Settling Behavior of Flocculated Bentonite Suspension in the Presence of Inorganic Electrolyte

Abstract

Settling behavior of three kinds of flocculated bentonite (mainly alkali ion form having swelling property) suspensions, A, B, and C, has been studied. Suspension A was prepared by dispersing bentonite in pure water and subsequent addition of inorganic electrolyte (final concentration : k), suspension B was prepared by dispersing bentonite directly in inorganic electrolyte solution (final concentration : k), and suspension C was prepared by dispersing bentonite in inorganic electrolyte solution (final concentration : α) and subsequent addition of the same inorganic electrolyte (final concentration : b, α+b=k). The results obtained are as follows :
(1) Differences in flocculation values between A and B (Table 1) for inorganic electrolytes were scarcely observed. (2) The settling rate of B was extremely higher than that of A, but the difference between them was small when bentonite, changed into calcium form, was used.
(3) The higher the valency and the smaller the hydration radius of cation, the higher was the settling rate of B (Fig. 3).
(4) The effect of addition of large amounts of anions on the settling rate of B was examined by using the inorganic electrolytes of Na_n⁺X^n- type which dissociate to produce the same amounts of sodium ions in the solution. As a result, the settling rate was found to be in the order : CO₃^2-<OH^-<SO₄^2-<NO₃^-≅/≈Cl^-(Fig. 4) .
(5) The settling curve, C, appeared between those of A and B (Fig. 6). Therefore, the suppression effect of swelling of montmorillonite with dilute inorganic electrolyte solution could be evaluated by the curve, C.