Pseudo-second Order Rate Equation Research Articles

Synthesis and adsorption characteristics of grafted hydrazinyl amine magnetite-chitosan for Ni(II) and Pb(II) recovery

The sorption properties of a functionalized magnetic chitosan sorbent have been investigated for the recovery of Ni(II) and Pb(II) from aqueous solutions. This material was prepared by one-pot co-precipitation of chitosan with formation of magnetic core, followed by a series of grafting steps to immobilize hydrazinyl amine derivative at the surface of chitosan layer. The physico-chemical characteristics of this composite material were investigated using FTIR, XRD, XPS, thermogravimetric, titration, elemental analyses. In a second step, the sorbent was tested for heavy metal sorption on synthetic solutions through the study of pH effect, sorption isotherms and uptake kinetics, selective sorption (in function of pH), metal desorption and sorbent recycling. Sorption isotherms were modeled using the Sips equation while the uptake kinetics was fitted by the pseudo-second order rate equation. The sorption capacity reached 4.3 mmol Ni g−1 and 2.5 mmol Pb g−1 but the sorbent was more selective to Pb(II) over Ni(II), especially in acidic conditions. The decrease in sorption capacity at the fifth cycle does not exceed 8%. In the final step of the study, the sorbents were successfully applied for metal recovery from multi-metal synthetic solution and from a contaminated stormwater collected in a local mining area.

Hydrogels with diffusion-facilitated porous network for improved adsorption performance

Porous alginate-based hydrogel beads (porous ABH) have been prepared through a facile and sustainable template-assisted method using nano-calcium carbonate and nano-CaCO3 as pore-directing agent for the efficient capture of methylene blue (MB). The materials were characterized by various techniques. The sorption capacities of ABH towards MB were compared with pure sodium alginate (ABH-1:0) in batch and fixed-bed column adsorption studies. The obtained adsorbent (ABH-1:3) has a higher BET surface area and a smaller average pore diameter. The maximum adsorption capacity of ABH-1:3 obtained from Langmuir model was as high as 1,426.0mg g-1. The kinetics strictly followed pseudo-second order rate equation and the adsorption reaction was effectively facilitated, approximately 50minutes to achieve adsorption equilibrium, which was significantly shorter than that of ABH-1:0. The thermodynamic parameters revealed that the adsorption was spontaneous and exothermic. Thomas model fitted well with the breakthrough curves and could describe the dynamic behavior of the column. More significantly, the uptake capacity of ABH-1:3 was still higher than 75% of the maximum adsorption capacity even after ten cycles, indicating that this novel adsorbent can be a promising adsorptive material for removal of MB from aqueous solution under batch and continuous systems.

Kinetics of europium sorption to four different aluminum (hydr)oxides: Corundum, γ-alumina, bayerite, and gibbsite

Kinetic studies can improve our understanding of the environmental mobility of radionuclides by providing insight into sorption mechanisms occurring at the mineral-water interface. While nearly identical equilibrium europium sorption edges are obtained for gibbsite (γ-Al(OH)3), bayerite (α-Al(OH)3), corundum (α-Al2O3), and γ-Al2O3, differences in surface acidity and crystal structure result in distinct reaction rates. Batch kinetic experiments were performed to investigate europium sorption to four aluminum (hydr)oxide minerals as a function of time (10–120 min), mineral concentration (0.5–50 m2 L−1), pH (5–7), and europium concentration (10−8–10−6 M). Linear and non-linear pseudo-first and pseudo-second order rate equations were used to fit the data. The overall reaction rates and reaction orders with respect to proton concentration, mineral concentration, and europium concentration were determined, leading to a governing rate law for each mineral system. Europium sorption is characterized by a two-step reaction with a fast initial sorption step followed by a slower sorption or aging process. The pseudo-second order equations resulted in better model fits of the data. Using the non-linear pseudo-second order rate constants, it was observed that the reaction orders for each mineral system were similar but resulted in different overall reaction rates following the trend bayerite ∼ γ-Al2O3 > corundum > gibbsite. However, the calculated reaction orders are similar to those previously reported for plutonium(IV/V) interactions with iron (oxyhydr)oxide minerals, suggesting that these binary systems share similar elementary reactions.

