Point of zero charge of amorphous aluminum hydroxide as a function of adsorbed carbonate.

The point of zero charge of 36 carbonate-containing aluminum hydroxide gels decreased with increased carbonate-to-aluminum molar ratio. Theoretical analysis supported this observation and showed that the point of zero charge was sensitive to low fractional coverage of surface sites by carbonate and that divalent carbonate is the predominant form of carbonate on the surface. The implications of the pH-point of zero charge relationship of aluminum hydroxide on the viscosity, adsorptive properties, rate of filtration, and removal of sodium are discussed.