Abstract
In order to investigate applications of manganese nodules as adsorbents, the adsorption of heavy metal ions such as Pb(II), Cd(II), Zn(II), Hg(II), Cr(III), and Cr(VI) was carried out in an acidic aqueous solution and the results obtained were compared with those of some wellknown adsorbents.
The results were as follows:
(1) The initial pH of the solution containing a metal ion should be kept above 3.0 to prevent dissolution of the metals constituting the nodule.
(2) Pb(II), Cd(II), Zn(II), and Hg(II), except for Cr(VI), were well adsorbed on the nodule. By applying the Langmuir isotherm equation to these adsorption data, it was shown that the order of activities of the ions for adsorption was: Pb(II)>Cd(II)>Zn(II)>Hg(II)_??_Cr(VI)_??_0
(3) The adsorption capacity of the nodule was almost the same as that of bone charcoal and of zeolite, and much larger than the capacity of activated carbon and of activated clay. The adsorption of metal ions on the nodule was partly irreversible and the complete recovery of the metal ions was much difficult.
(4) The saturated adsorption capacity of the nodule was related to the amount of the surface excess oxygen on the nodule. It was strongly suggested that the excess oxygen may play an important role in the adsorption of heavy metal ions.
