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Mononuclear and Polynuclear Aluminum Speciation through Differential Kinetic Reactions with Ferron¹

ABSTRACT

The kinetic reaction of ferron (8-hydroxy-7-iodo-5-quinoline-sulfonic acid) with partially neutralized Al solutions of varying basicity and age were investigated with the intent of separating mononuclear and polynuclear Al. Ferron solutions buffered with varying quantities of NaOAc, NH₂OH·HCl, and acetic acid suggested that reduction of ferron by NH₂OH·HCl may be essential before monotonically increasing absorbance vs. time functions occur for Al reactions with ferron. When ferron is buffered with appropriate quantities of NaOAc and NH₂OH·HCl it must be aged for 5 d at room temperature until reduction has slowed. This solution remains stable for 25 d and exhibits consistent kinetic reactions with Al during this time period. A large portion of ferron interactions with partially neutralized Al of varying basicity and age were described by a binary species first-order rate function, which provided the rates of monomer and small polymer reactions with ferron as well as the mole fraction of monomeric species present (f_a). Modelfitted f_a are based on the differential kinetic reactions of ferron with Al, thus arbitrary separation times for determining mononuclear and polynuclear Al are avoided. Rate parameters established for mononuclear Al solutions using a single species first-order equation compared well with those determined for mononuclear Al from partially neutralized solutions using the binary species model. Ferron reactions at longer times were related to the decomposition of large Al polymers, which were welldescribed by pseudo first-order kinetics.

¹ Contribution from the Dep. of Agronomy, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061. This research was funded in part by U.S. Dep. of Energy under contract number DE-ASO5-83ER60179.

² Former Graduate Research Assistant and Professor, respectively.

Received for publication October 24, 1985.