It is well known that China is rich in bentonite resources and the world’s largest producer of bentonite. The export value of bentonite is $53,536,119 in 2019 from China, of which activated clay accounts for about 10%. It is mainly used in the refining of edible oils and in the petroleum industry. It is also used in the refining, decolorization, and purification of minerals such as paraffin wax, wax oil, kerosene, etc., and is also used in the food and pharmaceutical industries.

So what is activated clay?

Activated clay is a type of bleached clay made from clay (main bentonite), treated with inorganic acidification or other methods, and then washed with water and tried. The appearance of the activated clay is a white powder or a light pink powder, and it has good adsorption capacity. It can absorb colored substances and organic substances, mainly used in the decolorization and purification process of oils, and it is an ideal substitute for activated carbon.

Activated clay will absorb water vapor in the air during storage, and it will reduce the adsorption performance after long-term storage. Therefore, it is necessary to measure the water content before use, and the drying temperature of the clay needs to be controlled to prevent the structure of the clay from being damaged under high temperatures.

1. The preparation method for activated clay.

Generally speaking, there are three main preparation and production methods for activated clay: semi-wet method, full wet method, and full dry method. Part of the process flow is shown in Graph 1 and Graph 2.

2. Factors affecting the quality of activated clay

The majority of research showed that there are mainly three factors that affect the quality of activated clay. the details as following:

1) Quality of raw soil:

The better the quality of the bentonite raw ore and the lower the impurity content, the easier it is to prepare activated clay and the better the quality of the product obtained.

2) Temperature:

The preparation should be carried out under heating conditions, and the slurry should be controlled in a slightly boiling state, but the temperature should not be too high. The too high temperatures will easily cause rapid evaporation of water, uneven contact between acid and bentonite, and insufficient reaction.

3) Time:

At least 3 hours of activation treatment. If the reaction time is not enough, the acid cannot fully activate the bentonite, but the reaction time should not be too long. Long-term acid treatment will cause a large amount of chlorate dissolution in the clay.

3. The performance of activated clay

1) Strong adsorption capacity, high decolorization rate, low oil-carrying rate, fast filtration speed, and the small addition amount

2) It can effectively remove the total phospholipid, soap, and trace metal ions in the oil, and can be used as a natural antioxidant

3) It can remove toxins and odor substances such as aflatoxin and pesticide residues in the oil

4) The acid value of the decolorized oil will not rise, will not revert to color, will be clear and transparent, with stable quality and long shelf life.

5)Especially suitable for the refining production of mineral oil, vegetable oil, and animal oil

4. The main use of activated clay.

1) Edible oil decolorization

The food health and safety of edible oil has always been a concern. The edible oil decolorization process refers to the removal of harmful substances such as pigments, impurities, and drug residues in the oil. Some scholars have studied the use of different materials to refine orange essential oil and explored the factors affecting the decolorization rate.

Experimental results show that the highest decolorization rate (84.5%) can be obtained by using 10% (w) activated clay at 60 degrees for 30 minutes. Sensory evaluation and color analysis show that the decolorization of activated clay can maintain the quality of orange essential oil and extend the storage time.

When activated clay is used as a decolorizing agent in the oil refining process, two types of solid waste will be generated: one is the inactivated waste clay generated after the decolorization of fat, the other is to reduce the amount of white clay and grease entrained in the decolorization process Removal of fine particles of activated clay.

2) Lubricating oil refining

In the production and preparation of lubricating oil, the data of lubricating oil after solvent refining and various processes have basically reached the standard, but the lubricating oil at this time contains a small number of impurities, even including the production equipment Brought on the iron cut. In order to further improve the quality of lubricating oil, it is necessary to refining activated clay.

For example, solid adsorbents such as acid-activated clay, shells, almond shells, walnut shells, and eggshells can be used to adsorb and refine the lubricating oil refined by the solvent. By analyzing the viscosity, flash point, density, and color of lubricating oil products, it is proved that the best quality lubricating oil products can be obtained by using acid-activated clay. The lubricating oil production process is shown in Graph 3.

3) Environmental protection

According to research, activated clay can clean up heavy metals and oil pollution in wastewater, odor in the air, and factory smoke. Studies have shown that the removal rate of activated clay for phenol in wastewater is about 81%, the removal rate for organic matter is as high as 71%, and the service life is at least 4 hours.

4) Catalysis

As an excellent carrier, activated clay can be used as a catalyst or solid acid reaction for various reactions after being modified by loading. There is research which used La2O3 to modify activated clay to remove olefins in aromatics, and tested it in a 450kt/a PX plant, the results showed that the modified activated clay was increased by 5.3 times.

The research mechanism proves that the modified clay serves as a solid acid to catalyze the alkylation reaction between olefins and aromatics. Activated clay was modified with metal halide, applied to mixed aromatic hydrocarbons to remove trace olefins, and was tested in the industry. The service life was longer than that of ordinary activated clay. At the same time, the acidity research of modified clay shows that weak L acid is the key to catalyzing the hardening between olefins and aromatics.

5) Other applications

Activated clay is also an important raw material for the production of carbonless copy paper. Adding binders, dispersants, and additives to activated clay can be used to produce color coatings for the production of paper such as invoices, computer recording paper, and bills file. In addition, activated clay can also be used as a moisture desiccant, rubber reinforcing agent, vitamin A, B adsorbent, and so on.

In short, activated clay can be widely used in the decolorization and purification of petrochemicals, medicines, oleochemicals, animal and vegetable oils, and can effectively remove pigments, mycins, and peculiar smells in edible vegetable oils. It is the most ideal substitute for activated carbon.

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