Sorption of Ni(II)-citrate complex from electroless nickel plating solutions onto chitosan

Spent electroless nickel plating solutions contain Ni(II)-citrate complexes which are hazardous to the environment. These, complexes can be removed by using chitosan as a sorbent. Kinetic investigations indicate that Ni(II) sorption front complex solutions onto chitosan can be described by a pseudo-second order rate model. The experimental data of the adsorption under equilibrium conditions for both Ni(II) and citrate correlate well with the Freundlich isotherm equation. During the sorption of Ni(II)-citrate complex on chitosan competition between Ni(H) and citrate ions takes place. The citrate sorption prevails. Adipate, the additive used in electroless nickel plating solutions, is not sorbed by chitosan, but its presence in solutions has an increasing effect on citrate sorption from citrate solutions without Ni(II) and the increasing effect on Ni(II) sorption from Ni(II)-citrate complex solutions. The other components of electroless nickel plating solution, i.e. hypophosphite, sulphate, phosphite have no influence on sorption.