Abstract: The copper grade the ore of an Anhui copper mine is somewhat reduced with the mining going deeper and averages about 0.62% at present.The copper concentrate produced in the on-site test adopting a process of copper-sulphur bulk flotation and middling recycling with conventional flotation reagents had a grade of 21.47% and a copper recovery of 85.52%.In the test adopting the new closed-circuit middling recycling process consisting of selective classification and regrinding, the copper recovery was raised to about 90%.Zeta potential analysis and XRD testing means were used in the analysis of the new process mechanism.The results indicate that the cycling of stepwise grinding, classification and flotation can change the surface properties of the valuable minerals and increase their floatability.

Key words: Selective regrinding of middling, Zeta potential, Infrared spectrum, XRD, Surface properties