EFFECT OF SURFACTANTS ON THE RATE OF DIFFUSION-CONTROLLED CEMENTATIONOF COPPER FROM DILUTE-SOLUTIONS ON A STATIONARY ZINC DISC IN STIRRED VESSELS

The effect of surfactants on the rate of diffusion-controlled cementat ion of copper from dilute copper sulphate solutions on a stationary zi nc disc in a stirred vessel was studied. Variables investigated were r otational speed of the impeller, concentration and type of surfactants and concentration of copper sulphate solution. These variables were s tudied for their affect on the mass transfer coefficient of copper cem entation. The mass transfer coefficient was found to increase with inc reasing rotational speed of the impeller and concentration of copper s ulphate solution. It was found that surfactants decrease the rate of m ass transfer during cementation by an amount ranging from 9.5 to 25% d epending on the rotational speed of the impeller and type of surfactan t added. Increasing surfactant concentration was found to decrease the mass transfer coefficient. The ability of different surfactants to de crease the mass transfer coefficient increases in the order: CTMAB < S ABS < NPPGE. Mass transfer data were correlated, in absence and in pre sence of surfactants, by the following equations respectively: Sh = 1. 55 Re-0.68 Sc-0.33 and, Sh = 4.1 Re-0.43 Sc-0.33 where Sh is Sherwood number, Re is Reynolds number and Sc is Schmidt number.