Effect of surface-active substances on the rate of production of copper powder from copper sulphate solutions by cementation on zinc rods in gas sparged reactors

The effect of surface-active substances on the rate of diffusion-controlled cementation of copper on a single vertical zinc rod from dilute copper sulphate solutions was studied. Variables investigated were: nitrogen superficial velocity, concentration and type of surface-active substance. These variables were studied for their effect on the mass transfer coefficient of copper cementation. The mass transfer coefficient was found to increase with increasing superficial gas velocity. Increasing surfactant concentration was found to decrease the mass transfer coefficient. It was found that surfactants decrease the mass transfer coefficient by an amount ranging from 14% to 39% depending on the superficial gas velocity and type of surfactant added. The ability of the four types of surfactants to decrease the mass transfer coefficient increases in the order: CTMAB < Aspecon-1030 < SABS < NPPGE. Mass transfer data were correlated by the equation: Sh = 7.25 We0.88 Sc0.33 for the conditions: Sc = 1430 and 4.2 < We < 43.6, where Sh is a Sherwood number, We is a Weber number and Sc is a Schmidt number. In parallel with measuring the mass transfer coefficient, gas hold-up and solution surface tension were also measured to assess how these parameters are affected by the presence of surface-active substances.