Binary Metal Ions Adsorption of Manganese and Silver from Aqueous Solution using Tea Leaf and Tea Fibre: Kinetics, Thermodynamics, and Isotherm Studies

Abstract

The adsorption behavior of tea leaves and tea fiber (Camellia sinensis) as low-cost adsorbent with respect to manganese and silver was investigated to justify its usage in wastewater treatment. The FTIR results of tea leaves exhibit N-H at 3697.5 cm^-1 indicating the presence of primary amine; O-H band at 3615.6 cm^-1  corresponding to alcohol, carbohydrate, proteins and phenols; C-H band at 2918.5 cm^-1 an indicative of alkane; P- band at 2322.1 cm^-1  corresponding to phosphine and C=O signaling an aromatic ketone. The FTIR results of tea fibre exhibit O-H stretch band at 3276.3 cm^-1 corresponding to alcohol, carbohydrate, proteins and phenols; C-H band at 2918.5 cm^-1 indicating an Alkane; a –C=O band at 1625.1 cm^-1 correspond to the amide; while a C-O band at 1144.2 cm^-1 correspond to secondary alcohol and C-O band at 1017.6 indicates an ether or/and primary alcohol. Adsorption study was performed by the batch adsorption method by varying different parameters including pH, adsorbent dosage, temperature, initial concentration and contact time to find best suited conditions for the removal silver and manganese from aqueous media. The Langmuir isotherm gives R² values of 0.5444 and 0.5795, 0.5444 and 0.5795 for both silver and manganese using tea leaves and tea fiber and Freundlich isotherm gives 0.5637 and 0.5795, 0.5637 and 0.5795 values for tea leaves and tea fiber correspondingly with the Langmuir isotherm having higher R² values considered the most suitable. R2 for the second order of both silver and manganese was 1.00 and 1.00 for tea leaves and tea fibre respectively, which both agrees well with the experiment data.