Study Of Thermodynamics Of Aqueous Solutions In The Bleaching Kaolins

Abstract:

Kaolins laundering is a process of selective leaching of minerals such as hematite (Fe2O3) and / or goethite (a-FeO (OH) attached to the surface of the white Kaolinite affect that characterizes it. The bleaching process involves using a strong reducing agent, as is the case, the sodium dithionite (Na2S2O4) acting on the surface of kaolinite hetatitico reducing iron and / or goethite (Fe 3 +) to ferrous iron (Fe +2) increasing the rate whiteness (% Whitness) of this mineral.This paper presents thermodynamic and kinetic study of electrochemical phenomena involved in the bleaching of kaolin ore, industrial and economic importance in Colombia. Laundering was studied four samples of Kaolin from Union Township in the department of Antioquia (Colombia) considered the main variable, the percentage of reducing agent (sodium dithionite, Na2S2O4), the processing time and the particle size in suspension. In the study of the physicochemical characteristics of the test samples, using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Atomic Absorption Spectrophotometer, Particle Size Distribution (DTP ), X-ray fluorescence (XRF) and colorimetry. In the thermodynamic study of the process, potentiometric titration was used in the measurement of redox potential and atomic absorption spectrophotometry to determine the concentration of dissolved iron, finally, species of potential contributors were placed in a Pourbaix diagram and determined the chemical and electrochemical equilibria in the system. In a kinetic approach to the study were drawn polarization curves obtained by voltammetry and potentiostatic mode according to the Tafel law were found equilibrium potentials and mixed system , the Tafel constant, the density of exchange current (I0) and the current limit (IL).

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