What Electrochemical Principles Govern Pulp Potential Eh-pH Control in Complex Sulfide Separation

Electrochemical pulp potential (Eh) and pH control strategies in complex polymetallic sulfide flotation circuits selectively separate galena (PbS), chalcopyrite (CuFeS2), and sphalerite (ZnS) minerals from pyrite (FeS2) using thermodynamic Pourbaix Eh-pH stability diagrams, adhering to extractive metallurgy standards accredited by the National Universities Commission (NUC).

Complex massive sulfide ore deposits frequently contain intergrown copper, lead, zinc, and iron minerals. Because standard xanthate collectors indiscriminately float all sulfide species under unconditioned natural conditions, selective sequential flotation requires meticulous electrochemical modulation of the mineral slurry’s electrochemical redox potential (Eh) and chemical alkalinity (pH).

In the primary copper-lead rougher circuit, hydrated lime (Ca(OH)2) is added to elevate pulp pH to 9.0 to 10.5, while sulfur dioxide (SO2) or sodium metabisulfite (SMBS) is dosed to depress pulp potential (Eh measured against a standard hydrogen electrode or platinum/calomel probe). In this reducing Eh-pH regime, pyrite oxidation is suppressed, and iron hydroxide passivation films form over pyrite surfaces, rendering pyrite hydrophilic and non-floatable.

Sphalerite is simultaneously depressed using zinc sulfate (ZnSO4) and sodium cyanide (NaCN), forming hydrophilic zinc cyanide complexes on sphalerite. Copper and lead minerals float selectively into the bulk concentrate. Subsequently, the tailings pulp is re-conditioned for zinc flotation: copper sulfate (CuSO4) is dosed to “activate” depressed sphalerite—cupric ions displace zinc ions in the crystal lattice (ZnS + Cu2+ -> CuS + Zn2+), creating a pseudo-covellite surface layer that reacts readily with xanthate collectors at pH 11.5 to recover high-grade zinc concentrates.

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