Sorption-regeneration Cycles Research Articles

Probing the Distribution and Mobility of Aminopolymers after Multiple Sorption-Regeneration Cycles: Neutron Scattering Studies.

Solid-supported amines are effective CO2 adsorbents capable of capturing CO2 from flue gas streams (10-15 vol % CO2) and from ultradilute streams, such as ambient air (∼400 ppm CO2). Amine sorbents have demonstrated promising performance (e.g., high CO2 uptake and uptake rates) with stable characteristics under repeated, idealized thermal swing conditions, enabling multicycle application. Literature studies suggest that solid-supported amines such as PEI/SBA-15 generally exhibit slowly reducing CO2 uptake rates or capacities over repeated thermal swing capture-regeneration cycles under simulated DAC conditions. While there are experimental reports describing changes in supported amine mass, degradation of amine sites, and changes in support structures over cycling, there is limited knowledge about the structure and mobility of the amine domains in the support pores over extended use. Furthermore, little is known about the effects of H2O on cyclic applications of PEI/SBA-15 despite the inevitable presence of H2O in ambient air. Here, we present a series of neutron scattering studies exploring the distribution and mobility of PEI in mesoporous silica SBA-15 as a function of thermal cycling and cyclic conditions. Small-angle neutron scattering (SANS) and quasielastic neutron scattering (QENS) are used to study the amine and H2O distributions and amine mobility, respectively. Applying repeated thermal swings under dry conditions leads to the thorough removal of water from the sorbent, causing thinner and more rigid wall-coating PEI layers that eventually lead to slower CO2 uptake rates. On the other hand, wet cyclic conditions led to the sorption of atmospheric water at the wall-PEI interfaces. When PEI remains hydrated, the amine distribution (i.e., wall-coating PEI layer thickness) is retained over cycling, while lubrication effects of water yield improved PEI mobility, in turn leading to faster CO2 uptake rates.

A photo-regenerable sponge filter to continuously remove hydrophobic and hydrophilic pollutants for water reuse

Zero-harmful discharge has become an urgent need for wastewater treatment and reuse, necessitating the removal of both hydrophobic and hydrophilic pollutants. In this study, titanate nanotubes loaded activated carbon (TNTs@AC) as an adsorptive photocatalyst was impregnated onto low-cost polyurethane (PU) sponge for elimination of both hydrophobic oils and hydrophilic phenols in water. The TNTs@AC@PU filter exhibits exceptional sorption, capturing pump oil and motor oil at 92 and 69 times their weight, respectively. Remarkably, the phenol sorption capacity was increased from 4.21 mg g−1 for pristine PU to 46.41 mg g−1 for TNTs@AC@PU. Furthermore, binary experiments revealed an effective simultaneous removal of both phenol and oil. The TNTs@AC@PU filter exhibited great robustness as demonstrated by 10 oil sorption-regeneration cycles showing no significant drop in oil sorption capacity and 5 phenol sorption cycles maintaining 70 % efficiency. Notably, 90 % regeneration efficiency was achieved within an hour under UV/PMS treatment revealing the high potential for filter regeneration. The TNTs@AC@PU filter showcases successful combination of sorption, regeneration, and reuse, offering insights for tackling hydrophilic and hydrophobic pollutants in water.

Preparation and characterization of calcined Ni/Mo hydrotalcite for the effective removal of lead from wastewater

