Fixed-bed Column Experiments Research Articles

Ammonium removal by metakaolin-based geopolymers from municipal and industrial wastewaters and its sequential recovery by stripping techniques

In this study, a technical scheme of an ammonium recovery process from diluted municipal or industrial wastewaters was developed, and the main operational parameters of adsorption/desorption and air-stripping/acid-scrubbing or membrane units were examined. The proposed approach combines the removal of ammonium nitrogen by an ion-exchange mechanism on metakaolin-based geopolymers (MKGPs) followed by adsorbent regeneration. A regeneration agent was purified by the air-stripping technique or membrane technology. A ready-to-use market-grade fertilizer or industrial-grade ammonia water could be obtained as the final product. The properties and regeneration ability of MKGP, prepared from activated kaolinite clay, were compared with new geopolymer adsorbents based on papermill sludge (FS MKGP). Adsorption fixed-bed column experiments with continuously circulated regeneration solution purified by air-stripping or the membrane approach were conducted to determine the limits of the regeneration solution’s application. Sodium and potassium salts were tested as regeneration agents, and the influence of regeneration solution composition on ammonium removal and recovery rates was investigated. Based on a breakthrough curve analysis, the removal rate of ammonium N by FS MKGP was found to be 3.2 times higher than that by MKGP for actual wastewater samples. Moreover, there were substantial differences in the regeneration regime between the two adsorbents. For the air-stripping technique, a liquid-phase temperature of 45°C was minimal and enough for efficient ammonia transfer to the gaseous phase. For the membrane technique, a feed-phase temperature of 40°C was enough for removing ammonia from the regeneration solution, while no heating of a receiving phase was required.

DMSA-incorporated silsesquioxane-based hybrid polymer for selective adsorption of Pb(II) from wastewater

It is a challenging task to remove Pb(II) ions efficiently from wastewater containing high concentrations of hardness ions. In this study, a novel hybrid polymer (DVP) for selective adsorption of Pb(II) ions was successfully prepared via photopolymerization of vinyl-POSS and dimercaptosuccinic acid (DMSA). The chemical structure and composition of DVP were characterized by FTIR, XPS, SEM, TEM, XRD and TGA techniques. DVP exhibited high efficiency in removing Pb(II) from aqueous solutions with a maximum adsorption capacity of 349.5 mg g−1 at pH 4, exceeding lots of adsorbents reported in the literature. The adsorption performance of Pb(II) by DVP was found to fit the Freundlich isotherm well and its kinetics followed the Elovich model. Moreover, DVP showed selective adsorption of Pb(II) in the presence of high concentrations of Ca(II) and Mg(II) ions and could reduce Pb(II) in real lake water to 25 ppb at a DVP dose of 1 g L−1. Moreover, the adsorption process of DVP was endothermic in nature. The adsorption mechanism demonstrated that Pb(II) ions can be chelated with the thioether and carboxyl groups of DVP simultaneously, which was confirmed by spectroscopic analysis and DFT calculations. Good reusability in continuous fixed-bed column experiments suggested that DVP was an ideal candidate for the selective removal of Pb(II) ions from contaminated aquatic systems.

Insight into the molecular interaction of trace As (III) and As(V) onto the hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn)

In this study, a hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn) was synthesized via two-step mixed metal oxide precipitation using 50:50 % DI: ethanol as solvent. Trace As(III) and As(V) removal efficiency was comprehensively validated in both equilibrium adsorption isotherms and kinetics. The maximum adsorption capacities of HA502P-Fe/Mn toward As(III) and As(V) were 21,590 and 18,930 µg/g, respectively. The kinetics of As(III) removal were best predicted (R2 = 0.986) using a pseudo-second order model (k2 = 0.001 g/µg As(III)·min). Adsorption mechanisms were further characterized using X-ray absorption spectroscopy (XANES and EXAFS), including a comparison with the density functional theory (DFT) data. The XANES results showed complex redox transformation of the adsorbed As(V) on HA502P-Fe/Mn. The EXAFS spectra indicate predominant inner-sphere complex formation of bidentate mononuclear edge-sharing (2E) complexes for Mn-As (bond distance 2.94 Å), and bidentate binuclear corner-sharing (2C) complexes for Fe-As (bond distance 3.34 Å) on HA502P-Fe/Mn surfaces. Based on the DFT simulation, the obtained 3D structures were optimized, and the bond lengths between Fe-As and Mn-As were comparable with the EXAFS. For practical purposes, the fixed-bed column experiments were fully investigated for both As(III) and As(V) removal using NSF standard 53 test water (As(III) 300 ppb, pH 6.5), including the regeneration. The HA502P-Fe/Mn demonstrated 2X treatable bed volumes (4,300 vs 2,000 BVs) more than the commercially available As selective adsorbent. The experiments demonstrated that HA502P-Fe/Mn is a promising novel adsorbent for As(III) removal owing to its relatively high As adsorption capacity and regenerating ability.

