Native gold and electrum are naturally-occurring alloys containing gold and silver and a little copper. They are the most common and important forms of gold in ores. Their recovery by gravity concentration, cyanidation, or flotation from ores, typically containing 0.1-20 g/t Au is of great commercial importance. This paper reviews the literature on their recovery by flotation. Little mention is made of the recovery of other gold minerals, but some comments are made on the flotation of host minerals (iron and base metal sulphides). Gold and electrum occur in a wide variety of ores in a wide spread of sizes ranging from large lumps (nuggets) to fine particles (0.1 mum) to even finer sizes below the resolution of scanning electron microscopes. The range of applicability of flotation is from about 200 mum flakes to 1 mum particles. Fundamental concepts of gold and electrum flotation are considered, including the possibility of collectorless flotation of the minerals. This question is not yet resolved properly, but gold in some ores does float without a collector. The theory of gold interaction with collectors such as xanthates and dithiophosphates is then considered as a guide to practical flotation and it is shown that for xanthate to adsorb on gold, electrochemical reactions involving xanthate ions and oxygen must occur. Practical aspects of gold flotation considered include the physical condition of the gold particles (size, shape, zonal variations in composition, composites, surface coatings), general ore mineralogy, specific host minerals for gold (pyrite, arsenopyrite, base metal sulphide minerals, quartz), interfering minerals (pyrophyllite, carbon), and non-ore materials (cement fill, mine timber, ferrous wear debris). General chemical conditions involved in flotation include collectors (xanthates, dithiophosphates, mercaptobenzothiazole, amines), frothers (MIBC, Aerofroth), activators (copper sulphate), depressants (lime, cyanide, sulphite, sulphide, guars), pH modifiers (sulphuric acid, sodium carbonate, lime), gaseous atmosphere (air, oxygen, or nitrogen), and others. Reagents need to be tailored for each ore. Physical parameters are also important. Those that can be varied, within limits, include pulp density (15-45% solids) and aeration in conditioners and flotation (either too much or too little is detrimental). Operating temperatures can be important but are not varied in a controlled manner. Flotation cell and impeller design can be important but are not a day-to-day variable. Nine specific applications of native gold and electrum flotation to the treatment of gold-containing ores were identified and are briefly discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.
