Comparative investigation of plain and silver impregnated activated carbons for the removal of cyanide from basic aqueous solutions in the batch process

ABSTRACT

Purolite AC-20 and Norit RB 0.8CC activated carbons impregnated with AgNO₃ were used for the removal of CN^– and Ag–CN complex from model wastewater. The formed Ag⁰ centers were approved by scanning electron microscopy micrographs and X-ray powder diffraction data. The degree of Ag⁰ participating in CN^– sorption varied from 100 to 45% on AC-20/Ag and from 100 to 73% on RB 0.8CC/Ag, by varying [CN^–]/[Ag] in the initial solution from 2.0 to 19.2. The Freundlich isotherm and Fleming kinetic models were consistent with the experimental data. The K_F values for the CN^– adsorption on AC-20/Ag and RB 0.8CC/Ag increased by a factor of 1.2 and 1.5, but they lowered for Ag–CN adsorption by a factor of 4.1 and 2.1, respectively, as compared to that of plain activated carbons. The removal of 90% cyanides is appropriate by combining two batches from activated carbon: impregnated, mainly for the removal of CN^–, and plain, removing the rest of Ag–CN.

KEYWORDS:

• Activated carbons
• adsorption
• electroplating
• free cyanide
• impregnation
• silver cyanide complex

Acknowledgments

The authors gratefully acknowledge the assistance of the Norit Company (Netherlands) and Purolite Ltd (UK) in providing the activated carbons.