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-Heavy metal removal by adsorption using rice husks as a bioadsorbent was evaluated as an alternative for wastewater treatment. Batch equilibrium experiments and kinetic sorption studies were performed using monocomponent solutions of Ni(II), Cd(II), Zn(II), Pb(II) and Cu(II) in surface samples of in natura (RH) and calcined rice husks (RHA). RHA showed higher potential for removing lead and copper. Experimental data for adsorption isotherms of lead and copper were adjusted by Langmuir, Freundlich and Dubinin-Radushkevick (D-R) models, being better represented by the Langmuir model. The calcination of RH increased its surface area, improving its adsorption properties. From a morphological analysis obtained by SEM and diffraction patterns (XRD), a longitudinal fibrous and amorphous structure was observed for RH. TGA results indicated a total mass loss of around 60% for RH and 24.5% for RHA.

-This study evaluated the kinetic adsorption of Pb and Cu ions using rice husk ash as adsorbent in a fixed bed. The maximum adsorption capacities obtained for lead and copper ions in the fixed bed were 0.0561 and 0.0682 mmol/g (at 20 °C), respectively. The thermodynamic studies indicated that the lead adsorption process was exothermic and spontaneous, while the copper adsorption process was endothermic and spontaneous. Characterization results indicated the presence of several functional groups, amorphous silica and a fibrous and longitudinal structure of rice husks. Rice husk ash (RHA) from northern Brazil can be used as a bioadsorbent for the individual removal of Pb(II) and Cu(II) ions from metal-containing effluents.

Cu (II) removal equilibrium from aqueous solutions using calcined clays "Bofe" and "Verde-lodo" has been studied by batch and fixed-bed in static and dynamic systems, respectively. Analyses were performed for physicochemical characterization of clays using the techniques: X-ray fluorescence (XRF), thermogravimetry (TG), N 2 adsorption (BET) and Cationic Exchange Capacity (CEC). Batch experiments were performed at a constant temperature, adjusting the pH of the solution in contact with clays. Adsorption assays in fixed bed were conducted at the flow rate determined through mass transfer zone (MTZ). Langmuir and Freundlich models were adjusted to equilibrium data. The results of characterization indicated that the temperature of 500 °C is best suited for the calcination of the clays. The maximum adsorption capacity was higher for dynamic system than fixed bed compared to static system, enhancing from 0.0748 to 0.1371 and from 0.0599 to 0.22 mmol.g -1 of clay for "Bofe" and "Verde-lodo", respectively.