The Inco Bessemer Matte Processing Plant (IBMPP) suffers a loss of chalcocite selectivity in flotation separation from heazlewoodite down the rougher bank. Energy dispersive X-ray spectroscopy (EDX) analyses of the feed, concentrate and tail samples reveal a decrease in Cu and corresponding increase in Ni recovery through the primary rougher banks; tail samples can contain on the order of 7% Cu. The aim of this work was to examine any loss of selectivity through the primary flotation stream due to surface chemistry. Mechanisms suggested have included inadvertent activation and depression by the dissolution and solution transfer of Cu and Ni ions, lack of collector selectivity and possible requirement for reaction of the chalcocite surface prior to collector adsorption. The combination of information from SEM/EDX, X-ray photoelectron spectroscopy (XPS) analysis and XPS imaging has clarified the following aspects of the surface chemical mechanisms and control factors in the rougher flotation separation: (1) chalcocite in the feed to the rougher circuit appears to be Unoxidized, i.e., all Cu(I) surface species, whereas the surfaces of the heazlewoodite appear to be entirely oxidized to hydroxide species; (2) chalcocite in the tails front the rougher circuit appears to be more oxidized with evident precipitates corresponding to Cu(OH)2 in both composition and morphology adhering to their surfaces; (3) the primary adsorption of diphenylguanidine (DPG) appears to be to Cu(I) sites on the unoxidized clialcocite surfaced (4) adsorption of the DPG collector to chalcocite surfaces appears to be inhibited by the formation or concentration of title Cu(II) hydroxide precipitates in the later rougher cells; (5) the crystalline morphology of some of the discrete, attached Cu(II) hydroxide precipitates may suggest formation in recycle water streams rather than by surface oxidation of the chalcocite through the circuit although this may not be the only form of Cu(II) hydroxide on chalcocite surfaces in cells C and D; (6) heazlewoodite flotation appears to be associated with the attachment or locking of fine unoxidized chalcocite rather than any direct adsorption of DPG; heazlewoodite lines are also found attached or locked to some chalcocite particles in concentrates contributing to loss of grade (i.e., heazlewoodite is not completely liberated); (7) heazlewoodite particles in tails have relatively high surface concentrations of attached rnore-oxidized chalcocite fines contributing to loss of recovery. (c) 2006 Elsevier Ltd. All rights reserved.