Spectroscopic and Thermodynamic Analysis of Cd²⁺Ion Sorption Kinetics by Manganese Dioxide in the Presence of Oxyanions

Abstract

The present study reports the effect of contact time, nature of electrolyte, and temperature on the sorption kinetics of Cd 2+ by manganese dioxide, which is the most active oxide in soils and sediments. The sorption kinetics of Cd 2+ by manganese dioxide is evaluated at pH 6 in different electrolytes in the temperatures range 293-323 K. The solid samples are equilibrated in 0.45 mmol.L −1 Cd 2+ and different electrolytes at pH 6. The results indicate that sorption of Cd 2+ increases with time and temperature and the system attains equilibrium within 60 min in KNO 3 as the electrolyte. However, in the presence of 0.001 M KH2PO 4 sorption of Cd 2+ increases and the time for equilibrium shifts to 90 min. The data second-order kinetics model and the calculated rate constant k and initial sorption rate h increases with increasing temperature phosphate treatment. Among the calculated thermodynamic activation parameters the positive values of H ‡ and G ‡ show the sorption process to be endothermic and nonspontaneous, while the S ‡ being negative indicates a decrease in randomness of the system during sorption process at the solid-liquid interface. The free energy of activation decreases from 15.95 kJ.mol −1 in nitrate to 8.76 kJ.mol −1 in phosphate. These observations suggest that the rate controlling step in Cd 2+ sorption is diffusionally controlled, a fact that has been proved by application of Fick's law.

Solanum xanthocarpum Plant as a Potential Low Cost Adsorbent for the Removal of Methylene Blue from Aqueous Solutions

“…However, most of these processes have limited applications due to some serious drawbacks associated with them such as time of operations, economic viability, sludge production, and disposal problem . Consequently, among all these processes adsorption has been shown to be the more effective way of wastewater treatment in terms of its initial cost, simple designing, ease of operation, and possibility of recycling and reuse of the adsorbent and adsorbate . In this connection the adsorption of different contaminants from wastewater by different materials has been thoroughly investigated.…”