Role of tartaric acid in the inhibition of the formation of Al-13 tridecamer using sulfate precipitation

Polynuclear Al-13 tridecamer species are the major hydrolyzed species of al uminum. but their occurrence in terrestrial environments has not been estab lished. X-ray diffraction (XRD), Al-27 nuclear magnetic resonance (NMR), an d scanning electron microscope (SEM) analyses show that the presence of tar taric acid (concentration range of 10(-5)-10(-3) M), one of thr commonly oc curring low-molecular-weight organic acids, inhibits the formation of the A l-13 tridecamer species. In the absence of tartaric acid, the basic aluminum sulfate crystals were o f tetrahedral morphology and conformed to isometric symmetry with a = 17.74 8 Angstrom and space group of p4(2)32. Increasing amounts of tartaric acid [tartaric acid/Al molar ratio (R) ranging from 0.01 to 0.05] modified the c rystal morphology from the tetrahedral particles of isometric symmetry (R = 0) to rod-shaped particles of monoclinic symmetry (R = 0.01) to irregularl y shaped X-ray noncrystalline microparticles (R = 0.05). Failure to detect the presence of Al-13 tridecamer, the dominant hydrolyzed species of alumin um, in terrestrial environments may be partially attributed to the presence of low-molecular-weight organic acids. which inhibit the formation of Al-1 3 tridecamer species.