Study On The Extraction Of Mixture Alumina And Gallium Oxide From High-alumina Fly Ash

At first, the generation and the harm of high-alumina fly ash was summerized.By analysizing the composition, structure and properties of fly ash, the application of fly ash in various fields was introduced. Extracting alumina and leaching gallium from high-alumina coal ash were emphasized on, which provided a valuable reference for us to study the extractaction of mixture of alumina and gallium oxide from high-alumina fly ash.Then, Na₂CO₃, CaCO₃ and Ca O were respectively taken as accessory ingredient during calcination process for activating fly ash. Then acid leaching of gallium from activated fly ash was studied. The effects of different calcination conditions?the variety of additives, the mass of the additives, calcination temperature and calcination time? on the leaching content of gallium was investigated. The results show that sodium carbonate is the optimal additive for activating fly ash in the three kinds of additives?sodium carbonate, calcium carbonate and calcium oxide?; when the calcination temperature was 800 ?, calcination time was 120 min,and mass ratio of fly ash and sodium carbonate was 1:1.5, the content of gallium leached from fly ash was 52.62 g/t.Na Cl and Na₂CO₃ were taken as accessory ingredient during calcination process for activating fly ash. Then acid leaching of gallium from activated fly ash was studied. The effect of different calcination conditions?mass of Na Cl, calcination temperature and calcination time? on the leaching content of gallium was investigated.The phase composition of fly ash and the samples obtained before and after adding Na Cl was characterized by XRD and the content of the gallium in the leaching solution was determined by ICP. The experimental results show that the leaching content of gallium can reach to 56.10 g/t under a defined leaching terms with calcination temperature is 800 ?, calcination time was 120 min, the content of Na Cl is 8%, the fly ash activation effect is better.Based on the high-alumina fly ash as the raw material, through the process of calcination of fly ash, alkali-leaching, filtraction and washing, the solution containing gallium was prepared. The effect of different calcination and leaching conditions?the types of sintering additives, kind of alkaline solution, the concentration of alkaline solution, solid-liquid ratio, leaching temperature and leaching time? on the leachingcontent of gallium was investigated. The experimental results show that the leaching content of gallium can reach to 41.438g/t under a defined leaching terms with the sodium carbonate as sintering additives, sodium hydroxide as the leaching solvent.The concentration of alkaline solution is 200 g/L, liquid-solid ratio is 40:1, leaching temperature is 80 ?, leaching time is 7 h.The content of alumina in coal fly ash is much more than that of gallium oxide.In order to increase the content of gallium oxide and obtain the mixture of alumina and gallium oxide, it is necessary to isolate a certain amount of alumina. In this part,the separation of alumina and gallium oxide by two-stage carbonization method was studied, based on the different acidity of gallium hydroxide and aluminum hydroxide precipitation in alkaline solution. Conditions of the first stage carbonization?that is,different p H, different flow rate and temperature? were explored. The experimental results show that the best conditions to separate alumina and gallium oxide are : the p H value is 11.23, the temperature is 80 ?, the flow rate of CO2 is 40 m L/min. The content of Ga in the mixture can reach 5.7550 mg/g.