Synthesis of α-aminophosphonate functionalized chitosan sorbents: Effect of methyl vs phenyl group on uranium sorption

A one-pot synthesis procedure was used for preparing two derivatives of chitosan bearing α-aminophosphonate moieties. Chitosan functionalization was performed by reacting chitosan with glutaraldehyde and triphenylphosphite or trimethylphosphite under selected experimental conditions. The materials (CS-Ph and CS-Me, respectively) were characterized using different analytical procedures for confirming their suggested structures: scanning electron microscopy (coupled to energy dispersive X-ray analysis), Fourier-transform infra-red spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy analyses, thermogravimetric analysis and elemental analysis. The sorption properties of these materials were compared for U(VI) recovery through the study of pH effect, sorption isotherms, thermodynamics, uptake kinetics and sorbent recycling (metal desorption and sorbent re-use). The sorption isotherms were modeled using the Langmuir and the Sips equations while the kinetic profiles were preferentially fitted by the pseudo-second order rate equation. The comparison of sorption properties shows that the methyl α-aminophosphonate derivative is much more effective in uranium recovery than the phenyl derivative: maximum sorption capacities reached at pH 5 around 245 mg U g−1 and 114 mg U g−1, respectively. Tentative explanations are suggested associated to the acid-base properties, the steric hindrance and the donor/acceptor behavior of reactive groups. Experimental data show that uranyl sorption process proceeds via an exothermic and spontaneous reaction for the two sorbents. Metal desorption was successfully tested using sodium bicarbonate solutions and the sorbent was recycled four times: the sorption and desorption efficiencies progressively decreased but remained relatively high at the fourth cycle (sorption: 88–90% of initial sorption and desorption decreasing by 5% between the first and the fourth cycles). Finally, the sorbents were efficiently tested on acidic ore leachate.

Synthesis of Chitosan@activated Carbon Beads with Abundant Amino Groups for Capture of Cu(II) and Cd(II) from Aqueous Solutions

In this study, chitosan and bio-based activated carbon obtained from sugarcane bagasse biowaste were used for the synthesis of efficient sorbent for Cu(II) and Cd(II) ion via precipitation method. The prepared material was enriched with amino groups through grafting tetraethylenepentamine and tested for heavy metal remediation from water samples. The influence of pH was investigated showing optimum sorption at pH 6 for Cu(II) and Cd(II). Sorption tests, explained by means of the most common sorption models, evidenced that the best performances were reached pointing out the promising application of the prepared sorbent for water purification treatments: Uptake kinetics are relatively fast: the equilibrium was reached within 140 min; and the kinetic profiles were preferentially fitted by the pseudo-second order rate equation. Sorption isotherms are fitted by Langmuir equation. The sorbent showed high metal ion sorption capacity with negligible influence of ion strength. The maximum sorption capacities reached 3.44 and 2.38 mmol g− 1 for Cu(II) and Cd(II), respectively at 298 K. Thermodynamic parameters were evaluated through variation of temperature. The sorption is unfavorable at elevated temperatures. Metal ions were successfully desorbed using 1 M HNO3 solution.

Uranium and europium sorption on amidoxime-functionalized magnetic chitosan micro-particles

Magnetic chitosan particles were successfully modified by amidoxime-grafting (as evidenced by FTIR analysis, SEM-EDX analysis, elemental analysis, X-ray diffraction (XRD), thermogravimetric analysis and titration). The effect of pH was investigated showing optimum sorption at pH 4 for U(VI) and pH 5 for Eu(III). Uptake kinetics are relatively fast: the equilibrium was reached within 60–90 min; and the kinetic profiles were preferentially fitted by the pseudo-second order rate equation. Sorption isotherms are equally fitted by the Langmuir and the Sips equations; under optimal conditions maximum sorption capacity reaches 1.5 mmol U g−1 and 2.47 mmol Eu g−1. In bi-component solution, at pH close to 4.9, uranyl is enriched on the sorbent (higher selectivity coefficient) while maintaining high sorption capacities. The selectivity for Eu(III) sorption is higher at pH 2.3 but at the expense of a decrease in sorption capacities. Metal ions can be readily and fast desorbed using 0.5 M HCl solutions: 30–90 min are sufficient for achieving the complete desorption of U(VI) and about 95% of Eu(III) desorption. Sorption and desorption performances are maintained almost constant over 5 cycles of sorption/desorption: the sorbent can be efficiently recycled. Uranium was successfully recovered from alkaline leachate of a sedimentary dolostone ore material.

