The Adsorption of Aluminium From Hydroxy‐aluminium Solutions on to Fithian Illite

Summary The adsorption of aluminium from hydroxy‐aluminium perchlorate solutions on to Fithian illite in the presence of 0.06M and 0.5M NaClO 4 is described by Langmuir‐type adsorption isotherms at constant OH/A1 ratio. The binding constant for aluminium, and the amount of aluminium that can be adsorbed, increases with increasing OH/A1 ratio of the solution from which it is adsorbed. The Langmuir‐type adsorption isotherms can be explained on the basis that hydroxy‐aluminium species present in solution are adsorbed in constant relative proportions and that the relative proportions of hydroxy‐aluminium species remain unchanged on dilution of the hydroxy‐aluminium solutions at constant ionic strength. If the ionic strength at which the isotherm is determined is decreased from 0.5M to 0.06M NaClO 4 , the binding constant for adsorption of aluminium is not significantly altered. This can be understood if the adsorption process is not one of exchange but rather the formation of H bonds between the hydrolysed polymer species and the surface. Negative adsorption measurement at low and increasing ionic strength indicates the changes in charge on the adsorbed hydroxy‐aluminium polymers as their concentration in solution is increased.