Aluminum production uses aluminum-containing minerals. Because of the similar properties of aluminum and silicon, minerals also contain silicon in addition to aluminum. The presence of silicon has a great influence on the production of aluminum. If the silicon content is too high, a large amount of aluminum is lost during the silicon removal process, and the amount of slag is also very large. Therefore, the extraction of aluminum from aluminum-containing minerals requires a higher aluminum to silicon ratio of minerals. Bauxite and aluminum-containing minerals as coal ash powder. In order to make effective use, it is necessary to pre-desiliconize fly ash and some bauxite to increase the ratio of aluminum to silicon.

The pre-desiliconization methods for aluminum-containing minerals currently used mainly include physical methods, chemical methods and biological methods.

First, the physical law

Physical desiliconization is characterized by the removal of silicon-containing impurity minerals in a natural form and the reduction of SiO 2 content in bauxite ore. Physical desiliconization is the main method for pre-desiliconization of bauxite, but the use of this method for pre-desiliconization of fly ash has not been reported. The physical desiliconization method mainly includes flotation method, selective disintegration method, washing, sieving and selective flocculation method. The most important one is flotation method, which is divided into positive flotation and reverse flotation.

(1) Positive flotation desiliconization-anion collector flotation desiliconization

Positive flotation refers to flotation using an anionic collector by inhibiting the aluminosilicate mineral.

M. A. Eygeles, et al. Studied the oleic acid, tall oil and oil mixture as collector, OP-7-ethoxy compound as the foaming agent, sodium silicate, sodium hexametaphosphate as a modifier, selectivity float A mixture of kaolinite, quartz and gibbsite is selected. However, due to the low recovery rate of bauxite concentrate and high flotation cost, this method has not been used in industry. L. M. Lyushnya, et al. Fatty acid, neutral oil, and a mixture of OP-7 collector, sodium silicate, sodium hexametaphosphate, sodium sulfite, copper, iron or spirit to adjust the flotation separation of alizarin gibbsite or a boehmite, and A mixed mineral such as kaolinite has obtained alumina, but the grade is low and the recovery rate is low. P. I. Andreev, et a1. The mechanism of the capture of gibbsite by oleate was studied. By washing with water, it was confirmed that oleate had chemisorption on the surface of gibbsite. VV Ishchenko, et al. confirmed the adsorption of sodium oleate on the mineral surface by infrared absorption spectroscopy, and also studied the adsorption of the collector on the mineral surface. The results showed that the adsorption of soap and sodium oleate on gibbsite, kaolinite and siderite increased with the increase of pulp pH, but the adsorption rate was different. Futian Kenji believes that the important work of bauxite flotation is to disperse gangue, using fatty acids, soaps, alkyl sulphates, alkyl sulfonates, etc. as collectors, sodium phosphate and sodium hexametaphosphate as regulators. In alkaline or weakly alkaline media, since gibbsite has a faster flotation rate than gangue minerals such as kaolinite, they can be separated.

Since the 1960s, China has carried out extensive flotation desiliconization experiments on diaspore bauxite. The aluminum-silicon ratio of a gibbsite-type bauxite ore in Hainan is 5.3, the ratio of aluminum to silicon in concentrate after de-siliconization is 8.32, and the recovery rate of Al 2 O 3 is 72.94%; one water in Shandong, Henan and other places. Dubarite bauxite: the ratio of aluminum to silicon in raw ore is 4.6 to 5.78, the ratio of aluminum to silicon in concentrate is 8.09 to 9.23, and the recovery rate of Al 2 O 3 is 71.12% to 88.50%. Using oxidized paraffin soap and tar oil as collectors, carboxymethyl cellulose (CCMC), sodium hydroxide, sodium sulfate, sodium hexametaphosphate, etc. as adjusting agents, mica -hydrophilic aluminum under alkaline conditions The flotation of stone-type bauxite shows that a small amount of sodium hexametaphosphate is beneficial to the recovery of alumina and increase the ratio of aluminum to silicon. Sodium carbonate and hexametaphosphate are effective regulators for gibbsite and kaolinite in the semi-industrial beneficiation test of Taihu stone bauxite mine in Yangquan, Shanxi Province with oxidized paraffin soap and tar oil as collectors. Alkaline flotation can increase the aluminum-to-silicon ratio of diaspore-mica-type bauxite from 5.53 to 10.35, and the recovery rate of Al 2 O 3 is 88.9%. Liang Aizhen replaced the expensive hexametaphosphate with cheap water glass, replaced the tar oil with a better selective azelaic acid fatty acid, and studied the flotation of bauxite with ammonium humate as an inhibitor. Ammonium humate can increase the floatability difference between aluminum minerals and silicon minerals, increase the floating speed of diaspore, and reduce the loss of alumina in tailings.

