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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]