Activation modification of bentonite

(3) Activation modification of bentonite

① Roasting modified bentonite Roasting activation is to roast the bentonite at different temperatures.
Through volatilization and combustion, the molecular water and organic matter on the surface and structural layers of the montmorillonite are evaporated, and the clay mineral structure becomes loose
.

At the same time, as the temperature increases, part of the hydroxyl groups of the clay minerals are lost, the number of exposed broken bonds increases, and the specific surface area of ​​the mineral increases, which increases its activity

②Acid-activated bentonite Natural bentonite has a microporous structure, and it is not easy to accept the macromolecular pigment components that cause the coloring of organic matter, such as carotene, etc.
, so the decolorization efficiency of unacidified bentonite is low
.

Acid activation is the use of sulfuric acid , hydrochloric acid , oxalic acid , nitric acid , etc.

Acid activation treatment can remove the soluble matter and mixed organic matter distributed in the bentonite channels, so that the pores can be dredged, which is conducive to the diffusion of adsorbate molecules; on the other hand, the radius of hydrogen atoms is smaller than that of sodium, potassium, magnesium, calcium and other atoms.
Therefore, the smaller hydrogen ions can replace the sodium, magnesium, calcium, and potassium ions between the bentonite layers to increase the pore volume and weaken the original interlayer bond force, the layered crystal lattice cracks, and the pores are dredged.
, The adsorption performance is improved
.

Bentonite treated with acid may produce two forms of Brønsted acid centers
.

The first acid center is generated at the edge of the surface of the montmorillonite layer.

E.
Gonalez-Pradas et al.
studied the surface properties of bentonite after activation with sulfuric acid and heat treatment
.

They found that with the increase of acid concentration, the surface acid center and micropore volume of bentonite increased; within the test temperature and acidity range, bentonite activated by 2.

Acid activation method: There are currently two methods for activating bentonite with acid solution, namely dry method and wet method
.

Dry activation is to immerse a certain fineness of bentonite (120-200 mesh) in sulfuric acid, hydrochloric acid or phosphoric acid solution and mix thoroughly, squeeze, dry, and then pulverize to obtain activated clay products

Influencing factors of acid activation of bentonite: There are many factors that affect the quality of acid activated bentonite, such as the quality of bentonite original clay, feeding order, beating time, solid-to-liquid ratio, activator, reaction acidity, reaction time, reaction temperature, drying temperature, stirring speed and rinsing conditions
.

The author of this book and many scholars have conducted a lot of experimental research work on this and determined the best conditions for acid-activated bentonite

a.
Quality of original soil The higher the grade of montmorillonite in the original bentonite soil and the lower the sand content, the higher the activity of the manufactured activated clay, the stronger the adsorption, and the higher the decolorization rate of the product
.

The particle size of the raw material also has a great influence on the degree of activity.

b.
Feeding sequence Because the swelling capacity of the original soil is relatively large, if the water-soil-acid feeding sequence is adopted, there will be many problems such as small feeding amount, low recovery rate, small output, and high consumption
.

Therefore, the water acid-soil feeding sequence is adopted, and as long as the conditions are controlled well, products of qualified quality can be produced

c.
Beating time If the beating time is too long and energy consumption is large, the production cost will increase.
If the time is too short, the bentonite will not be fully dispersed, which is not conducive to the acid activation reaction
.

d.
The solid-liquid ratio beating concentration experiment results show that if the solid-liquid ratio is large, the slurry concentration is large and the volume is small, and the reaction cannot be fully carried out; the solid-liquid ratio is small, the slurry concentration is small, and the volume is large, the production cost is high and uneconomical
.
Generally, a solid-liquid ratio of 1:10 is the best choice
.

e.
Activator Use different activators to activate bentonite, and their activation effects are different
.
The author conducted a comparative experimental study on different acid activators.
The results show that the activation effect of acetic acid and phosphoric acid is poor; the activation effect of nitric acid and aqua regia is better, but due to the production of nitrogen oxides during the reaction, it will cause serious pollution to the environment , So it is not advisable; the quality of activated products with hydrochloric acid and sulfuric acid is better; the combined activation effect of hydrochloric acid and sulfuric acid is better
.
Using sulfite as a bleaching agent for iron removal, the product has a general bleaching effect; using sodium carbonate , acetic acid, and sodium acetate has a better effect; using sodium carbonate , acetic acid, and sodium acetate to enhance the reduction performance of sodium carbonate is better
.

f.
The product quality of reaction acidity increases with the increase of the acidity of the activation reaction; but the product quality begins to decline after a certain acidity is exceeded
.
The quality of the original soil is different, the activator is different, and the acidity of the reaction is also different
.

g.
Reaction time It is generally believed that the extension of the acid activation reaction time of bentonite can deepen the completeness of the reaction and improve the quality of the product, but it is not the longer the better
.

h.
Reaction temperature When the bentonite acid is activated, the reaction temperature is too low, and the reaction rate is too slow, which is not conducive to the completion of the reaction; increasing the temperature can speed up the reaction rate, and obviously increase the activity and decolorization rate, but the temperature is too high and the energy consumption is too large.
, The degree of activation and decolorization rate have little change
.

i.
Drying temperature If the drying temperature is too high, the activity of the activated bentonite will decrease.
Generally, it is better to exceed 100°C and not exceed 220°C, and 160-220°C is the best
.

j.
Rinsing conditions Considering the cost issue, the rinsing should be rinsed with hard water (tap water) at room temperature.
The number of rinsing is generally 5-6 times, and the pH value is 4-5
.
The activity of acid-activated bentonite decreases with the increase of rinsing times, and the decolorization rate increases with the increase of rinsing times
.
However, excessive rinsing will also reduce the decolorization rate due to the destruction of the ion exchange balance
.

Related links: Purification and modification of bentonite