Abstract The performance of Salvinia natans macrophyte to recover lead and chromium from single and bicomponent solutions in batch and fixed bed systems was investigated. Equilibrium data were obtained through isotherms and fitted to Langmuir, Freundlich and D-R models for a single component system. In the fixed bed study the breakthrough curves were carried out at three different ratios of concentrations for the bicomponent study and at the concentration of 1 mmol.L-1 for the single system. In order to know the biosorption mechanism, FT-IR analyses were performed for S. natans before and after the uptake of metal ions. The results showed different functional groups in the biomass and the ability of these groups to bind Cr+3 and Pb2+. Studies of the binary system of Cr3+/Pb2+ are not common in the literature, which makes the experimental data obtained in this work very important for providing information that could be used in adsorption processes.

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.

Batch experiments were carried out for biosorption of Remazol Brilliant Blue R dye onto the macrophyte Salvinia natans. Effects of parameters such as initial dye concentration, pH, biosorbent dosage, contact time and temperature were investigated. Chemical and morphological characteristics of the biosorbent were evaluated before and after the biosorption process using methods such as Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TA), Differential Scanning Calorimetry (DSC) and Infrared Spectroscopy (FT-IR). Sorption kinetics were conducted and followed a pseudo-second order kinetic model. Equilibrium data were well represented by the Langmuir model. Salvinia natans exhibited a maximum uptake of 61.9 mg.g-1. The Dubinin-Radushkevich model indicated that the adsorption takes place by a physical process. Thermodynamic parameters were estimated. The negative values of the Gibbs energy indicated the spontaneous nature of the adsorption. The entropy was positive and the positive value of the enthalpy showed that the process is endothermic.

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.

The objective of this work is to analyze and compare the natural and forced convective drying of handmade recycled paper. Drying of recycled cellulose pulp was carried out under laboratory environment conditions and in a convective dryer with forced air circulation and controlled conditions of air temperature and velocity. The tests were conducted following a two-factor central composed factorial design of experiments, with six runs at the central point. The drying results were analyzed and fitted to mathematical models of Fick, Henderson and Pabis (Fick’s modified equation), Page and He (considering the nonlinear Fick effect). The model of Page represented best the experimental data and the one of Henderson and Pabis resulted in an adequate fit for the paper drying kinetics. Sorption isotherms were determined for the dried paper and the models of GAB (Guggenheim-Anderson-de Boer) and GDW (Generalised D’Arcy and Watt) resulted in excellent fits of the experimental data. The water sorption mechanism was suggested by the analysis of the calculated parameters of the GDW model.