Use of Electrodialysis to Bentonitics Clays Dispersions
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Use of Electrodialysis to Bentonitics Clays Dispersions L. V. Amorim1, C. M. Gomes1, F.L.H. of Silva2, K.B. França2, H.L. Lira1 and H.C. Ferreira1 Av. Aprígio Veloso, 882 ZIP CODE: 58109-970 Campina Grande, PB [email protected] 1 Chemical Engineering Department/ Federal University of Campina Grande 2 Materials Engineering Department/ Federal University of Campina Grande ABSTRACT The aim of this work is to study the uses of electrodialysis to bentonitics clays dispersions from Boa Vista City, PB, to improve the rheological properties. The dispersions were prepared with natural clay in the concentration of 4.86% w/w and submitted to electrodialysis process by using cationic polymeric membranes. Following, the dispersions were treated with Na2CO3. After cure, it was evaluated apparent (AV) and plastic (PV) viscosity and water loss (WL). The tests was setting up according to 22 experimental design, with three measures in the central point, to estimate the best applied voltage and time and the influence on AV, PV and WL. The results showed that variables (voltage and time) have significant influence on the rheological properties. It was observed an increase in PV and decrease in WL, with values that satisfy the specifications for water based drilling fluids. INTRODUCTION Electrodialysis is an electrochemistry separation process, in which, electrically charged membranes and an electrical potential are used to separate ionic species from an aqueous solution. In this process, positive ions (cations) move in direction to the negative electrode (cathode), and the negative ions (anions), move in direction to the positive electrode (anode). The membranes, electrically charged, are used to control the migration of the ions and can be classified as cation-exchange and anion-exchange membranes; the cation-exchange membranes carrying fixed negative electric charges just allow the passage of positive ions, while the anionexchange membranes carrying positive electric charges just allow the passage of negative ions [1]. The application of electrodialysis to bentonite clays dispersion was preliminary studied by Amorim [2] and using clays from Boa Vista, PB. Those clays, naturally polycationic, were studied initially by Souza Santos [3]. In this study it was verified the capacity of these clays to transform in sodium bentonite when treated with a right concentration of sodium carbonate, however, the clays dispersion shown inadequate viscosities to be used as a components of water based drilling fluids. Also, Souza Santos presented several theories to explain the “no-swelling” of the clays and the low values of viscosities. Among of them, the presence of cations Ca2+ and Mg2+ in the clay structure as exchangeable cations, with flocculants character, would be responsible for the rheological behavior not very satisfactory. From this point, several works were done to improve the rheological properties of these clays, including different cure methods, dialysis, thermal treatments and the use of additives. A summary of those treatm
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