Optimization of the Viscosity of Wack (Cameroon) Clay Slurry for Coating of a Filtration Layer over a Tubular Ceramic Support Layer by the Slip Casting Technique for Domestic Water Treatment

Abstract

The objective of this work is to optimize the viscosity of Wack clay slurry for coating of a filtration layer over a tubular ceramic membrane support by the slip casting technique for application in domestic water treatment. Coating of a slurry over tubular ceramic membrane support by the slip casting technique requires a clay slurry of appropriate viscosity for it to adhere to the ceramic support by capillary suction. The clay slurry is elaborated using a mixture experimental design with constraint used to determine the optimum viscosity of the slurry, the proportions of raw materials in the slurry and the level of influence and interactions between the proportions of raw material on the viscosity of the slurry. The experimental domain used for the raw materials was: proportion of clay between 10% and 12%, proportion of binder between 11% and 22% and proportion of water between 66% and 79%. It resulted that the proportion of clay has the highest positive influence on the viscosity of the slurry and the interaction proportion of clay-proportion of binder influences positively the viscosity of the slurry. The optimal viscosity was found to be 40.4 mPa∙s for optimal proportions of clay, binder and water/dispersant of 10%, 11% and 79% respectively. The prepared optimal slurry was then cast over the support for contact times of 2, 4 and 6 minutes in order to determine the effect time on the compromise homogeneity (no cracks) and thickness (5 - 15 µm) of the deposited layer. When each contact time was attended, it was dried, sintered at 900˚C and characterized. It resulted that as the contact time increases, there is an increase in the thickness of the deposited layer from 8.8 to 23 µm with the gradual appearance of cracks from 4 minutes. The tubular membrane coated for 2 minutes gave the best results in terms of homogeneity and thickness of 8.8 µm. The porosity, permeability and average pore size this multilayer membrane were determined. It resulted from this that the membrane had a porosity of 32.6%, permeability of 305.67 L/h∙m 2 bar and an average pore size of 0.48 µm adapted for microfiltration.