Isotherm model analysis for the adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) on anaerobically digested sludge

Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) from aqueous solutions on anaerobically digested sludge has been investigated. Experimental data has been fit to Langmuir, Freundlich, and Redlich-Peterson isotherms to obt ain the characteristic parameters of each model. Based on the maximum adsor ption capacity obtained from the Langmuir and the Redlich-Peterson isotherm the affinity of the studied metals for the sludge has been established as Cu (II) > Cd (II) > Zn (II)> Ni (II). Adsorption tests from multi-metal sys tems confirm the affinity order obtained in the individual metal tests. The adsorption capacity for Cu (II) measured in individual tests is not reduce d by the presence of the other above referred metals. Desorption of Zn (II) and Cd (II) previously bound to the sludge in front of Cu (II) and HCl sol utions is also reported. (C) 2000 Academic Press.