Silver recovery by rotating film pertraction. Process modelling

A mathematical model for recovery of silver from dilute nitrate solutions applying the Rotating Film Liquid Membrane technique was proposed. A 0.06 M solution of tri-isobutylphosphine sulfide (TIBPS) in n-octane was used as membrane liquid and ammonia as a stripping reagent. The model is based on the assumption that a fast chemical reaction between the carrier (TIBPS), dissolved in the feed, and the nitrate and silver ions takes place in a reaction zone - an aqueous layer, adjacent to the feed/membrane interface. It was found that the stripping is the slower step, although the reaction between the silver-TIBPS complex and ammonia is instantaneous. With the aid of the TUTSIM dynamic simulator it was established that at the conditions of the experiments, the mass transfer coefficients in the aqueous films are nearly 10 times higher than the membrane side coefficients, but due to the very high partition coefficient of the silver-TIBPS complex (m(c) = 1.45 . 10(6)), mass transfer through the aqueous film is actually the rate controlling step during extraction.