The attapulgite, also known as palygorskite, is a layered chain clay mineral dominated by aqueous magnesium -rich silicate. In natural attapulgite, the content of attapulgite is 70-80%, the content of montmorillonite and sepiolite is 10%-15%, the content of quartz sand is 4%-8%, and the content of calcite and dolomite is 1%. -5%. The color of the attapulgite sticks varies in light gray, light green or light brown depending on the type and content of the impurities.
1. Why should the concave soil rod be dispersed and purified?
The presence of these impurities such as montmorillonite, illite and quartz sand will inevitably weaken the original adsorption, colloidality and bonding properties of the attapulgite. Therefore, in practical applications, it is usually necessary to prepare a high-purity attapulgite sample by dispersion purification. .
The large specific surface and surface electrical properties of the attapulgite make it have good adsorption, but the rod crystals in the attapulgite ore usually exist in the form of rod bundles and aggregates, which inevitably affect its specific surface area and thus affect its Adsorption performance limits the application range of attapulgite. Therefore, the attapulgite ore usually requires a certain dispersive purification method to remove impurities, dissociate the rod crystals and aggregates to improve the microstructure, make it porous, improve specific surface area, adsorption performance and Colloidal properties. Therefore, the purification and dispersion of the attapulgite has great significance for its industrial application.
2. Purification technology of attapulgite
(1) Drying of attapulgite
The attapulgite dry purification is that the purification process of this method is too simple, the purification effect can not significantly improve the quality of the attapulgite, and the product with low requirements can be used according to this method. Dry process products are mainly used in plastics, rubber and other industries, often as a carrier and filler.
The attapulgite dry purification is carried out by using the density and particle size of the material in the attapulgite. By pulverizing the mineral, separation by gravity difference (such as cyclone separation, centrifugal separation, classifier, etc.) generally involves crushing and grinding. , grading, etc., the key to this purification method is the grinding and grading process. Generally, it is pulverized by Raymond mill, and non-clay impurities such as quartz sand and carbonate which are not easily ground in the attapulgite can be easily removed.
The method has low cost and simple process, but the purification effect is limited. It is only suitable for ore with good ore grade and high content of attapulgite. The obtained products are mainly used as carriers and fillers in rubber and plastic industries.
(2) attapulgite wet purification
The wet purification technology is mainly based on the difference of physical and structural characteristics of attapulgite and impurity minerals. The process mainly includes:
1 crush or grind the attapulgite, and add water to soak;
â‘¡ Wet purification techniques key is dispersed, an appropriate amount of dispersant is generally added (phosphate, sodium hexametaphosphate, sodium pyrophosphate, polyacrylic acid, sodium silicate, etc.), the solid phase content was controlled at 5% to 22%; purified claim The higher the solid content, the lower the solid content; on the contrary, the lower the requirement, the higher the solid content; for the nano-scale, the solid content is lower and more dispersed;
3 sedimentation or centrifugal separation, the obtained attapulgite slurry is separated by natural sedimentation or hydrocyclone, and the impurities are separated from the slurry to obtain a concave concentrate slurry;
4 Dehydration and drying. Due to the expansion, high viscosity and colloidal properties of the attapulgite itself, the dewatering and drying of the attapulgite is difficult; during the dehydration process, some of the original mineralization properties can be added. Substance to reduce the viscosity of the slurry and choose efficient filtration equipment .
The recovery process of the attapulgite wet purification process is low, the resource waste is serious, and the production cost is high. Wet-purified attapulgite products are mainly used in industries where high purity of the concave soil is required, such as cosmetics, detergents, pharmaceuticals, catalysts and filter aids.
(3) attapulgite extrusion pretreatment
Mechanical extrusion of the attapulgite is a simple, convenient and widely used pretreatment method. After the attapulgite clay ore is treated by simple mechanical extrusion, the internal microstructure becomes loose and porous, and the original crystal bundle and aggregate form fine crystal bundles and rod-like crystals, and the crystal bundles become loose and disorderly interlaced. A large number of overhead holes are formed, as well as microscopic gaps and cracks.
