Comment on 'Removal of Ni~(2+) and Cu~(2+) Ions from Aqueous Solutions on to Lignite-based Carbons', by S.E. Samra

摘要

Recently, Samra (2000) published the paper entitled as above. In the section on kinetic measurements, Samra mentioned that "Coleman et al. (1956) assumed that the adsorption of a divalent metal ion on carbon proceeds via a pseudo-second order mechanism in which adsorption is the rate-limiting step". In fact, Coleman et al. (1956) reported the formation constants for Cu~(II)-peat complexes. The peat-Cu~(II) reaction may be written in two ways, in which P refers to the concentration of peat functional groups: 2P~- + Cu~(2+) <-> CuP_2 K_c = [CuP_2]/[Cu~(2+)[P~-]~2] 2HP + Cu~(2+) <-> CuP_2 + 2H~+ B = [CuP_2][H~+]~2/[Cu~(2+)[HP]~2] where K_c is a constant for a reaction between a metal ion and charges on a colloidal particle, B is the product of K_c and the ionization constant K_a, and should be independent of the ionic strength.