The reasons for the different results of water swelling on sodium bentonite and calcium swelling are:
1) The cations can link the bentonite particles together, which restricts the dispersion of the bentonite particles. The charge density of multivalent ions is larger than that of monovalent ions, and a strong electrostatic attraction is generated between particles, which makes the binding ability of bentonite particles strong. Therefore, the dispersing ability of calcium bentonite is weaker than that of sodium bentonite.
2) The negative charge generated by the lattice replacement of montmorillonite needs to adsorb ions with opposite electrical properties to balance the electrical properties of the solution. These oppositely charged ions exist in solution in the form of hydrated ions, and the negatively charged montmorillonite particles adsorb the hydrated cations to form an electric double layer. The thickness of the electric double layer is inversely proportional to the square of the valence of the counter ions, that is, the higher the cation valence, the thinner the hydration film, and the lower the expansion ratio; the lower the cation valence, the thicker the hydration film, and the higher the expansion ratio.
3) The thickness of the sodium bentonite crystal layer to absorb water is three layers, and the thickness of the calcium bentonite crystal layer to absorb water is four layers. Under the action of polar water molecules, due to the small electrostatic attraction, a large interlayer spacing can be generated between the crystal layers of sodium bentonite, while the polar water molecules of calcium bentonite have large electric attraction between the crystal layers. It is not easy to enter between the crystal layers. Therefore, the distance between the calcium bentonite crystal layers is significantly smaller than that of the sodium bentonite, which is manifested in that the calcium bentonite is more difficult to disperse in water than the sodium bentonite, and the expansion ratio is lower. In essence, the expansion of montmorillonite is controlled by its chemical composition, and the montmorillonite containing more sodium ions can continue to expand until it becomes a gel state. Montmorillonite with more calcium ions can only swell from the dry state to the water state, which is limited. After we understand the deep-seated reasons that affect the swelling and swelling, we can artificially and effectively control the swelling performance of bentonite minerals to achieve the best use effect.