ABSTRACT In this investigation, calcined Ni/Mo hydrotalcite was prepared via co-precipitation method and used as a sorbent for efficient removal of lead from aqueous solutions. The Pb2+ removal efficiency reached 99% at pH 6 and a sorbent dose of 2 g/L. The equilibrium data were satisfactorily fitted by the Langmuir and Hill models with a maximum capacity of 196.87 mg/g, indicating the monolayer sorption for lead over calcined Ni/Mo hydrotalcite. The Pb2+ sorption kinetic follows a pseudo-second-order reaction due to high correlation coefficients (R 2 > 0.99), while the Boyd’s plots confirm the external mass transfer as the rate-limiting step in the Pb2+ sorption. The temperature effect indicated a spontaneous and exothermic Pb2+ uptake. Mechanisms involved in the removal process include surface precipitation, diffusion into the solid pores and isomorphic substitution with Ni2+ of the sheets. The results showed excellent selectivity for Pb2+ removal from multi-divalent cation solutions and good reusability of the sorbent for up to 10 consecutive sorption–regeneration cycles without significant loss of the removal efficiency. As an application, the treatment of wastewater containing Pb2+, generated from the battery industry has been undertaken. The Pb2+ concentration was reduced from 5.7 to 0.6 mg/L, corresponding to an abatement of 89.5%. Therefore, the sorption using calcined Ni/Mo hydrotalcite is an efficient and suitable method for the elimination of Pb2+.

Cyclic zinc capture and zeolite regeneration using a column method, mass transfer analysis of multi regenerated bed.

Treatment of wastewater and reuse of purified water in an industrial process can provide an alternative source of fresh water as well as reduce pollution load by discharging a lower quantity of wastewater. When adsorption is used for treatment, the regeneration of the used adsorbent may also account for a large portion of the operational cost and cause secondary pollution. This problem may be solved by cyclic repetition of adsorption/regeneration cycles using a column method. In this paper, a total of nine successive cycles of zinc capture and zeolite bed regeneration using a column method have been investigated. The derived form of the breakthrough curve was used for analysing mass transfer in the column. For that purpose, the Dose-response, the Thomas, the Bohart-Adams, the Yoon-Nelson and the Wolborska models were used for modelling the breakthrough curve by nonlinear regression analysis. Simulation results and mathematical similarities between the models were discussed. This is the first study that used derived form of Dose-response model to analyse the inflection points of the breakthrough curve and mass transfer during nine consecutive sorption-regeneration cycles of zinc ions on natural zeolite. Obtained peak shape rate profiles were analysed for all cycles. Optimal operation conditions were evaluated with respect to the inflection point, the model parameters, and the residence time.

3D porous superoleophilic/hydrophobic grapefruit peel aerogel for efficient removal of emulsified-oil from water

Aerogel with ultra-lightweight, special wettability and porous structure played a potential role in the separation of oil layer/water mixture. In this research cost-effective mesoporous three-dimensional (3D) aerogel was designed and fabricated through a simple and green hydrothermal, synthetic method as a sorbent for efficient treatment of emulsified oil. The -prepared grapefruit peel aerogel exhibits mesoporous structures (2–50 nm) with an average pore size/diameter of 10.21 nm, a surface area of 17.31 m2/g and pore volume up to 0.0321 cm3/g. Excellent hydrophobicity of DMS-MGA aerogel with a water contact angle of 143.1° depicting great potential of this material for effective separation of water-oil emulsion. Furthermore, the prepared aerogel displayed excellent regeneration capability of more than 98% after eight cycles of sorption–regeneration. The carbonization process destroyed graphite crystals, and a new peak confirmed the alteration. PDMS raised crystallinity indices to 86%. Raman spectroscopy also revealed two peaks at 1498 and 1588 cm−1 linked with carbon's D and G bands. The effective grafting of dimethyl siloxane on DMS-MGA surface resulted in two new strong bands in the FT-IR spectra at 1254 cm−1 (C-H in Si-CH3) and 796 cm−1 (Si-O). TGA showed that the total carbon output was 28.5%, which is indicative of its good stability at elevated temperatures. DMS-MGA demonstrated near-complete sorption at a neutral pH of 7 of a crude oil-in-water emulsions. After 15 sorption-regeneration cycles, DMS-MGA still had a sorption efficiency of more than 95% despite being in contact with oil, and its anti-compression stability hadn't changed in the slightest.