Selective recovery of glyphosine from glyphosate mother liquor using a modified biosorbent: Competitive substitution adsorption

Here, an easy to prepare, environmentally friendly, and highly efficient biosorbent was synthesized for the selective recovery of glyphosine from glyphosate mother liquor. Batch adsorption and continuous fixed-bed column experiments were conducted to determine its adsorption properties and evaluate its potential towards practical applications. The results showed that the biosorbent exhibited a fast adsorption rate and high adsorption capacity (296.1 mg/g) toward glyphosine. Further, the biosorbent performed better under acidic conditions, and was easily regenerated using an alkaline solution, maintaining a high removal efficiency even after 5 adsorption-desorption cycles. Competitive adsorption experiments in binary and ternary systems revealed that the biosorbent showed a higher adsorption affinity toward the target glyphosine compared with glyphosate and phosphorous acid (which are the other main constituents of glyphosate mother liquor), enabling the selective recycling of glyphosine. These observations were further supported through density functional theory (DFT) calculations of the adsorption energy. Moreover, fixed-bed column experiments showed that the prepared biosorbent could maintain its high performance in actual glyphosate mother liquor. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses revealed that the adsorption mechanism is strongly associated with electrostatic attraction and hydrogen bonding between –NH3+ and glyphosine. Overall, the prepared biosorbent can be considered as an excellent candidate for the selective recovery of glyphosine from complicated industrial wastewater systems.

Removal of hexavalent chromium via biochar-based adsorbents: State-of-the-art, challenges, and future perspectives

Chromium originates from geogenic and extensive anthropogenic activities and significantly impacts natural ecosystems and human health. Various methods have been applied to remove hexavalent chromium (Cr(VI)) from aquatic environmental matrices, including adsorption via different adsorbents, which is considered to be the most common and low-cost approach. Biochar materials have been recognized as renewable carbon sorbents, pyrolyzed from various biomass at different temperatures under limited/no oxygen conditions for heavy metals remediation. This review summarizes the sources, chemical speciation & toxicity of Cr(VI) ions, and raw and modified biochar applications for Cr(VI) remediation from various contaminated matrices. Mechanistic understanding of Cr(VI) adsorption using different biochar-based materials through batch and saturated column adsorption experiments is documented. Electrostatic interaction and ion exchange dominate the Cr(VI) adsorption onto the biochar materials in acidic pH media. Cr(VI) ions tend to break down as HCrO4-, CrO42-, and Cr2O72- ions in aqueous solutions. At low pH (∼1-4), the availability of HCrO4- ions attributes the electrostatic forces of attraction due to the available functional groups such as -NH4+, -COOH, and -OH2+, which encourages higher adsorption of Cr(VI). Equilibrium isotherm, kinetic, and thermodynamic models help to understand Cr(VI)-biochar interactions and their adsorption mechanism. The adsorption studies of Cr(VI) are summarized through the fixed-bed saturated column experiments and Cr-contaminated real groundwater analysis using biochar-based sorbents for practical applicability. This review highlights the significant challenges in biochar-based material applications as green, renewable, and cost-effective adsorbents for the remediation of Cr(VI). Further recommendations and future scope for the implications of advanced novel biochar materials for Cr(VI) removal and other heavy metals are elegantly discussed.

Evaluation the feasibility of using clinoptilolite as a gravel pack in water wells for removal of lead from contaminated groundwater.

