RESUMO
The modification of the Tetraselmis sp. algae material (Tetra-Alg) with surfactant Cethyltrimethylammonium Bromide (CTAB) yielded adsorbent Tetra-Alg-CTAB as an adsorbent of methyl orange (MO) and methylene blue (MB) solutions. The characterization of the adsorbent used an infrared (IR) spectrometer to identify functional groups and Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX FEI Inspect-S50, Midland, ON, Canada) to determine the surface morphology and elemental composition. Methyl orange and methylene blue adsorption on the adsorbent Tetra-Alg, Tetraselmis sp. algae-modified Na+ ions (Tetra-Alg-Na), and Tetra-Alg-CTAB were studied, including variations in pH, contact time, concentration, and reuse of adsorbents. The adsorption of MO and MB by Tetra-Alg-CTAB at pH 10, during a contact time of 90 min, and at a concentration of 250 mg L-1 resulted in MO and MB being absorbed in the amounts of 128.369 and 51.013 mg g-1, respectively. The adsorption kinetics and adsorption isotherms of MO and MB and Tetra-Alg, Tetra-Alg-Na, and Tetra-Alg-CTAB tend to follow pseudo-second-order kinetics models and Freundlich adsorption isotherms with each correlation coefficient value (R2) approaching 1. Due to the modification with the cationic surfactant CTAB, anionic dyes can be strongly sorbed in alkaline pH due to strong electrostatic attraction, while MB is more likely to involve cation exchange and hydrogen bonding. The reuse of Tetra-Alg-CTAB was carried out four times with adsorption percent > 70%, and the adsorbent was very effective in the adsorption of anionic dyes such as MO.
RESUMO
The change of composition of an adsorbent material has been widely used as a method to increase its adsorption capacity, particularly concerning adsorbents made of polysaccharides. Introducing magnetic adsorbents into contaminated water treatment systems is a highly promising strategy, as it promotes the metal ions removal from water. Considering this, gum Arabic (GA) was associated with alginate (Alg), when magnetite nanoparticles were present or absent, to produce beads that were utilised to take up Cu(II), Cd(II), and Pb(II) from aqueous solution. After a complete characterisation (for which Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and swelling were used), the adsorption properties were established using batch and column tests. The magnetic beads (MAlg/GA) demonstrated improved adsorption in comparison with the beads made without magnetite (Alg/GA) under the same conditions. In normal adsorption conditions (pH 6.0, 25 °C, 2.5 g L-1 of adsorbent dosage), the highest uptake capacities recorded for the MAlg/GA beads were: for Cu(II), 1.33 mmol g-1; Cd(II), 1.59 mmol g-1; and for Pb(II), 1.43 mmol g-1. The pseudo-second-order kinetics and Langmuir isotherm models provided good fits for the adsorption of these metals. Overall, ion exchange and physical forces led to the uptake of these metals by both Alg/GA and MAlg/GA; moreover, the functional groups on the beads played crucial roles as binding sites. Additionally, it was observed that flow rates of >2 mL min-1 did not produce noticeable changes in uptake levels over the same flow period. It was found that the efficient eluting agent was HNO3 (0.2 M). In some cases, the metals were not removed fully from the used beads during the first five cycles of regeneration and reuse. The results of this investigation show that these beads are efficient adsorbents for the removal of metal ions from spiked well water samples.
