Abstract: Aminoguanidyl-chitosan imprinted polymers (AGCIPs) were synthesized and applied to the selective extraction of silver and gold cyanocomplexes from aqueous solutions. Batch adsorption parameters for the recovery of silver and gold cyanocomplexes from aqueous solutions by the AGCIPs viz., contact time, solution pH, initial metal concentrations and temperature, were optimized by a two-level fractional factorial design and the Box-Behnken matrix. The equilibrium data correlated well with Langmuir isotherm model; and the maximum adsorption capacities for silver cyanide calculated from the Langmuir equation were 429.2 mg Ag g-1 and 319.5 mg Ag g-1 at pH 6.9 and 10, respectively; whereas they were 319.5 mg Au g-1 and 312.5 mg Au g-1 for gold cyanide in the same order. Adsorption kinetics suggested that these materials predominantly display a pseudo-second-order kinetic mechanism, while thermodynamic parameters revealed that the adsorption process was spontaneous and of exothermic nature. Investigation on the adsorption selectivity showed that the selectivity coefficients of AGCSIP (gold cyanide) with respect to Ag(CN)2-, Fe(CN)6-, and Hg(CN)2- were 8.675, 26.005 and 5694.667 respectively whereas for AGCIP (Silver cyanide) they were 3.017, 75.478 and ¥ for Au(CN)2-, Fe(CN)6-, and Hg(CN)2- respectively. This indicates that AGCSIPs have excellent selectivity for silver and gold cyanide complexes. Regeneration and reusability studies also revealed that 2M solution of KNO3 at pH 10.5 could be used to regenerate the AGCIPs; and these materials could be recycled up to five times without significantly diminishing their adsorption capacity.
Template and target information: potassium dicyanoargentate, potassium aurocyanide
Author keywords: Aminoguanidyl-chitosan imprinted polymers, Silver and gold cyanocomplexes, selective adsorption, Experimental design, Equilibrium isotherm, kinetics