Application of Quadratic Polynomial Model for the Uptake of Iron from Aqueous Solutions by Natural and Modified Egyptian Bentonite

Mostafa Ragab Abukhadra

doi:10.11648/j.ajac.20150306.11

Abstract

The natural Egyptian bentonite, collected from south El Hammam area, was modified at three different temperatures 100°C, 200°C and 300°C for 1 h. The raw and modified bentonite samples were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and BET surface area. The bentonite modified at 100°C exhibited more flaky grains with smooth surface and high surface area as compared to the two other modified types. Response surface methodology in conjunction with central composite rotatable design was used in optimizing and modeling the effect of different parameters such as contact time, initial concentration and dose on the removal of iron ions. Second order quadratic polynomial model was selected to represent the removal process. The mathematical equations of quadratic polynomial model were derived from Design Expert Software (Version 6.0.5). The predicted values from the mathematical equations were highly correlated with the experimental results (R<sup>2</sup> above 0.9) for the required responses in untreated and modified bentonite at 100°C for 1 h. 3D and linear graphs were used to understand the effect of the studied variable parameters and the interaction between them. Under the predicted conditions suggested by the quadratic programming, the modified bentonite at 100°C is more promising and the removal efficiency could be enhanced to 100%. The quadratic polynomial model could be efficiently applied for the modeling of iron removal from aqueous solutions by bentonite.

Highlights

The intensive industries and agriculture activities with rapid expansion in human population in recent years lead to a continuous influx of toxic materials such as heavy metals into water resources causing water pollution
Bentonite treated at 100°C shows no change in the d-spacing value of the main peak of montmorillonite while bentonite samples heated at 200°C and 300°C show collapse in the crystal structure and this appear in the reduction of the intensity of montmorillonite main peak and the d-spacing to 11.26 Å and 10.15 Å for those treated at 200 and 300°C respectively
The mathematical equations of the quadratic polynomial model, which represent the relations between the required responses (removal efficiency of iron % (Y)) and the selected variables, were obtained from Design Expert Software (Version 6.0.5) for coded units as follows: For raw bentonite

Summary

Introduction

The intensive industries and agriculture activities with rapid expansion in human population in recent years lead to a continuous influx of toxic materials such as heavy metals into water resources causing water pollution. Iron ions in water caught the eyes of many researchers as one of the common heavy metals that cause serious problems specially at higher concentrations [1, 2]. Iron ions commonly occur in nature mainly in deeper wells with little or without oxygen [3]. They may occur in dissolved forms as single ions (Fe2+) or in undissolved forms as Fe (OH)3 [2]. Concerning health problems, iron ions can be precipitated as insoluble Fe3 hydroxide forming toxic derivative in human body which cause some diseases such as neoplasia, cardiomyopathy, arthropathy, anorexia, oliguria and biphasic shock [11, 12]. According to the World Health Organization (WHO), 0.3 mg/L is the maximum permissible limit of dissolved iron in drinking water [13], while a concentration of 0.2mg/L is the accepted limit according to the European Union [14]

Objectives

Results

Conclusion