Abstract
Synthetic zeolite Na-A was prepared from Egyptian kaolinite by hydrothermal treatment to be used as an adsorbent for removal of phosphate from aqueous solutions. The present work deals with the application of response surface methodology (RSM) and central composite rotatable design (CCRD) for modeling and optimization of the effect of four operating variables on the removal of phosphate from aqueous solution using zeolite Na-A. The parameters were contact time (0.5 - 6 h), phosphate anion concentrations (10 - 30 mg/L), adsorbent dosage (0.05 - 0.1 g), and solution pH (2 - 7). A total of 26 tests were conducted using the synthetic zeolite Na-A according to the conditions predicted by the statistical design. In order to optimize removal of phosphate by synthetic zeolite Na-A, mathematical equations of quadratic polynomial model were derived from Design Expert Software (Version 6.0.5). Such equations are second-order response functions which represent the amount of phosphate adsorbed (mg/g) and the removal efficiency (%) and are expressed as functions of the selected operating parameters. Predicted values were found to be in good agreement and correlation with experimental results (R2 values of 0.918 and 0.905 for amount of phosphate adsorbed and removal efficiency of it, respectively). To understand the effect of the four variables for optimal removal of phosphate using zeolite Na-A, the models were presented as cube and 3-D response surface graphs. RSM and CCRD could efficiently be applied for the modeling of removing of phosphate from aqueous solution using zeolite Na-A and it is efficient way for obtaining information in a short time and with the fewer number of experiments.
Highlights
Wastewater is one of the biggest environmental problems all over the world [1]
The aim of this paper focuses on applying, response surface methodology (RSM) and statistical Central Composite Rotatable Design (CCRD) to evaluate the interactive effect of the selected factors and to obtain the optimum conditions for maximum removal of phosphate from aqueous solution by synthetic zeolite Na-A from Egyptian kaolinite
Fitness of the Statistical Model The results of analysis of variance (ANOVA) show that, the Model F-values for amount of phosphate uptaking and the removal efficiency are 8.88 and 8.16 respectively which imply that the model is significant; and there is only a 0.04% and 0.06% chances that a “Model F-Value” resulted from noise for the previous stated responses
Summary
Wastewater is one of the biggest environmental problems all over the world [1]. It is usually hazardous to human populations and the environment and it is critical to be treated prior to disposal into streams, lakes, seas, and land surfaces [2]. There are several methods which have been applied to eliminate phosphorous in waste water including chemical precipitation, biological removal, crystallization, adsorption and ion exchange [9]-[11]. Co-precipitant materials for phosphate removal include limestone, gypsum, fly ash and natural calcite [13] [14], but such material has low adsorption capacities [4]-[15]. The aim of this paper focuses on applying, response surface methodology (RSM) and statistical Central Composite Rotatable Design (CCRD) to evaluate the interactive effect of the selected factors and to obtain the optimum conditions for maximum removal of phosphate from aqueous solution by synthetic zeolite Na-A from Egyptian kaolinite
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