A collector is the heart of the flotation process (Wills and Napier-Munn, 2006). Its purpose is to selectively produce a hydrophobic layer on the surface of the valuable minerals without adsorbing on the gangue materials in the slurry. The hydrophobized mineral particles to attach to air bubbles, which can be recovered in the froth product.
The important characteristics of a good collector include the ability to selectively adsorb onto desired mineral surfaces and to lower the water/mineral surface energy. The general composition of a conventional molecular collector is a hydrocarbon chain with a reactive or functional head group.
The head group reacts with the surface of mineral and the hydrocarbon group chain is oriented away from the surface towards the aqueous environment (Bulatovic, 2007). Xanthates for example, are the most common type of collectors used for sulfide minerals.
The invention of xanthate as flotation collector in 1925 was a significant development for froth flotation (Keller, 1925). Xanthates are known as low-cost, easy-to-produce collectors which usually give good flotation efficiency, which has allowed for their application for almost a century.
In order to obtain a good flotation efficiency, a collector needs to adsorb optimally on the mineral surfaces which can be achieved either by chemisorption or physical adsorption (e.g., electrostatic interaction). Adsorption of xanthates on a sulphide mineral is an example of chemisorption, whereas adsorption of cationic amine-based collector onto negatively-charged kaolinite is an example of physical adsorption (Hu et al.
There have been many studies discussing chemical aspects of the adsorption of xanthate collectors on the mineral surface (Hodgson and Agar, 1989; Andreev and Barzev, 2003; Hu et al., 2005; Grano et al., 1997; Vucinic et al., 2006). For example, through electrochemical investigations, Hodgson and Agar proposed that xanthate chemisorption at the nickel sites of pentlandite was because of oxidization that took place at the surface of pentlandite to form a dixanthogen (Hodgson and Agar, 1989).
Similarly, Andreev et al.’s studies via Raman spectroscopy of chalcopyrite-xanthate flotation products confirmed the formation of a diethyldixanthogen (Andreev and Barzev, 2003; Yang, 2011). The schematic drawings shown in Figure 3 illustrate their proposed dixanthogen formation on mineral surfaces.