CHEMISTRY OF THE CIP PROCESS

This chapter examines the fundamental chemistry underpinning the carbon-in-pulp (CIP) process for gold extraction, with particular emphasis on leaching, solution speciation, and carbon adsorption. It begins with an overview of gold’s properties, units of assay and fineness, and a brief historical context of gold leaching technologies, tracing the evolution from chlorine-based methods to cyanidation and the development of CIP. The thermodynamic basis of gold dissolution is discussed using Eh–pH (Pourbaix) diagrams for the Au–H₂O and Au–CN⁻ systems, demonstrating the role of cyanide in stabilizing dissolved gold as Au(CN)₂⁻ and identifying the optimal pH range for leaching. The chapter then details the cyanidation reaction mechanism, distinguishing between non-refractory and refractory ores and describing the impact of cyanicides such as copper and reactive sulphide minerals on cyanide consumption and leach efficiency. Kinetic factors influencing the rate of gold dissolution—including particle size, surface coatings, gold mineralogy, cyanide concentration, oxygen availability, and temperature—are systematically analyzed. The behavior of cyanide in aqueous solution, the critical importance of pH control to prevent HCN volatilization, and the roles of common alkalis (lime, caustic soda) are addressed, with special consideration of saline process water and scaling. Finally, the chapter highlights the central role of dissolved oxygen, compares various oxygenation strategies (air, oxygen, hydrogen peroxide, calcium peroxide), and introduces the principles and historical development of activated carbon adsorption in CIP circuits.