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The process of hydrolysis-precipitation of aluminum from aqueous aluminum chloride solution at 25 °C and for a concentration of 10"1 M has been studied by using solutions with a neutralization ratio r = (NaOH) / (A1T) equal to 2 and 2.5, by small-angle X-ray scattering using a synchrotron source. In the former case, the aluminum ion is embodied principally in a polymer with the formula AluO^OH)^3* with an experimental radius of gyration of 9.8 Á, which corresponds to an ionic radius of 12.6 Á. In the second case, the aluminum is embodied partly in the species described above and partly in a colloidal species of chemical composition similar to that of the trihydroxide. The particle morphology of the colloidal species changes as a function of time. After aging for 1.5 h, the particles are cylindrical with a radius of about 15 Á and a length of 310 Á. After 24-h aging, the cylinders have agglomerated into more homogeneous platelets of diameter 500 Á and thickness 60 Á.

Hydroxy‐Al solutions were prepared and characterized with sulfate precipitation, resin treatment, and rate of Al‐ferron color development. The results suggest that the soluble Al species can be grouped into at least four categories: (i) high OH‐Al polymers — these have a residual positive charge of 0.33 or less per Al atom and are rapidly precipitable by Na2SO4, giving rise to the formation of noncrystalline basic aluminum sulfate; (ii) medium OH‐Al polymers — these form crystalline basic aluminum sulfate of composition Al(OH)2.50(SO4)0.22 · xH2O slowly and enter resin slowly; (iii) low OH‐Al polymers — these are not precipitable with Na2SO4, and they enter resin rapidly; and (iv) monomeric ions — these enter resin rapidly and react with ferron rapidly.

The advantages of organic polymers, or polyelectrolytes, in water treatment are many. But what is the fate of a polymer subjected to typical treatment processes? What by‐products are formed by ozonation and chlorination? Are there manufacturing impurities accompanying the polymers? What are the toxic and mutagenic effects of these impurities and by‐products? An anionic organic polymer commonly used in France was analyzed by several methods. It was found to be generally acceptable for drinking water standards in the United States and France. But the by‐products and impurities that were detected require more research to determine their potential health effects and demonstrate the need for adequate quality controls during manufacture of the polymer.