Research On Preparation Of Gallium From Zhungeer Circulating Fluidized Bed Ash

The burning technique of circulating fluidized bed(CFB) is a new technique, which have the advantages of wide adaptability of fuel, high rate of burning, low quantity of NOx senting out, wide load adjust. With the developing of electric power, the burning technique of CFB will become the main burning technique. At the same time, it will bring the new solid waste, circulating fluidized bed ash. At present, China's metal gallium reserve is approximately 80% to 85% of total reserves, ranking first in the world. In the nature, gallium coexist with Zn, AI, In, Ge,and Ti in many minerals. AlO (OH) and GaO (OH) , diaspore structure, whose crystal packet parameters and divalent cations radius are very close, thus accompanied by bauxite ore. Metal gallium is the main source of alumina production, the return of liquor, water zinc smelting plant output, such as zinc leaching slag, slag kiln, fire zinc distillation tank residue and dust. Nowadays, metal gallium produced mainly in these tow residua. November 2005, the team composed by doctor Dai Shi-feng, Ren Yi in China Mining University and other experts found a large number of Ga associate with Zhungeer coal seam. In 2006, Jilin University with the Shenhua Group Corporation Zhungeer energy cooperation sut up a project on the comprehensive utilization of fly ash Zhungeer mine research and development.Because of the content of gallium is very small in substances, so the separation and enrichment of Gallium is relatively difficult. Mainly by solvent extraction, levextrel resin, film, carbonate. In this paper, using solvent extraction method to treat the liquor in the process of acidic system, at the same time, using carbonation method to treat the alkaline liquor system for gallium separation and enrichment. Extraction agent used under the acid system is TBP. The main advantages of TBP is non-aluminum ion extraction , and its disadvantage is that the Fe3+will be a interference of the extraction of gallium, therefore, in the acidic extraction system will be required a process to deoxidize Fe3+ to Fe2+ the before the extraction process.In the process of using TBP as extraction agent in the acid system of gallium extraction, Factors affect the extraction of gallium main include: the amount of extraction, extraction time, thinners types, phase ratio (organic phase and the aqueous phase volume ratio) and acidity (HCl mol. And the amount of extraction in the organic phase of the volume ratio from 5-20%; there are thinner such as carbon tetrachloride, xylene, butyl acetate and ethyl acetate mixture; acidity is range from 1 mol / L to 6mol / L; phase ratio is range from 0.5 to 2; extraction reaction time is span from 10 to 40 minutes. To study effection of these factors on the gallium extraction, this paper designed a L16 (45) orthogonaltable on the extraction experiment. The experimental results show that: the impact of gallium extraction rate array from the major factors to the minor factors following the order: acidity, TBP concentration, diluent types, and compared the time. The best conditions when using TBP as extraction agent extract gallium from the of acid leaching solution is for acidity in the water 4 mol / L, ethyl acetate and carbon tetrachloride 1 +1 as thinner, TBP volume percentage of the organic phase is 20 %, phase ratio is 1.5, the extraction time is 10 min. Gallium can be completely extracted. In order to better study the various factors which play a role in the extraction rate and extent of the situation, on the basis of this orthogonal experiment, several groups of single factor experiment is designed to detail the study of the extraction rate of gallium impact. Experiments show that single factor when carbon tetrachloride is used as thinner, the extraction rate is increased as acidity, the organic phase TBP content, phase ratio increased, the increase of time will not increase the extraction rate. Ideal conditions for the extraction is the acidity of> 4 mon / L , TBP content of 20%, compared to> 1, extraction time 10 min. extraction rate of 97.73%. Under the low of extraction and anti-extraction principles, arranged L9 (34) orthogonal extraction experiments to examine the effect of experiment conditions such as anti-extraction thinner, composed of organic phase, phase ratio, and anti-extraction time. The experimental results show that: the impact of anti-extraction from the main factor to the minor factor is: the anti-extraction agent, the anti-extraction time, and the anti-extraction thinner types. The best anti-extraction conditions is carbon tetrachloride, the extraction time is 30 min, anti-extraction thinner is 1mol / L of sodium hydroxide, phase ratio is 1, under this condition,you can achieve full-extraction. It was the organic phase cycle efficiency which were also studied, the results showed that with the use of organic phase cycle of the increase in the number extraction rate decreased gradually, when more than four cycles when gallium extraction rate lowered to 76%.The working principle of using step-by-step method to separate and enrich gallium from alkaline carbonate system is: the concentration Al, Ga ion in the Solution is different vary greatly, and coprecipitation pH value of the two ions is also different, Al (OH)3 will precipitate before Ga (OH)3, so by this way aluminum and gallium will be separated, and, separation is achieved through the carbonation mathod. The beginning precipitation pH value of Al (OH)3 in the alkaline solution is 10.6, and that of Ga (OH)3 is 9.7. Therefore, to admit CO2 in partial sodium aluminate solution can regulate the solution to the appropriate pH value, at the same time the most of the aluminum can be precipitated, and gallium remain in the solution, the relative content of gallium and aluminum in the solution rise. Achieve a gallium and aluminum initial separation, we get gallium enriched solution. Its process is: a. the first carbonated: after alkali dissolve of crude alumina we obtain partial sodium aluminate solution, regulate the CO2 gas flow regulator to ensure the uniformity of response in the appropriate conditions to the PH value which precipitate Al(OH)3 and Gallium will remain in solution, and realizing the initial separation of gallium aluminum; b. Second carbonated: After the first carbonated which isolated Al(OH)3 by precipitation, continue to admit in CO2 gase to precipite Al(OH)3 All precipitation as many as possible, and to precipitate most of the gallium. Then dissolve the secondary aluminum gallium-salt in sodium aluminate liquor, repeat the process until the rehabilitation of gallium aluminum salt ratio is significantly enhanced to the extent of the recovery so far. During the first carbonate process, due to the high content of aluminum in the system, the reaction rate is high, in the CO2 admission process, if controlled inproperly, there will be a large number of gallium coprecipitated and, therefore, strictly control the reaction rate is very important. In the process, the main factors which affect the result of the experiment are as follow: the admission velocity of CO2 , reaction time, the reaction temperature, CO2 concentration, the alkalinity, as well as the chemical composition in the liquor, and so on. The aim of the second carbonated is to precipitate all of the aluminum and most of the gallium left in the solution after the first carbonate. It is generally believed that when consumption of some substances in the solution precipitated by the sediments below 1.0×10-5mol / L, it is considered to be complete precipitated. A number of factors impact the second carbonation, it is analysis primarily in the paper of the admission velocity of CO2, time and temperature. Comprehensive results can draw a more reasonable carbonate conditions they are as follow: the admission velocity of CO2 in the first carbonation is 100 mL /min/L, time in the first carbonation is six hours, temperature in the first carbonation is 80℃; the admission velocity of CO2 in the second carbonation is 140 mL / min /L, time in the second carbonation is five hours, temperature in the second carbonation is 40℃.Through the comparison gallium extraction method of acidic extraction system and alkaline carbonate system, we can see the extraction process of acidic extraction system is simple and short , experimental conditions can be controlled easily, but it need to use organic solvents, and the price of raw materials is somewhat high; process of carbonate method is simple, the price of raw materials is low, the production cost of gallium also lower that the former one. But the carbonate alumina process in different from the process of the alumina producing process which is called seed segregation. This difference makes the cost of gallium extraction higher than it should be. As the market price of gallium is not very high, and the high cost of raw materials, thus, and this method will spreate the gallium extraction process from the process of alumina preparation, therefore, it is not suitable enough to put in industrial production.