Sensitivity of pentlandite flotation in complex sulfide ores towards pH control by lime versus soda ash: Effect on ore type

doi:10.1016/j.minpro.2014.01.001

International Journal of Mineral Processing

Volume 127, 10 March 2014, Pages 44-51

https://doi.org/10.1016/j.minpro.2014.01.001 Get rights and content

Highlights

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An extreme sensitivity of pentlandite towards pH control by lime vs soda ash documented.
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Pentlandite with ultramafic association is completely depressed in the lime system.
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Chalcopyrite is unaffected by lime, just like pentlandite with mafic association.
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Soda ash improves flotation of all sulphides at the same reference pH of 10.

Abstract

An extreme sensitivity of pentlandite flotation towards pH regulator at pH 10 has been documented using two types of complex nickel–copper sulfide ores in Northern Ontario, Canada. The samples studied are from Sudbury and Timmins areas and differ in their mafic and ultramafic associations and degree of dissemination. It has been shown that the pentlandite in the Timmins ore is completely depressed in the lime system at a collector dosage that readily floats the pentlandite in the Sudbury ore. The general mechanism of pentlandite depression by lime is believed to be similar to that of pyrite. However, the sensitivity of pentlandite in the Timmins ore is greatly affected by its ultramafic associations and is likely related to slime coating by serpentine minerals. The tenacity of hydrophilic calcium species in the case of the Sudbury ore is believed to be counteracted by a greater activation potential (e.g., level of Cu/Ni) and collector action. When lime is replaced by soda ash, adverse effect induced by adsorbed calcium species on pentlandite is largely eliminated. Benefit resulting from better dispersion of serpentinized species in the Timmins ore is also observed using soda ash. Chalcopyrite's strong floatability overcomes difficulties experienced by pentlandite and floats well both in the lime and soda ash systems. Pyrrhotite is less floatable than chalcopyrite and pentlandite in both lime and soda ash systems. In the lime system, pyrite depression is almost the same as pentlandite depression, but unlike pentlandite it continues to be non-floatable even in the soda ash system.

Graphical abstract

Introduction

One of the most common process variables controlled in flotation practice is pH. The effect of pH is quite central to the chemistry of flotation. As such, it is also one of the most frequently investigated parameters in fundamental studies on flotation, e.g., the development of critical pH curves in relation to collector action (Sutherland and Wark, 1955). In practice, the pH level of flotation slurries is most commonly regulated by lime. It is readily available and the most economical pH regulator in use. In addition, lime is known to be an effective depressant for iron sulfides (especially for pyrite), inducing flotation selectivity in favor of other metal sulfides, which are often present in the same sulfide ores (Sutherland and Wark, 1955, Gaudin, 1957, Klassen and Mokrousov, 1963).

This issue is coupled with the presence of calcium ions in the recycled process water (Rao and Finch, 1989, Slatter et al., 2009). The recycled water includes high levels of calcium ions, which, due to the use of the relatively large dosages of lime in the processing of complex massive sulfide ores, may approach concentration levels dictated by solubility of gypsum (CaSO₄). The sulfate part originates from oxidation of sulfide minerals in the ore, especially iron sulfides, which tend to be dominant sulfide gangue minerals in the complex sulfides such as nickel–copper sulfides and copper–lead–zinc sulfides, respectively. Galvanic interactions that are expected to occur upon mineral–mineral contact and mineral contact with steel grinding media can influence oxidation of sulfide in ground slurries (Rao et al., 1976, Cheng and Iwasaki, 1992). The sulfate oxidation level is reached by gradual build-up of metastable forms of sulfoxy-species, i.e., “thiosalts”, of which thiosulfate (S₂O₃^2 −) is a prominent member. Therefore, the effect of calcium ions has been studied together with the effect of associated thiosulfate ions.

Hodgson and Agar (1989) reported that adsorption of calcium ions and sulfoxy species in process water contribute to hydrophilicity of pentlandite and pyrrhotite. The studies on a Finnish nickel–copper sulfide sample by Kirjavainen et al. (2002) showed that the presence of calcium and thiosulfate ions improved flotation of nickel and copper sulfides following grinding of the ore in an iron mill. They noted a depression when the mill was ceramic. Malysiak et al. (2003) carried out an investigation on the effects of calcium solutions on single minerals and reported that the adsorption of calcium species onto pentlandite and pyrrhotite surfaces resulted in an increase in the hydrophilicity of these minerals, which required a greater dosage of xanthate to restore their hydrophobicity. In a series of bench scale tests with South African ores containing platinum group metals (PGM's), Muzenda (2010) observed somewhat lower PGM recoveries and higher concentrate grades with use of process water from recycle sources compared to use of potable water, which indicated an opposite trend. It should be stated that unlike the pentlandite–chalcopyrite ores of the Sudbury Basin with large amounts of pyrrhotite, where platinum group metals are obtained as by-products, South African ores contain only 1–3% metal sulfides such as pentlandite and pyrrhotite, but with higher levels of PGM's, so the recovery of PGM concentrate is much more important than the concentrate grade.

