Electrochemical SHINERS investigation of the adsorption of butyl xanthate and 2-mercaptobenzothiazole on pyrite

In this paper, shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been applied to investigate the adsorption of typical collectors, butyl xanthate and 2-mercaptobenzothiazole (MBT), on pyrite surface. With the help of inert shell isolated gold nanoparticles as electric field enhancers, high quality electrochemical spectra were obtained in relation to real-world flotation conditions, enabling the quantitative identification of the chemical reactions occurring only on the mineral surface. It has been found that polysulphide anions are predominant oxidation product of pyrite after abrading and above 0 mV vs Ag/AgCl. Both the adsorption of xanthate and MBT are suppressed on pre-oxidized pyrite surface. The pre-formed polysulphide is diminished at negative potentials, which are favourable for collector's adsorption. Compared to xanthate, MBT shows greater resistance to pyrite oxidation and a broader potential window for adsorption due to the presence of two "minerophilic" groups (endocyclic nitrogen atom bonding in addition to the interaction through the exocyclic S atom). Single exocyclic S atom bonding is predominant in more favarouble adsorption environments. Dithiolate, the oxidation products of xanthate and MBT, has been precluded due to the high stability of adsorbed collector. This is inconsistent with the ex-situ XPS measurement where air exposure may induce oxidation.