Equilibrium and kinetic studies on the adsorption of copper onto paddy straw powder

Batch adsorption studies were conducted in the laboratory to explore the possibility of paddy straw powder as a low-cost adsorbent for the removal of copper from wastewater. The parameters affecting adsorption process such as time of contact, metal ion concentration, quantity of adsorbent and pH are also evaluated, and the results are fitted using adsorption isotherm models. It is observed from the experimental results that almost 90-95% copper can be removed from the solution using paddy straw powder. Biosorption of metal ion depends on pH, and the results indicated the optimum pH for the removal of copper as 7.0. To describe the distribution of copper between the liquid and solid phases in batch studies, Langmuir adsorption isotherm and Freundlich isotherm model have been used and it has been observed that Freundlich isotherm better represents the phenomenon. Using the Langmuir model, the maximum copper adsorption capacity was calculated to be 37.17mg/g. The adsorption process is found to adhere to the pseudo-second-order rate equation. The ability of paddy straw powder to remove copper(II) ions from aqueous solution was also investigated in a packed bed column and an S-shaped profile was achieved for the breakthrough curve. Hence, paddy straw powder can be effectively used for future practical applications in industries considering the high copper adsorption capacity, perspective of waste utilization and freely abundant availability of this low-cost adsorbent.