EFFECTS OF ELECTROLYTES AND CATIONIC SURF ACTANT ON COLLOIDAL PROPERTIES OF MMH MT SYSTEM/

The effects of electrolytes (NaCl, Na2SO4 and MgCl2) and cationic surf actant (cetyltrimethylammonium bromide) on colloidal properties of mix ed metal hydroxide (MMH)/montmorillonite (Mt) suspension were studied through measurements of electrophoretic mobilities, rheology and pH. T he results show that all the electrolytes and surfactant studied in th is work decreased Bingham yield point (YP) of MMH/Mt system, but exert ed different effects on fluid loss (FL) and pH of MMH/Mt system. The r esults are interpreted as means that the cationic ions of electrolytes mainly displace the charge-balancing ions of Mt particles, such as H and Na+, so enhance their aggregation, leading to the decrease of pH and the increase of FL, but the anionic ions of these electrolytes mai nly displace the charge-balancing ions of MMH particles, such as OH- a nd Cl-, so weaken the aggregation effects of MMH on Mt particles, ther efore, cause the increase of pH and the decrease of FL. In another wor d, the overall effects of electrolytes on MMH/Mt system depend on the relative ability of anionic and cationic ions to exert the opposite ef fects on FL and pH. As for cetyltrimethylammonium bromide (CTAB), the adsorption of CTAB on Mt particles does not only displace H+ and cause the aggregation of Mt particles but also reverses their wetting abili ty, therefore, CTAB decrease FL and YP of MMH/Mt system to a larger ex tent than inorganic electrolytes although it can only decrease pH slig htly.