The ability of clinoptilolite zeolite as a filter in water wells to remove lead from polluted groundwater was tested in batch and fixed-bed column experiments. XRF, XRD, SEM, and BET were used to characterize the zeolite. Because of the pH variation in groundwater, batch experiments were performed at pH = 6, 7, and 8, with the highest removal efficiency (84.2%) at pH = 6 and 298K within 90min. The Freundlich model accurately predicted metal ion adsorption behavior and indicated a multilayer adsorption of Pb(II) molecules on the inhomogeneous surface of clinoptilolite. The best-fitting kinetic model for clinoptilolite is the pseudo-second order equation, highlighting that the rate of adsorption is dependent on absorbent capacity. Next, the effect of flow rate, bed depth, and grain size of clinoptilolite on lead removal was investigated in column experiments at an initial concentration of 450mg pb/L. The highest removal efficiency was achieved in column experiments with a flow rate of 1mL/min, a bed height of 10cm, and a grain size of 0.6 to 0.8mm. Breakthrough curves were predicted by the Thomas and Yoon-Nelson models, with excellent agreement with the corresponding experimental data. This research will be used to develop a new in situ remedial approach for removing lead from polluted groundwater.

Preparation of composite hydrogel with high mechanical strength and reusability for removal of Cu(II) and Pb(II) from water

An adsorbent with good reusability, rapid adsorption kinetics, cost-effectiveness, and high adsorption capacity is desired in practical adsorption processes. A new strategy was proposed herein, combining the ball-milling biochar (MBC) and double network to synthesize a composite hydrogel. The ball-milling biochar /carboxymethylcellulose/polyacrylic acid (MBC/CMC/PAA) composite hydrogel was prepared using a one-step method. Both the carboxymethylcellulose (CMC) and polyacrylic acid (PAA) were used to form double networks, immobilized and crosslinked with MBC. The MBC/CMC/PAA possessed a higher allowable compression force of 133.52 N. The FTIR and XPS results confirmed that -COOH, -OH, and -NH- functional groups were the main adsorption sites. The proposed adsorbent maintained a stable removal efficiency of 100 % for Cu2+ and Pb2+ within five cycles of use. Thomas model better described the Cu2+ and Pb2+ in the individual dynamic adsorption process. In the alternate fixed-bed column experiments, the treatment volume of Cu2+-containing water reached 13.7 L and produced 300 mL eluent. This work not only developed a new strategy for preparing composite hydrogel but also verified that the MBC/CMC/PAA could have great applicability for removing Cu2+ and Pb2+ in real solutions.

Competitive removal of textile dyes from solution by pine bark-compost in batch and fixed bed column experiments

Compost from pine bark has been previously suggested as an effective low-cost biosorbent for different classes of textile dyes, although the existing studies have been performed in non-competitive batch conditions, so the effect of competition or adsorption in continuous-flow conditions has not been assessed. In this work, the removal of Basic Violet 10 (BV10) and Direct Blue 151 (DB151) by pine bark compost from single and bi-solute mixtures has been studied in batch and fixed-bed column experiments. Adsorption capacity of pine bark compost was three times higher for BV10 than for DB151 in batch conditions, where competition reduced the uptake of both dyes, with competition factors of 0.63 for DB151 and 0.82 for BV10. Dye adsorption capacity was lower in column than in batch tests, with 112.6 and 34.7 mg g −1 for BV10 and DB151, respectively, versus 127.1 and 42.1 mg g −1 in batch conditions. The presence of both dyes in solution also reduced their affinities with respect to non-competitive conditions in column tests, with saturation capacities of 71.6 mg g −1 for BV10 and 16.8 mg g −1 for DB151. The effect of competition between dyes was higher in columns than in batch conditions, with competition factors of 0.76 for BV10 and 0.59 for DB151. The column biosorbent was effectively regenerated using ethanol, thus enabling reuse in the practical application of compost for textile dye removal. The concentration of dyes in the eluted ethanol was higher than the influent concentration, what would give compost value for pre-concentration of textile dyes. • Competitive dye removal by pine bark compost has been studied for the first time. • Competition among dyes was stronger in column studies than in batch conditions. • Maximum adsorption capacity of compost was 127 mg g -1 for BV10 and 42 mg g -1 for DB151. • Pine bark compost adsorber was effectively regenerated using ethanol, enabling reuse.

