RSM-CCD design of volcanic ash/ rice husk ash based geopolymer for crystal violet adsorption: kinetics and isotherms

In this work, the application of central composite design (CCD) was used for optimization of the synthesis of voclcanic ash/ rice husk ash based geopolymer in acid media. The effect of three factors such as volcanic ash mass, rice husk ash mass and phosphoric acid concentration were investigated on the responses of methylene blue index and iodine index. At an optimized conditions of voclanic ash 3.72g, rice husk ash mass 1.97g and phosphoric acid concentration 5M, the model predicted and experimental values for both responses were highly comparable. The optimized geopolymer and their precursors were characterized by XRF, FTIR and XRD. The effect of various parameters such as initial pH, adsorbent dose, contact time and initial concentration on the adsorption of crystal violet dye on optimized geopolymer was studied. The kinetic study showed that de model of pseudo-second order could very well describe adsorption kinetics. The adsorption isotherm showed that retention of crystal violet dye follows the Langmuir model.