Continuous and interrupted electroosmotic dewatering of clay suspensions

Suspensions of Bentonite, kaolin and red clay were dewatered electroosmotically under continuous and interrupted DC voltage and current. The suspension was held in a vertical 5-cm diameter column between two platinum mesh electrodes, an upper anode and a lower cathode. Suspensions were prepared with CaCl$ sb2$ in distilled water at concentrations up to 10$ sp{-2}$ M. The initial solid content was between 9.1 and 15 wt% for Bentonite and between 25 and 45 wt% for kaolin and red clay. The initial bed height ranged from 0.5 to 2 cm. Constant voltages from 2.75 to 5.0 V and constant currents from 30 to 90 mA were used. In the interrupted regime the off-time ranged from 0.5 to 20 s with the on-time fixed at 30 s. A short circuit or an open circuit was applied during the off-time. The interrupted process with a short circuit was also applied at the end of a DC run when dewatering had stopped.Electroosmosis removed 20-70% of the water with an energy expenditure well below the heat of vaporization. The water removal rates were increased by the addition of CaCl$ sb2$. Beds of 0.5 cm thick were dewatered faster and with less energy consumption than thicker beds. Interruption with a short circuit applied during a 0.5 s off-time removed about 20-40% more water than DC for equal energy consumption. Interruption at the end of a DC run removed nearly the same amount of water as interruption applied from the beginning of a run. Relative motion between the electrodes in the form of rotation of the upper electrode at 40 or 70 rpm had no significant effect on dewatering. The Helmholtz/Smoluchowski theory did not agree with the experiment results for the effects of interruption in power and electrolyte content