EFFECT OF ELECTROLYTES ON ZETA-POTENTIAL OF BENEFICIATED INDIAN BENTONITES

Zeta-potential of beneficiated Na- and Ca- bentonites obtained from Bh avnagar locality, Gujarat,India and treated with varying amounts of Ca (OH)(2) are measured by a NORTHROP-KUNITZ horizontal cell and non-pola rising Zn-ZnSO4 electrodes. Dependence of zeta potential on particle s ize, clay concentration and electrolyte concentrations respectively ar e also studied. The results indicate a four-stage change in zeta- pote ntial and viscosity when Ca(OH)2 is added in increasing amounts to Na- bentonite suspensions. In the first stage, the addition of up to 2 pe r cent (w/v) of lime caused no change in zeta-potential indicating a c ounteracting effect of Ca++ adsorption and reaction of OH- ions to inc rease the negative surface charge and a slight change in viscosity. In the second stage, the addition of more lime (upto 3 per cent) resorte d in a rapid decrease in zeta- potential and sudden increase in viscos ity. In the third stage, additional lime (from 3 to 6 per cent) led to a slow decrease in zeta-potential but a continued rapid increase in v iscosity and the formation of distinct large flocs. In the fourth stag e, the additional Ca(OH)(2) (from 6 to 12 per cent) caused only a very slight change in Zeta- potential and slight decrease in viscosity. In the Ca-bentonite- Ca(OH)(2) system, the first stage was an increase i n zeta-potential due to dominant influence of OH- potential-determinin g ions. The second stage was a rapid decrease in zeta-potential and an increase in viscosity and this situation corresponding to the third s tage of treatment in the Na--(+) clay. The end of the second stage is the time retention point, after which excess lime is used for pozzolan ic reaction. Soils have been stabilized with lime since ancient times, and lime is now being used in road building throughout the world. Add itions of hydrated lime, Ca(OH)(2), to plastic clays rapidly reduces t heir plasticity and facilitates handling. The montmorillonite clays wh ich are most common are improved (1) already calcium saturated.