The sodium dithionite influence during complex precipitation of Au + -S 2 O 3 2 −

This paper reports on the influence of dithionite (S2O4 2−) as a reducing agent in the Au+-S2O3 2− complex and the main kinetic parameters involved during the precipitation reaction. Results show that it is possible to achieve recoveries of 99% Au+ in the system Au+-S2O3 2−-S2O4 2−-O2 in a time of 60 min at room temperature. The precipitation reaction is characterized by an induction period, followed by a period of gradual precipitation in which the maximum recovery of Au+ occurs until a stabilization period is reached. The apparent reaction order of [S2O4 2−] was n = 0.45, [S2O3 2−] was n = −0.8, with respect to [OH−] was n≈0 (between 10−10and 10−7 M) and with respect to [Au] was n = 0.81. The apparent activation energy was Ea = 32.6 kj mol−1. This indicates that under these conditions the precipitation of Au+ in the system Au+-S2O3 2−-S2O4 2−-O2 is carried out by a mixed control, although the value obtained tends to be more of a chemical control, this being independent from hydrodynamic variables of the system.