Acid treatments of montmorillonite-rich clay for Fe removal using a factorial design method

Lindiane Bieseki,Fabio G Penha,Sibele B C Pergher,Helen Treichel,Francine Bertell

doi:10.1590/s1516-14392013005000114

Abstract

Montmorillonite clays are of great interest for industrial processes such as catalysis and adsorption. The textural properties of clays can be modified in an attempt to increase their uses. This paper describes the acid treatment of natural montmorillonite clay. The materials were characterized using X-ray diffraction (XRD), atomic absorption spectroscopy (AA) and BET surface area measurements. Three different acids (HCl, HNO3 and H2SO4) were tested, and HCl and H2SO4 were more efficient for removing Fe from the clay. The results indicate that HCl better preserves the material structure because less Al is removed. A central composite design (CCD) 22 was applied to evaluate the treatment using HCl. The temperature and concentration presented positive effects on the removal of Fe, Al and Mg. Combinations of the HCl acid solution concentration and temperature, such as 4 mol.L-1/50 °C and 1 mol.L-1/75 °C, assured that Fe was removed with less damage to the structure.

Highlights

Smectite clays consist of layers of two silica tetrahedral sheets surrounding a central alumina octahedral sheet
The natural montmorillonite clay was supplied by Colorminas Colorifício e Mineração S/A, Içara, Brazil, and was called Clay A
Sulfuric and hydrochloric acids were efficient in the removal of Fe from the montmorillonite-rich clay used in this work

Summary

Introduction

Smectite clays consist of layers of two silica tetrahedral sheets surrounding a central alumina octahedral sheet. The authors used a maximum acidity of 1.5 N for the samples treated with H SO or HCl. The increased aggressiveness of the acid treatment decreases the catalytic activity of clays because of the impairment of the octahedral layers, which reflects a decrease in the Brönsted acidity and is higher in acid-treated materials at lower concentrations[6]. The increased aggressiveness of the acid treatment decreases the catalytic activity of clays because of the impairment of the octahedral layers, which reflects a decrease in the Brönsted acidity and is higher in acid-treated materials at lower concentrations[6]

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Conclusion