Application of high alumina minerals in zeolite synthesis

by admin

Hu Hongjie, Zhao Hengqin, Wang Lizhuo

(Zhengzhou Institute of comprehensive utilization of minerals, Chinese Academy of Geological Sciences, National Engineering and Technology Research Center for comprehensive utilization of non-metallic mineral resources, Zhengzhou 450006)

Abstract artificial zeolite is a synthetic aluminosilicate mineral, and aluminum hydroxide is the main raw material of traditional zeolite synthesis industry. In recent years, the demand for electrolytic aluminum has increased rapidly, resulting in a shortage of alumina in the international market. Therefore, the price of aluminum hydroxide as a raw material for zeolite industry has been rising. In order to reduce costs, many domestic zeolite factories have begun to use bauxite resources as raw materials to synthesize boiling stone raw powder. Based on the research work of Zhengzhou Institute of comprehensive utilization of minerals, this paper analyzes and compares the industrial application of bauxite resources in this field [1 ~ 4]

keywords zeolite synthesis; Bauxite; Sodium aluminate; Purification

Introduction to the first author: Hu Hongjie, male, Han nationality, born in Yiyang County, Henan Province, was born on December 1, 1965. He is a researcher and graduate supervisor of Zhengzhou Institute of comprehensive utilization of minerals, Chinese Academy of Geological Sciences. He is mainly engaged in the research of metallurgy and chemical industry. Tel: 0371-60206201,; E-mail:@hotmail。

I. market demand and development of manufacturing technology of zeolite

zeolite is an aluminosilicate mineral with regular pore size, which can selectively adsorb gas according to molecular diameter and selectively catalyze organic synthesis reaction according to molecular shape and structure. Cations in the structure can also be selectively exchanged with other cations. Therefore, zeolite is an important adsorption, catalysis and ion exchange material, It is widely used in various industrial fields. According to the structure, zeolite molecular sieve products widely used in industry include type A, type X and type Y: for example, zeolite 4 replaces sodium tripolyphosphate, which is a new detergent additive in detergent products, and the demand in the international market has reached nearly one million tons; The hollow glass molecular sieve made of 3 Å zeolite as a functional material is one of the core components of hollow glass, a new energy-saving building material. The international market demand is about 300000 ~ 500000 tons; Moreover, zeolite minerals play an important and unique role in the drying of refrigerator refrigerant, natural gas, petrochemical process gas, air separation, petrochemical catalytic cracking process and many other industrial technology fields

due to the rapid growth of the demand for zeolite, its manufacturing technology has attracted more and more attention. Artificial zeolite (type A and type X) was first produced and applied in industry by United carbide in the 1950s. So far, it is still in a leading position in this field. In the 1990s, Shanghai global molecular sieve Co., Ltd., the first production plant, was built in Shanghai, China. CeCar of France, zeochem of Switzerland, UOP, grace Davison and Mobil of the United States have also conducted a lot of research on the synthesis and molecular manufacturing technology of zeolite. China’s zeolite synthesis technology began in the 1960s, mainly including Shanghai molecular sieve plant, Dalian molecular sieve plant and Nanjing inorganic chemical plant; Today, the factories in Shanghai and Dalian no longer exist, but nearly 100 manufacturers engaged in molecular sieve manufacturing have been hatched. Foreign molecular sieve industry is generally monopolized by large enterprises, while China’s molecular sieve industry is more refined, which is divided into two categories: Zeolite Synthesis and molecular sieve manufacturing. The zeolite synthesis industry is represented by Shandong Aluminum Plant, Fujian Huiying, Shanxi Changli, Luoyang Jianlong and Zhengzhou Xueshan. The total output of the country is about (50 ~ 60) × 104t。

foreign zeolite industry generally uses aluminum hydroxide and water glass as aluminum source and silicon source to synthesize zeolite. The synthesis process of type a zeolite represented by UOP company of the United States is shown in Figure 1. China’s zeolite synthesis process started late, but in order to reduce the cost, most of them directly synthesize zeolite from natural minerals quartz sand and bauxite. It should be said that this process is one of China’s important contributions to zeolite synthesis industry