Preparation and Utilization of the Precursor Activated Carbon from Carbon Enriched Fuel Oil Fly Ash: Part II Removal and Speciation of Chromium(III and VI) from Wastewater

Activated carbon (AC) prepared from residual fly (FA) was activated by combined CO2-steam gasification and physically modified with procaine hydrochloride (PQ+Cl-). Modified AC was used as low cost and effective solid phase extractor (SPE) for removal, total determination and chemical speciation of chromium(III&VI) in wastewater. Pseudo-second order rate equation is proposed for assigning the kinetics of chromium(VI) sorption in aqueous HCl (1.0 mol L-1) by PQ+Cl-- modified AC . The data were correlated with surface structure of the SPE. A dual separation mechanism of chromium(VI) as a binary complex ion associate [PQ+.CrO3Cl-] in/on the modified AC via "weak base anion exchanger" and an added component of “surface adsorption” is proposed. At 2 mL min-1 flow rate Sorption of spiked chromium(VI) at known concentrations (0.5-20 mg mL-1) from water onto modified AC packed columns at 2 mL min-1 was achieved. The sorbed chromium(VI) species were successfully recovered (106.0±2- 110 ±3%, n=3) from AC packed column with NaOH (10 mL, 1.0 mol L-1). Chromium(III) after oxidation to chromium(VI) was also enriched and eluted from the AC packed column and analyzed. Modified PQ+Cl- AC packed column was also used for total determination and speciation of chromium(III & VI) species at trace levels in environmental water samples. Good apparent recovery percentage (94.6±6.3-102.0± 8.5 %) of chromium species was achieved confirming the analytical utility of the modified AC-packed column for removal, total determination and speciation of chromium(III & VI) species in environmental water samples.

Synthesis of Cu-BTC/Mt composites porous materials and their performance in adsorptive desulfurization process

This paper highlights the synthesis of Cu-BTC supported on Montmorillonite (Mt) to form Cu-BTC/Mt composite materials and examines their important role in adsorptive desulfurization process of fuel liquids. Cu-BTC/Mt composites were synthesized by solvothermal synthesis using varying Cu-BTC content (30%, 40% and 50%) and a well-known and constant amount of montmorillonite was used as support. The synthesized composites were then characterized using XRD, FT-IR, TEM and BET techniques. The adsorptive desulfurization performance of the as-prepared composite materials was investigated and their ability to remove thiophene from thiophene/n-octane model oil was studied under mild operating conditions namely: temperature near room temperature, atmospheric pressure and at different model oil/adsorbent mass ratio. Investigation results have shown that the 40%Cu-BTC/Mt composite sample has the best desulfurization performance for thiophene removal. After 6 h of desulfurization, under the reaction conditions of temperature of 30 °C and at a model oil/adsorbent mass ratio of 100:1, the percentage of sulfur removal was 76% while the adsorption desulfurization capacity reached 28.95 mgS/gMOF. The 40%Cu-BTC/Mt composite sample could be reused for at least five consecutive rounds. The adsorption kinetics fit well both the pseudo-first order rate equation and pseudo-second order rate equation models.

Adsorption of methyl red on activated carbon derived from custard apple (Annona squamosa) fruit shell: Equilibrium isotherm and kinetic studies

Activated carbon prepared from custard apple (Annona squamosa) shell by K2CO3 (ACCO3) and H3PO4 (ACPO4) activation were used to study the removal of methyl red (MR) from aqueous medium. The BET surface area, pore volume and pore size of the ACCO3 was 431.3m2/g, 0.054cm3/g and 21.63Ǻ and that of ACPO4 was 1065.0, 0.269cm3/g and 31.91Ǻ, suggesting mesoporous nature of the activated carbons. The FT-IR spectra established the occurrence of –COOH and –OH functional groups. SEM images suggested porous and heterogeneous surface. The contact time, adsorbent dose, initial concentration of MR, initial solution pH and temperature were optimized by batch method. The isotherm modeling of the adsorption data over the concentration range (80–130mg/L) at 303, 313 and 323K was performed using non-linear regression analysis. The data best described by Langmuir isotherm over the entire concentration range. The negative ΔG° and positive ΔH° values indicated spontaneous and endothermic adsorption process. The kinetic modeling revealed that the experimental data followed the pseudo-first order and pseudo-second order rate equations for ACPO4 and ACCO3, respectively.

