Assessing the depression of high-concentration pyrite in copper flotation by high pH

Treating high-pyrite-containing ores has been problematic in copper flotation plants where selective separation of copper minerals from pyrite is challenging to achieve. Raising pulp pH is common for pyrite depression when pyrite feed grade is low. Whether raising pulp pH can equally depress pyrite in copper flotation when pyrite feed grade is high remains unanswered. Hence, this research examined the effect of increasing grinding and flotation pH on pyrite depression in chalcopyrite flotation with 25% pyrite feed grade, compared to the effect on pyrite depression with 5% pyrite feed grade. It was found that increasing pH from 9.0 to 10.5 and then to 11.5 progressively depressed pyrite in chalcopyrite flotation with 5% pyrite, but a different phenomenon occurred in the flotation with 25% pyrite. In the flotation with 25% pyrite, increasing pH from 9.0 to 10.5 promoted pyrite flotation unexpectedly, while increasing pH from 10.5 to 11.5 depressed pyrite flotation, but this depression was limited. Pulp chemistry measurements and electrochemistry studies on tri-phase galvanic systems indicated that the strong pyrite flotation at pH 10.5 in the case of 25% pyrite feed grade was mainly due to the strong chalcopyrite surface activity and surface oxidation producing a high amount of copper ions available to activate pyrite, while the limited pyrite depression at pH 11.5 was mainly due to the strongly cathodic role of pyrite and weak pyrite surface oxidation, which allowed copper activation on pyrite even with a limited amount of copper ions available. This study demonstrated an apparent deficiency of high pH in depressing high-concentration pyrite in copper flotation and pointed a direction towards the depression of high-concentration pyrite through further oxidising pyrite at high pH.