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A magnetic geopolymer was prepared from the silica and metakaolin under presence of zero–valent iron (ZVI). The magnetic geopolymer was characterized by Fourier–Transform Infrared spectroscopy, X-ray diffraction, N2 adsorption/desorption isotherms, scanning electron microscopy, and vibrating sample magnetometer. The geopolymer was employed as adsorbent of Acid Red 97 dye. The results showed that the magnetic geopolymer have mesoporous structure and sufficient magnetization to be removed by a magnetic field from aqueous solution. Both the pseudo–first and pseudo–second order models satisfactorily described the adsorption kinetics, and the isotherms were properly adjusted by the Henry's model. High adsorptive capacity of dye (1814 mg g−1) was obtained, and the geopolymer can be used for five times with the same initial adsorption capacity. An efficient adsorbent was developed from low cost materials. This adsorbent presented extremely high adsorption capacity and can be easily separated from the treated liquid effluent. [ABSTRACT FROM AUTHOR]

Rare earth elements such as neodymium (Nd) are important elements used mainly in developing new technologies. Although they are found in low concentrations in nature, they can be obtained by extracting solid samples such as phosphogypsum. Among the techniques, adsorption has been used successfully with several adsorbent materials. In this work, two strains of Spirulina platensis (LEB-18 and LEB-52) were employed as biosorbents for efficiently removing the Nd element from the aqueous media. Biosorption tests were carried out in a batch system, and the results of the biosorption kinetics showed that for both materials, the biosorption of Nd was better described by the Avrami model. Moreover, it could be considered that 80 min would be necessary to attain the equilibrium of Nd(III) using both biosorbents. The result of the biosorption isotherms showed that for both strains, the best-fitted model was the Liu model, having a maximum biosorption capacity of 72.5 mg g−1 for LEB-18 and 48.2 mg g−1 for LEB-52 at a temperature of 298 K. Thermodynamics of adsorption showed that for both LEB-18 and LEB-52 the process was favorable (∆G° < 0) and exothermic (∆H° −23.2 for LEB-18 and ∆H° −19.9 for LEB-52). Finally, both strains were suitable to uptake Nd, and the better result of LEB-18 could be attributed to the high amount of P and S groups in this biomass. Based on the results, a mechanism of electrostatic attraction of Nd3+ and phosphate and sulfate groups of both strains of Spirulina platensis was proposed. [ABSTRACT FROM AUTHOR]

The production and consumption of cassava (Manihot esculenta) occur in several places worldwide, producing large volumes of waste, mostly in the form of bark. This study sought to bring a new purpose to this biomass through producing activated carbon to use as an adsorbent to remove the herbicide Diuron from water. It was observed that the carbon contains the functional groups of methyl, carbonyl, and hydroxyl in a strongly amorphous structure. The activated carbon had a surface area of 613.7 m2 g−1, a pore volume of 0.337 cm3 g−1, and a pore diameter of 1.18 nm. The Freundlich model was found to best describe the experimental data. It was observed that an increase in temperature favored adsorption, reaching a maximum experimental capacity of 222 mg g−1 at 328 K. The thermodynamic parameters showed that the adsorption was spontaneous, favorable, and endothermic. The enthalpy of adsorption magnitude was consistent with physical adsorption. Equilibrium was attained within 120 min. The linear driving force (LDF) model provided a strong statistical match to the kinetic curves. Diffusivity (Ds) and the model coefficient (KLDF) both increased with a rise in herbicide concentration. The adsorbent removed up to 68% of pollutants in a simulated effluent containing different herbicides. Activated carbon with zinc chloride (ZnCl2), produced from leftover cassava husks, was shown to be a viable alternative as an adsorbent for the treatment of effluents containing not only the herbicide Diuron but also a mixture of other herbicides. [ABSTRACT FROM AUTHOR]

