CADMIUM METAL SCAVENGING CAPABILITY OF SPENT TEA GRAINS-AN AGRICULTURAL BIOMASS WASTE AS A LOW-COST ADSORBENT

Abstract

Over the past decade, there has been heightened attention to the advancement of eco-friendly technologies aimed at purifying heavy metal-contaminated water, recognizing the substantial risks these metals pose to human health and the environment. Amidst these emerging technologies, biosorption emerges as a highly promising method that harnesses the potential of naturally available waste materials to efficiently eliminate heavy metals. A sequence of batch experiments was performed under normal room temperature to evaluate the crucial factors that influence the adsorption of cadmium ions from synthetic solutions prepared using double distilled water onto STG, including the particle size (1180 – 75 microns) of STG, contact time provided (30-180 min), adsorbent dosage (1-10 g/L), rotary shaker speed (25-200 rpm), pH (2-7) and cadmium ion concentration (2-16 ppm). By implementing optimal conditions found through various batch study experiments, such as an initial cadmium ion concentration (Co) of 5 ppm, a dose of 1 g/L STG, an adsorbate pH value of 6.04, a shaker speed of 200 rpm, and a 90-minute duration of exposure, the Langmuir equilibrium isotherm model revealed a maximum uptake rate (qmax) of 28.16 mg/g. Upon evaluating different conventional kinetics models, it was observed that the batch study data aligned with the rate kinetics well explained by the pseudosecond-order rate kinetics equation. The equilibrium state between the adsorbate and adsorbent was achieved within a period of approximately 75 to 90 minutes, following an initial rapid adsorption rate. Additionally, it was observed that both % removal and uptake capacity exhibited a direct correlation with the pH level; as the pH level transitioned from acidic (2) to nearly neutral (7), there was a substantial increase in both the percentage removal and uptake capacity. The FTIR spectroscopy analysis suggests that the adsorption mechanism of spent tea grains (STG) can be attributed to the existence of carboxyl and hydroxyl groups in the material. Based on the experimental data acquired under optimal conditions, it can be inferred that spent tea grains (STG) hold significant potential for utilization as a highly effective adsorbent. © 2023 Chauhan S.S. and Dikshit P.K.S.