Fly ash has long been stored as waste in ash storage yards. It is called waste. It is caused by the understanding of fly ash and the limitation of economic and technical conditions, which causes some ash storage yards to be full. When the rain breaks over the dyke, the farmland or pastures and trees are destroyed, and the farmland is covered. When the soil is severe, the soil is destroyed. In the frequent winds, the dust is full in the sky, and sometimes it can cause sandstorms locally; some fly ash contains trace harmful elements and pollution. Water source, etc. The research proves that fly ash is not only a good building material, but also contains a large number of certain national key minerals, with good development conditions and easy selection. Therefore, it has enormous economic and social benefits and is an effective way to achieve the safety of mineral resources and the sustainable development of mining.
The use of fly ash to extract aluminum or produce aluminum products has been tested and patented at home and abroad.
The extraction of Al203 from fly ash is usually carried out by chemical treatment, and the residue can still be used as a concrete raw material. In the early 1990s, Huaiyin Power Plant of China established an industrial test workshop for extracting alumina from fly ash to produce zeolite products.
The American Rubber Ridge Laboratory (ORNL) studied the extraction of various metals from fly ash in the 1980s, such as direct acid leaching and reaction-acid leaching. The former is mainly easily released into the environment. The leaching rates of metal, alumina and Fe203 are 50% and 80%, respectively. The latter is to increase the pretreatment process before chemical treatment, changing the properties of fly ash, so as to maximize the recovery of metal, the leaching rate of aluminum and iron is up to 90%. %the above. Poland studied the possibility of extracting Al203 from fly ash by lime sintering-self-pulverization method. The fly ash and limestone were ground into raw materials in a certain proportion, sintered into balls, and burned in air after high temperature combustion. It was made into a powder, and then Al203 was leached with a soda solution at a concentration of 60 g/L. This method was semi-industrial test at the Grosovitz Cement Plant and was successful. In 1977, China’s Zhuzhou Power Plant conducted an experimental study on the extraction of aluminum by lime sintering. The extraction rate of Al203 was 80%.
Jilin Province is a province lacking aluminum ore resources. This survey found and evaluated fly ash-type aluminum ore and ended the history of no-aluminum mines in Jilin Province. The key now is to develop an economical and rational process for extracting aluminum or producing aluminum products, so that the advantages of aluminum resources can be transformed into economic advantages. Only in this way can the high value-added utilization of fly ash be combined with high volume and low cost. Make the best use of the technical route.
1 The results of this study prove that Al203 in fly ash in Jilin Province mainly exists in mullite and glass beads. The mullite particle size is micron to nanometer, and the current level of technology cannot be sorted out, so the chemical extraction process is the only choice. 2 There are many processes for extracting aluminum from fly ash or developing aluminum products. Through the collection of data, and scientific comprehensive analysis and comparison, grasp the advantages and disadvantages of various processes and key technologies, and absorb the advantages to optimize or improve the desirable chemical extraction process. So far, there have been many reports on the extraction of aluminum from fly ash. According to its principle, it is summarized as follows: alkaline, acid leaching, acid-base combination, gas chlorination and electrothermal direct reduction. The disadvantages are shown in Table 1. Combined with the characteristics of fly ash in Jilin Province, the acid leaching method is more suitable, but it must solve the key technology of iron and other impurities.
Table 1 Process list for extracting aluminum from fly ash
Crystallized aluminum trichloride [AlCl3.6H20] was obtained by leaching fly ash with hydrochloric acid and hydrochloric acid. Although this method was successful, it formed [FeCl2] during the reaction due to more iron minerals in the raw ash. -FeCl3], so that the crystalline aluminum trichloride (actually a mixture of AlCl3.6H20 and FeCl2-FeCl3) has a brownish red color and contains many impurities, which cannot fully meet the product requirements. In order to solve the impurities such as iron removal, the design is to increase the re-election or flotation process, and then the fly ash with heavy minerals removed after panning is extracted with hydrochloric acid to obtain crystalline aluminum trichloride, but the product still contains a small amount of iron impurities. . For this purpose, an alkali-purified industrial crystalline aluminum trichloride product having a higher purity can be obtained.
