Boosted Cr(VI) sorption coupled reduction from aqueous solution using quaternized algal/alginate@PEI beads.

APEI beads (algal/alginate-PEI) were quaternized for enhancing the sorption of Cr(VI) (Q-APEI). The readily reduction of Cr(VI) into Cr(III) in acidic solution and in the presence of organic material constitute an additional phenomenon to be taken into account for the removal of Cr(VI) by Q-APEI. The optimal pH value for both the sorption and reduction of Cr(VI) was close to 2. The sorption isotherm was well described by the Sips model in batch system; the experimental maximum Cr(VI) sorption capacity of Q-APEI was 334 mg Cr(VI) g-1, including a reduction yield close to 25%. The pseudo-second-order kinetic model (PSORE) and the Yan model fit the uptake kinetics and breakthrough curves, in a fixed-bed system with circulation or single-path modes, respectively. The mechanism of reduction-assisted sorption allows boosting the global removal of chromate. Furthermore, the testing of Cr(VI) for three successive sorption and desorption cycles shows the remarkable stability of the sorbent for Cr(VI) removal. The Cr(VI) sorption coupled reduction mechanism and interactions between the sorbent and Cr(VI) were further explained using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).

Investigation of mercury(II) and copper(II) sorption in single and binary systems by alginate/polyethylenimine membranes.

This study investigates Hg(II) and Cu(II) sorption in single and binary systems by alginate/polyethylenimine membranes. Batch experiments are conducted to assess the metal sorption performance. FTIR and SEM-EDX analyses are used to identify metal binding mechanism. The sorption kinetics are better fitted by the pseudo-second-order-equation compared to the pseudo-first-order-equation. Three isotherms are compared for fitting the sorption in mono-component solutions and the Sips model gives the best simulation of experimental data. The competitive-Sips model fits well sorption data in Hg-Cu binary solutions and finds that the Cu uptake is drastically reduced by Hg competition. Copper(II) uptake remains negligible at low pH whereas it increases with pH up to 6 because of material deprotonation. Mercury(II) sorption behaves differently, it slightly changes from pH 1 (qeq: 0.76 mmol g-1) to pH 6 (qeq: 0.84 mmol g-1) due to chloro-anion formation. Therefore, playing with the pH allows separating Hg(II) from Cu(II).

Se(VI) sorption from aqueous solution using alginate/polyethylenimine membranes: Sorption performance and mechanism.

New high percolating alginate membranes are designed without using sophisticated drying methods: negatively charged alginate reacts with positively charged polyethylenimine (PEI), prior to be crosslinked with glutaraldehyde and air-dried. This is sufficient to obtain a highly macroporous structured membrane. Highly percolating properties of these new A-PEI membranes make the material applicable in natural drainage systems. The high density of amine groups in composite membranes explain their high affinity for anions in acidic solutions. FTIR, SEM-EDX and XPS analysis are used to explore the sorption mechanism. Se(VI) is sorbed through electrostatic attraction between positive amine groups and negative selenium anions; in a second step, bound Se(VI) is reduced by amine and hydroxyl groups in acidic conditions. A-PEI membranes are successfully used for recovering Se(VI) anions at pH 2. The maximum sorption capacity is close to 83 mg Se g-1; the sorption isotherm is described by the Sips and Langmuir equations. The membranes are poorly sensitive to flow rate in the range 15-50 mL min-1. The kinetic profiles are fitted by the pseudo-first order rate equation. Solute desorption is operated using NaOH solutions; the sorbent shows a remarkable stability in sorption and desorption properties for a minimum of 4 cycles.

Selenium(VI) and copper(II) adsorption using polyethyleneimine-based resins: Effect of glutaraldehyde crosslinking and storage condition.

This study synthesizes polyethyleneimine-glutaraldehyde (PEI-GA) resins using different amounts of GA to crosslink with a certain amount of PEI and compares these adsorbents for the adsorption of Cu(II) (cations) and Se(VI) (anions). Moreover, the stability of adsorption affinity of PEI-GA resins stored in open or sealed conditions is also studied. Results show that the amount of GA for PEI crosslinking does not affect the adsorption performance for Se(VI), especially when PEI/GA mass ratio is less than 2, while for Cu(II), the increase on GA amount decreases Cu(II) adsorption capacity. This difference is directly correlated to the change in the adsorption mechanism from electrostatic attraction to chelation. The primary and secondary amine groups on PEI can easily react with CO2 in the air to form carbamate, potentially affecting the adsorption performance of PEI. Results also indicate that the adsorption efficiency for Se(VI) is hardly affected by the storage condition, while that for Cu(II) decreases significantly after 20-day storage compared to the freshly prepared ones. In addition, all of the adsorbents can selectively remove Se(VI) from Se(VI)-As(V) system and Cu(II) from Pb(II)-Cu(II) system, indicating that the crosslinking has no significant influence on the selectivity.

New highly-percolating alginate-PEI membranes for efficient recovery of chromium from aqueous solutions.

Highly percolating membranes are prepared by the interaction of polyethylenimine and alginate (with glutaraldehyde crosslinking). SEM illustrates the macroporous structure of the material. The material is characterized by FTIR before and after chromate anions sorption. Batch-simulated continuous sorption experiments revealed that the maximum sorption occurred at pH 2 and the flow rate has limited effect on sorption efficiency. Uptake kinetics and sorption isotherms are well fitted by the pseudo-second-order rate and Sips equations, respectively. Maximum sorption is found close to 314 mg g-1. Competition effects from Ca(II), Cu(II), Cl-, NO3-, and SO42- are investigated to evaluate sorbent selectivity. The membranes are applied to remediate a simulate of Cr(VI) contaminated electroplating wastewater. Successive cycles of sorption and desorption show that the membranes maintain sorption capacity higher than 200 mg Cr g-1 for both Cr(VI) and total chromium for the first two cycles. These new highly percolating membranes have promising performances for Cr(VI) removal.

Regeneration of magnetic biochar derived from eucalyptus leaf residue for lead(II) removal.

Regeneration of Pb-loaded magnetic biochar prepared with eucalypts leaf residue was studied by using EDTA-2Na as a regenerant. The desorption efficiency was found to be 84.1% in 120 min with iron leaching amount of 1.1 mg g(-1). Higher SBET and pore volume were observed in regenerated magnetic biochars and no significant band shifts occurred in FTIR spectra during 6 regeneration cycles. The decrease of Pb(II) adsorption capacity (from 52.4 to 41.5 mg g(-1)) was only found in the first regeneration cycle. Magnetic separation performance of adsorbents was not significantly affected by multiple regeneration cycles.

Combined performance of biochar sorption and magnetic separation processes for treatment of chromium-contained electroplating wastewater.

Magnetic biochar was prepared with eucalyptus leaf residue remained after essential oil being extracted. Batch experiments were conducted to examine the capacity of the magnetic biochar to remove Cr (VI) from electroplating wastewater and to be separated by an external magnetic field. The results show that the initial solution pH plays an important role on both sorption and separation. The removal rates of Cr (VI), total Cr, Cu (II), and Ni (II) were 97.11%, 97.63%, 100% and 100%, respectively. The turbidity of the sorption-treated solution was reduced to 21.8NTU from 4075NTU after 10min magnetic separation. The study also confirms that the magnetic biochar still retains the original magnetic separation performance after the sorption process.