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New process for extracting Al 2 O 3
The world's high-quality soft-alumina bauxite is mainly distributed in Australia, Brazil, India, Canada, the United States, Guyana, Russia and other countries. Countries such as Europe and the United States rely on abundant high-quality bauxite resources. Most of the countries that use the Bayer process to extract Al 2 O 3 use Bayer method combined with soda lime sintering to extract Al 2 O 3 . As far as the current global production of Al 2 O 3 is concerned, due to resource and technology constraints, the Bayer method is widely used in countries rich in bauxite resources such as the United States and Australia, and the soda lime sintering method and the joint method are more commonly used in European countries.
For high-alumina raw materials with an aluminum-to-silicon ratio of less than 3.5, due to the serious interference of Na 2 O·A1 2 O 3 ·2SiO 2 on the extraction of Al 2 O 3 during the conversion of raw materials, the countries in the world cannot basically use them directly. To extract Al 2 O 3 from fly ash, coal shale, low grade bauxite, kaolin and other raw materials with low Al 2 O 3 content and high SiO 2 content, can only be used for stacking, burying, backfilling tunnels, Filling or processing for the production of ceramic products, cement, bricks, roadbed materials, etc. for low value-added use. China is a country with very poor bauxite resources. It is reported that the per capita bauxite reserves are less than 300 kg, and most of the bauxite mines in China are low-grade aluminum-silicon low-grade diaspore aluminum. Earth mines can no longer guarantee domestic demand in 2010. Considering the prospective reserves, they can only guarantee about 20 years. According to customs statistics, in order to meet domestic needs, in 2005, the country imported a total of 2.17 million tons of bauxite, which increased to 9.25 million tons in 2006, and soared to 23.26 million tons in 2007, and only in January-June 2008, the country has already A total of 13.4492 million tons of high-grade bauxite was imported from abroad, most of which was used to blend with domestic low-grade bauxite, and alumina production was carried out by soda lime sintering. Some analysts have said:. "Bauxite imports alarming development, tight supply, or as 'second iron ore.'"
Solving the interference of Na 2 O·A1 2 O 3 ·2SiO 2 in the process of extracting Al 2 O 3 , developing a new technology for extracting Al 2 O 3 from high-alumina with a ratio of aluminum to silicon of less than 3.5, which can be obtained from all over the country. The extraction of Al 2 O 3 from the accumulated raw materials of nearly 10 billion tons of high silicon aluminum ore is of great practical significance for China's Al 2 O 3 production industry, as shown in Table 1.
Table 1 Chemical composition of high silico-alumina raw materials (%)
In fact, when Al 2 O 3 is extracted, the newly formed sodium aluminosilicate in the conversion process in an alkaline environment is a crystal having a loose structure of zeolite type, which is easily decomposed by a high concentration of caustic soda. By using the "C-JSTK" technology, by increasing the Na2O concentration of the solution and increasing the reaction temperature, it is possible to completely decompose Na 2 O·A1 2 O 3 ·2SiO 2 formed during the conversion in an alkaline environment into Na 2 O· A1 2 O 3 ·2SiO 2 , and separation is carried out to simultaneously extract Al 2 O 3 and SiO 2 from the high-alumina.
Test materials and process
The raw materials for the production of high-silicon aluminum ore are taken from a mining area in Zhenjiang, Jiangsu Province, and industrial products for soda ash and caustic soda. The chemical composition of the high silico-alumina raw materials is listed in the table. The process of the experimental study is described below (see Figure 1): 
Figure 1 "C-JSTK" technology process flow diagram
The high-silica-aluminum powder and the soda ash are mixed in a certain proportion and then subjected to alkali-melting conversion reaction, and the obtained melt-pressed contact body is quenched into a fine particle pressure of 1 to 5 mm by cold water. Wet finely grind fine material into thick slurry, dilute and filter. The filter cake is dissolved in concentrated caustic soda, heated and concentrated, and baked and dried. The obtained dry powder was dissolved and filtered; the filter cake was dissolved in concentrated caustic soda and filtered. The filtered filtrate was combined and diluted to give an Al(OH) 3 precipitate and a filtrate. The CO 2 gas generated by the alkali fusion process is collected, purified, pressurized, and introduced into the filtrate after dilution and hydrolysis to be carbonized and decomposed, thereby sequentially obtaining the remaining Al(OH) 3 precipitate, H 2 SiO 3 precipitate and Na 2 . A dilute solution of CO 3 . The washing fluid is concentrated and used to replenish the water quenching liquid and to dissolve and dilute the water. After the Na 2 CO 3 dilute solution is concentrated, the soda ash Na 2 CO 3 solution and the caustic soda NaOH solution are recovered, and the by-product precipitates CaCO 3 . The recovered soda ash Na 2 CO 3 solution is circulated to the previous batching process and mixed with the high silico-alumina powder, and dried for recycling to the soda ash alkali-melting process. The caustic soda NaOH solution is recycled to the previous two-stage caustic soda dissolution process. The soda ash-melted high-temperature flue gas is exchanged into clean hot air for drying of Al(OH) 3 and H 2 SiO 3 and CaCO 3 , and finally the industrial product Al(OH) 3 precipitates SiO 2 and precipitates CaCO. 3 .