II. Economic analysis of synthesizing 4 Å zeolite from different aluminum sources

the purpose of using bauxite or aluminum hydroxide as aluminum source is to prepare sodium aluminate solution, mix it with sodium silicate in a certain proportion, and synthesize zeolite through unit processes such as gelation, aging, crystallization, filtration, washing, drying and packaging

Figure 1 zeolite synthesis process

the content of alumina in zeolite is about 15% ~ 20%. According to the calculation of 4 Å zeolite with large market demand, the consumption of aluminum hydroxide per ton of product is about 480KG; Due to the rising price of alumina, the price of aluminum hydroxide is also 2000 ~ 3000 yuan /T, while the price of 4 Å zeolite is only 2600 ~ 3000 yuan /T. the cost of aluminum hydroxide accounts for 30% ~ 45% of the sales price of 4 Å zeolite. In order to reduce the production cost and improve the profit margin, many zeolite manufacturers are seeking to directly extract sodium aluminate solution from bauxite to synthesize 4 Å zeolite

according to the calculation of Chinalco and other alumina manufacturers, the manufacturing cost of aluminum hydroxide is about 1200 ~ 1500 yuan /T. in the process of zeolite synthesis, the purified sodium aluminate solution can be directly used to eliminate the further decomposition, filtration and drying process. Therefore, the cost per ton of aluminum hydroxide can be controlled at 1000 yuan /T. The selling price of aluminum hydroxide is calculated at 2500 yuan /T. If 4 Å zeolite is synthesized from bauxite, the cost per ton of product can be saved by about 600 yuan

III. selection of bauxite raw materials for synthetic zeolite

sodium aluminate solution is actually an intermediate product of alumina industry. Therefore, the process of preparing sodium aluminate solution from bauxite can learn from the main process of traditional alumina production process

alumina production process can also be divided into sintering process and Bayer process according to different bauxite resources. Bauxite in nature can be divided into diaspore, boehmite and gibbsite; Boehmite monohydrate and gibbsite are relatively easy to dissolve. Bayer process is generally used for direct dissolution. In terms of equipment, it has developed from high-pressure dissolution to pipeline dissolution; Diaspore is difficult to dissolve, and sintering method is often used in industry. According to the difference of bauxite grade and silicon content, diaspore is further developed into alkali lime sintering method and enhanced sintering method. Alumina industry is a kind of high energy consumption operation with large investment and long production process. Generally, the best economic balance point for plant construction must be 10 × More than 104t, equivalent to annual production of 15 tons × 104t aluminum hydroxide

compared with the alumina industry, the consumption of aluminum hydroxide in the synthesis of zeolite is much smaller, with an annual output of 10 × The 104t 4 Å zeolite plant needs only 43000 tons of aluminum hydroxide per year. Due to its small scale, the supporting sodium aluminate preparation system cannot completely copy the alumina production process in the design. In the selection of key equipment such as dissolution and sodium aluminate solution pu
rification, we must combine the characteristics of bauxite and the requirements of zeolite synthesis process, and fully consider factors such as investment cost and operation cost

different manufacturers adopt different processes due to different sources of bauxite: Shandong Aluminum Plant uses low-grade bauxite, and its 4 Å zeolite plant uses some sodium aluminate solution produced by alumina sintering process. The raw material solution has been purified, and the mother liquor of crystallization alkali can be directly fed into the evaporation process of sintering process. Therefore, although the production process is long, the manufacturing cost of sodium aluminate is not high; Through research, Zhengzhou Institute has proposed two processes: Limestone Sintering and gibbsite atmospheric pressure dissolution to synthesize zeolite from sodium aluminate solution, which has been used in Shanxi Changli and Fujian Huiying zeolite factories. The sodium aluminate solution prepared by lime sintering method has low alkali consumption, but the amount of red mud slag is large, the pipeline is blocked, and the filter cloth is easy to agglomerate, which makes the production operation difficult; Using gibbsite to directly dissolve sodium aluminate, although the ore grade is low, the sintering process is omitted, and the manufacturing cost of sodium aluminate is low. The disadvantage is that the dissolution rate of alumina in the ore is low; There are other smaller zeolite factories that use scab material or aluminum calcium powder to dissolve alumina to synthesize zeolite

