The reasons for the different results of water swelling on sodium bentonite and calcium swelling are:
2022-03-11
1) cation can be bentonite particles in the binding, restricting the dispersion of bentonite particles. The charge density of multivalent ions is larger than that of monovalent ions, and strong electrostatic attraction is generated between particles, which makes the bentonite particles have strong bonding ability. Therefore, the dispersion ability of calcium bentonite is weaker than that of sodium bentonite.
2) the negative charge generated by the replacement of the montmorillonite lattice should be adsorbed on the opposite ion to balance the electric property of the solution. These opposite ions exist in the form of hydrated ions in the solution, and the negatively charged montmorillonite particles adsorb hydrated cations to form an electric double layer. The thickness of the double layer is inversely proportional to the two square of the counter ion valence, that is, the cation valence is high, the hydration film is thin, and the expansion ratio is low; while the cation valence is low, the hydration film is thick, and the expansion ratio is high.
3) The thickness of the sodium bentonite crystal layer adsorbed water is three layers, and the thickness of the calcium bentonite crystal layer adsorbed water is four layers. Under the action of polar water molecules, due to the small electrostatic attraction, large crystal layer spacing can be generated between the crystal layers of sodium bentonite, while calcium bentonite can not easily enter the crystal layers due to the large electric attraction between the crystal layers. Therefore, the distance generated between the crystal layers of calcium bentonite is obviously smaller than that of sodium bentonite, the calcium bentonite is more difficult to disperse in water than the sodium bentonite, and the expansion ratio is low. In essence, the expansion of montmorillonite is controlled by its chemical composition, and montmorillonite containing more sodium ions can continue to expand until it becomes a gel state. The expansion of montmorillonite with more calcium ions can only be limited from the dry state to the water-bearing state. After we understand the deep-seated reasons that affect the expansion of swelling, we can artificially effectively control the expansion performance of bentonite minerals to achieve the best use effect.
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