NC State


Alum has been used in pa papermaking for about 200 years. Despite the enormous amount of theoretical work done, the chemistry of alum in the papermaking process is still not adequately understood. To explain the chemistry of aluminium salts, three basic approaches have been taken by the various investigators. One is the use of classical analytical techniques to identify the ionic species formed by hydrolysis of Al-salts. Another approach uses coagulation of extremely small anionic colloids, such as silver halides. The third approach is surface-chemical, whereby the structure of the complex aluminium ions is deduced from the interaction patterns with mono-molecular rosin films. Conclusions drawn from the hydrolysis studies dominate the explanations of alum chemistry in the papermaking process. Many authors have used the Hayden-Rubin distributions (1) as a basis for deducing that the octamer structures of type Al₈⁺⁴ (OH)₂₀ or Al₈⁺⁴ (OH)₁₀ (SO₄)₅ are the active species in the papermaking process (2,3).

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