Bentonite is a non-metallic mineral whose main component is montmorillonite. Because of its excellent performance, rich resources, environmental friendliness and wide application fields, it has become a veritable "universal soil".
The modification of bentonite is to change the composition of bentonite to change the physical and chemical properties of bentonite by roasting or using acid, inorganic salt, organic matter and other means. At present, many people have done research on the modification of bentonite, and the physical and chemical properties of modified bentonite have been greatly improved.
(1) Sodium Modification
Practice has proved that sodium-based bentonite is superior to calcium-based bentonite in terms of process performance. The principle of sodium modification is to use sodium-containing reagents to replace cations between calcium-based bentonite layers. Commonly used sodium agents include sodium carbonate, sodium acetate, sodium hydroxide, and sodium pyrophosphate. In practical applications, small and medium-sized enterprises often use excavators to mix bentonite and soda ash and stack them for aging, resulting in poor stability of sodium formation. If the Internet of Things technology is introduced to implement online monitoring and control, the sodium formation process can be stabilized.
(2) Acidification Modification
Use different concentrations of acids and different types of acids to treat bentonite under more suitable conditions. During the acidification process, the cations between the structural layers of bentonite were replaced by H+, and the interlayer spacing of the structure became larger, which improved the adsorption capacity of acidified bentonite. Commonly used acidifying agents are sulfuric acid, hydrochloric acid, acetic acid and so on.
(3) Organic Modification
The adsorbed cations between the bentonite layers are replaced by organic long carbon chains or their functional groups to obtain organic composite bentonite. When the long carbon chain of organic matter or its functional group enters the interlayer of bentonite crystal structure, the interlayer distance is increased.
(4) Roasting Modification
Roasting bentonite at a higher temperature (less than 550°C), bentonite loses surface free water, interlayer adsorbed water, and bound water in the structure in sequence, and at the same time, some impurities in bentonite will also be removed with the evaporation of water, making The structure of bentonite is more loose, which improves the adsorption capacity of bentonite.
(5) Composite Modification
At the same time, two or more treatment agents are used to modify the bentonite, and the modified bentonite has remarkable excellent properties. The modified bentonite obtained by a single modification treatment agent has certain defects. For example, after the bentonite is activated by acid, although it contains less impurities and has improved activity and adsorption capacity, the acid activation process is not easy to be controlled, and it is easy to cause The problem of excessive acid consumption; after organic modification, bentonite has a good adsorption effect on organic substances, but has a small specific surface area and poor thermal stability.
Pure bentonite is relatively rare, and most bentonites are often mixed with varying amounts of impurities, which are mainly quartz, feldspar, mica, kaolinite, etc. Normally, the color of bentonite is white. If it is mixed with color elements, such as iron, the bentonite will also appear light red, brick red, etc. The content of montmorillonite is an important indicator to measure the quality of bentonite. Therefore, the purification of bentonite has received widespread attention.
(1) Winnowing Method
Utilizing the difference in density between montmorillonite and other impurities in bentonite, soil powder and air are mixed into a fluid state, and the separation of specific mineral impurities (fine sand, etc.) and target particles is achieved under the action of classifying centrifuge and fan suction. This method also requires that the content of montmorillonite in bentonite be greater than 80%.
(2) Hydrocyclone Method
The difference in the sedimentation velocity of particles of different sizes in the hydrocyclone is used to separate the target particles from impurities and achieve the purpose of purifying bentonite. However, for impurities such as fine-grained quartz and water-soluble salts, the removal effect of the cyclone limited;
(3) Free Sedimentation Method
The principle is based on the Stokes sedimentation formula, and the bentonite is prepared into a slurry, and the montmorillonite expands after absorbing water, and the buoyancy suffered by it is greater than that of the impurities, so that the montmorillonite can be separated from the impurities to achieve purification The purpose of bentonite, but the settling time required by this method is long, the slurry interface is unclear and easily causes problems such as unstable quality, and when the impurity particles in the bentonite are too fine, the effect of this purification method is not good.
(4) Chemical Purification Method
Use appropriate chemical reagents (such as NaOH) to react with impurities in bentonite (such as quartz), so that the impurities enter the external solution to achieve the separation of montmorillonite and impurities, and achieve the purpose of purification. Especially when dealing with some fine-grained impurities, the effect is very good.