A Continuous Flow Evaluation of the Galvanic Stripping Process

Abstract

The concept of galvanically stripping cations such as Fe3+, Cu2+, Pb2+, and Au3+ from organic solvents using solid metal reductants has been demonstrated on a batch test basis in a number of previous studies. In this research the first evaluation of a continuous flow system for the process was made, with Fe3+ removal from D2EHPA being the primary objective. The effect of operation type (separate or simultaneous stripping), the iron concentration in the organic feed, the organic flow rate, the aqueous-to-organic volume ratio (A/O), the metal reductant (pure zinc vs lead-zinc alloy), the reductant surface area and acidity of the stripping phase on the iron and zinc removal percentages, and the process rate and stoichiometry were evaluated by using continuous flow mixed reactors. The steady-state condition was reached in all the tests after about 40 minutes. In particular, the rate of iron removal was found to be greater for simultaneous than for separate galvanic stripping. A longer organic residence time produced a slightly lower rate, but increasing the aqueous-to-organic ratio augmented the overall rate. The pH of the aqueous phase controlled the iron and zinc stripping percentages, and increasing the reductant surface area increased the iron removal percent. In general, the results agreed with previous batch-type studies on galvanic stripping, and the data indicated that the galvanic stripping process rate and reactor behavior can be assessed by using mechanically agitated continuous flow mixed reactors.