One-pot synthesis of a novel P-doped ferrihydrite nanoparticles for efficient removal of Pb(Ⅱ) from aqueous solutions: Performance and mechanism

The developments of environmentally friendly and efficient heavy metal adsorbents face challenges. A new adsorbent, P-doped ferrihydrite (P-FH) was designed to remove Pb(Ⅱ) from the aqueous solution. Various techniques are implemented to characterize P-FH. P-FH was confirmed the formation of the second-line ferrihydrite phase by X-ray diffraction. Scanning electron microscopy (SEM) indicated that P-FH composed of a large number of uniform nanoparticles with a specific surface area (SBET) of 431.2 m2/g, and it is an ultra-small mesoporous material. Batch adsorption experiments showed that adsorption capacity of P-FH for Pb(II) increases with the increase of pH value or temperature. P-FH possesses a high adsorption capacity of 246.8 mg/g (25 ℃, pH = 6) for Pb(Ⅱ) in solution, which is very competitive compared with other representative adsorbents. The adsorption process of Pb(Ⅱ) onto P-FH is more in line with the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model. Moreover, P-FH has a high selectivity for Pb(II) adsorption. Cation exchange, complexation electrostatic attraction jointly contributed to the efficient adsorption of Pb(Ⅱ) on P-FH from aqueous solution. Additionally, a high adsorption rate of 81% was held after six sorption-regeneration cycles. This work provides a simple one-pot method to prepare an environmentally friendly adsorbent for Pb(Ⅱ) efficient adsorption.

Sorption of 4-n-nonylphenol, 4-n-octylphenol, and 4-tert-octyphenol on cyclodextrin polymers.

Alkylphenols are industrial pollutants commonly present in wastewater. They are difficult to eliminate by conventional treatment processes, ending up in the sludge of wastewater treatment plants. In this study, we propose to use cross-linked cyclodextrin-based polymers (ECP) as sorbents to treat three alkylphenols, namely, one nonylphenol (4-n-NP) and two octylphenols (4-n-OP and 4-tert-OP), present in aqueous solution by a batch method. The experiments were carried out with five cyclodextrin polymers (α-ECP, β-ECP, γ-ECP, α,β,γ-ECP, and HP-β-ECP). Sorption results showed that all polymers, with the exception of α-ECP, had high sorption capacities between 60 and 100% of the alkylphenols in the concentration range studied (between 25 and 100 μg/L). In all cases, HP-β-ECP has shown the highest removals, regardless of the structure of the molecule. The order obtained was HP-β-ECP >> β-ECP ~ α,β,γ-ECP >> γ-ECP > α-ECP. The 4-tert-OP compound was the best adsorbed, regardless the material and the solution studied. Sorption results also indicated that (i) the sorption efficiency decreased with the increasing of alkylphenol concentration; (ii) sodium chloride had a strong negative effect on the sorption process; and (iii) the performance remained unchanged after five sorption-regeneration cycles. The main sorption mechanism of alkylphenols occurring in ECP was the inclusion within the cyclodextrin cavities. The obtained results proved that cyclodextrin polymers could serve as efficient sorbents for the removal of alkylphenols from real effluents.

Next generation amino acid technology for CO2 capture

A flexible strategy to prepare a scalable CO2 absorbent (LAHPs) via encapsulating amino acid salt solutions in a polymer matrix.

Investigations of molybdenum-promoted manganese-based solid sorbents for H2S capture

