ENHANCEMENT OF MASS-TRANSFER USING MICROPOROUS SPARGER MATERIALS

Copper mass-transfer coefficients in the range 58-440 x 10(-5) cm s-1 (with an error of +/-1%) have been obtained with the use of microporou s membranes and tubes and of Perspex tubes with drilled holes as sparg er materials. The values are as much as ten times greater than can be obtained without gas sparging and tend to increase with the rate of ga s flow per unit length of electrode. Addition of 0.001% (wt/vol) of th e surfactant cetyltrimethyl ammonium bromide to a silver-containing cu pric sulphate electrolyte was observed to result in high values of the silver mass-transfer coefficient, k(Ag)+, on electrowinning. Restrict ing the flow of the generated gas bubbles close to the surface of the cathode gave a further increase in the mass-transfer coefficient. High values of k(Ag)+ in the presence of smaller gas bubbles were attribut ed to the dissipation of the energy input by the formation of micro-sc ale eddies. On the other hand, macro-scale eddies associated with larg e bubbles tend to induce circulation of electrolyte.