The above flotation desiliconization process stays in the laboratory stage and has no industrial application. There are several reasons: 1) the grinding particle size is too fine, generally -0.074mm is greater than 95%; 2) alumina recovery in concentrate The rate is 80%, the average aluminum to silicon ratio is 8-9, the index is not very satisfactory; 3) the concentrate water content is large.

(2) Reverse flotation desiliconization-cation collector flotation desiliconization

In general, the content of useful minerals in bauxite is relatively high, and the content of minerals containing silicon impurities is relatively small, especially diaspore. With the positive flotation process, the amount of foam is large, so people naturally consider reverse flotation to pre-desilicon. Reverse flotation desiliconization is achieved by inhibiting diaspore and flotation of aluminosilicate minerals using a cationic collector.

The literature shows that when the pulp pH is 7-8, the amine-based cation collector can effectively select silicate minerals such as smectite chlorite, and sodium hexametaphosphate can help the pulp to disperse. VVIshchenko, et al. used dodecylamine for reverse flotation. The ratio of aluminum to silicon in raw ore is 1.7-2.4, the stirring speed of flotation is 1750r/min, and the ratio of liquid to solid is 3:1. The final refined aluminum silicon is obtained. The mass ratio is about 7 and the concentrate yield is 27.40%. Spectroscopic studies have shown that the amount of amine adsorption on the surface of kaolinite and gibbsite is different. In neutral and weakly alkaline solutions, amines are co-adsorbed on the surface of kaolinite in molecular and ionic states. SATikhonov, et al. Flotation separation of quartz in bauxite by a mixture of ANP-14 and industrial oil in the presence of cationic agent 2B and aluminum sulfate. Tests have shown that the acetate of rosin amine can also selectively float out of quartz. VVIshchenko, et al. Research shows that cation collectors such as dodecylamine, ANP-14, hexadecylamine, ANP-2, and lower aliphatic amines can float quartz and kaolinite in bauxite; pH value It has a great influence on the amount of collector adsorbed. The disadvantage is that the amount of collector is large and the alumina recovery rate is low.

Zhang Yunhai cetyl bromide or the like to adjoin collector pyridine salt, Arbacol-H and quebracho adjusting agent is removed from low grade 80% -90% of the kaolinite in the laboratory, However, the cost of the agent is higher and the alumina recovery rate is lower. Liu Guangyi et al. used a dodecylamine acetate as a collector to conduct a flotation test on a single mineral. In the range of pH 6-8, SA combined with dodecyl acetate can inhibit more than 90% of the hard aluminum. The stone floats out, while the floating rate of soft kaolinite and pyrophyllite is greater than 80%. Li Yaowu and other C10-C20 fatty amines are used as collectors to float most of the pyrophyllite from the diaspore-type bauxite. The disadvantage is that the recovery rate of alumina concentrate is low, and the operating system is also compared. strict.

Second, the chemical law

The chemical structure is used to destroy the crystal structure of the aluminosilicate mineral in the ore to increase the activity of SiO 2 . The less active SiO 2 is soluble in the alkali solution under low temperature conditions, thereby achieving the purpose of increasing the ratio of aluminum to silicon.

The chemical pre-desiliconization study of aluminum-containing minerals was first introduced in the 1940s by the German Lauta plant to deal with high-silicon bauxite mines in Hungary, Austria and the former Yugoslavia. The bauxite is calcined at 700 to 1000 ° C, and then the calcine is dissolved at 90 ° C with a 10% caustic solution. The optimum calcination temperature is between 900 and 1000 °C, the desiliconization rate is up to 80%, the aluminum to silicon ratio of concentrate is increased from 4.5 to 20, and the loss rate of Al 2 O 3 is below 5%. The problem is that the mass ratio of the liquid solid product at the time of dissolution is too large, and the dissolution time is too long.

Yan Guodong et al. used the different reaction speeds of different mineral phases of SiO 2 and Al 2 O 3 in fly ash at the same temperature to study the low temperature stepwise dissolution of silicon and aluminum to separate the silicon in fly ash. The optimum conditions for the test are as follows: the fly ash is pretreated by 950 ° C high temperature calcination, and then dissolved in 2 to 3 mol / L of alkali solution, the liquid solid product mass ratio is 50, the dissolution temperature is 120 ~ 130 ° C, and the dissolution time is 4 to 6 h, the amount of silica eluted was 29.23%, the amount of alumina eluted was 1.26%, and the dissolution ratio was 23.2.

Zhang Zhanjun et al. established a process for extracting amorphous SiO 2 from NaOH based on the chemical and phase composition characteristics of high alumina fly ash. When the mass concentration of NaOH is 250 g / L, the mass ratio of ash and alkali is 1:0.5, the reaction temperature is 95 ° C, and the reaction time is 4 h, the extraction rate of SiO 2 is 41.8%, and the mass ratio of aluminum to silicon is increased from 1.29 to 2.39.

