Spectroelectrochemical Investigation of Hydroxamate Reagents on Copper Oxide Minerals

Abstract

Raman scattering spectroscopy, XPS and electrochemical experiments have been undertaken to determine the composition and structure of n-octanohydroxamic acid, its potassium compound (the fl otation collector AM28) and the copper compound. The potassium salt was found to be an acid salt of composition KH(C8H16NO2)2 where the hydroxamate ligands are equivalent. Voltammetry of a copper electrode in hydroxamate solution exhibited a dependence on hydroxamate concentration with the inhibition of copper oxidation observed for concentrations above 1 mM at potentials greater than -0.35 V vs Ag/AgCl. The formation of cupric hydroxide was suppressed and cupric hydroxamate was observed on the copper surface in this potential range by Raman spectroscopy. Atomic absorption spectroscopy was used to determine the copper content of synthesised cupric n-octanohydroxamate. The cupric salt exhibited a 1:1 stoichiometry and vibrational spectroscopy demonstrated that the cupric hydroxamate retained neither of the ionizable hydrogen atoms of the hydroxamate. The salt was found to contain a C = N bond and the two singly-bonded O atoms that may coordinate with a cupric ion to form a 5 membered ring. Model cupric salts of hexanoic acid and benzoin oxime were synthesised in order to simplify the identifi cation of the C = N and C = O Raman band locations expected for the cupric n-octanohydroxamate spectra. In contrast, the acid and potassium salt exhibit a structure containing a C-N bond and a C = O functional group. For malachite, the surface interaction results in formation of a substantial layer of copper n-octanohydroxamate. On reactive metals, compound formation can be observed, following monolayer adsorption.