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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]

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]

In this work, Moringa oleifera seed husk (MOSH) and Moringa oleifera seed pulp (MOSP) were converted via a green route into efficient biosorbents for biosorption of Acid Blue 9 (AB9) synthetic dye from the wastewater. The textural properties, morphologies, and structures of both biosorbents were analyzed using Fourier infrared spectroscopy (FTIR), N 2 adsorption/desorption isotherms, pH of point-zero-charge (pH PZC), and scanning electron microscope (SEM). The characterization results showed that the biosorbents have heterogeneous surfaces with a diversity of functional groups. The experimental data of biosorption kinetics were best described by the nonlinear Avrami fractional. The isothermal empirical data were supported by the nonlinear Liu equation, and the maximum biosorption capacities of MOSH and MOSP at 55 °C for AB9 synthetic dye are 329.5 mg g–1 and 694.2 mg g–1, respectively. The evaluation of thermodynamic parameters showed that the biosorption processes of both biosorbents were spontaneous, endothermic, and occurred by physisorption. The availability, low-cost, high adsorption capacity, and fast adsorption kinetics of MOSH and MOSP make them alternative, promising, and attractive green biosorbents for removal AB9 synthetic dye from aqueous solutions. [Display omitted] • Green preparation of highly efficient biosorbents. • Moringa oleifera seed (husk and pulp) were utilized as biosorbents. • Functional groups have a notable influence on the adsorption process. • MOSH and MOSP present adsorption capacities of 329.5 and 694.2 mg g−1. • Biosorption process are described by Liu isothermal and Avrami kinetic models. [ABSTRACT FROM AUTHOR]

Textile effluents contain a series of dyes and salts, and their decolorization is strongly affected by salinity. In this work, the influence of salinity on methylene blue (MB) adsorption by comminuted raw avocado seeds was investigated. The adsorbent was firstly characterized. The optimal conditions for MB adsorption on the avocado seeds were determined by response surface methodology (RSM). Subsequently, the influence of ten salts in MB adsorption was evaluated using kinetic and equilibrium studies. The optimal conditions for MB adsorption on the avocado seeds were pH = 10 and adsorbent dosage = 1 g L−1. General order model was able to describe the kinetic profile, and its parameters showed that the adsorption rate and capacity were affected by the presence of salts. The equilibrium was adequately represented by the Sips model. The maximum adsorption capacity without the presence of salts was 97.97 mg g−1. The maximum adsorption capacity was found in the presence of sodium carbonate, which was 103.13 mg g−1. The presence of sodium citrate reduced the adsorption capacity to 80.42 mg g−1. Therefore, even in the presence of salts, comminuted raw avocado seeds demonstrated great potential to treat colored effluents containing MB dye. [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]