The comparison between amine thioacetate and amyl xanthate collector performances for pyrite flotation and its application to tailings desulphurization

Abstract

A comparative study of the adsorption mechanisms of an amine thioacetate collector (Armac C) and the well-known amyl xanthate collector on pyrite is presented in this paper. These results allowed a better understanding of the behavior of these two collectors during pyrite flotation. The adsorption isotherms were constructed both at natural pH and alkaline pH (pH=11). Colorimetric technique was used to measure both Armac and xanthate concentration in solution. The effect of the pH regulator types was taken into account by testing soda ash (NaOH) and hydrated lime Ca(OH)₂. Xanthate collector adsorbs onto pyrite surfaces in the form of amyl dixanthogen and can be detected on pyrite surface using diffuse reflectance infrared Fourier transform (DRIFT) when the statistical surface coverage (θ) was greater than 0.9. Xanthate affinity towards pyrite decreases at alkaline pH and the depressant role of the hydrated lime is greater than the one of soda ash.

The adsorption isotherms allowed us to notice the Armac affinity for pyrite at alkaline pH levels. Contrary to the KAX effect, the Armac seems to be indifferent to the type of pH regulator. Even if Armac molecules are detected at a statistical surface coverage greater than 0.3, hydrophilic functionalities (–C–CS, –CNH– and –COH) are only observed for θ>12. No information was obtained on the adsorption mechanisms in the monolayer capacity. Finally, flotation tests on sulphidic mine tailings were conducted. Armac gave the best results for cyanide bearing tailings compared with KAX even after cyanide destruction, washing and sulphide activation. The obtained results corroborate the findings from the pure pyrite sample study.

Introduction

Throughout the world, mining operations extract both base and precious metals from sulphide ores. The mining process generates substantial quantities of tailings containing various amounts of sulphides, with pyrite being the most common component. Sulphide minerals oxidize in the presence of water and oxygen (Lowson, 1982; Evangelou, 1995). The presence of Thiobacilli bacteria can accelerate sulphide oxidation under certain geochemical conditions. It result from this reactions acid mine drainage pollution (AMD). Although numerous, the methods used to prevent AMD are usually quite expensive. A relatively new alternative has been recently proposed to reduce mine site reclamation costs. This alternative method consists of separating the sulphide fraction from the mine waste prior to final storage. The obtained concentrate can be later managed more easily due to its reduced volume (Bussière et al., 1995; Benzaazoua et al., 1998a).

There is extensive literature on sulphide flotation, especially on pyrite. Many authors have worked on sulphide concentration by non-selective flotation for mineral processing purposes (preparation of concentrates intended for gold and/or silver hydrometallurgy) and some for waste management strategy. From the available literature, we can mention the work of Benzaazoua et al. (2000) who demonstrated the feasibility of environmental desulphurization on four different Canadian tailings. McLaughlin and Stuparyk (1994) evaluated the production of low sulphur tailings at INCO’s Clarabelle concentrator. Balderama (1995) worked on different tailings impoundments in the United States to control acid mine drainage. Leppinen et al. (1997) focused on recovering residual sulphide minerals from the tailings at the Pyhasalami Cu–Zn mine in Finland. Others authors who have studied this topic are Luszczkiewicz and Sztaba (1995), Humber (1995), Bussière et al. (1995) and Benzaazoua et al. (1998b).

For the non-selective flotation of sulphide mineral, the most commonly used and most investigated reagents are the xanthate-based collectors, which are characterized by their ability to collect sulphides in general. They are very selective because of the length of their radical chains (Crozier, 1992). Amyl xanthate is generally used for the non-selective flotation of sulphides (including pyrite) because of its collecting ability. However, in some cases, pyrite flotation may be inhibited. The main factors for the phenomenon of pyrite inhibition are:

• The surface state of the grains can be affected by natural oxidation or oxidation by dissolved cyanides as demonstrated by Wet et al. (1997).

• The pH of the pulp: especially when the xanthate concentration is low, a pH of above 10 causes depression of the mineral (Duc, 1992). At higher xanthate concentration, this effect disappears (Kongolo, 1991; Benzaazoua and Kongolo, 2003).

Other collectors have also been used successfully for non-selective sulphide flotation. This has been demonstrated by the works of Bradshaw and O’Connor (1994) on thiocarbamates, O’Connor and Dunne (1991) on mercaptobenzothiazoles and Hodgkinson et al. (1994) on amines.

The paper presents the results of a work on the optimization of pyrite flotation conditions. This process is intended to be used in an environmental tailings desulphurization process. Two main collectors investigated were, the well-known potassium amyl xanthate (KAX) and the cocoalkyl amine thioacetate (Armac). Two techniques were used to find qualitative and quantitative evaluation data for the two collectors in this study. The method for determination of KAX and Armac concentration in solution was developed using an UV–Vis spectrophotometer. The superficial phases within the pyrite grain surfaces were analyzed by diffuse reflectance infrared spectroscopy. The pH conditions (natural pH and alkaline pH in the presence of soda ash and hydrated lime) of collector adsorption were the primary subjects of study. Due to the need for simplification, pure pyrite doted with like-tailings particle size distribution was used for surface characterization. Finally, the potential application to mine tailings is shown in presence of cyanides for both collectors. It was necessary to destroy the cyanides for tailings desulphurization with KAX by washing and sulphide activation.