Optimization of adsorption conditions using central composite design for the removal of copper (II) and lead (II) by defatted papaya seed

The prime conditions for the removal of Cu (II) and Pb (II) onto defatted papaya seeds (DPS) from aqueous solution were studied. The effects of three adsorption variables (adsorbent dosage, shaking speed as well as initial concentrations) were investigated using central composite design (CCD) which is a subset of response surface methodology (RSM). Quadratic models were developed for both Cu (II) and Pb (II) percentage removals. The optimum adsorption conditions obtained were adsorbent dosage of 0.30 g, shaking speed of 180 rpm as well as initial concentration of 150 mg/L with desirability of 0.987. The predicted and experimental values obtained were 96.65% and 97.55% for Cu (II) as well as 98.07 and 99.96% for Pb (II), showing good agreement between the experimental values and those predicted from the models with relatively small errors which were only 0.89 and 1.89, respectively. Langmuir isotherm model was found to be the best fit for the equilibrium adsorption data of both Cu (II) and Pb (II) on DPS giving rise to monolayer adsorption capacities of 17.29 and 53.02 mg/g respectively.

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