THE ADSORPTION OF COMPLEX ALUMINUM SPECIES BY CELLULOSIC FIBERS FROM DILUTE SOLUTIONS OF ALUMINUM CHLORIDE AND ALUMINUM SULFATE

The study of the interactions of complex aluminum species in papermaking systems has generally been inhibited by the complicated aqueous solution chemistry of the aluminum ion. Recent work on the hydrolysis and precipitation of aluminum by Hayden and Rubin has provided a better understanding of the aqueous equilibria of the aluminum ion and the precise nature of the complex aluminum species. Using their work as a basis for understanding the interactions of aluminum, this investigation was undertaken to improve the general understanding of the adsorption of complex aluminum species by cellulosic fibers under conditions of a papermaking system.;The amount of aluminum adsorbed onto a cellulosic fiber of a given carboxyl content and surface area was found to be primarily a function of the pH and the aluminum concentration of the system. At each aluminum concentration, the adsorption of aluminum as a function of pH was characterized by a sharp increase occurring between pH 4-5. As the aluminum concentration was raised, the characteristic sharp increase in adsorption was observed to occur at a lower pH. The increase in adsorption between pH 4-5 was established to be primarily the result of a change in the aqueous solution chemistry of the aluminum ion, specifically the formation of a polynuclear complex aluminum species, and not the ionization of the carboxyl groups.;The Hayden and Rubin solution to the aqueous equilibria had an excellent correlation to the adsorption behavior of aluminum by cellulosic fibers from a dilute solution of aluminum chloride. Using the Hayden and Rubin aluminum species distribution curves, it was possible to consider the adsorption of aluminum from aluminum chloride solutions in three distinct regions. Al('3+) is believed to be the primary aluminum species to adsorb in the low pH region (4.0-4.5). In the intermediate pH region (4.4-4.8), Al('3+) and Al(,8)(OH)(,20)('4+) are the primary species to adsorb. The positively charged aluminum hydroxide precipitate is believed to be the principal aluminum species adsorbed by the fibers in the high pH region (4.7-5.5).;The adsorption behavior of aluminum from a dilute solution of aluminum sulfate was found to be predictable and quite analogous to the adsorption pattern for aluminum chloride with the characteristic sharp increase in adsorption occurring between pH 4-5. The only observed differences in adsorption between the two salts were that the aluminum sulfate curve broke upward to 0.25-0.30 pH units lower than for aluminum chloride, and the amount of adsorbed aluminum was greater for aluminum sulfate in the high pH region where the precipitate is formed. The observed differences could be explained by known differences in their aqueous solution properties. It was concluded that the adsorption of aluminum from aluminum sulfate solutions was controlled by adsorption mechanisms similar to these occurring in aluminum chloride solutions, although the exact composition of the polynuclear species was not known.;The adsorption of aluminum from dilute solutions of aluminum chloride and aluminum sulfate was studied at aluminum concentrations ranging from 2.5 x 10('-4)M to 1.0 x 10('-3)M and between pH 4.0 and 5.5. A fines-free, oxidized cotton linters pulp was used as the cellulosic substrate.;In summation, for aqueous conditions similar to those occurring in a paper-making system, the adsorption of aluminum by cellulosic fibers from a dilute solution of aluminum chloride or aluminum sulfate was found to occur in a systematic and predictable manner directly related to and principally governed by the aqueous solution chemistry of the aluminum ion.