Improving the separation of diamond from gangue minerals

Abstract

Clean diamonds are naturally hydrophobic, which makes it possible to recover large diamonds using greased tables (or belts). It is also possible to recover diamonds smaller than approximately 2mm by flotation using hydrocarbon oils as collectors. However, flotation of such large particles is a challenge in view of the fact that mineral flotation is usually effective in a narrow range of particle sizes, i.e., 0.01–0.25mm. It is also well known that the hydrophobicity of diamonds becomes seriously compromised, when they are exposed to the water that has been in contact with kimberlite ore slurries. This phenomenon, known as secondary hydrophilization, is caused by the deposition of the species derived from the gangue minerals. Some investigators attempted to overcome the detrimental effect using thiol-type collectors, while others used mild acids to remove the hydrophilic surface coatings. The present communication describes a two-step hydrophobization process, in which diamonds are rendered hydrophobic first by overcoming the secondary hydrophilization effect or using a thiol-type collector and subsequently by using a strong hydrophobicity-enhancing reagent. It has been found also that the harmful effect of the secondary hydrophilization mechanism can be overcome using sodium silicate and a hydrophobicity-enhancing reagent. Based on the successful laboratory test results, a set of continuous flotation tests was conducted using a Hydrofloat column cell to achieve high recoveries of small diamonds.