Zhang Kaiyuan pointed out that when the volume ratio of fly ash to sodium hydroxide solution is 1/5, the concentration of NaOH solution is 160g/L, the dissolution temperature is 100°C, and the temperature is 2h, the pre-desiliconization effect is the best.

Qin Jinuo proposed a method for pre-desiliconization of fly ash to increase the ratio of aluminum to silicon in the patent No. 200710061662. The method firstly activates the fly ash by acid leaching, alkali leaching or roasting, and then leaches at 80-150 ° C with a NaOH solution having a mass concentration greater than 400 g/L, and the silicon is sodium silicate. The form is dissolved so that the ratio of aluminum to silicon in the alkali leaching residue is ≥2. In the patent of 200710065366.7, the mass concentration of the sodium hydroxide solution is 150-300 g/L, the mass ratio of sodium hydroxide to fly ash is (0.3-0.8):1, the reaction temperature is 90-150 ° C, and the reaction time is Under the condition of 2 to 4 hours, the mass concentration of SiO 2 in the desiliconization solution is 50 to 80 g/L, and the mass ratio of aluminum to silicon is 40 to 50.

The chemical pre-desiliconization effect is better, and the aluminum-silicon ratio in the fly ash can be well improved, but there are also many disadvantages such as the use of high-concentration alkali liquor, large mass ratio of liquid solid product, large material flow rate, and high consumption of caustic alkali. Moreover, the chemical desiliconization removes amorphous SiO 2 , and the α-SiO 2 originally present in the ore cannot be removed, so this method has not yet been industrially applied.

Third, the biological law

Decomposing silicate and aluminosilicate minerals with microorganisms, the aluminosilicate mineral molecules can be broken into alumina and silica, and the silica can be converted into soluble matter, while the alumina is insoluble, and the two can be separated. . Compared with other desiliconization methods, the biological desiliconization method has obvious advantages and is currently the most promising desiliconization method. With this method, higher process specifications can be obtained and there is basically no pollution to the environment.

The commonly used microorganisms are mainly heterotrophic bacteria. These microorganisms require organic matter as a source of carbon and energy. Representative microorganisms are Bacillus circulans, Bacillus licheniformis, Bacillus polymyxa and Aspergillus niger. These bacteria can be mutagenized by ultraviolet irradiation or the like, and the solvency of the mutants to the minerals is greatly enhanced. These bacteria are characterized by the need for silicon during their growth.

In the former Soviet Union, kaolinite for the Kazakhstan deposit proposed leaching of fine mud and magnetic products using Bacillus colloidal bacteria. At a leaching temperature of 28 to 30 ° C, a liquid solid mass ratio of 5:1 and a leaching time of 9 d, the desiliconization rate is about 62%, and the Al 2 O 3 recovery is about 99%.

Andreer P. L. Treatment of concentrate containing bauxite (37.4%)-boehmite (12%)-kaolinite (16%)-quartz (20.06%) with Bacillus heterolepticus The composition is boehmite (53%) - boehmite (17%) - kaolinite (11.6%) - quartz (12%).

S. Grudeu used Bacillus circulans and Bacillus licheniformis to soak bauxite for 7 days at 35-37 ° C, pH 5.6-6.5, stirring speed 180-240 r / min, and the ratio of aluminum to silicon of ore increased from 1.7 to 5.4.

S. Grudev treated quartz-kaolinite-shuishui soft aluminum bauxite with laboratory-accumulated Bacillus circulans, and the recovery rate of Al 2 O 3 in the concentrate was as high as 93.3%.

Bandyopadhyay used a strain of Aspergillus to remove 59.5% of the iron and 56.2% of the silicate in the bauxite.

The biological desiliconization can be completed at room temperature without high temperature and high pressure conditions; the selectivity is good, the alumina loss is small; the equipment is simple and the cost is low. However, at present, biological desiliconization is still in the laboratory and small test stage, and there is still a long way to go from industrial production. The main reasons are: 1) slow leaching rate of bacteria, long cycle, poor stability of microbial agents, harsh conditions, low productivity, and difficulty in forming scale; 2) bacteria is a heterotrophic organism that requires organic matter as a nutrient, but it has not yet Find an inexpensive medium as an organic nutrient for cultivating bacteria; 3) In terms of microbial selection, it has not yet been able to solve the technical problems of heterotrophic bacteria removal and degradation from genetics and variation; 4) if the leachate is not handled properly, It may pollute the environment.

Fourth, the conclusion

The combustion temperature of fluidized bed fly ash is relatively low, the mineral components such as kaolinite in coal are not destroyed, and the mineral composition is similar to bauxite. Therefore, the pre-desiliconization treatment method of bauxite can be used to treat fly ash. Pre-desiliconization is carried out. The fluidized bed fly ash can be treated by first calcination and then treated by alkali dissolution or flotation. For this reason, the modification conditions such as calcination temperature, type of reagent added and reagent amount added, and floatation are also considered. Select the type of agent and flotation conditions.

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September 26, 2024