Process principle
1, soda ash
The high-alumina powder was first treated with soda ash Na 2 CO 3 in order to convert SiO 2 and Al 2 O 3 in high-alumina to Na 2 CO 3 to form soluble Na 2 O·SiO 2 and Na 2 . O.Al 2 O 3 is separated from other components in the high silicate raw material.
According to the mass ratio, high silica-alumina powder: Na2CO 3 = 1:1.2-1.3, after reacting at 1300 ° C for about 30 minutes, Na 2 CO 3 decomposes about 70% to release Na 2 O and precipitate CO 2 ; Most of the SiO 2 and A1 2 O 3 in the sillimanite are combined with Na 2 O to form Na 2 O·SiO 2 and Na 2 O·Al 2 O 3 , leaving part of the free A1 2 O 3 and the melted Na. 2 CO 3 ; part of Na 2 O·Al 2 O 3 and Na 2 O·SiO 2 are further reacted to form Na 2 O·Al 2 O 3 ·2SiO 2 .
Most of Fe 2 O 3 is converted into Na 2 O·Fe 2 O 3 ; CaO and MgO are converted into 2CaO·SiO 2 , CaO·Fe 2 O 3 , Na 2 O·CaO·SiO 2 , MgO·SiO 2 , MgO· 2CaO·Fe 2 O 3 , CaO—TiO 2 , MgO—TiO 2 , and the like.
2, wet grinding and slurry dilution and dissolution
The newly formed Na 2 O·Al 2 O 3 ·2SiO 2 is easily decomposed by NaOH to release Na 2 O·Al 2 O 3 and Na 2 O·SiO 2 .
Na 2 O·Al 2 O 3 partially hydrolyzes in the presence of water, producing Al(OH) 3 and NaOH; Na 2 O·Fe 2 O 3 is completely hydrolyzed with water to produce Fe(OH) 3 and NaOH.
By wet grinding and water-soluble dissolution of the wet slurry, the NaOH produced by the hydrolysis of Na 2 O·A1 2 O 3 and Na 2 O·Fe 2 O 3 reacts with Na 2 O·A1 2 O 3 ·2SiO 2 , Part of Na 2 O·A1 2 O 3 ·2SiO 2 is decomposed into Na 2 O·A1 2 O 3 ·2SiO 2 dissolved in water and entering the solution. After filtration, the dissolved Na 2 O·A1 2 O 3 and Na 2 O·SiO 2 and the unreacted Na 2 O·A1 2 O 3 ·2SiO 2 solid and Fe(OH) 3 , part of Al(OH) 3 The impurity solids are separated first.
In the wet-milled, dissolved slurry, the dissolution of SiO 2 at 70 ° C is shown in Figure 2.
As can be seen from Figure 2, the maximum solubility of SiO 2 in solution was about 55 g/l over 2 hours. The wet-milled, dissolved slurry should be separated by filtration within 2 hours.
3, caustic soda alkali melting
The caustic soda NaOH solution is added to the wet-milled and dissolved filter cake and baked to dry powder. The effect is that as the solution is continuously evaporated and concentrated, the NaOH concentration is also continuously increased, and finally the NaOH concentration will be close to the maximum pure NaOH melt. State concentration. At the same time, as the solution is evaporated to dryness, the reaction temperature of the material also reaches the highest temperature close to the heating environment, and the reaction power reaches the maximum, thereby decomposing Na 2 O·A1 2 O 3 ·2SiO 2 in the filter cake into Na 2 . O·A1 2 O 3 and Na 2 O·SiO 2 .
At the same time, Al(OH) 3 and Fe(OH) 3 contained in the filter cake are also reconverted into Na 2 O·A1 2 O 3 and Na 2 O·Fe 2 O 3 .
