Sir: Recently, Liao et al. 1 published the paper entitled as above. In section 3.5, Adsorption Kinetics of Au(III) on Immobilized Tannins, a pseudo-second-order rate model (eqs 4 and 5) was used to descripe sorption of Au-(III) by collagen-fiber-immobilized tannins. In fact, the second-order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho. 2 To distinguish the kinetic equation based on the adsorption capacity of a solid from

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... he concentration of the solution, Ho's second-order rate expression has been named pseudo-second-order. [2][3][4][5][6][7][8][9] 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. 3 In addition, a modified pseudo-second-order kinetic expression was reported in 1997 4 and has also been presented in the following years. 5-9 The pseudosecond-order rate expression of Ho has been widely applied to the sorption of metal ions, dyes, herbicides, and oil and organic substances from aqueous solutions. 8,9 I suggest that Liao et al. cite Ho's original pseudosecond-order kinetic expression paper or relevant works. Literature Cited (1) Liao, X.; Zhang, M.; Shi, B. Collagen-Fiber-Immobilized Tannins and Their Adsorption of Au(III). Ind. Eng. Chem. Res. 2004, 43, 2222-2227 (2) Ho, Y. S. Adsorption of heavy metals from waste streams by peat. Ph.D. Thesis, The University of Birmingham, Birmingham, U.K., 1995. (3) Ho, Y. S.; Wase, D. A. J.; Forster, C. F. Kinetic studies of competitive heavy metal adsorption by sphagnum moss peat. McKay, G. Pseudo-second-order model for sorption processes. Process Biochem. 1999, 34, 451-465. (7) Ho, Y. S.; McKay, G. The kinetics of sorption of divalent metal ions onto sphagnum moss peat. Water Res. 2000, 34, 735-742. (8) Ho, Y. S. Letter to the Editor "Kinetic modeling and equilibrium studies during cadmium biosorption by dead Sargassum sp. biomass" by C. Bulut, Y.; Tez, Z. "Removal of heavy metal ions by modified sawdust of walnut" by Y.