Algal Foams Applied in Fixed-Bed Process for Lead(II) Removal Using Recirculation or One-Pass Modes.

The incorporation of brown algae into biopolymer beads or foams for metal sorption has been previously reported. However, the direct use of these biomasses for preparing foams is a new approach. In this study, two kinds of porous foams were prepared by ionotropic gelation using algal biomass (AB, Laminaria digitata) or alginate (as the reference) and applied for Pb(II) sorption. These foams (manufactured as macroporous discs) were packed in filtration holders (simulating fixed-bed column) and the system was operated in either a recirculation or a one-pass mode. Sorption isotherms, uptake kinetics and sorbent reuse were studied in the recirculation mode (analogous to batch system). In the one-pass mode (continuous fixed-bed system), the influence of parameters such as flow rate, feed metal concentration and bed height were investigated on both sorption and desorption. In addition, the effect of Cu(II) on Pb(II) recovery from binary solutions was also studied in terms of both sorption and desorption. Sorption isotherms are well fitted by the Langmuir equation while the pseudo-second order rate equation described well both sorption and desorption kinetic profiles. The study of material regeneration confirms that the reuse of the foams was feasible with a small mass loss, even after 9 cycles. In the one-pass mode, for alginate foams, a slower flow rate led to a smaller saturation volume, while the effect of flow rate was less marked for AB foams. Competitive study suggests that the foams have a preference for Pb(II) over Cu(II) but cannot selectively remove Pb(II) from the binary solution.

Studies on the uptake of Am(III) and Eu(III) on ionic liquid modified polystyrene-divinyl benzene

Abstract Imidazolium bis(2-ethylhexyl)phosphate ionic liquid was anchored on a polystyrene-divinylbenzene (PS-DVB) copolymer and the product (R-Im-DEHP) was studied for the extraction of Am(III) and Eu(III) from dilute nitric acid medium to examine the feasibility using the anchored adsorbent for their mutual separation. The effect of various parameters such as the duration of equilibration, concentration of nitric acid, europium ion, and diethylenetriaminepentaacetic acid (DTPA) in aqueous phase on the distribution coefficient (K d) of Am(III) and Eu(III) was studied. The distribution coefficient of Am(III) and Eu(III) decreased with increase in the concentration of nitric acid. Rapid extraction of metal ions in the initial stages of equilibration followed by the establishment of equilibrium occurred within 4 h. The data on the rate of uptake of Am(III) and Eu(III) were fitted into pseudo-first order and pseudo-second order rate equation. The extraction isotherm was fitted to Langmuir and Freundlich adsorption models and the apparent europium extraction capacity was determined. The mechanism of extraction was elucidated and the conditions needed for efficient separation of Am(III) from Eu(III) was optimized using DTPA. The study indicated the possibility of using R-Im-DEHP for the separation of Eu(III) from Am(III) with high separation factors.

Preliminary study on zinc ion removal from synthetic aqueous solutions using hard almond peel as a low-cost sorbent material

In the present work, a preliminary study on the potential of hard almond peels for the removal of zinc ions from aqueous synthetic solutions has been investigated. Kinetic data and equilibrium sorption isotherm were measured in batch conditions. For an initial metal concentration of 100 mg/L tested here, the quantity of zinc sorbed was contact time dependent: it increased with an increase of this parameter. The necessary time to reach the sorption equilibrium was about 6 h and an increase of removal time to 24 h did not show notable effects. At equilibrium, about 24 % of initial zinc solution was removed by hard almond peels (q e = 23.86 mg/g) under these experimental conditions. Two simplified kinetic models including a first-order rate equation and a pseudo second-order rate equation were selected to describe the metal sorption kinetics. The process followed a pseudo second – order rate kinetics. Langmuir and Freundlich models were used to describe sorption equilibrium data at natural pH of solution. Results indicated that the Langmuir model gave a better fit to the experimental data than the Freundlich model. Maximum zinc uptake obtained was q m = 56 mg/g under the investigated experimental conditions.