4, dry powder dissolution
Generally, the stable solubility of SiO 2 in Na 2 O·Al 2 O 3 solution is very low, and excess SiO 2 will form Na 2 O·A1 2 O 3 ·2SiO 2 precipitate with Na 2 ·A1 2 O 3 to make A1 The extraction rate of 2 O 3 and SiO 2 is lowered, and the Na 2 O alkali consumption (Na 2 CO 3 consumption) is increased.
Figure 3 shows the dissolution of SiO 2 in a Na 2 O·Al 2 O 3 solution at 70 °C.
In Fig. 3, above the curve AB (Zone III) is a supersaturation zone (unstable zone) of SiO 2 , between AB and AC (II zone) is a metastable state zone, and below AC (I zone) is an unsaturated zone (I zone) Stable dissolution zone).
From Fig. 3, when the MR in the Na 2 O·Al 2 O 3 solution is 2.0 and the A1 2 O 3 is 75 g/liter, the maximum metastable concentration of SiO 2 is only about 2 g/liter.
The test results show that when the MR of the solution is increased to 4.2 or more and the Al 2 O 3 is about 75 g/L, the dry powder obtained by caustic soda is dissolved in water, and Na 2 O·SiO 2 is in Na 2 O·Al. In the 2 O 3 solution, a supersaturated solution of SiO 2 will be formed. After stirring or heating for 2 hours or for 4 hours, SiO 2 will gradually reach a metastable state of dissolution equilibrium, and amorphous Na 2 O·Al will be produced in the solution. 2 O 3 · 2SiO 2 . Since there is no seed crystal, no crystal precipitation occurs in Na 2 O·Al 2 O 3 ·2SiO 2 within 10 to 15 days, and the solution can be stably present.
Therefore, after the dry powder is dissolved in water, it should be separated by filtration within 2 hours or 4 hours at the natural temperature of the solution to avoid substitution of the impurity particles in the solution for the Na 2 O·Al 2 O 3 ·2SiO 2 seed crystal to promote Na 2 O. · Formation of AlO 3 · 2SiO 2 crystal.
After the dry powder is dissolved, Na 2 O·Al 2 O 3 and Na 2 O·SiO 2 are all dissolved in water, and some Na 2 O·Al 2 O 3 is hydrolyzed to produce Al(OH) 3 and NaOH; Na 2 O·Fe 2 O 3 is completely hydrolyzed to produce Fe(OH) 3 and NaOH. The NaOH produced by the hydrolysis further increases the stability of dissolution of SiO 2 (Na 2 O·SiO 2 ) in the solution.
The solution in which the dry powder was dissolved was separated by filtration, and in addition to impurities, the filter cake also had a part of Al(OH) 3 .
5, screaming out
The cake of the dry powder dissolved in the caustic soda solution is dissolved, and the Al(OH) 3 in the filter cake is reacted with NaOH to be converted into Na 2 O·Al 2 O 3 to be dissolved into the solution and separated from the impurities.
6, dilution hydrolysis
The filtrate obtained by the previous three filtration separations was combined and diluted with water, and about 85% of Na 2 O·Al 2 O 3 was hydrolyzed to obtain most of Al(OH) 3 .
7, carbonization separation
The diluted and hydrolyzed filtrate is carbonated with CO 2 gas, neutralized NaOH, and the pH of the solution is lowered to almost completely hydrolyze the remaining Na 2 O·Al 2 O 3 in the solution to form Al(OH) 3 precipitate. the residual Na 2 O · Al 2 O 3 concentration is less than 10--3 mole.
After separating Al(OH) 3 , the solution became a mixed solution of Na 2 CO 3 and NaHSiO 3 .
The Na 2 CO 3 and NaHSiO 3 mixed solution is further subjected to carbonation treatment by pressurization with CO 2 gas, and the pH of the solution is lowered to almost completely hydrolyze NaHSiO 3 in the solution to form a H 2 SiO 3 precipitate.
After separating H 2 SiO 2 , the solution became a dilute Na 2 CO 3 solution.
8. Alkali recovery
The dilute Na 2 CO 3 solution was directly subjected to causticization with quicklime to obtain a by-product CaCO 3 and a dilute NaOH solution. After the NaOH solution is properly concentrated, it is used as a concentrated caustic soda circulation for caustic soda alkali melting and caustic soda dissolution as a raw material.
