A STUDY OF THE INTERACTION OF DI-P-CRESYL MONOTHIOPHOSPHATE WITH NOBLE-METALS USING ELECTROCHEMICAL, WETTING, AND SPECTROSCOPIC METHODS

Monothiophosphorous acids were recently discovered to float gold values selectively from base metal sulfide containing ores in a mildly alkaline medium. The corresponding dithiophosphorous acids, which are used traditionally in the industry and often with xanthates, do not exhibit such selectivity since most of the associated sulfide minerals are also floated. In order to explain this "unusual" selectivity of monothio acids for "gold", the interactions between ammonium di-p-cresyl monothiophosphate (DCMTP) and noble metals were studied using electrochemical (cyclic voltammetry and open circuit potentials), wetting (contact angles), and surface spectroscopic techniques (X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and external reflection Fourier transform infrared spectroscopy). Our results indicate that DCMTP interacts poorly with gold, except under highly oxidizing conditions which may not be very practical. DCMTP also adsorbs poorly on sulfide minerals and copper at mildly alkaline pH. We have demonstrated that selective flotation of gold values from ores by DCMTP is linked to alloying elements, such as silver, present in such gold values. DCMTP interacts rather strongly with silver over a wide range of conditions, presumably by forming a silver complex on the surface. It also adsorbs effectively onto gold-silver alloys, the amount adsorbed increasing with increasing silver content. The origin and mechanism of selective adsorption of DCMTP onto silver are discussed in this paper.