2016 IN ASSOCIATION WITH CONCENTRATION Dr D.R. Nagaraj Flotation chemicals constitute a most powerful tool in enhancing mineral separation performance, affecting overall economic and environmental impacts of the process. Dr D.R. Nagaraj (Nag) has more than 35 years of outstanding and innovative achievements in the design, development and commercialisation of numerous families of novel flotation reagents (collectors, depressants, dispersants, etc.) and in advancing the art and science of flotation agents for sulphide and non-sulphide mineral separations. His seminal 1987 paper titled The chemistry and application of chelating or complexing agents in minerals separations formally introduced the donor-acceptor model, which paved the way for rational design of flotation reagents. During his entire career he has been involved in a bridge building exercise between academic research and practical applications. However, his persistence at requiring knowledge to be useful has made him sought after by both communities. His holistic approach to reagent selection and flotation optimisation is one example of his devising a rational and practical scheme for dealing with real, complex ores. His pioneering work in the use of SIMS surface analytical technique, for determining the disposition of collectorsMinCa on 26 mineral surfaces started a trend in the academic community and is an example of the high quality work for which he is known. In addition to devising schemes to optimise chemical usage, Nag has developed and patented many organic and polymeric materials for flotation and toxic metal removal. Here are a few examples: • Alkyl and Aryl monothiophosphates as acid circuit sulphide collectors: Nag pioneered the use of alkyl and aryl monothiophosphates (modifications of existing dithiophosphates) as acid circuit sulphide collectors. Under alkaline conditions the monothiophosphates are excellent collectors for precious metals such as Au and Ag. The largest mines in North America and Asia currently use the monothiophosphates to improve their gold and silver recoveries. • Synthetic functionalised polymers as depressants in sulphide flotation: Using insights from his donor-acceptor model, Nagaraj et al conceptualised and synthesised polymeric depressants containing mineral-specific functional groups for use in enhancing sulphide flotation. The most important application for these depressants has been for Cu-Mo separation, where they can greatly reduce the use of inorganic Cu sulphide depressants such as NaSH, Na2S, and Nokes. These inorganic reagents are known to have serious safety, health and environmental (SHE) concerns such as stench and H2S formation. Mitigation of those SHE issues through the use of polymeric depressants protects operators and also improves economics and logistics as a result of greater reagent efficiency. A number of mines around the world currently use these depressants. • Alkoxycarbonyl thionocarbamates as collectors for mildly alkaline circuits: A major gangue mineral present in sulphide copper ores is pyrite, which readily responds to sulphide collectors at pH <10, resulting in results in significant grade dilution of the concentrate. In order to deal with this problem, plants typically use large amounts of lime to raise the pH to greater than 10.5 to depress pyrite. Lime consumptions can be quite high, and most plants run multiple lime kilns in order to generate enough lime, even though they are notoriously energy inefficient. The collectors developed by Nag allow for the flotation of copper ores at pH 9.5, resulting in significant energy savings. These reagents, now in use at multiple mining operations around the world, also brought unprecedented dose-efficiency, leading to significantly reduced reagent footprint at mining operations. Plants in Africa are known to use as little as 1ppm of this family of reagents to achieve desired performance, as compared to 20-30ppm of other reagents. • New Collectors for PGMs and gold: Nag developed a new family of modified dithiocarbamates. When using these reagents by themselves, the recovery of metallics improved considerably, and in combination with existing reagents, overall Au and sulphide recovery could be improved. As a result these reagents are now in use at multiple Au operations around the world. Nagaraj’s productive career has been characterised by the application of good fundamentals to the solution of practical problems in flotation, elevating both the academic and industrial communities.