Fixed bed column performance of Al-modified biochar for the removal of sulfamethoxazole and sulfapyridine antibiotics from wastewater

In this study, biochar derived from bamboo pretreated with aluminum salt was synthesized for the removal of two sulfonamide antibiotics, sulfamethoxazole (SMX) and sulfapyridine (SPY), from wastewater. Batch sorption experiments showed that Al-modified bamboo biochar (Al-BB-600) removed both sulfonamides effectively with the maximum sorption capacity of 1200–2200 mg/kg. The sorption mechanism was mainly controlled by hydrophobic, π-π, and electrostatic interactions. Fixed bed column experiments with Al-modified biochar packed in different dosages (250, 500 and 1000 mg) and flow rates (1, 2 and 4 mL/min) showed the dosage of 1000 mg and flow rate of 1 mL/min performed the best for the removal of both SMX and SPY from wastewater. Among the breakthrough (BT) models used to evaluate the fixed bed filtration performance of Al-BB-600, the Yan model best described the BT behavior of the two sulfonamides, suggesting that the adsorption process involved multiple rate-liming factors such as mass transfer at the solid surface and diffusion Additionally, the Bed Depth Service Time (BDST) model results indicated that Al-BB-600 can be efficiently used in fixed bed column for the removal of both SMX and SPY in scaled-up continuous wastewater flow operations. Therefore, Al-modified biochar can be considered a reliable sorbent in real-world application for the removal of SMX and SPY from wastewater.

Silver ions and silver nanoparticles removal by coffee derived biochar using a continuous fixed-bed adsorption column

Even low concentration monovalent silver (Ag+) and silver nanoparticles (Ag NPs) are emerging environmental threats, seeking an eco-friendly and cost-effective continuous treatment process to mitigate their pollution. In this study, an attempt has been made to investigate the potential of spent coffee grounds (SCGs) biochar in a fixed-bed column, to remove silver ions and silver nanoparticles from wastewater. A series (adsorption and desorption) of fixed-bed column experiments were performed under different operating conditions to determine the breakthrough curves (BTCs) and understand the effect of initial concentration (50–100 mg/L), the quantity of biochar (0.5–1 g), and the form of silver Ag+ and Ag NPs on biochar removal capacity. Thomas and Yoon-Nelson models were applied to simulate different column parameters, such as breakthrough time, saturation time, the volume of treated effluent, and percentage of removal. These simulated results could assist in the scale-up of the process for an actual industrial operation. Experimental data showed good agreement with both Thomas and Yoon-Nelson models, where the simulated values were closely matched with the experimental values. Biochar was collected after the adsorption and characterised to confirm the morphology, crystal structure, and ionic state of silver. The saturated column was regenerated by 0.05 M HNO3 as eluent and used at least 3 times with 15% capacity loss compared to initial performance, which demonstrated the viability and effectiveness of the biochar adsorption process.

Highly efficient removal of cadmium (II) ions using cellulose-based monolith with a hierarchically porous structure fabricated through phase separation method

In this study, a functionalized cellulose-based monolith was utilized as a highly efficient adsorbent to remove heavy metal ions. Firstly, cellulose-based monolith (CE MONOLITH) was obtained via combination of thermally induced phase separation and post-alkaline hydrolysis. Afterwards, the functionalized monolith (EDTA-CE MONOLITH) was prepared through esterification with ethylenediaminetetraacetic dianhydride. The fabricated EDTA-CE MONOLITH showed a hierarchically porous morphology containing macro- and mesopores simultaneously with an excellent compressive strength, which was extremely suitable for heavy metal removal. The porous structure and chemical properties of CE MONOLITH and EDTA-CE MONOLITH were characterized through SEM, N2 adsorption/desorption isotherm, FT-IR, elementary analysis, EDS, and XPS. Finally, the batch and fixed-bed column experiments were performed to evaluate the adsorption behaviors of EDTA-CE MONOLITH for Cd2+. The results revealed that EDTA-CE MONOLITH exhibited a relatively fast Cd2+ adsorption rate with a maximum adsorption capacity of 110.1 mg/g. And EDTA-CE MONOLITH could be regenerated easily and displayed excellent reusability without significant loss of absorption capacity. The fixed-bed column adsorption implied that EDTA-CE MONOLITH showed high efficiency for Cd2+ adsorption. Therefore, the EDTA-CE MONOLITH fabricated in this work had large potential to be used as an efficient adsorbent for the removal of heavy metal ions in wastewater treatment.