The promotion effect of Mo-addition to alumina-supported Mn-based sorbents for high-temperature desulphurization was explored. A series of Mn-based sorbents with fixed Mn-loading and different Mo-loadings were prepared by the wet impregnation method and both fresh and used sorbents were characterized with respect to their physical and chemical properties. The sorbents were active for H2S removal at 600 °C and could be regenerated by oxidation in diluted air. The sorbents were subjected to 10 repeated sorption/regeneration cycles, and some loss of capacity occurred during the cycles. The results show that Mo-addition promotes the Mn-based sulfur sorbent performance both in terms of capacity and stability. Over the range investigated (0–8 wt% Mo added to a 15 wt% Mn sorbent), the improvement increased with an increasing amount of Mo added. The sample with the highest Mo-addition (15Mn8Mo) also retained the capacity best, as over 90% of the capacity remained after 10 sorption-regeneration cycles, in spite of suffering the most from sintering (observed as loss in surface area, increased pore size, and growth in Mn particle size). Characterization of the fresh and used samples using XRD and Raman spectroscopy indicates that a mixed Mn–Mo oxide suggested to be MnMoO4 plays a role in the promotion mechanism. The sorbent, 15Mn8Mo, is suggested to be promising for high-temperature desulphurization of bio-syngas.

Facile reactivation of used CaO-based CO2 sorbent via physical treatment: Critical relationship between particle size and CO2 sorption performance

Herein we report a new and facile mechanical approach for maximizing the CO2 sorption performance of CaO sorbents, and also for recovering the sorption performance of the used (or deactivated) sorbent. We compared the physicochemical properties of CaO-based sorbents, which could change depending on their preparation methods, and determined that the CaO particle size was the most critical factor that affected their CO2 sorption performance. The CO2 sorption performance of CaO-based sorbents could be maximized via the simple physical reduction of their particle size, and this was experimentally demonstrated using ball-milling. The CO2 sorption uptake of CaO prepared using the conventional solid-state method was significantly increased to the highest ever reported level after ball-milling, and it reached 98.0% of the theoretical maximum CO2 sorption capacity. The most important application of the particle-size-dependency of CaO-based sorbents on their CO2 sorption uptake is the reactivation of used sorbents via reducing the size of the aggregated or sintered bulky particles that form after cyclic usage. The CO2 sorption uptake of the used CaO (~32.9 wt% after 10 alternative sorption–regeneration cycles) was successfully recovered (almost doubled) to ~64.7 wt% after ball-milling. This is the first time a facile mechanical-grinding-based reactivation method, which appeared to be highly efficient and directly applicable to the continuous calcium looping technology, has been developed and used.

Encapsulation of Phase-Changing Eutectic Salts in Magnesium Oxide Fibers for High-Temperature Carbon Dioxide Capture: Beyond the Capacity-Stability Tradeoff.

Eutectic mixture (EM)-promoted MgO sorbents exhibit high CO2 sorption capacities but experience a significant decrease in uptake after multiple sorption-regeneration cycles due to EM movement and redistribution at high temperatures. Encapsulation of a pseudoliquid, phase-changing EM promoter with MgO may thus prevent the loss of active interface by confining the EM within a fixed area inside a MgO shell. In this work, we successfully embedded an EM composed of KNO3 and LiNO3 in a MgO fiber matrix via core-shell electrospinning. The synthesized sorbent achieved relatively high and steady sorption capacities, maintaining a stable uptake of ∼20 wt % after 25 sorption-regeneration cycles. The sorbent was also characterized using various techniques including in situ transmission electron microscopy (TEM) to describe its morphology, from which it was confirmed that the eutectic salt existed in distributed hollow pockets within the MgO fiber matrix and stayed confined within these fixed areas, favorably limiting its movement and redistribution when exposed to high temperatures where it exists in the liquid form. The EM may also be described as a glue that holds the fiber together, while MgO acts as a protective shell that prevents structural changes and rearrangement caused by EM movement, allowing the sorbent to retain its cyclic stability after multiple cycles and demonstrating its potential for industrial use after further improvement. Thus, the microencapsulation of a phase-changing EM material with pure MgO metal oxide was successfully achieved and might be explored for various material applications.

