Influence of Various Physio-Chemical Parameters on the Adsorption of Copper Ions using Activated Charcoal

Abstract

The work presented in this thesis was carried out in three parts. The first part deals with the characterization of a commercial activated charcoal. This includes the instrumental and chemical methods for the determination of moisture content, elemental analysis, total volatile product, bulk density, particle size analysis, surface area measurement, FTIR study, XRD, surface functional groups and point of zero charge (PZC). The results reveal that the activated charcoal is semi-crystalline having C 69.34 %, S 0.431 %, H 0.982 %, N 0.195 %, surface area 1073 m2/g, total volatile product 27.66 %, ash content 0.183 %, moisture content 5.10 %, pH(PZC) 6.93 and average particle size 36.20 μm. The surface of the activated charcoal contains 7.5 mmoles/g and 1.5 mmoles/g of acidic and basic functional groups respectively. FTIR study also indicates the presence of acidic groups (i.e. phenol –OH and lactones). The second part deals with the adsorption studies of copper ions on activated charcoal from solutions. The adsorption experiments were performed by batch techniques to study the effects of stirring speed, shaking time, pH, concentration of copper ions and temperature etc. The results obtained reveal that the adsorption of copper ions is dependent on shaking time, pH, copper ions concentration, and temperature. The optimum shaking time and pH are found to be 120 minutes and 7 respectively. Low copper ions concentration and low temperature favors the adsorption process. Adsorption dynamics models such as intra-particle diffusion model, pseudo-first order kinetic model and pseudo-second order kinetic model were applied to the adsorption data to elucidate the adsorption process and its mechanism. Results show that pseudo-second order model best describes the adsorption process and the overall rate of adsorption process appears to be controlled by more than one step, namely the external mass transfer (boundary layer diffusion) and intra-particle diffusion mechanism. Rate constant values for intra-particle diffusion and boundary layer thickness were calculated as 1.06 x 10-4 (g/g.min1/2) and 7.93 x 10-3(g/g) respectively. Equilibrium adsorption data was tested for the Freundlich, Langmuir, Dubinin-Radushkevich (D-R) and Temkin equations. The data indicates that the Freundlich isotherm equation fits better with high value of correlation of coefficient (R2 = 0.994) and the adsorption of copper ions on activated charcoal is Physi-sorption process as evident from the adsorption energy values as Ea= 2.425kJ.mol-1. The adsorption of copper ions decreased with the increase of temperature i.e., low temperature favors the adsorption process. Calculated values of thermodynamic quantities such as ΔH, ΔS and ΔG points towards the exothermic (ΔH -6.3868 kJ.mol-1) and spontaneous (negative ΔG and Δ S values) adsorption process. Desorption studies reveals that ~98% of the adsorbed copper ions on activated charcoal is recovered with 0.1 M HCl solutions. In the third parts, the developed method was applied to remove the copper ions from actual waste solution generated in a local copper electro-plating industry for copper ions recovery. About 97% of the copper ions are recovered from waste effluents. Results reveal that the locally available commercial activated charcoal could be used to clean up the waste solution for ions before discharge to water stream.