Montmorillonite-reduced graphene oxide composite aerogel (M−rGO): A green adsorbent for the dynamic removal of cadmium and methylene blue from wastewater

In this study, a type of montmorillonite-reduced graphene oxide aerogel (M−rGO) was successfully prepared by the sol–gel method and used for the effective removal of heavy metals (cadmium, Cd) and cationic dyes (methylene blue, MB) in wastewater. The chemical composition and micromorphology of the resulting M−rGO were characterized utilizing scanning electron microscopy and energy dispersive spectrometry, Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, and X-ray diffraction. Furthermore, the effects of the initial concentration, adsorption time, and temperature on the static adsorption process were systematically studied. Equally important, the effects of the concentration, pH, ionic strength (IS), and pumping flow rate of contaminated solution on the dynamic removal of Cd and MB by M−rGO were investigated by a fixed-bed column experiment. The kinetics, isothermals, and thermodynamic adsorption experiment results showed that the Langmuir and pseudosecond-order models best suited the adsorption process in which physical adsorption and chemical adsorption act together. Functional groups containing O and C were involved in the adsorption of Cd and MB, and the hydrogen bonds, π-π, n-π interaction, and hydrophobic interaction between M−rGO and MB made important contributions to adsorption. The lower initial concentration, higher pH value, and slower pumping flow rate of the contaminated solution can effectively increase the dynamic adsorption capacity of Cd and MB on M−rGO. Contrary to that of Cd, the adsorption capacity of MB on M−rGO increased with IS. Both static adsorption and dynamic column experiments confirmed that the presence of Cd promoted the adsorption of MB, and MB inhibited the adsorption of Cd by M−rGO. In addition, the Cd/MB combined pollution wastewater experiment and the regeneration study showed that M−rGO could be a cost-effective and promising sorbent for Cd and MB wastewater treatment due to its high efficiency and excellent reusability.

Batch and continuous fixed-bed column adsorption of tetracycline by biochar/MOFs derivative covered with κ-carrageenan/calcium alginate hydrogels

Due to the high dependence on tetracycline in the daily production and life of human beings, its abuse problem is serious, which affects the safety of the ecological environment. How to effectively remove residual tetracycline in the environment is an urgent problem to be solved. In this study, HKUST-1 was successfully composited with rice husk and wheat straw biochar by hydrothermal method, and then combined with κ-carrageenan and calcium alginate by cross-linking replacement method to prepare a novel modified biochar composite gel. Through a series of static adsorption experiments, the adsorption of TC on the two modified biochar composite gels reached equilibrium within 24 h and was dominated by chemical adsorption, and the maximum adsorption capacities for TC could reach 313.00 and 396.09 mg·g−1, respectively. The adsorption mechanism of TC on the modified biochar composite gels is mainly hydrogen bonding, electrostatic attraction, metal-organic complexation and π-π interaction. At the same time, the dynamic adsorption process was simulated through a fixed-bed column experiment, and the results showed that the modified biochar composite gels as a new type of adsorption material can be effectively applied to the removal of organic pollutants in actual sewage, providing basic support for future practical application research.

Synthesis of ε-MnO2@MIL-100(Fe) composite for p-arsanilic acid removal

p-Arsanilic acid (p-ASA), a feed additive in poultry and swine production, tends to be converted into more toxic inorganic arsenic in the environment, thus posing hazards to the environment and humans. In this work, novel ε-MnO2@MIL-100(Fe) nanocomposites were successfully synthesized by a wet impregnation method to remove p-ASA by simultaneously oxidation and adsorption. Batch experiments demonstrated that the ε-MnO2@MIL-100(Fe) had an outstanding adsorption capacity toward p-ASA and the oxidized products (486.99 μmol g-1), and the adsorption fitted well with pseudo-second-order kinetic model and Freundlich isotherm model, while intra-particle diffusion was a rate-limiting step. In the composites, manganese oxide was responsible for the oxidation of p-ASA and MIL-100(Fe) played a dominant role in the in-situ adsorption through a joined force from coordination, hydrogen bonding, and π-π stacking. Thus the combination of adsorption and oxidation resulted in excellent removal performances. Additionally, ε-MnO2@MIL-100(Fe) achieved good removal efficiency for p-ASA in a wide pH range (5−11) and was robust to some co-existing substances, which enables its good removal performance towards p-ASA in natural water bodies. The fixed-bed column experiments further confirmed the continuous removal of p-ASA from the water flow by ε-MnO2@MIL-100(Fe).

