Diatomaceous earth and mineral soil (2)

2, various mineral soils Naturally occurring mineral soils, many types have adsorption capacity (or after chemical treatment activation). Such as bleaching earth (also known as fuller's earth); montmorillonite (also known as bentonite), goods often referred to as bentonite , or simply clay; and attapulgite (abbreviated as attapulgite) Wait. China also has abundant resources and a variety of products.
The chemical composition of montmorillonite is: Al ₂ (Si ₄ O ₁₀ )(OH) ₂ •xH ₂ O, or Al ₂ O ₃ .4SiO ₂ •xH ₂ O, where (SiO ₂ /Al ₂ O ₃ ) The ratio is approximately 4:1. The montmorillonite contains SiO ₂ (50% to 70%) and Al ₂ O ₃ (15% to 20%), and also contains a small amount of oxides of iron , calcium, magnesium , sodium and potassium. The ingredients of different origins can vary greatly. The chemical structure of montmorillonite has a large number of pores and can absorb a large amount of water. The natural montmorillonite has a water content of about 50% to 60%, and a large amount of pores are formed inside after drying, and the superior one can reach 60% to 70% of its volume, and the specific surface area is about 120 to 140 m ² /g. It has good adsorption performance and can absorb 12% to 15% of its own organic impurities. It also has a strong cation exchange capacity, which is related to its chemical composition.
The newly mined montmorillonite is quite soft and plastic. It is white or has a light yellow, light red, green, purple color; it is a dense scaly crystallite aggregate. Wax or greased. It is processed into a product by sorting, crushing, drying, grinding and sieving.
Treatment of montmorillonite with hydrochloric acid or sulfuric acid activates it to increase its adsorption capacity by a factor of 3 to 5. This product is called activated clay or acid clay. Mixing montmorillonite with water to form a slurry, adding hydrochloric acid (HCl is 28% to 30% of soil) or sulfuric acid to the reactor, and heating for 2 to 3 hours to remove organic matter and calcium, magnesium and sodium in the soil. The potassium and other components are dissolved, and then the residual acid and the dissolved matter in the reactant are separated and removed, washed with water until near neutral (the free acid content in the product should be less than 0.2%), and then dried to a moisture content of less than 8%, and pulverized to The 200 mesh sieve passes through more than 90%, which is the active clay.
Activated clay is a white or beige powder or granule. The main component is Al ₂ O ₃ .4SiO ₂ .nH ₂ O. The apparent density is 0.55 to 0.75 g/cm ³ and the relative density is 2.3 to 2.5. Do not dissolve in water, have a greasy feel. It has many irregular cavities on its surface, large specific surface area, good adsorption properties, and can remove bad odors and colored substances in animal and vegetable oils and mineral oils. It also has ion exchange capacity and selective adsorption. Activated clay has been widely used in the food, brewing and chemical industries to decolorize and refine various oils and organic materials.
The quality indicators of activated clay are divided into several levels according to their use. The quality requirements for edible oil processing are high.
Atta attapulgite is a kind of clay mineral with magnesium silicate as the main component and containing elements such as aluminum and iron. It was first discovered in the United States. The United States has a large production volume and has been used in petrochemical industries in the 1940s. China's Jiangsu, Anhui and other provinces also have minerals and products. It is white, light gray or light brown, with earthy luster, hardness of 2 to 3, density of 2.05 ~ 2.3g / cm ³ , with a layered chain structure, monoclinic system, multi-groove surface, internal porous channel, It has a large surface area, allowing cations, water molecules and certain size organic molecules to enter, exchange cations, and has strong adsorption and decolorization ability.
Several units in China have conducted preliminary tests, indicating that both activated clay and attapulgite have a certain decolorization effect on sugar liquid. Due to the abundant sources and low prices of these substances, and the good decolorization of some varieties (including processed and refined), their application to the decolorization and refining of sugar liquids is worthy of further study.
3. Adsorption performance The primary function of diatomaceous earth is to adsorb and remove fine particles in the solution, increase the filtration speed and obtain a clear filtrate. The same requirements apply to the use of other soil adsorbents.
Bennett has studied the effects of a variety of such solid adsorbents on aerosols in cane juice, including diatomaceous earth, bentonite, acid clay, kaolin , fullerite, montmorillonite, Lanxite and other mineral soils as well as ordinary charcoal and pickling. Charcoal, etc. The results show that there are several kinds of objects that can adsorb the suspended particles in the cane juice and exchange the calcium ions in the adsorption solution. The performance of these two aspects has a proportional relationship. Some experimental results are shown in the figure below. Its ordinate is the ability of these adsorbents to adsorb particles, expressed as the number of particles that can be adsorbed per gram; the abscissa indicates their ion exchange capacity for calcium ions in solution.
The test results of many different samples show that there is a regular proportional relationship between these two values. It can be seen that the adsorption of the adsorbent by these adsorbents mainly acts by adsorbing calcium ions, and the essence is that calcium ions bridge the adsorbent and the suspended particles and connect them. Undoubtedly, the realization of this adsorption requires the formation of a large number of calcium ion bridges. According to the above experimental data, in order to adsorb a suspended particle, the capacity of the exchange Ca ²⁺ required for the adsorbent was 8 × 108. However, calcium ions are only a small part of the bridge between the particles.
His research also showed that some of the original adsorptive adsorbents, if washed with concentrated NaCl solution for a period of time and then washed, can significantly improve their ability to adsorb Ca ²⁺ (as Na ⁺ replaced the original contained in the adsorbent Part of the other cations), at this time its performance of adsorbing the cane juice suspension particles is also proportionally increased, in line with the law of the figure. This kind of law should be taken seriously. Therefore, sugar mills use such adsorbents (including filter aids), should choose a higher exchange capacity for calcium ions, or be treated with brine to improve its performance.

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