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Inhibition of Aluminum Oxyhydroxide Precipitation with Citric Acid

Summary: Inhibition of Aluminum Oxyhydroxide Precipitation with
Citric Acid
Daniel M. Dabbs, Usha Ramachandran, Sang Lu, Jun Liu,
Li-Qiong Wang, and Ilhan A. Aksay*,
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544, and
Pacific Northwest National Laboratory, Richland, Washington 99352
Received March 29, 2005. In Final Form: July 29, 2005
Citric acid has been shown to act as an agent for increasing the solubility of aluminum oxyhydroxides
in aqueous solutions of high (>2.47 mol/mol) hydroxide-to-aluminum ratios. Conversely, citric acid also
colloidally stabilizes particles in aqueous suspensions of aluminum-containing particles. Solutions of
aluminum chloride, with and without citric acid added, were titrated with NaOH(aq). The presence and
size of particles were determined using quasi-elastic light scattering. In solutions that contained no citric
acid, particles formed instantaneously when NaOH(aq) was added but these were observed to rapidly
diminish in size, disappearing at OH/Al ratios below 2.5 mol/mol. When the OH/Al ratio was raised beyond
13 aluminum atoms were detected by 27Al solution NMR in citric-acid-free solutions with OH/Al ratios
slightly lower than 2.5. In comparison, adding citric acid to solutions of aluminum chloride inhibited the
formation of large aluminum-containing polycations. The absence of the polycations prevents or retards
the subsequent formation of particles, indicating that the polycations, when present, act as seeds to the
formation of new particles. Particles did not form in solutions with a citric acid/aluminum ratio of 0.8 until


Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University


Collections: Materials Science