The powdered biomass of paddle cactus (Tacinga palmadora), a rustic plant of great occurrence in the driest regions of Brazil, was evaluated as a low-cost adsorbent to treat textile effluents containing crystal violet (CV) dye. The powdered paddle cactus (PPC) was mainly composed by lignin and holocellulose, as well as, a variety of functional groups. Best results for CV adsorption were found using an adsorbent dosage of 0.5 g L−1 at solution pH equivalent to 10.0. Fast adsorption kinetics was verified, being the equilibrium reached within 100 min, and the curves were well modeled by the pseudo-first-order model. The isotherms were well-represented by the Langmuir model. The maximum adsorption capacity was 228.74 mg g−1 at 328 K. The estimated thermodynamics parameters were ΔG0T = 328K of –9.08 kJ mol−1, ΔH0 of 12.44 kJ mol−1, and ΔS0 of 0.065 kJ mol−1 K−1. In addition, PPC was able to treat a simulated textile effluent containing organic and inorganic compounds, reaching 93% of color removal efficiency. These findings show that powdered paddle cactus can be applied as potential low-cost adsorbent to treat textile effluents containing CV. [ABSTRACT FROM AUTHOR]

• Quaternary adsorption of Cu2+, Co2+, Ni2+ and Ag+ ions was investigated. • Development of a new quaternary adsorption model. • Adsorption of Cu2+, Co2+ and Ni2+ ions was endothermic, while the Ag+ adsorption was exothermic. • Ag+ adsorption was reduced from single-compound to quaternary system. Quaternary adsorption of Cu2+, Co2+, Ni2+ and Ag+ ions on an adsorbent obtained from the alkaline fusion of wastewater treatment sludge was investigated. Adsorption tests in both single-compound and quaternary systems were carried out and the analysis of adsorption mechanism was done by the application of a new quaternary model. This model was developed from a general methodology based on the application of grand canonical ensemble in statistical physics. This adsorbent was characterized by different analytical techniques. Experimental data showed that the adsorption of Cu2+, Co2+and Ni2+ ions was endothermic, while the Ag+ adsorption was exothermic. Ag+ adsorption was significantly reduced from single-compound to quaternary system due to the competitive effect caused by the other divalent ions, while the adsorption capacities of Cu2+, Co2+ and Ni2+ were not significantly affected in the multicomponent solution. A significant competitive effect of Cu2+, Co2+ and Ni2+ ions on the adsorption of Ag+ ions occurred. Modelling analysis showed that the adsorption of Cu2+, Co2+ and Ni2+ ions was a multi-ionic process at all tested temperatures, while the adsorption of Ag+ was a multi-ionic process only at low temperatures (298 and 308 K). Finally, the statistical physics model confirmed that the adsorption energies corresponded to physical interactions forces and the water molecule adsorption played a relevant role during the removal of these trace metals. [ABSTRACT FROM AUTHOR]

• Two new adsorbents were prepared for dye adsorption from aqueous solution. • Statistical physics modeling was performed to characterize dye adsorption mechanism. • Physical interactions were involved in the endothermic dye adsorption. • Dye adsorption capacities ranged from 281 to 632 mg/g. Activated carbons were prepared from ashitaba waste and a walnut shell to study the adsorption mechanism of congo red and methylene blue dyes in aqueous solution. These adsorbents were characterized via XRD, FTIR and SEM techniques and the dye adsorption isotherms at three temperatures were quantified. A statistical physics model was applied to interpret the adsorption mechanism of tested dyes and adsorbents. Modeling results showed that these dyes were practically separated in the solution leading to an absence of the aggregation process. Adsorption orientations of dye molecules on the adsorbents changed depending on the temperature and nature of systems. The adsorption capacity of ashitaba waste activated carbon for the removal of congo red was significant thus indicating strong interactions between this dye and tested adsorbent. Calculated adsorption energy varied from 7.25 to 20.43 kJ/mol and they showed that the adsorption of both adsorbates occurred via physical interactions at different temperatures where the removal process was endothermic. [ABSTRACT FROM AUTHOR]