Comment on 'Biosorption of Cadmium Using the Fungus Aspergillus niger.' by Barros, L.M., Macedo, G.R., Duarte, M.M.L., Silva, E.P. and Lobato, A.K.C.L.

In a recent publication Macedo et al. (2003), the section Results and Discussions, authors mentioned a pseudo-second-order Lagergren equation in Eq. (3). In fact, it is Ho (1995) who first developed a pseudo-second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat. The earlier application of the pseudo-second order equation to the kinetic studies of competitive heavy metal adsorption by sphagnum moss peat was undertaken by Ho et al. (1996). The pseudo-second order rate expression of Ho has also been applied to the sorption of metal ions, dyes, and organic substances from aqueous solutions (Table 1). In addition, discussion of the reaction order has been reported such as the comparison of chemisorption kinetic models (Ho and McKay, 1998a) and pseudo-second order model (Ho and McKay, 1999a). Furthermore, Ho’s kinetic expression has also been applied to a multi-stage batch sorption design (Ho and McKay, 1999b) and a two-stage batch sorption optimized design (Ho and McKay, 1998b). Numerous applications of Ho’s kinetic expression have been reported in recent years. A list of pseudo-second order systems is given in Table 1. I suggest that Macedo et al. cite Ho’s original pseudo-second order kinetic expression paper.