A novel algal-based sorbent for heavy metal removal

Two sorbents have been synthesized for the efficient removal of heavy metals (e.g., Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II)) from aqueous solutions. Originally, the Alginate/PEI (A-PEI) sorbent containing calcium alginate (as an encapsulating matrix) and polyethylenimine derivatives was manufactured by using internal ionotropic gelation and tested in batch and continuous system. The introduction of Fucus vesiculosus alga improved this material by partially replacing the industrial alginate contained in the biosorbent; it provided a practical one-pot process for faster fabrication, and allowed the manufacturing of a novel environmentally-friendly material (Alginate/Fucus vesiculosus/PEI; AF-PEI). The sorbents have been compared in batch system and characterized using ESEM−EDX and FTIR analyses. The uptake kinetics data were modeled using pseudo-second order rate equation and the sorption isotherms were fitted using the Langmuir, Freundlich and Sips equations. Experimental data were better described with the Sips model and the sorption capacities followed the order: Pb(II)≈Cu(II)>Cd(II)≈Ni(II)>Zn(II) for A-PEI and Cu(II)>Pb(II)>Zn(II)≈Ni(II)>Cd(II) for AF-PEI. Among the synthesized beads, AF-PEI material had the highest sorption capacities for heavy metal removal (1.44mmolg−1 for Cu(II); 1.09mmolg−1 for Pb(II); 1.03mmolg−1 for Ni(II); 1.07mmolg−1 for Zn(II); 0.87mmolg−1 for Cd(II) at pH 4). The recycling of the sorbents was tested with 0.1MHCl/0.05M CaCl2 solution; the materials had a higher selectivity for Pb(II) and Cu(II), maintaining the removal efficiency over 70% and 40% for these species in five successive sorption-desorption cycles.

Functionalization of polyacrylonitrile/Na-Y-zeolite composite with amidoxime groups for the sorption of Cu(II), Cd(II) and Pb(II) metal ions

A composite material (PAN-Na-Y-zeolite) was prepared by polymerization of acrylonitrile in the presence of Na-Y zeolite. The composite was functionalized by amidoximation through the reaction of hydroxylamine on nitrile groups of the composite. The sorbent (APNa-Y-zeolite) was fully characterized by FTIR spectrometry, XRD diffraction, thermogravimetric analysis, scanning electron microscopy, zetametry and BET analysis. The sorption properties of APNa-Y-zeolite were investigated for the recovery of Cu(II), Cd(II) and Pb(II) from synthetic solutions before being tested for the purification of local tap water. Sorption properties were characterized through the study of pH effect, uptake kinetics, sorption isotherms. The pseudo-second order rate equation fitted well kinetic profiles. Sorption isotherms were modeled using the Langmuir, the Freundlich and the Sips equations. Thermodynamic parameters were evaluated through variation of temperature. While the sorption of Cu(II) and Cd(II) was endothermic, Pb(II) recovery was exothermic. Metal ions were successfully desorbed using 5MHCl solutions. High concentrations of NaCl hardly alter sorption performance, contrary to humic acid that slightly reduces metal binding.

Efficient Retention of Chromate from Industrial Wastewater onto a Green Magnetic Polymer Based on Shrimp Peels

Magnetic chitosan grafted with Schiff’s base polymer (M-Schiff’s-Chit) was prepared as a green sorbent starting from shrimp peels for the effective removal of hexavalent chromium. Chitosan extraction involved three main stages as preconditioning, demineralization deproteinization and deacetylation. The grafting process is confirmed by elemental analysis, Fourier transform infrared spectroscopy. Adsorption experiments were carried out in batch sorption mode to investigate the effect of pH, contact time, sorbent dose, concentration of Cr(VI) and evaluating the thermodynamics. Sorption kinetics are effectively modeled using the pseudo-second order rate equation while Langmuir equation successfully fits sorption isotherms. The sorption is endothermic, spontaneous and entropic. Chromate desorption can be successfully performed with 2 M of NaCl in 0.5 M NaOH and the sorbent can be recycled for at least three sorption/desorption cycles without significant loss in sorption/desorption performances. Furthermore, the environmentally friendly and low-cost M-Schiff’s-Chit could be applied as an effective sorbent to remediate Cr(VI) contamination from tannery effluent.

