The equilibrium, thermodynamics and kinetics of the biosorption of Hg(II) onto moss (Drepanocladus revolvens) biomass from aqueous solution were investigated. Optimum experimental parameters were determined to be pH 5.5, contact time 60 min, biomass concentration 4 gL(-1) of solution, and temperature 20 degrees C. From the Langmuir model the maximum biosorption capacity of the moss biomass was found to be 94.4 mg g(-1). The mean free energy value (10.2 kJ mol(-1)) evaluated by using the Dubinin-Radushkevich (D-R) model indicated that the biosorption of mercury ions onto D. revolvens was taken place by chemical ion-exchange. The kinetic studies indicated that the biosorption process of mercury ions followed well pseudo-second-order model. The calculated thermodynamic parameters (Delta G degrees, Delta S degrees, Delta H degrees) showed the biosorption to be exothermic and spontaneous with decreased randomness at the solid-solution interface. The recovery of the Hg(II) from D. revolvens biomass was found to be 99% using 1 M HCl. It was concluded that the D. revolvens biomass can be used as biosorbent for the treatment of wastewaters containing Hg(II) ions. (C) 2009 Elsevier B.V. All rights reserved.