Investigation of the behavior of sodium dichloroisocyanurate in aqueous solutions

Global gold consumption has steadily increased in recent decades, driven by expanding industrial applications and reserve accumulation by many countries. In parallel, depletion of high-grade deposits has shifted processing toward low-grade and refractory ores. These trends—together with tighter environmental regulations—highlight the need for alternative lixiviants for gold extraction. Although cyanide remains the industry standard, it is highly toxic and often ineffective for refractory sulfide ores. Other systems—thiosulfate (including ammoniacal thiosulfate), thiourea, and bromide/iodide lixiviants—are used far less frequently due to significant disadvantages. Among acidic chloride lixiviants, sodium dichloroisocyanurate (NaDCC) was investigated as a promising candidate. Use of NaDCC requires strongly acidic solutions (pH < 1.0) and an excess of Cl – , i.e., conditions consistent with the stability domain of the Au(III) chloride complex (AuCl 4 – ). Using the rotating-disk technique, we examined the effects of temperature, disk rotation rate, and HCl concentration on the specific dissolution rate of the reagent (NaDCC), as well as on solution pH and redox potential (Eh). NaDCC hydrolyzes in water to form hypochlorous acid (HClO)—the primary source of active chlorine—while the concurrent pH decrease arises from formation of weak acids (hypochlorous and cyanuric). Adding HCl to NaDCC solutions generates molecular chlorine (Cl 2 ), which evolves once its solubility limit is exceeded. Gold-dissolution tests across NaDCC and HCl concentrations identified an optimum at [HCI] = 14.4 g/dm 3 and [NaDCC] = 3.0 g/dm 3 , yielding a maximum gold dissolution rate of υ Au = 0.118 mg/(cm 2 ·min).