IV. purification of sodium aluminate solution and product quality control

sodium aluminate is prepared by using aluminum hydroxide as aluminum source. As the purity of industrial alumina is more than 99%, the content of iron, silicon, potassium, calcium, magnesium, chloride, carbonate and sulfate in the product is very low. Therefore, the sodium aluminate solution is very pure and does not need to be purified. The synthesized zeolite product has uniform particle size, crystallinity of more than 90%, whiteness of more than 98%, thermal stability of more than 600 ℃, and excellent dynamic adsorption and regeneration performance

sodium aluminate solution is dissolved from various bauxites, including soluble ions K +, Ca2 +, Mg2 +, Fe2 + and Cl -, <> <>

, <>

<> <>

directly enter sodium aluminate solution. During the gelation and crystallization of zeolite, a small amount of Fe2 + circulates in the mother liquor, which can cause product dyeing; Other hydrated cation ions have the ability of structure guiding and promoting or destroying “a certain polymer structure”. They accelerate or inhibit the formation of crystal nuclei of various zeolites by affecting the structural characteristics of various silicate ions or aluminosilicate colloidal particles. The charge, concentration and size of cations play an important role in the formation of zeolite structure: for example, at low temperature (60 ~ 250 ℃), Na + tends to form Sodalite, type a zeolite, analcite, hydrated calcium zeolite, Sodalite and octahedral zeolite; Under the same conditions, K + is conducive to the formation of rhombite, calcium crucite and barium zeolite

cations directly affect the thermodynamic and kinetic process of zeolite mineral crystallization. The result is the formation of heterocrystalline minerals and the reduction of zeolite crystallinity; Finally, it has an impact on the dynamic adsorption, thermal stability, particle size distribution, whiteness and regeneration performance of zeolite. Therefore, this kind of solution requires special treatment to reduce the influence of impurity ions in the solution on the zeolite synthesis process as much as possible. After a large number of tests, the influence of impurity ions on zeolite synthesis process can be controlled through mother liquor purification, partial discharge, changing synthesis conditions and many other measures. The test results have been applied in large-scale industrial practice

v. balance of alkali mother liquor

the synthesis and crystallization process of zeolite is carried out in excess alkali solution. Alkali is a kind of accelerator, which accelerates the fracture and rearrangement of aluminum oxide group and silicon oxide group to form a new aluminum silicon oxygen tetrahedron structure. When preparing aluminum source and silicon source solutions, in order to stabilize the solution, the molecular ratio of sodium aluminate solution (Na2O /Al2O3) of synthetic zeolite is generally 1.7 ~ 2.0, and the modulus of sodium silicate solution (SiO2 /Na2O) is also more than 3.1. In order to promote the crystallization process of zeolite, the alkali concentration of solution during the synthesis of zeolite A and zeolite X should be controlled between 20 ~ 70 (H2O /Na2O). After crystallization, the mother liquor still contains 40 ~ 50 g /L Na2O and a small amount of SiO2. Recycling the sodium oxide in the mother liquor can save the cost of environmental protection and reduce the consumption of alkali

in the production process of zeolite synthesized by aluminum hydroxide in foreign companies, especially for X-type zeolite, the crystallization mother liquor contains a small amount of SiO2 in addition to Na2O. If the crystallization mother liquor is recycled, it will be prepared in dissolution

Related Articles

Leave a Comment