A3, D2 and F with coarse, medium and fine particles are selected as test samples. Take A2, D2, F artificially washed, remove 1g of fly ash sample of heavy mineral, add 5mL of 20% hydrochloric acid, heat at 100 °C on the heater, heating time is 0.5h, 1h, 2h, measure the leaching of Al The amount of leaching is shown in Table 2.
Table 2 Leaching amount and leaching rate of Al in A2, D2 and F samples
Take 300g of heavy mineral F sample, add 20% hydrochloric acid 300mL, heat at 100 °C for 1-2 hours, filter while hot, adjust the pH of the filtered solution with 20% NaOH solution to 3, filter and remove iron, filtrate Evaporation and crystallization gave [AlCl 3.6H20].
(1) Compared with the production of crystalline aluminum trichloride [AlCl3.6H20] by the method of coal ash acid, the process of preparing crystalline aluminum trichloride by gangue acid method requires pulverization, roasting and ball milling. More complicated than the fly ash acid method.
The coal gangue Al203 used must be 37.8% or more, and each production 1t[AlCl3.6H20] consumes 2.54t of coal gangue. Therefore, the utilization rate of Al203 in coal gangue is only 22%, and the utilization of Al203 containing <20% powder The preliminary test of coal ash can reach 16.95%. It also reduces mining, transportation, crushing, roasting, ball milling and many other processes.
(2) Control factors for the production of crystalline aluminum trichloride by the method of fly ash acid: In the small test, the mass fractions of Al203 in samples A2, D2 and F were (22.86-22.8)%, (19.8~19.35)%, respectively. (32.57 ~ 32.60)%, an average of 22.83%, 19.57%, 32.85%. The experiment found that there was no significant positive correlation between the leaching rate of Al and the mass fraction of aluminum in the sample.
Figure 1 Flow chart of producing crystalline aluminum trichloride using fly ash
When industrially producing aluminum trichloride with aluminum ash, it was found that the amount of Al leaching is directly proportional to the concentration of hydrochloric acid of 1.5. The relationship between the leaching rate of Al and the concentration of hydrochloric acid in the test is to be proved.
In the small test, the test and the small test are carried out at a constant temperature of 100 ° C, using different time, the relationship between time and Al leaching rate (see Figure 2), in the case of temperature and salt concentration, Al The leaching rate was positively correlated with time, but not significant. The maximum time was 1 h and the leaching rate was increased by 1.35%. Is there a significant increase in the leaching rate of Al if there is a temperature increase or an increase in temperature and a time delay? It will be verified by further small tests.
Figure 2 A2, D2, F sample Al leaching rate versus time
(3) Chemical process extraction test proves that the leaching rate X and the selected sample grade (x1), acid or alkali concentration (X2), temperature (X3) and reaction time (X4) are complex functions, f(x)= f(xl, X2, X3, X4, x5…). For a certain sample, x1 is an invariant, and other factors are all variables; but how to optimize each variable is the key to the technical process. The process of extracting aluminum from fly ash, if the acid concentration is too large, contains strong corrosiveness. If the dosage is increased, the cost will increase. If the reaction time is too long, the production efficiency will be affected. Therefore, adjusting the temperature appropriately and increasing the reaction rate should solve the leaching rate. Low technical key. Although the laboratory test obtained qualified products, the leaching rate is not high, and the optimal combination of test parameters has not been well solved, so further research is needed.
(4) The composition of fly ash in Jilin Province is basically the same as that of national fly ash. The content of quartz is high, the content of vitreous and mullite and iron mineral is low, but RA and Cor are common. The discovery of RA minerals is the first in the country. If aluminum and RA minerals in fly ash are converted into productivity in power plants, the integration of thermal-electricity-mineral resources will be realized, and the operation of reducing electricity costs will be realized. Value and maintaining the sustainable development of the mining industry have an inestimable effect.
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