POST POX/SOX/BIOX Treatment

Technical Limitations of Cyanidation on POX Discharge

Post-pressure-oxidized slurries present a highly challenging matrix for cyanide chemistry. POX converts sulfides to sulfates and iron to ferric iron, generating acidic solutions (pH ~1–2), high sulfate concentrations (30–80 g/L), soluble iron species, jarosite/hematite precipitates, and entrained arsenic complexes. To operate cyanide, the slurry must first be neutralized to pH 9–10.5, driving massive lime consumption and producing large volumes of gypsum and iron hydroxide precipitates that encapsulate liberated gold particles. Residual ferric iron oxidizes cyanide to cyanate and thiocyanate, consuming reagent and suppressing leach kinetics. Likewise, sulfur and arsenic intermediates react parasitically with CN⁻, forming SCN⁻ and complexing species that further reduce free cyanide availability. Even after neutralization, cyanidation suffers ORP instability and passivation, resulting in suboptimal leach rates, poor carbon loading, and—commonly—overall recoveries well below the theoretical liberation achieved by POX.

RZOLV™ Performance Advantages in the POX Chemical Environment

RZOLV™ is designed to operate within the natural chemical envelope of POX discharge, eliminating the need for full neutralization and avoiding the failure modes intrinsic to cyanide. RZOLV™ functions at mildly acidic pH (1.2–2.6) and controlled ORP (typically 150–350 mV), where gold exists in a stable oxidized complex without generating parasitic by-products. Ferric iron does not destroy the reagent; instead, it can participate beneficially in redox cycling without reducing leach efficiency. Because RZOLV™ avoids thiocyanate formation entirely, sulfate and sulfur intermediates do not consume reagent or suppress kinetics. Jarosite and hematite do not passivate gold surfaces under RZOLV conditions, allowing consistent dissolution rates even in iron-rich slurries. High-sulfate environments (20–80 g/L) remain fully compatible, with no precipitation or reagent deterioration. The stable gold complexes produced by RZOLV™ are readily adsorbed on activated carbon or ion-exchange resins, enabling conventional downstream recovery without redesigning plant flowsheets. Electrochemical regeneration further maintains reagent strength while minimizing OPEX. The overall effect is a leach environment that matches or exceeds cyanide’s dissolution rates on POX residues—without the detrimental side reactions, high lime consumption, or detoxification burdens.