Role of Tartaric Acid in the Inhibition of the Formation of Al13 Tridecamer Using Sulfate Precipitation

G.S.R. Krishnamurti, M.K. Wang and P.M. Huang
Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8
Present address: CSIRO Land and Water, PMB 2, Glen Osmond, South Australia 5064, Australia.
Present address: Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 10764.

Abstract: Polynuclear Al13 tridecamer species are the major hydrolyzed species of aluminum, but their occurrence in terrestrial environments has not been established. X-ray diffraction (XRD), 27Al nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) analyses show that the presence of tartaric acid (concentration range of 10−5–10−3 M), one of the commonly occurring low-molecular-weight organic acids, inhibits the formation of the Al13 tridecamer species.

In the absence of tartaric acid, the basic aluminum sulfate crystals were of tetrahedral morphology and conformed to isometric symmetry with a = 17.748 Å and space group of P4232. Increasing amounts of tartaric acid [tartaric acid/Al molar ratio (R) ranging from 0.01 to 0.05] modified the crystal morphology from the tetrahedral particles of isometric symmetry (R = 0) to rod-shaped particles of monoclinic symmetry (R = 0.01) to irregularly shaped X-ray noncrystalline microparticles (R = 0.05). Failure to detect the presence of Al13 tridecamer, the dominant hydrolyzed species of aluminum, in terrestrial environments may be partially attributed to the presence of low-molecular-weight organic acids, which inhibit the formation of Al13 tridecamer species.

Key Words: Al-Hydroxy Sulfates • Al13 Tridecamer • Powder XRD Data • SEM • Solid-State NMR • Tartaric Acid

Clays and Clay Minerals; October 1999 v. 47; no. 5; p. 658-663; DOI: 10.1346/CCMN.1999.0470512
© 1999, The Clay Minerals Society
Clay Minerals Society (www.clays.org)