Sol-gel derived, Na/K-doped Li4SiO4-based CO2 sorbents with fast kinetics at high temperature

Li4SiO4 is considered as one of the most potential high-temperature sorbent materials for CO2 capture from the flue gas of fossil fuel-fired power plants. However, it usually suffers from slow kinetics at low CO2 concentrations. In this work, a series of Na- and K-doped Li4SiO4-based sorbents with Na/Si (or K/Si) atomic ratios of 0.05, 0.1 and 0.2 were prepared by a citrate sol-gel method. The prepared materials were characterized by various techniques, which revealed the presence of Li3NaSiO4 (for Na-doped sorbents) and LiKCO3 (for K-doped sorbents) on the surface of Li4SiO4 particles. All Na- and K-doped Li4SiO4 showed greatly enhanced CO2 sorption rates and capacities in 15% CO2 as compared to the heteroatom-free Li4SiO4, and in particular, the Na-doped sorbents had the fastest rates. The improved performance of K-doped Li4SiO4 resulted from the formation of eutectic Li2CO3-K2CO3 molten carbonates during CO2 sorption, while for Na-doped Li4SiO4, both the carbonation of Li3NaSiO4 and the presence of eutectic Li2CO3-Na2CO3 molten salts contributed to the improvement. In addition, both Na- and K-doped Li4SiO4 exhibited incomplete regeneration during cyclic operation, but the latter had better stability. In this context, we deliberately prepared a Na,K-codoped Li4SiO4-based sorbent with a Na:K:Si atomic ratio of 0.1:0.1:1, which showed fast kinetics and good cyclic stability. During 30 consecutive sorption-regeneration cycles (10 min of sorption in 15% CO2 at 650 °C, 5 min of regeneration in pure N2 at 750 °C), the Na,K-codoped Li4SiO4 presented a stable CO2 capture capacity of 0.22 gCO2/gsorbent after the first 10 cycles.

Magnetic Fe3O4 nanocubes coated by SiO2 and TiO2 layers as nanocomposites for Cr (VI) up taking from wastewater

Magnetic Fe3O4 (FO) nanocubes coated by SiO2 (FO–S) and TiO2 (FO-T) layers with perfect adsorption characteristics were successfully fabricated by a simple technique, and characterized by Fourier-transform infrared spectroscopy (FTIR), Field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), High resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS) and Brunauer-Emmett-Teller (BET) specific surface area. HR-TEM analysis confirms the susccess of Fe3O4 coating with TiO2 and SiO2 with a shell thickness ranged from 24 to 33 nm and 12–16 nm, respectively. Cr (VI) elimination from wastewater by the fabricated materials was carried out using a batch adsorption method at varying initial [Cr(VI)] (10–200 ppm), initial pH (1–8), shaking speed (200–400 rpm), temperature (293–333 K), contact time (0–180 min) and adsorbent dose (0.1–0.5 g). The point of zero charges (PZC) for adsorbents was estimated. The equilibrium findings of Cr (VI) ions removal were illustrated by Freundlich and Langmuir isotherm models and their kinetic results of ions were followed the pseudo-second-order sorption. The maximum adsorption capacity of Cr (VI) onto FO, FO-T, and FO-S were estimated to be 25.3, 28.7 and 32.6 mg/g, respectively. Further, the utilized adsorbents can be readily renovated and the adsorption capacity was still excellent after six sorption-regeneration cycles.

Combined sorbent and catalyst material for sorption enhanced reforming of methane under cyclic regeneration in presence of H2O and CO2

