Central composite and factorial design of experiments for textile dye removal from solution by pumice, KOH-pumice, HCl-pumice, kaolinite, KOH-kaolinite, HCl-kaolinite clays

Abstract

The pollution of surface waters by the textile dye-containing wastewaters causes to an increasing concern throughout the world. Methyl violet is a toxic, mutagenic and harmful textile dye against humans. Clays are cheap and vast adsorbents in the nature. Methyl violet dye removal from solution was studied by raw pumice and raw kaolinite using the central composite experimental design method. Firstly, raw kaolinite and raw pumice were tested for the dye adsorption and then capacities of raw kaolinite and raw pumice were aimed to increase by KOH and HCl modification. The experimental parameters studied for the central composite design were initial pHs (2-10), adsorbent amounts (0.2-1 g/50 mL) and initial concentrations (100-500 mg/L). In central composite experimental design of raw kaolinite and raw pumice, the all parameters were found as statistically unimportant for kaolinite and pH, pH-pH, concentration-concentration parameters were found statistically important and other parameters were unimportant for raw pumice. Maximum capacities for raw pumice and raw kaolinite were calculated as 7.15 and 18.31 mg/g, respectively. The dye removal of KOH-pumice and KOH-kaolinite were not high from raw pumice and raw kaolinite. HCl modified kaolinite and pumice were ineffective for dye removal. Kinetics of dye removal by raw kaolinite fitted to the pseudo second order model. pHpzc values of raw pumice and raw kaolinite were found as 6, respectively. Dye removal was obtained as 90% for 50 mg/L dye concentration by kaolinite. Raw kaolinite was determined as the most effective adsorbent for dye concentrations especially below 100 mg/L.