The effect of carbon dioxide and nitrogen on pyrite surface properties and flotation response

In 1997 Newmont USA Ltd. introduced the N2TEC process for the flotation recovery of auriferous pyrite and other sulfide minerals in Carlin type ores, using nitrogen as the flotation gas, and low pH to prevent oxidation and hydrolysis of the pyrite surface. However, increased amounts of carbonate gangue minerals in certain Carlin type ores adversely affect the flotation recovery due to difficulties with pH control in the presence of carbonate minerals, i.e. calcite, dolomite, etc. Subsequently, it was discovered that by using CO2 for flotation, the pH of the system can be more effectively controlled, and consequently the recovery and rate of pyrite flotation can be improved significantly. In our current laboratory research on pyrite flotation chemistry these results were confirmed, as both fresh and oxidized pyrite particles exhibited an increased flotation response in CO2 saturated solution. It was found that the water contact angle at the pyrite surface increased in CO2 and N-2 saturated solutions, while surface oxidation and bubble attachment time decreased. In addition to decreased surface oxidation and the influence of pH on surface hydrolysis, the significance of bubble attachment phenomena in these CO2 flotation systems helps to explain the improved flotation response.