Lead and Chromium Adsorption from Water using L-Cysteine Functionalized Magnetite (Fe3O4) Nanoparticles

L-Cysteine functionalized magnetite nanoparticles (L-Cyst-Fe3O4 NPs) were synthesized by chemical co-precipitation using Fe2+ and Fe3+ as iron precursors, sodium hydroxide as a base and L-Cysteine as functionalized agent. The structural and morphological studies were carried out using X-ray powder diffraction, transmission electron microscopy, dynamic light scattering, scanning electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis spectrophotometric techniques. The zeta potential of bare Fe3O4 and functionalized L-Cyst-Fe3O4 NPs were +28 mV and −30.2 mV (pH 7.0), respectively. The positive surface charge changes to negative imply the presence of L-Cyst monolayer at particle interface. Band gap energy of 2.12 eV [bare Fe3O4NPs] and 1.4 eV [L-Cyst-Fe3O4 NPs] were obtained. Lead and chromium removal were investigated at different initial pHs, contact time, temperatures and adsorbate-adsorbent concentrations. Maximum Cr6+ and Pb2+ removal occurred at pH 2.0 and 6.0, respectively. Sorption dynamics data were best described by pseudo-second order rate equation. Pb2+ and Cr6+ sorption equilibrium data were best fitted to Langmuir equation. Langmuir adsorption capacities of 18.8 mg/g (Pb2+) and 34.5 mg/g (Cr6+) at 45 °C were obtained. Regeneration of exhausted L-Cyst-Fe3O4 NPs and recovery of Pb2+/Cr6+ were demonstrated using 0.01 M HNO3 and NaOH. L-Cyst-Fe3O4 NPs stability and reusability were also demonstrated.

Retention of copper, cadmium and lead from water by Na-Y-Zeolite confined in methyl methacrylate shell

The adsorption of Cu(II), Cd(II) and Pb(II) from aqueous solution onto methyl methacrylate-Na-Y-Zeolite (MMA-Na-Y-Zeolite) composite was analyzed in a batch system with respect to pH, contact time, initial metal ion concentration, adsorbent dosage and temperature. The sorbent was characterized by FT-IR spectrometry, SEM analysis and X-ray diffraction (XRD). Kinetic profiles are successfully modeled with the pseudo-second order rate equation. The Langmuir, the Dubinin–Radushkevich and Temkin equations fit well-adsorption isotherms of Cu(II) and Cd(II), while the distribution of Pb(II) at equilibrium did not fit any of the studied adsorption isotherms. The change of free energy (ΔGo), enthalpy (ΔHo) and entropy (ΔSo) of adsorption were also evaluated. The thermodynamics of the adsorption Cu(II) and Cd(II) indicated endothermic nature, on the other side exothermic adsorption was recorded for Pb(II). The regeneration efficiency of MMA-Na-Y-Zeolite reached 96.6%, 98.18% and 98.4% for Cu(II), Cd(II) and Pb(II), respectively. The results indicate that MMA-Na-Y-Zeolite composite could be employed as low-cost material for the removal of heavy metals from real water samples.

Extractant Immobilization in Alginate Capsules (Matrix- and Mononuclear-Type): Application to Pb(II) Sorption from HCl Solutions.

