Protein fractionation using selective adsorption on clay surface before filtration

Protein fractionation by membrane filtration has been investigated through the selective adsorption on clay particles. The micro-filtration of bovine serum albumin, haemoglobin and montmorillonite mixtures was carried out. Both proteins have similar molecular weights, bovine serum albumin (BSA) has an isoelectric point at pH 4.8 while haemoglobin (Hb) is positively charged up to pH 7.0. The aim was to improve the selectivity of the separation by exploiting the different electrostatic interactions and in the meantime to reduce membrane fouling by proteins, thanks to the formation of a secondary membrane by the clay particles on top of the original membrane. We have studied the effects of suspension characteristics (pH, ionic strength, protein and clay concentrations) on adsorption isotherms of protein on clay particles and on separation performances such as micro-filtration limiting flux, protein transmission and separation factor. The optimum results were obtained with an ionic strength of 10−3 M and a pH value around 7.0. In these conditions, only Hb was adsorbed on clay particles while BSA stayed free in solution.