After diluting the dilute Na 2 CO 3 solution appropriately, mixing with the high silica-alumina powder, drying and removing the water to obtain a mixed dry powder, and mixing the mixed powder for the soda alkali alkali melting process as a raw material.
Al 2 O 3 and SiO 2 extraction rate and alkali loss rate
The main factors affecting the extraction rate of Al 2 O 3 include the temperature and time of alkali fusion conversion and the concentration and temperature at which the filter cake after dissolution of the dry powder is dissolved by caustic soda. If the alkali-melting temperature is too high or the time is too long, the loose structure of the formed zeolite-type Na 2 O·Al 2 O 3 ·2SiO 2 will be transformed and become denser, which will increase the difficulty of subsequent caustic treatment and further reduce Al 2 O. The extraction rate of 3 ; the concentration and temperature of the filter cake eluted with caustic soda increased, and the extraction rate of Al 2 O 3 increased.
The main factors affecting the SiO 2 extraction rate include the CaO and MgO contents in the raw materials and the temperature and time of the alkali fusion reaction. The content of CaO and MgO in the raw material increases, the amount of SiO 2 consumed during alkali fusion increases, and the extraction rate of SiO 2 decreases. When the alkali fusion temperature is too high or the time is too long, the extraction rate of SiO 2 also decreases.
The alkali loss during the treatment depends primarily on the temperature and time of the alkali fusion reaction. If the temperature is too high or the time is too long, the evaporation of Na 2 CO 3 and the formation of Na 2 O·Al 2 O 3 ·2SiO 2 tend to be dense and increase the difficulty of subsequent processing, so that part of Na 2 O cannot be released, and Na will be caused. 2 The loss rate of CO 3 increases.
The test results on the industrial production equipment for processing 3,000 tons of high silicon-aluminum ore raw materials per year prove that for the raw materials listed in Table 1, high-silica-aluminum ore powder: soda ash powder = 1:1.2-1.3 ingredients, alkali-melting temperature 1150～1350 °C, reaction time 40 to 25 minutes, discharge temperature 1050 ~ 1150 ° C, caustic soda concentration of about 50%, caustic soda dissolution temperature of 70 ~ 80 ° C, the extraction rate of A1 2 O 3 and SiO 2 can reach 95% and 90%, respectively Above, the circulation ratio of soda ash Na 2 CO 3 can reach 98% or more.
Exhaust gas, waste liquid circulation and waste heat utilization
The dilute solution of Na 2 CO 3 formed by carbonization is separated from the precipitate of AI(OH) 3 and precipitated by H 2 SiO 3 , and then appropriately concentrated, recycled for compounding, mixed with high-alumina powder to obtain a slurry, and then used in the process. The waste heat is used to dry the obtained slurry to obtain a “high silica-alumina powder-Na 2 CO 3 †mixed dry powder, which is recycled to the soda ash alkali-melting section for re-dosing, thereby realizing the circulation application of soda ash.
The caustic soda consumed in the production is subjected to caustic treatment with a dilute solution of Na 2 CO 3 formed by carbonization and quicklime, and the caustic soda is recovered, and after being concentrated, it is recycled to the alkali caustic soaking and caustic soda dissolution section to realize the circulation application of caustic soda.
The washing liquid of each process section is collected intensively and used as water for quenching liquid and dissolved water in the corresponding section.
The alkali loss in the production process can be basically achieved by the recycling of the washing liquid and the supplementation of K 2 O and Na 2 O contained in the high silico-alumina raw material.
The high-temperature flue gas generated by soda ash is firstly treated with clean room temperature air and water, and the clean hot air and hot water at 550 ° C and 350 ° C and the medium temperature smoke at 500-600 ° C are obtained. The gas; the medium temperature flue gas of 500-600 ° C is directly used for drying the mixed slurry of the concentrated Na 2 CO 3 solution obtained by the second carbonization and concentrated by evaporation and the high silica aluminum ore powder. Mixing dry powder with low temperature flue gas of about 200 °C; low temperature flue gas of about 200 °C is washed and purified to obtain clean flue gas at room temperature containing CO 3 , and used as CO 2 raw material gas after pressurization The carbonization and two carbonization processes respectively obtain Al(OH) 3 and H 2 SiO 3 precipitation; the clean hot air of about 550 ° C is used for the heating of the caustic soda melting section; the clean hot air of about 350 ° C is used for the product drying; Water is used for filter cake washing in each respective section.
