A typical mixed hydrated oxide cake of iron and manganese (FMC) was used to adsorb and separate tungsten from Mo-rich leach liquor obtained from the ammonia leaching of oxidatively roasted, spent hydro-desulfurization catalysts. The FMC considered in this study is itself a byproduct of the ammoniacal leaching of reduced manganese nodules. To yield a maximum tungsten-to-molybdenum separation factor of 199.6, the following optimum conditions were determined: FMC/W = 2.1, temperature = 50 degrees C, and time = 120 mm. The adsorption kinetics was investigated and correlated with the common isotherm equations of Langmuir and Freundlich; the data fitted well with the Freundlich model and exhibited first-order kinetic behavior. The plot of q(t) vs t(0.5) suggests boundary layer diffusion as the rate-limiting step of the adsorption process. The calculated thermodynamic parameters, Delta G degrees, Delta H degrees, and Delta S degrees, indicate that the adsorption of tungsten onto FMC is a spontaneous, exothermic, and physical sorption process.