Heavy metal cation retention by unconventional sorbents (red muds and fly ashes)

Toxic heavy metals, i.e. copper (II), lead (II) and cadmium (II), can be removed from water by metallurgical solid wastes, i.e. bauxite waste red muds and coal fly ashes acting as sorbents. These heavy-metal-loaded solid wastes may then be solidified by adding cement to a durable concrete mass assuring their safe disposal. Thus, toxic metals in water have been removed by sorption on to inexpensive solid waste materials as a preliminary operation of ultimate fixation. Metal uptake (sorption) and release (desorption) have been investigated by thermostatic batch experiments. The distribution ratios of metals between the solid sorbent and aqueous solution have been found as a function of sorbent type, equilibrium aqueous concentration of metal and temperature. The breakthrough volumes of the heavy metal solutions have been measured by dynamic column experiments so as to determine the saturation capacities of the sorbents. The sorption data have been analysed and fitted to linearized adsorption isotherms. These observations are believed to constitute a database for the treatment of one industrial plantʹs effluent with the solid waste of another, and also to utilize unconventional sorbents, i.e. metallurgical solid wastes, as cost-effective substitutes in place of the classical hydrous-oxide-type sorbents such as alumina, silica and ferric oxides.