Abstract

Raman Spectroscopy to identify Cyanide/ Glycine Base Metal (Copper) Complexes and Sulfur Speciation in Conventional Cyanidation and Glycine–Cyanide Hydrometallurgical Solutions

Accurate chemical speciation is essential for controlling reagent efficiency, copper solubility, and gold extraction performance in both traditional cyanidation and the emerging GlyCat™ (glycine–cyanide) leaching technology. However, industrial monitoring methods still rely on partial measurements such as free cyanide, WAD cyanide or total copper, which do not reveal the distribution of cyanide among metal complexes, oxidation products, sulfur–nitrogen derivatives, or organic ligands. This analytical limitation results in oversupply of reagents, unaccounted cyanide losses, and sub-optimal process control.

This work presents Raman spectroscopy as a single, reagent-free analytical technique capable of simultaneously distinguishing and quantifying the main chemical species that define cyanide behaviour in hydrometallurgical liquors. The method resolves, in a single measurement:
• copper–cyanide complexes relevant to dissolution and soluble copper loss,
• cyanide oxidation products such as cyanate (OCN⁻),
• sulfur–nitrogen derivatives such as thiocyanate (SCN⁻),
• stable iron–cyanide species that remove cyanide from solution,
• free glycine and copper–glycine complexes in GlyCat™ systems, and
• major dissolved sulfur species including sulfate (SO₄²⁻) and thiosulfate (S₂O₃²⁻), which govern part of the cyanide degradation pathway and strongly influence copper speciation.

The dual-process applicability is central: the same Raman workflow can be used whether the plant is operating under conventional cyanidation or under partial or full glycine substitution. In cyanidation circuits, Raman enables direct tracking of cyanide consumption through oxidation, metal complexation, and sulfur reaction pathways. In GlyCat™ circuits, Raman allows quantification of the competitive complexation between cyanide and glycine for copper, providing insight into reagent distribution, dissolution kinetics, and the transition from Cu–CN to Cu–Gly species. This is not possible using standard titration-based methods, where each analyte requires a separate chemical procedure.

The method was validated using synthetic and real plant samples from multiple metallurgical projects across different regions worldwide. Raman predictions were benchmarked against Metrohm DET titration for total glycine, UV-Vis for copper–cyanide equilibria, ICP-OES for dissolved copper, and ion-exchange extraction for ligand differentiation. Agreement demonstrated that Raman can replace multiple laboratory workflows, while also providing species-level resolution that conventional methods cannot offer.

The ability to measure sulfate and thiosulfate alongside cyanide species is especially relevant in sulfidic ores, where sulfur oxidation controls cyanide losses and affects SCN⁻ formation. Unlike traditional methods where thiosulfate and sulfate require additional titration or chromatography steps, Raman provides instantaneous measurement in the same scan used to quantify cyanide, copper and glycine.

These results show that Raman spectroscopy is not only a rapid analytical technique but a process-control enabler: it allows closed-loop monitoring of reagent dosing, copper deportment, cyanide destruction chemistry, and the transition between cyanidation and GlyCat™ operation modes. Its ability to quantify multiple species without reagents, derivatization or sample preparation makes it the first viable single-platform speciation tool for modern hydrometallurgy.