Interactions of chelating agents in the processing of complex nickel-copper sulphide ores with emphasis on pyrrhotite rejection

In this study, interactions of chelating agents in the processing of Ni-Cu complex sulphide ores have been investigated with a special emphasis on rejection of pyrrhotite (Po) that is the most abundant mineral significantly contributing to the SO2 emission problems from the Sudbury area. The action of triethylenetriamine (TETA) and its combined use with sodium metabisulphite (SMBS) has been the main focus in this study although other chelating agents such as diethylene-triamine (DETA), ethylenediamine tetraacetic acid (EDTA), and citric acid (CA) have also been used for comparative purposes. The chelation power of these reagents, and their metal ion specificity have been correlated with their effect on Po depression. TETA, with its highest stability constant for chelation with Cu2+ and Ni2+ ions, which often causes the inadvertent activation of Po, indicated the greatest potential for Po rejection. However, the individual effects of these chelating agents for Po depression proved to be inconsistent and inefficient.; A remarkable synergistic effect on Po depression was brought about through a combined use of TETA and SMBS. This allowed for excellent separation of both pentlandite (Pn) and chalcopyrite (Cp) from the Voisey's Bay Po. A key factor in this synergistic effect is the conversion of a bulk flotation mode (promoted through the effective formation of dixanthogen) into a selective flotation mode (promoted through the effective disruption/destruction of dixanthogen). It is further recognized that electrochemistry (reduction/destruction of dixanthogen and/or sulphur-rich layers by SMBS), metal ion-chelation (sequestration, prevention of catalytic oxidation, TETA) and kinetics of hydrophobisation reactions (e.g., dixanthogen re-formation) play important roles in the achievement of this flotation selectivity. The recovery by size analysis indicated that the use of TETA/SMBS combination knocked down Po flotation virtually in all particle sizes.; The bench-scale investigations were accompanied by a series of fundamental studies. FT-IR spectroscopy showed no indication of TETA/DETA adsorption on the Po surfaces; however, some adsorption was recorded on the Cp surface. The adsorption/desorption behaviour of the xanthate in the presence of TETA/DETA and SMBS has also been investigated. The adsorption of xanthate on the Po surface was observed to occur linearly. Decomposition of xanthate-bearing species has been identified. A reductive decomposition route for ferric dihydroxy xanthate has been proposed. Through titration studies, it has been clearly shown that the metal ions such as Cu2+ and Ni2+ act as catalysts and increase the rate of SO2 oxidation. Thus, DETA/TETA can inactivate these metal ions and prevent their catalytic effect. Contact angle studies indicated, that under conditions giving rise to the formation of stable copper chelates, no evidence of collector action on Cp has been observed in acidic solutions, relative to the self-induced hydrophobicity of this mineral. EH-pH stability diagrams and speciation diagrams have been prepared for DETA/TETA under conditions representing flotation experiments. These diagrams have provided a reasonable explanation for the impact of xanthate dosage on Po depression.