ADSORPTION OF ALUMINUM(III) ON CELLULOSIC FIBERS IN NEUTRAL TO ALKALINE-SOLUTIONS - INFLUENCE OF CHARGE AND SIZE OF THE PARTICLES FORMED

In the present investigation, a new flash neutralization technique has been used to neutralize AlCl3 solutions to different OH/Al ratios and the colloids formed have been characterized with regard to size, zeta potential and titratable charge using KPVS (potassium polyvinyl sulph ate) titration. The colloids were then exposed to cellulosic fibres an d the adsorption of Al onto-the fibres was determined. Apart from pure adsorption measurements, the specific surface area of the treated pul p was determined. The results of the investigation show that: Colloids of aluminum hydroxide with certain sizes and charges can be formed by mixing exact amounts of AlCl3 and NaOH. At an OH/Al ratio of 2.9-3 th ere is a rapid growth of the particles from a diameter; of 400 nm to a size of 3 mu m or above (instrumental limit). Zero mobility is reache d at a ratio of 3.2-3.3 where the pH is about 9.5. The adsorption of A l colloids on cellulose fibres passes through a maximum at an OH/Al ra tio of 3.0-3.1. Before the maximum is reached, the charge balance betw een the fibres and the colloids is the determining factor in how much Al can be adsorbed onto the fibres. At OH/Al ratios higher than 2.9, t he colloids are adsorbed in larger agglomerates consisting of smaller primary particles. Simple calculations from the increase in specific s urface area of the fibres due to the Al adsorption showed that the siz e of these primary particles is about 12 nm at an OH/Al ratio of 3.3. This also indicates that the available specific surface area of the fi bres never becomes limiting for the Al adsorption at higher ratios.