Ion-exchange recovery of cyanide from alkaline effluents: kinetic and equilibrium modelling under controlled alkaline conditions.

In hydrometallurgical and electroplating processes, cyanide serves as a cornerstone reagent but poses substantial environmental and regulatory challenges due to its toxicity and persistence in effluents. This work establishes a rigorous calibration-first framework for cyanide recovery using strong-base ion-exchange resins under alkaline, process-relevant conditions. Matrix-matched cyanide ion selective electrode (ISE) calibrations were generated at pH values of 10-13 with validated slope, linearity, and stability criteria, enabling accurate speciation accounting and eliminating measurement uncertainty typical of high-alkalinity systems. Among the resins evaluated, Purolite A500-L, a type I strong-base macroporous anion-exchange resin based on a polystyrene-divinylbenzene matrix with quaternary ammonium functional groups and a total exchange capacity of approximately 1.15 eq L⁻1 (Cl⁻ form), demonstrated superior performance. Rapid cyanide uptake from an initial cyanide concentration of 20 mgL-1 occurred within the first 10-20 min, with > 90% removal at pH 11 and 1 g L⁻1 resin. Kinetic modelling showed excellent agreement with the pseudo-second-order model (R2 > 0.999) and close alignment between experimental and predicted capacities, indicating a chemisorption-controlled ion-exchange process. Langmuir isotherms provided the best fit to equilibrium data (R2 = 0.994-0.998), yielding high monolayer capacities (7.315-7.593 mg g⁻1) and increasing affinity constants (KL = 0.129-0.247 L mg⁻1). Freundlich parameters supported favorable adsorption with moderate site heterogeneity. Overall, the study provides a decision-grade dataset for cyanide recovery modelling and demonstrates the necessity of analytical QA/QC in adsorption research. The methodology offers a robust foundation for designing sustainable, circular hydrometallurgical systems that recover cyanide while ensuring environmental compliance.