Improving diamond flotation

Diamond Grease Table

Clean diamonds are naturally hydrophobic as they have no polar groups on the surface. Therefore, a fraction of the coarser diamonds is separated by grease tables (or belts), while finer diamonds less than 2 mm are collected by the air bubbles in flotation, with hydrocarbon oils as collectors.


However, the hydrophobicity of diamond can be seriously compromised when exposed to process water that has been in contact with kimberite ore, due to the deposition of hydrophilic species (secondary hydrophilization) on the surface of the diamond.

Diamond flotation requires larger contact angles than required for mineral flotation in view of the substantially larger particle sizes involved in the former. Therefore, some investigators have attempted to overcome the detrimental effect of the secondary hydrophilization using thiol-type collectors, while others used mild acids (or anolites) to remove the hydrophilic surface coatings.

A new method has been developed in the USA and will be presented at Flotation ’11 in a paper co-authored by Michael Rylatt of BHP Billiton, Base Metals, USA. Michael is one of the foremost experts in the beneficiation of diamonds., who designed, installed and operated the first diamond plant in Canada. In recognition of this, in 2003 he was awarded the Bill Moore Special Achiever Award, presented from time to time to a member of the Canadian Mineral Processors Division of CIM who warrants special recognition for meritorious service to the Division or for an outstanding technical contribution to the mineral processing industry (see MEI Online for the full story).

The paper “Improving the separation of diamonds from gangue minerals” is co-authored by workers from the Nalco Company and Virginia Tech, USA, and will be presented by Roe-Hoan Yoon, who was awarded the patent for the process. He will describe the development of a new method of removing the hydrophilic coatings in alkaline media and increasing the contact angles of diamonds using hydrophobicity-enhancing reagents that are specifically designed for diamond flotation. They have also found that the harmful effects of secondary hydrophilization can be overcome by using a water-conditioning agent and a hydrophobicity-enhancing reagent. The new process has been tested successfully in an operating Canadian diamond plant. I have no doubt that this paper will be of great interest to all in the diamond mining industry.