Effect of pyrite content on chalcopyrite flotation under different regrinding conditions

Abstract

This study aimed to investigate the effect of varying pyrite (Py) content on copper (Cu) in the presence of different regrinding conditions, which were altered using different types of grinding media: iron, ceramic balls, and their mixture, followed by flotation in the cleaner stage. The flotation performance of rough Cu concentrate can be improved by changing the regrinding conditions based on the Py content. Scanning electron microscopy, X-ray spectrometry, ethylenediaminetetraacetic acid disodium salt extraction, and X-ray photoelectron spectroscopy studies illustrated that when the Py content was high, the use of iron media in regrinding promoted the generation of hydrophilic FeOOH on the surface of Py and improved the Cu grade. The ceramic medium with a low Py content prevented excessive FeOOH from covering the surface of chalcopyrite (Cpy). Electrochemical studies further showed that the galvanic corrosion current of Cpy–Py increased with the addition of Py and became stronger with the participation of iron media.

1. Introduction

As an indispensable nonferrous metal on earth, copper (Cu) has played a vital role in various economic and modern industrial development fields. Chalcopyrite (Cpy, CuFeS2) is one of the most widely distributed Cu–iron–sulfur compounds; pyrite (Py, FeS2), which is often associated with Cpy, is the most abundant sulfide mineral in the earth’s crust and is widely distributed in various types of geological deposits [1–2]. Cpy and Py are the primary sulfide minerals found in porphyritic Cu mines and one of the primary sources of Cu, constituting over 60wt% of production [3]. The separation of these minerals serves as the basis for efficient Cu recovery. Flotation is the most widely used separation method for industrial operations, given its efficiency and affordability [4–5].

For the flowsheet of porphyry Cu ore, regrinding rougher concentrate is often used to liberate Cu from other easy-floating minerals, such as Py. In Chilean porphyry Cu plants, as most concentrators have inadequate fineness, especially for Cpy and nonsulfide middling liberation, the regrinding process is often monitored [6]. During the regrinding process, particle size is reduced, valuable minerals are released from the intergrowth composed of valuable and gangue minerals, and fresh surfaces are provided for flotation. Such as the concentrators at Bougainville Copper Pty. Ltd. exhibit finer regrind during ore treatment [7].

In addition, the contact between sulfides or between sulfides and grinding media can lead to galvanic corrosion. As gangue is liberated during primary grinding, corrosion between sulfides intensifies during regrinding. Galvanic interaction governs the dissolution of ferrous ions from iron media; these ions are usually absorbed in the form of iron oxy-hydroxides on the sulfide surface, especially in wet grinding, which decreases the floatability of minerals [8]. The proportion of Py is another essential factor that influences Cu flotation. As global copper mine resources continue to be exploited, low-grade and difficult-to-process copper ore resources have gradually become the mainstream, and these low-grade ores often contain higher levels of pyrite. Compared with the traditional Py content (up to 10wt%) found in ores, Australians and Americans began reporting 18wt% to 50wt% Py contents, whereas some European mines started reporting up to 80wt% [9]. Pulp oxidation potential and Cpy flotation rate, recovery, and grade decrease with the increase in Py content.

After regrinding, although the final grade of Cu concentrate is improved, the extent of grade improvement shows no considerable difference regardless of the high/low Py content in the rougher concentrate. The grinding process involves complex electrochemical reactions that may be manipulated by the grinding media. Thus, this study aimed to investigate the effect of varying Py contents on Cu in the presence of different regrinding conditions, which were altered using different types of grinding media, followed by flotation in the cleaner stage. Scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) was used to obtain the atomic content of oxygen on the Py surface after regrinding with different media [10]. The flotation feed after regrinding and the composition of product layers that formed on the surface were investigated via ethylenediaminetetraacetic acid disodium salt (EDTA) extraction and X-ray photoelectron spectroscopy (XPS) measurements. Electrochemical studies, including open-circuit potential (OCP), Tafel polarization curves, and galvanic corrosion current measurements [11–13], were used to investigate the galvanic corrosion between the minerals and the media.