Using the Response Surface Methodology to Optimize the Extraction of Silica and Alumina from Coal Fly Ash for the Synthesis of Zeolite Na-A

Abstract

Response surface methodology and inductively coupled plasma-optical emission spectroscopy were used to analyze the silicon (Si) and aluminum (Al) ion concentrations extracted from microwave-assisted hydrothermal fusion reactions between coal fly ash (CFA) and sodium hydroxide solution. The extracts containing Si and Al ions were successfully converted to zeolites by hydrothermal treatment at 95 • C for 72 h. Fifteen experimental conditions for the extraction process were obtained using Box-Behnken design through the manipulation of three independent variables. These variables include NaOH concentration (2, 4 and 6 M), power level of microwave irradiation (10, 50 and 100 W)+++ and exposure time (1, 3.5 and 6 min). The statistical analysis result indicated a significant interaction effect with a p value of 0.001. Increasing the values of all the three variables led to an increase in the concentration of Si and Al ions in the CFA extract. The optimized combinations of the three variables within the experimental range for Si and Al extraction were 5.6 M for NaOH concentration, 5.5 min time of exposure to microwave irradiation and 100 W of microwave power level. Based on the extracted concentration values of Si and Al, three products were isolated; zeolite Na-A, sodalite octahydrate and gibbsite which were characterized by their XRD images. Plots of percent yield of the final products versus [Si 4+ ] and [Al 3+ ] revealed a trend of the types of product for various ranges of concentrations of the ions in the extracts prior to hydrothermal treatment at 95 • C.

Optimization of Silica Extraction from Diatomaceous Earth using the Central Composite Design of Response Surface Methodology

“…In Table S1, the p-values for all the models were less than 0.05, which usually indicates that the models are significant, 2 meaning that the quadratic model of the CCD chosen was sufficient to represent silica extraction. This model is in agreement with what was found by Adebisi et al 13 , Olawale et al 22 , Matlob et al 23 and Qisti et al 24 However, p-values for many of the terms in the CSE and acid UAE methods were greater than 0.05. This value means that those terms are not significant model terms implying that they do not directly impact the percentage yield or the percentage purity of silica extracted.…”

“…For example, all modelled factors directly impact the percentage yield and purity of silica extracted in the alkali UAE method since the change in Na + ions, time, and transient temperature will affect the amount of sodium silicates produced. A study by Matlob et al 23 also found that a change in NaOH concentration, exposure time and microwave power level significantly affected the concentration of Si in coal fly ash extracts. On the other hand, neither concentration of alkali nor stirring time nor the interaction as their crossed vector of both nor their quadratic functions had any effect on percentage yield in the CSE method.…”

The influence of the amorphous SiO2 content on the characteristics of red mud based geopolymers

“…sialate ions. As the result of these reactions, stable material similar to zeolite is formed [10,11].…”

Manufacturing Brick from Attapulgite Clay at Low Temperature by Geopolymerization

“…A polysialatesiloxo (SiO2/Al2O3 =4) is obtained from metakaolin and NaOH. These inorganic polymers have a chemical composition somewhat similar to zeolite A [19,20], but exist as amorphous solids rather than having a crystalline microstructure [22,23].…”