A New Ferric Iron Controlled Grinding Mechanism in Iron Oxide Copper Gold Ores and Its Impact on Copper Flotation

Iron oxide copper gold deposits are major global sources of copper, yet the electrochemical role of iron oxides during grinding remains poorly understood. Hematite is commonly considered inert; however, this study demonstrates that it actively participates in galvanic interactions with grinding media, producing oxidation conditions that differ fundamentally from those in iron sulfide copper gold systems. Mixtures of chalcopyrite, hematite, and quartz were ground using forged steel, 18 percent chromium steel, and 30 percent chromium steel media. Flotation tests showed that copper recovery was highest when using 30 percent chromium steel, while forged steel and 18 percent chromium steel produced lower and nearly identical recoveries. Pulp redox conditions were governed primarily by ferric and ferrous iron cycling originating from hematite rather than by dissolved oxygen. Electrochemical measurements confirmed strong galvanic coupling between hematite and all grinding media, with reductive dissolution of hematite dominating the cathodic reaction. Chemical extraction and elemental analysis revealed that forged steel and low chromium steel generated greater amounts of iron oxide and hydroxide species, which deposited on chalcopyrite surfaces and depressed flotation. High chromium grinding media suppressed these processes through improved passive film stability, resulting in enhanced copper flotation performance.