Response surface methodology for a green synthesis of zeolite Na-A

Abstract

The study aims to utilize the "green synthesis" of Na-A zeolites from the waste material, CFA, which is produced from the combustion of coal in coal-fired power plants. Fifteen experimental conditions for the extraction process were obtained using the Box-Behnken Design of the Response Surface Methodology (RSM) by manipulating the concentration of NaOH at 2, 4 and 6 M; controlling the percent power level of microwave irradiation at 10, 50 and 100 and exposure time 1, 3.5 and 6 minutes. Contour plots of Si and Al ions concentrations showed that increasing the three variables led to an increase in the concentration of Si and Al ions in the extracts. Upon hydrothermal treatment at 95oC after 72 hours on the extracts, gibbsite, Na-A zeolite and sodalite octahydrate were produced which were characterized by their XRD images. Na-A zeolite would crystallize when the Si ion concentration in the extract is higher than 2000 ppm and the base used in the extraction not more than 4M. The optimum conditions of the three variables for maximum extraction of Si and Al from CFA to meet the synthesis of zeoliteNa-A were: 5M NaOH concentration, 1.3 min time of exposure to microwave irradiation and 100% microwave power level.