Structure evolution of brick-red palygorskite induced by hydroxylammonium chloride

Brick-red clay mineral with palygorskite (PAL) as the main ingredient has huge reserves in the nature, but the congenital brick-red color limits its applications in industrial fields. In light of the prospective application value of such mineral, researchers have been looking for a feasible way to turn it into white one. Herein, a simple one-step reaction process in the presence of hydroxylammonium chloride (HAC) was developed and used to turn brick-red PAL into white one. The change of textural structure and physicochemical features of the brick red PAL was investigated. It was shown that the brick-red PAL was converted to white after the reaction in 5 mol/L of aqueous solution of HAC at 80 degrees C. The rod-like crystal morphology of PAL still remain well after the reaction, and the associated minerals such as quartz, feldspar and muscovite did not change obviously. The dissolution of associated hematite (alpha-Fe2O3) and the leaching of Fe(lll) and Fe(II) in acidic and reductive HAC solution mainly contributed to the whitening of brick-red PAL, as confirmed by Mossbauer spectroscopy. This research would lay a theoretical basis for extending the industrial application of naturally abundant brick-red clay minerals. (C) 2018 Elsevier B.V. All rights reserved.