Statistical optimization for adsorption of Rhodamine B dye from aqueous solutions

Low cost raw orange peel (ROP) and modified orange peel (MOP) adsorbents were developed and characterized for the adsorption of Rhodamine B from aqueous solutions. The morphology and the surface functional groups revealed that the surface was observed with heterogeneous pores within the adsorbents. The predominant functional groups were O[sbnd]H, C[dbnd]O, C[dbnd]C and C[sbnd]O. The effectiveness of the adsorbents was investigated for the equilibrium adsorption of colour removal and the reduction of chemical oxygen demand (COD) under the operational condition of pH, adsorbent dosage and contact time. The experimental design of the batch study was conducted using the central composite design (CCD) consisting of 20 experimental runs which was implemented by the 2 ³ factorial design of the response surface methodology. The result of the second order quadratic model revealed that the working parameters significantly influenced the reduction of the investigated parameters. A confidence level of (P < 0.05) was achieved for the reduction of the responses on the adsorbents. The adsorption on ROP achieved a correlation coefficient (R ² ) of 73.33% (colour removal) and 74.55% (COD reduction) while MOP achieved R ² value of 96.92 and 90.06% for the colour removal and COD reduction, respectively. Canonical analysis of the regression equations revealed that the actual values agreed with the predicted values which indicated the aptness of the model. Investigation showed that the equilibrium isotherm data fitted better to the Freundlich model compared to the Langmuir model except for the colour removal on MOP which indicated the effectiveness of the adsorption of colour and COD on heterogenous surface of ROP and MOP.