When preparing a suspension of attapulgite, moisture can easily enter the interior of the particle through pores, pores and micropores inside the crystal, and further penetrate into the rod bundle and the fiber aggregate, thereby making the interior of the particle The microstructure is expanded by high hydration due to hydration. When the bubble is quenched, a high pressure is generated, causing large crystal beams and aggregates to dissociate. As the distance is increased, the gravitational force is gradually reduced. As long as it is subjected to a small external force (weak dispersion condition), the attapulgite is easily dispersed into a fine crystal beam or even a rod crystal in the dispersion medium. The highly dispersed crystal or rod crystal forms a three-dimensional network structure in the dispersion medium, thereby enclosing a large amount of free water therein, causing it to lose fluidity and forming a solution having a higher viscosity.
On the other hand, if the attapulgite is not "swelled" by extrusion or the like, the granules can be disintegrated from the surface and the inside to achieve the same viscosity only under the action of strong shearing force. It can be seen that the extrusion does not improve the intrinsic viscosity of the attapulgite, but is a modification treatment that loosens the microstructure, so that it is easily dispersed in a medium such as water and reaches an intrinsic viscosity. Therefore, before the wet purification, the attapulgite is usually disassembled by a physical extrusion process, and the densely arranged aggregates and the crystal beams are formed into a loose porous structure to prepare for the purification and dispersion of the attapulgite.
3. Research progress in attapulgite purification technology
Tang Qingguo et al. used a high-speed centrifugal classifier to carry out beneficiation of the dispersed attapulgite ore, and obtained an attapulgite content of 93% concentrate with an average particle diameter of 0.92 μm. After the slurry is treated with dilute hydrochloric acid and ultrasonic treatment, the mineral content of the attapulgite can reach 95%.
Cao Yaohua and others used a grinding-classification process to purify the Guanshan landscaping (about 5% of attapulgite content) in Jiashan County, Anhui Province, and obtained a concentrate with an attapulgite content of 80.92%. 49.30%, product fineness is less than 1μm.
Jin Yeling et al. used a dispersant and ultrasonic hydrothermal method to purify the attapulgite. The attapulgite slurry containing 3% sodium hexametaphosphate was heated to 40 ° C, and stirred at a medium speed for a period of time. The attapulgite obtained after purification was loose. The needle crystal has a particle size D90 of less than 4.7 μm, a whiteness of 87%, a purity close to 100%, and is easily redispersed in water.
Xiong Yu et al. used the pickling process to purify the attapulgite. The optimum pickling process parameters were: at 80 ° C, the liquid-solid ratio 5:1 attapulgite slurry was pickled with 60% sulfuric acid for 2.5 h; purification An attapulgite concentrate having a SiO2 content of 76% or more can be obtained.
4, the problem of attapulgite purification
Although scholars at home and abroad have carried out many meaningful studies on the purification of attapulgite and obtained attapulgite with high purity, it is estimated that the quality of the attapulgite obtained from the purity of the attapulgite is relatively one-sided. Considering the problem of purification recovery, and in industrial applications, to solve the problem of attapulgite purification, the following core issues must be considered:
(1) Selection of attapulgite ore
At present, how to separate montmorillonite from attapulgite is still a very difficult problem. Therefore, when selecting and purifying attapulgite ore, we must first consider the type of ore selected, and choose the easy-purified concave ore (ie, impurity minerals). Quartz or dolomite ore).
(2) Dispersion of attapulgite
How to make the attapulgite better disperse in the water, which kind of dispersion technology is more effective, more energy-saving and environmentally friendly is an urgent problem to be solved in the attapulgite purification.
(3) The problem of water and soil separation
After removing the impurity mineral contained in the attapulgite, the attapulgite contained in the remaining aqueous suspension is dispersed in water, how to separate the pure attapulgite from the water without consuming a large amount of energy It is also a problem that needs to be solved now.
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