The filter residue obtained after the caustic soda is dissolved is combined with the caustic waste residue for flocculation purification treatment of the sewage after washing the flue gas. The clean water cycle after the purification treatment is used for flue gas washing.
Conclusion
The use of "C-J STK" technology to extract Al 2 O 3 and SiO 2 from high-alumina raw materials, and as a new process for waste gas, waste liquid recycling and waste heat classification and utilization, is a high-alumina resource, high-addition An effective way to comprehensively utilize values. The application of this technology process, as long as the content of Al 2 O 3 in the raw material reaches 20% or the total content of Al 2 O 3 and SiO 2 reaches 70%, economic development and utilization value. After an industrial production test of the raw materials listed in Table 1, for each ton of the high-alumina raw material, about 360 kg of Al(OH) 3 and about 820 kg of H 2 SiO 3 and about 500 kg of by-produced CaCO 3 can be obtained. The output value exceeds 5,500 yuan, and the profit and tax reaches more than 2,500 yuan.
By further deep processing the obtained Al(OH) 3 and H 2 SiO 3 , it is also possible to produce various kinds of high-value-added various aluminum salts and silicates as well as alumina, aluminate and precipitated white. Dozens of chemical products such as carbon black and silica gel. These products can be used as raw materials in more than 10 industrial industries such as paper, ink, printing and dyeing, textile, medicine, grease, catalyst, plastic, rubber, daily chemical, petroleum , environmental protection, inorganic salt, etc. Ten million tons.
The process not only realizes the comprehensive recovery of aluminum resources and silicon resources and the rational conversion and utilization of thermal energy resources in high-silicon aluminum mines, realizes the rational utilization of high-silicon-aluminum resources, and greatly improves the economic benefits of high-silicon-aluminum resources utilization. It avoids waste of resources, reduces environmental pollution, reduces production costs, eliminates secondary pollution in production, and achieves clean production purposes, especially for China's soft-aluminite-type aluminum ore and high-grade aluminum ore resources. The actual situation that is in short supply has enormous economic, social and environmental benefits.
Refers to high silicon aluminum ore aluminum silicon aluminum ratio is less than 3.5 of mineral raw materials, including low grade bauxite, kaolin, powder coal ash, coal gangue, cats and yellow sand soil. In the conventional process, when Al 2 O 3 is extracted from aluminum ore, sodium aluminosilicate Na 2 O·A1 2 O 3 ·2SiO 2 is often produced due to the presence of SiO 2 in the raw material, and the extraction efficiency of Al 2 O 3 is lowered. Therefore, Bayer method can only choose soft-alumina bauxite with low SiO 2 content as raw material to avoid the interference of Na 2 O·A1 2 O 3 ·2SiO 2 . The soda lime sintering method only replaces most of Na 2 O in Na 2 O·A1 2 O 3 ·2SiO 2 with CaO in lime, and releases part of Al 2 O 3 regardless of the Bayer process or the soda lime sintering method. To completely solve the interference problem of Na 2 O·A1 2 O 3 ·2SiO 2 in the process of extracting Al 2 O 3 , only aluminum-containing minerals with an aluminum-silicon ratio of at least 3.5 can be selected as the raw material for the extraction of Al 2 O 3 .
Component
Al 2 O 3
SiO 2
Fe 2 O 3
CaO
MgO
TiO 2
K 2 O
Na 2 O
P 2 O 5
SO 3
other
content(%)
24.86
62.76
4.50
0.67
1.23
0.90
1.85
1.20
0.49
0.54
1.00
FIG SiO 2 content in solution 2 70 ℃ Na 2 O200 g / l, Al 2 O 3 120 g / l
Time curve
Figure 3 Dissolution of SiO 2 in a Na 2 O·Al 2 O 3 solution with a molecular ratio (MR) of 2.0
Degree and metastable state solubility (70 ° C)
However, when SiO2 is dissolved in a Na 2 O·A1 2 O 3 solution, it is often supersaturated at the beginning, and does not immediately precipitate Na 2 O·Al 2 O 3 ·2SiO 2 , which needs to be stirred for a long time. In order to reduce its concentration to the equilibrium content, the metastable concentration is reached.
In the soda ash process, high-silica-aluminum powder will release a large amount of CO 2 gas due to combustion of fuel and decomposition of Na 2 CO 3 . The carbonization process in the process needs to introduce CO 2 to produce soda ash. When the CO 2 is recycled to the carbonization step, not only the CO 2 concentration can satisfy the requirements, but also the total amount of CO 2 is surplus.