Sulfide ores can show a great deal of variability in the floatability of their target minerals potentially due to the influence of many variables related to their surface chemistry, oxidation tendencies, reagent interaction, ionic composition of aqueous environment, and grinding media in which they are liberated and processed. Flotation behavior of pyrrhotite is important from two points of view. One is related to efficient recoverability (i.e., when an ore contains sufficiently high amount of pentlandite and/or precious metals) and the other one is to design its improved rejection (i.e., when it degrades the concentrate quality due to its predominance in the ore). In recent years, various process characteristics of pyrrhotites were reviewed in relation to flotation separations as well as stability and chemical reactivity in extractive processes (Miller et al., 2005, Wang, 2007). Most recently, based on single mineral studies, differences in floatabilities were studied in relation to mineralogical types and dependence on flotation collectors (Becker et al., 2011, Allison and O'Connor, 2011, Ming-fei et al., 2012). In general, factors related to ore genesis and complexity of mineralogy, add to lack of understanding on recovery and selectivity issues. Pentlandite is a critical source of nickel and cobalt as well as precious group of elements, thus, its flotation behavior is equally important. As part of our interest in processing issues related to complex ores, various opportunities have arisen to investigate flotation behavior of pentlandite ores from different origin. The objective of the current contribution is to highlight sensitivity of pentlandite flotation to pH assessed through a series of comparative bench scale tests at an identical pH of 10 adjusted by lime and soda ash.

Section snippets

Ore samples, mineralogy–genesis

Two kinds of massive complex nickel–copper sulfide ore samples were used. One sample was a sample received from Onaping area of the Sudbury Basin. This area of Canada consists of several groups of geological importance, including an igneous complex that is believed to be a stratified impact melt sheet composed from the base up of sublayer norite, mafic norite, felsic norite, quartz gabbro, and granophyre. The brecciated footwall, as another group, consists of fragments of country rock: some

Pentlandite and chalcopyrite

The effects of lime and soda ash on flotation behavior of pentlandite and chalcopyrite are shown in Fig. 1, Fig. 2, respectively. It can be noted that, in both cases, these minerals of commercial importance float quite well even in the absence of xanthate. Present views indicate that possible causes of the collectorless floatability of sulfide minerals include elemental sulfur, sulfur-rich/metal deficient sulfide and polysulfide layers (Walker et al., 1989). Since processing conditions always

Summary and conclusions

The flotation of two types of complex nickel–copper sulfide ores was examined to emphasize the differences in behavior of pentlandite at the pH 10 using lime versus soda ash. One sample was typical of the Sudbury region and the other one was from Timmins area. These two ores differ not only by degree of dissemination, but also by their mafic and ultramafic associations. Although these two characteristics can be somewhat overlapped in various deposits, their proportions still make them

Acknowledgments

The financial support to the research work reported was made available partly through a Discovery Grant from the Natural Sciences and Engineering Council of Canada (NSERC), for which the authors are grateful.

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Sensitivity of pentlandite flotation in complex sulfide ores towards pH control by lime versus soda ash: Effect on ore type

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Ore samples, mineralogy–genesis

Pentlandite and chalcopyrite

Summary and conclusions

Acknowledgments

Int. J. Miner. Process.

Int. J. Miner. Process.

J. Colloid Interface Sci.

Int. J. Miner. Process.

Int. J. Miner. Process.

Can. Metall. Q.

Miner. Eng.

Miner. Eng.

Int. J. Miner. Process.

Miner. Eng.

Miner. Eng.

Int. J. Miner. Process.

Geochemical constraints on the genesis of the Montcalm gabbroic complex and Ni–Cu deposit, Western Abitibi Subprovince, Ontario

Can. Mineral.

The mineralogy of pyrrhotite from Sudbury CCN and Phoenix nickel ores and its effect on flotation performance

Can. Metall. Q.

A Novel approach spectroelectrochemical

Flotation characteristics of pyrrhotite with xanthates

Trans. AIME

Pulp potential and its implications to sulphide flotation

Miner. Process. Extr. Metall. Rev.

Flotation

Adsorption of calcium and sodium on pyrite

AIME Trans.

Detection and control calcium suphate precipitation in the lead circuit of the Hilton concentrator of Mount Isa Mines, Australia

Probing surface interactions of collectors and inhibitors with piezoelectrodes

The flotation of pyrite and pyrrhotite in the absence of conventional collectors

Electrochemical investigations into the flotation chemistry of pentlandite and pyrrhotite: process water and xanthate interactions

Can. Metall. Q.