The bentonitic clays show good adsorptive characteristics, being used as alternative material for removing metals. This study evaluates several treatments (calcination, acid activation and treatment with sodium) of bentonite type Bofe in the removal of nickel and copper. Analyses were performed for physicochemical characterization of clay using the techniques: X-ray fluorescence (XRF), thermal analysis (TG and DTA), X-ray Diffraction (XRD), the ethylene glycol monoethyl ether (EGME) method, N2 adsorption (BET) and Scanning Electron Microscopy (SEM). Among the changes induced by acid activation and sodium transformations, the treatment with sodium chloride in fixed bed showed the highest performance in the monocomponent removal of nickel and copper.

This study aims to characterize the complex metal-clay formed by adsorption of lead. In this work, the bentonite clay named Fluidgel was calcined at 750 ºC and was used as adsorbent for lead removal. The characterization of this clay and complex metal-clay was carried out by X-ray diffraction (XRD), Fourier transformer infrared spectroscopy (FTIR), surface area (BET method), scanning electron microscopy (SEM) and chemical composition by energy dispersive X-ray (EDX). The removal of lead from aqueous solution was carried out in a fixed bed. Dynamic experiments were performed to evaluate the effect of flowrate on adsorption efficiency. The experiments were accomplished at room temperature, the clay adsorbent particle diameter was of 0.855 mm and the flow rate varied from 0.6 to 2 mL/min. The feed concentration of lead was about 0.24 mmol/L. Comparing the chemical compositions of the clays obtained by EDX before and after removal of the lead, it was concluded that the ion exchange process might be important to lead removal. From the semi-quantitative analysis of chemical composition in clays with and without adsorbed lead it was observed a reduction of the amount of Ca2+, K+ cations and the disappearance of Na+ cations, which was caused by cation exchange process.

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 ºC), 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.

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 resultsindicated a total mass loss of around 60% for RH and 24.5% for RHA.