The decontamination of dilute industrial effluents is a critical challenge for decreasing the environmental impact of mining and metallurgical activities. As an alternative to conventional processes, new extractant impregnated resins (EIRs) have been synthesized by the immobilization of Cyanex 301 and Cyanex 302 in alginate capsules using two different procedures (matrix-type immobilization vs. mononuclear encapsulation). These materials have been tested for Pb(II) sorption from acidic solutions. The Langmuir equation fitted well the sorption isotherms and the maximum sorption capacities vary between 24 and 80 mg·g−1 at pH 1, depending on the type and loading of the extractant in the EIR. Uptake kinetics were controlled by the resistance to intraparticle diffusion; though both the Crank equation (intraparticle diffusion) and pseudo-second order rate equation equally fitted uptake profiles. The amount of extractant immobilized in mononuclear capsules is lower than in matrix-type beads; this leads to lower sorption capacities but slightly better mass transfer properties. The balance between the advantages and drawbacks of the different systems makes more promising matrix-type capsules. The desorption of Pb(II) is possible using 1 M HNO3 solutions: metal ions were completely desorbed. However, the probable oxidation of the extractants (conversion to oxidized forms more sensitive to pH) reduces the sorption efficiency when they are re-used.

Innovative conditioning of algal-based sorbents: Macro-porous discs for palladium sorption

Algal biomass (AB) was used for green synthesis of porous discs by one-pot extraction and shaping procedure without adding pure alginate. Glutaraldehyde-crosslinked polyethyleneimine (GLA-PEI) was incorporated into AB discs. These two sorbents (AB and AB/PEI) along with alginate discs (as a reference) were applied in a fixed-bed-like system using a recirculation mode or a single-pass flow mode for palladium recovery. Recirculation experiments show that the incorporation of 9% (w/w, dry weight) GLA-PEI remarkably improves (more than 100%) sorption property for Pd(II). The flow rate (5–45mLmin−1) hardly affects the sorption rate regardless of sorbent type. The pseudo-second order rate equation well fits the kinetic profiles. Sorption isotherms of Pd(II) onto alginate and AB discs are well described by the Langmuir equation, while the prediction of that onto AB/PEI sorbent requires the Sips model with a larger number of fitting parameters. The maximum experimental sorption capacity is 46.8mgg−1 for alginate, 56.9mgg−1 for AB and 121.6mgg−1 for AB/PEI discs. The so-called Yan equation fits well the data obtained from single flow experiments. The Pd-loaded discs can be desorbed using 2MHCl/0.1M Thiourea as the eluant with desorption efficiency approaching 100%. FTIR analysis confirms that after desorption, the sorbents are chemically modified: thiourea brings amine groups, which improve Pd(II) binding in the next sorption cycle. Sorption/desorption experiments show that all the sorbents can be reused for at least 4times with a concentration factor (CF) of 7.9–8.4, 7.8–8.1 and 4.2–6.3 for alginate, AB and AB/PEI discs, respectively in the recirculation mode, while CFs in single-pass mode are 5.8, 4.4 and 6.1 for alginate, AB and AB/PEI sorbents, respectively.

Functionalization of Magnetic Chitosan Particles for the Sorption of U(VI), Cu(II) and Zn(II)-Hydrazide Derivative of Glycine-Grafted Chitosan.

A new magnetic functionalized derivative of chitosan is synthesized and characterized for the sorption of metal ions (environmental applications and metal valorization). The chemical modification of the glycine derivative of chitosan consists of: activation of the magnetic support with epichlorohydrin, followed by reaction with either glycine to produce the reference material (i.e., Gly sorbent) or glycine ester hydrochloride, followed by hydrazinolysis to synthesize the hydrazide functionalized sorbent (i.e., HGly sorbent). The materials are characterized by titration, elemental analysis, FTIR analysis (Fourrier-transform infrared spectrometry), TGA analysis (thermogravimetric analysis) and with SEM-EDX (scanning electron microscopy coupled to energy dispersive X-ray analysis). The sorption performances for U(VI), Cu(II), and Zn(II) are tested in batch systems. The sorption performances are compared for Gly and HGly taking into account the effect of pH, the uptake kinetics (fitted by the pseudo-second order rate equation), and the sorption isotherms (described by the Langmuir and the Sips equations). The sorption capacities of the modified sorbent reach up to 1.14 mmol U g−1, 1.69 mmol Cu g−1, and 0.85 mmol Zn g−1. In multi-metal solutions of equimolar concentration, the chemical modification changes the preferences for given metal ions. Metal ions are desorbed using 0.2 M HCl solutions and the sorbents are re-used for five cycles of sorption/desorption without significant loss in performances.