly wraps the exposed surface of AlN particles in the secondary aluminum ash,making it unable to contact with water and thus inhibiting the occurrence of its hydrolysis reaction.(3)In the experiment of oxidizing roasting of secondary aluminum ash after pretreatment,the experiment selected the four different types of additives(Na2CO3、CaCO3、NaOH、Ca(OH)2),and tested them under different temperature and secondary aluminum ash conversion reaction as a result,the results show that:using Na2CO3 as additive,in 1200℃ can complete conversion transformation and secondary aluminum ash containing NaAlO2 are generated from Al phase and a small amount of aluminum in the sodium silicate material,reaction except N rate can reach 86.35%.When CaCO3 is used as additive,the reaction before 1200℃ is mainly dominated by decomposition of CaCO3,with the reaction dividing N rate up to 63%.When the temperature rises to 1400℃,a large number of calcium aluminate of different mineral phases will appear,and due to the reaction,part of Ca3N2 substances will be produced,leading to a decrease in the division of N.When NaOH is used as reaction additive,NaAlO2 can be generated and smelted at a lower temperature of 700℃ with a division rate of 83.39%and close to the highest division rate of 83.6%at 800℃.However,when using Ca(OH)2 as an additive,there is no conversion reaction within the low temperature range of 500～800℃,but only decomposition reaction of Ca(OH)2.If the temperature continues to rise,the experimental result is the same as that of CaCO3 as an additive. |
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