The Removal of Silicate(IV) by Adsorption onto Hydrocalumite from the Sodium Hydroxide Leaching Solution of Black Dross

Thi Thuy Nhi Nguyen,Man Seung Lee

doi:10.3390/pr7090612

Abstract

Alkaline leaching of mechanically activated black dross resulted in an aluminate(III) solution with a small amount of silicate(IV). To obtain pure aluminate(III) solution, the removal of silicate(IV) from the alkaline leaching solution was investigated by adsorption with hydrocalumite (Ca2Al(OH)6Cl·2H2O). The hydrocalumite was synthesized by the coprecipitation method. The characterization of the synthesized hydrocalumite was analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM) images and Fourier-transform infrared spectroscopy (FTIR). In our experimental conditions, silicate(IV) was selectively adsorbed onto hydrocalumite over aluminate(III). The reaction time greatly affected the removal percentage of aluminate(III) owing to mass action effect. When the reaction time was longer than 2 h, no aluminate(III) was adsorbed onto hydrocalumite and thus it was possible to selectively remove silicate(IV). When the dosage of hydrocalumite was in excess, the removal percentage of silicate(IV) was rather reduced. Complete removal of silicate(IV) from the solution was accomplished in the reaction temperature between 50 and 70 °C. By selective adsorption of silicate(IV) from the solution at the optimum condition (30 g/L hydrocalumite, 50 °C, 400 rpm, and 2 h), an aluminate(III) solution with purity higher than 99.9% was obtained. The adsorption of silicate(IV) onto hydrocalumite followed the Freundlich isotherm.

Highlights

IntroductionMetal oxides and nitrides, and some salts [1]
Aluminum dross contains alumina, metal oxides and nitrides, and some salts [1]
The NaOH leaching solution of mechanically activated aluminum dross contains a small amount of silicate(IV) with a major component of aluminate(III)

Summary

Introduction

Metal oxides and nitrides, and some salts [1]. Black dross results from the treatment of used aluminum cans to recover aluminum. Alumina can be dissolved in either acidic or alkaline solution. Some oxides in black dross are dissolved together with alumina and the removal of these impurities is necessary to obtain pure alumina solution [2]. An alkaline leaching solution has some selectivity for alumina because the oxides of Ca, Fe, and Mg would not dissolve in this medium, resulting in pure aluminate(III) solution with a small amount of silicate(IV) [3]. Various methods have been developed to remove silicate(IV), such as adsorption, coagulation, nano-filtration, reverse osmosis, and precipitation [4,5,6].

Methods

Results

Conclusion