Adsorption of Organic Diacids and Sodium Polyacrylate Onto Montmorillonite

Organic diacid (oxalic and succinic) adsorption onto montmorillonite is feasible, but weak (~1 mg/g). The comparison of chemical and radiochemical determinations reveals that 80% of the acid in contact with the smectite is used to attack the clay lattice. The pH is the main parameter involved in adsorption, and fixation passes through a minimum for pH 6 to 7. Polyacrylate adsorption is also weak (~1.5 mg/g). It changes with the nature of the exchangeable cation of smectite. Its pH-dependence displays a pronounced maximum for a value corresponding to the pKa of the acidic functions (pH ~6.8), and a minimum at about pH 8. On the assumption that a polyacrylate macromolecule is 100% hydrolyzed, it follows that the-COOH groups carried by 20% hydrolyzed Polyacrylamide molecules (such as those used in the tertiary recovery of petroleum) contribute at the very most to 10% of the total adsorption onto clay. Fixation, therefore, involves predominantly protonation of the amide functions at the edge surfaces of the clay. The acidic functions play a minor role in the adsorption phenomenon in that they affect the length of the macromolecule. The extent of this contribution, however, is virtually impossible to estimate.