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

Abstract

Abstract 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 ( R 2 > 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 ( R 2 = 0.994–0.998), yielding high monolayer capacities (7.315–7.593 mg g⁻ 1 ) and increasing affinity constants ( K L = 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.