Research On The Generation Process And Carbonation Properties Of Hydrogarnet

China is a big aluminum producer country.By the end of 2014,electrolytic aluminum production capacity of China has reached to 24 million tons,and alumina production capacity has reached more than 4700 million tons,which is 5.6 times than 2005.The number ranks the forefront of the world.Aluminum industry has become one of the pillar industries in China.However,with the shortage of high aluminum silicon ratio bauxite,export restrictions of other countries and stockpiling of red mud,Chinese aluminum industry's green and sustainable development has encountered a bottleneck.Under this background,research group proposed calcification-carbonation method by utilizing low grade bauxite(or disposal of red mud)to produce alumina.On this basis,this paper conducted thermodynamics calculation to analysis the direction of hydrogarnet generation and carbonation decomposition reaction.According to the related theory of insoluble electrolyte to calculate the solubility of sodium aluminosilicate and hydrogarnet.The paper also prepared hydrogarnet by pure substances to reveal calcification mechanism,and carried out carbonation experiment to clarify carbonation and digestion mechanism.The mechanism of the dissolution was investigated by dissolution experiments.So as to provide a strong theoretical foundation support to the method.The main research contents are as follows:(1)Thermodynamic calculation showed that:With the increase of temperature,the formation of hydrogarnet was more difficult;Carbonation decomposition process was much easier at low silicon saturation coefficient and had little effect of carbon dioxide partial pressure.(2)Three methods of determining the saturation coefficient of hydrogarnet were concluded.The saturation coefficient calculated by peak intensity method and interplanar spacing method had smaller error and better stability.Cell edge length method had poor stability but high accuracy.(3)Calcification experiment showed that:Hyrogarnet and calcium aluminate hydrate co-existed;Temperature had great influence on silicon saturation coefficient of hydrogarnet,with the temperature increased,silicon saturation coefficient increased;Calcium silicon saturation formula was about 3:1;With caustic concentration increased,calcium aluminate hydrate dominated.Mechanism of calcification process:Calcium oxide hydrated to calcium hydroxide,Ca(OH)2 and aluminate ion reacted and formed calcium aluminate hydrate,calcium aluminate hydrate reacted with silicate ions generated hydrogarnet.(4)Carbonation experiment showed that:After 120 min,hydrogarnet was completely decomposed by carbonation.Carbonization mechanism:carbon dioxide dissolved in solution to form carbonate ions,and then causticized with Ca(OH)2 to generate calcium carbonate,hrogarnet and calcium aluminate hydrate gradually decomposed.(5)Digestion.experiment showed that:A/S of digestion slag decreased significantly after separion process,the minimum was up to 0.9;Calcium hydroaluminocarbonate was found in digestion slag.Calcium carbonate anti-causticizing reaction generated calcium hydroaluminocarbonate which limited full recovery of alumina.Caustic ratio had a great impact on anti-causticizing reaction;Digestion mechanism:hydrated alumina dissolved in alkaline solution,CaCO3 draw anti-causticization reaction.Calcium hydroxide,aluminate ions and carbonate ions reacted and generated calcium hydroaluminocarbonate,which discharged with digestion slag.