An investigation on an innovative calcium‑nickel Combined Sorbent and Catalyst Material (CSCM) for Sorption Enhanced Reforming (SER) of methane is presented in this paper. After hydrothermal synthesis, a nominal 30 wt% CaO-based sorbent supported on mayenite was physically mixed with a commercial reforming catalyst and granulated to obtain bifunctional particles of 200–300 μm. Materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface analysis (BET) and Mercury- intrusion prosimetry (Hg-porosimetry). A novel thermo-gravimetric analysis (TGA) approach was employed for investigating SER activity, particularly the materials performance during multicycling methane reforming and sorbent carbonation followed by regeneration in oxidative atmosphere – either in the presence of steam or CO2 at high temperature. When regeneration is carried out in 100 vol% CO2 at 925 °C, an intermediate reduction step between cycles was crucial to maintain the catalytic activity of the CSCM for 100 consecutive sorption-regeneration cycles. In spite of a stable catalytic activity, the initial sorption capacity of the CSCM sorbent function (~16gCO2/100gCSCM) declined progressively with cyclic runs and stabilized at ~10gCO2/100gCSCM from cycle 90 onwards. This decline in capacity has been related to CaO depletion by solid phase reaction with the catalyst support.

Stabilization of NaNO3-Promoted Magnesium Oxide for High-Temperature CO2 Capture.

NaNO3-promoted MgO sorbents are known to achieve enhanced CO2 sorption uptake but fail to maintain their capacity after multiple sorption-regeneration cycles. In this study, commercially available hydrotalcites (Pural Mg30, Pural Mg70, and synthetic hydrotalcite) were used as stabilizers for NaNO3-impregnated MgO (MgONaNO3) sorbents to improve their cyclic stability. Results show that the Mg30-stabilized MgONaNO3 attained higher and stable overall CO2 sorption performance as compared to bare MgONaNO3 after multiple sorption cycles. XRD analyses reveal that the hydrotalcites act as templates for MgCO3 by restricting the formation of large and nonuniform product crystallites. Furthermore, CO2-TPD results show that the hydrotalcites cause a change in the basic sites of the sorbent, which may be attributed to its high interaction with both MgO and NaNO3. This interaction becomes stronger as cycles proceed due to the structural rearrangements occurring, thus contributing to the stable behavior of the sorbents. However, these characteristics were not found on MgONaNO3 and the α-Al2O3-stabilized samples, thus proving the unique ability of hydrotalcites. From these results, we then derived the formation scheme of MgCO3 on the hydrotalcite-stabilized sorbents. This study presents a simple yet effective method of improving the stability of molten salt-promoted sorbents with promising potential for industrial use.

Biosorption of ibuprofen from aqueous solution using living and dead biomass of the microalga Phaeodactylum tricornutum

Ibuprofen has become an emerging pollutant in aquatic ecosystems, and therefore, it is necessary to develop efficient methods for its elimination. Bioremediation based on the use of a biological material as sorbent is a good alternative. For this reason, the sorption characteristics of ibuprofen using living or dead biomass of the microalga Phaeodactylum tricornutum have been tested in this study. Kinetics, isotherms, and maximum sorption capacity were investigated and discussed. Both living and dead biomass showed a similar efficiency; around 99.9% of ibuprofen was removed even when the initial concentration of ibuprofen tested reached 2 mg L−1 and 0.8 g L−1 of biomass used. Based on the Langmuir isotherm, the maximum sorption capacity was 3.97 mg g−1 at 18 °C, agitation speed 200 rpm, and pH 8.2 after 6 h of contact time. Results indicated that the removal efficiency increased as pH decreased and was higher at pH 2. Six consecutive sorption-regeneration cycles were assayed, and after 3 cycles, there was a loss of only 10.7% in efficiency, which remained stable thereafter. Therefore, the results indicate that the biomass of this microalga is a good and eco-friendly alternative for applications that require the removal of ibuprofen from aqueous solutions.

An environmentally friendly carbon aerogels derived from waste pomelo peels for the removal of organic pollutants/oils

The frequent occurrence of organics/oils leakage incidents has caused a chain of serious negative influence on local water environment and ecological environment in the past few decades. In this paper, a novel family of biomass-based carbon aerogels was fabricated through the hydrothermal carbonization, freeze-drying and pyrolysis process using waste pomelo peels as the precursors. The internal morphology, structure, and chemical composition were characterized and investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and the nitrogen adsorption–desorption isotherm. The BET analysis showed that the specific surface area of the carbon aerogel could reach up to 466.0–759.7 m2/g when the carbonization temperature was in a range from 600 °C to 800 °C. It was found that the carbon aerogels derived from waste pomelo peels had excellent sorption ability for a variety of organic pollutants/oils and the sorption ability dropped slightly as the calcination temperature increased. In addition, the sorbent could be easily regenerated by simple physical treatments and kept a high sorption rate after five sorption-regeneration cycles.

