Cementation of Lead From Lead Sulfate Slurries. III. Kinetics and Reaction Mechanisms With Iron Precipitant

Abstract

The cementation of lead from lead sulfate powders with iron metal precipitant has been studied in stirred aqueous slurries. The kinetics followed two alternative regimes analogous to those observed previously for the lead sulfate/zinc system. Kinetic regime No. 1 was characterized by an initial fast reaction and a subsequent period of stagnation or even apparent reversal. For this regime, the percentage yield for constant reaction period increased with decrease in the initial partial pulp density (IPPD) of lead sulfate. With regime No. 2, the initial reaction was slower but the reaction continued to completion at a steady rate. Also, the percentage yield for constant reaction period increased with increase in IPPD of lead sulfate.

Two mechanisms (Mech. 1 and Mech. 2) corresponding to the two kinetic regimes are proposed to explain the observed kinetics and these mechanisms operate in the same way as they do for the lead sulfate/zinc system.

However, the particle size/surface area of the iron was found to be the important parameter in determining which mechanism controlled the reaction, whereas it was the effective particle size/surface area of the lead sulfate when zinc was the precipitant. For the same iron powder, control of the reaction can be transferred from Mech. 1 to Mech. 2 by commencing the slurry cementation in ferrous sulfate solution rather than water. Comment is made concerning the use of iron precipitant in a commercial operation.