Investigation on the effective remediation of quinoline at solid/solution interface using modified agricultural waste: an inclusive study

This research work explores the potential of modified agricultural waste for the sorption of quinoline from aqueous media. A quinoline removal efficiency of around 97 % and sorption capacities of ~20 (batch) and ~35 mg g−1 (fixed-bed) were achieved. Pseudo-second-order kinetics and Temkin isotherm best represented the equilibrium sorption data. The sorption of quinoline is exothermic and spontaneous in nature with a slight increase in the system entropy. The quinoline sorption mechanism is controlled by H-bonding, π–π dispersive interactions, boundary layer, and intraparticle diffusion. Microwave–chemical integrated regeneration technique retrieves the sorption capacity of the exhausted sorbent with 99.15, 97.64, and 95.55 % of the original, in three sorption–regeneration cycles. Energy recovery (19.365 MJ kg−1) from the quinoline-loaded sorbent and the potential utilization of left-over ash materials enhanced the prospective of the sorbent for the remediation of pollutants for a clean and green environment.

Removal of phosphate from industrial wastewater using uncalcined MgAl-NO3 layered double hydroxide: batch study and modeling

In this study, the sorption ability of nitrate containing MgAl layered double hydroxide as an anion-exchanger to remove phosphate from a real effluent was investigated. The LDH material was prepared via coprecipitation method and characterized by X-ray diffraction, SEM, Fourier Transform Infrared, BET surface area, and pHzpc. The effect of physico–chemical key parameters on phosphate removal, such as sorbent dosage, solution pH, initial concentration, and contact time, has been studied in batch mode. The sorption reached equilibrium within 30 min. Furthermore, the sorption mechanism of phosphate onto MgAl-NO3 LDH is a combination of both anion-exchange and electrostatic attraction. The equilibrium 8 data were tested using Langmuir, Freundlich, and Dubinin–Radushkevich isotherms. The results show that the Langmuir isotherm describes sufficiently the sorption equilibrium, offering a maximum sorption capacity of 64.10 mg/g. Sorption kinetic follows accurately pseudo-second-order reaction. The sorbent reusability shows that regenerated LDH can be reused in subsequent sorption–regeneration cycles with a slight decrease in sorption capacity.

Zinc remediation of aqueous solutions by natural hemp fibers: batch desorption/regeneration study

A hemp waste material resulting from the textile industry has previously been shown to be a very efficient material in removing Zn(II) from diluted aqueous solutions. In this work, batch studies on desorption and multiple sorption–regeneration cycles for zinc(II) removal by natural hemp fibers have been carried out. The best desorption results were performed in acidic medium, where the protons in solution replaced the Zn(II) ions on the loaded hemp. The efficiency of Zn(II) desorption with 0.1M hydrochloric acid is higher than that achieved using sulfuric acid of the same concentration. The amount of Zn(II) desorbed by 0.1M HCl, 0.1M H2SO4, and 5% NaCl increases sharply in the first 15–20 min of the process, attaining values that subsequently stay almost constant (for 0.1M HCl) or sligtly increase (for 0.1M H2SO4 and 5% NaCl). The sorptive potential of the tested hemp remains almost unchanged after three cycles of sorption–desorption of Zn(II) from solutions with a high mg Zn/g of hemp in the initial ratio. The results of this study are important in order to demonstrate that regenerated hemp could be used for zinc metal removal from water sources without the threat of the sorbent becoming another source of zinc pollution for the environment.