One-pot synthesis of brewer's spent grain-supported superabsorbent polymer for highly efficient uranium adsorption from wastewater

High-efficient and fast adsorption of uranium is important to reduce the hazards caused by the uranium contamination of water environment due to the increased human activities. Herein, brewer's spent grain (BSG)-supported superabsorbent polymers (SAP) with different cross-linking densities are prepared as cheap and eco-friendly adsorbents for the first time via one-pot swelling and graft polymerization. A 7 wt% NaOH solution is used to swell BSG before grafting and subsequently neutralize the acrylic acid to control the reaction rate without producing alkaline wastewater. Compared with the traditional methods, swelling improves the grafting density and the utilization of raw materials due to the increased disorder degree of the BSG fibers. This results in the grafting of abundant carboxyl and amide groups onto the BSG backbone, forming a strongly hydrophilic polymer network of the BSG-SAP. Compared with the reference polymers without BSG, BSG-SAP presents higher adsorption capacity and enhanced reusability. The highly cross-linked BSG-SAP (BSG-SAP-H) shows an outstanding adsorption capacity of U(VI) (1465 mg/g at pH0 = 4.6), a fast adsorption rate (81% of equilibrium adsorption capacity in 15 min), and a high selectivity in the presence of competing ions. Adsorption mechanism studies reveal the involvement of amide groups, a bidentate binding structure between UO22+ and the carboxyl groups, and a cation exchange between Na+ and UO22+. More importantly, the adsorption capacity of BSG-SAP-H reaches 254.4 mg/g in the fixed-bed column experiment at a low initial concentration (c0(U) = 30 mg/L) and keeps 80% of the adsorption capacity after four cycles, indicating a great potential for uranium removal from wastewater. This work shows a suitable approach to explore the untreated biomass to prepare SAP with enhanced adsorption performance via a general and low-cost strategy.

Humic acid-coated hydrated ferric oxides-polymer nanocomposites for heavy metal removal in water

Water pollution by toxic heavy metals poses a threat to the environment and human bodies. Herein, a novel hydrated ferric oxide nanoparticle (HFO) based hybrid adsorbent was fabricated for the removal of toxic Cu(II), Cd(II) and Pb(II) from water. HFOs were immobilized into a porous resin D-201, and then this nanocomposite HFO-D201 was coated with humic acid (HA) to enhance the binding sites of target metals. Both HFOs and HA contribute to the sequestration of heavy metals. The as-synthesized hybrid adsorbent HA-HFO-D201 exhibited excellent performance on the removal of Cu(II), Cd(II), and Pb(II) in a pH range of 3–9, while no Fe leaching was observed. The presence of natural organic matter (20 mg C/L) has limited influences on the adsorption, and more than 85% of the target metals can be removed after treatment. HA-HFO-D201 showed preferable adsorption toward Cu(II) and Pb(II) (1 mg/L) from the background Ca2+ solution at much higher concentrations (100 mg/L), while the retention of Cd(II) (1 mg/L) decreased to some extent. Fixed-bed column experiments exhibited that the treatment capacities of HA-HFO-D201 are 90 bed volumes (BV) for Cd(II), 410 BV for Pb(II) and > 800 BV for Cu(II) of simulated contaminated water to meet the WHO drinking water standard. Meanwhile, depleted HA-HFO-D201 can be readily regenerated by a chelating agent Na2EDTA for repeated use. The hybrid adsorbent HA-HFO-D201 has excellent potential to remove heavy metals in water treatment systems.

Feasible synthesis of a novel and low-cost seawater-modified biochar and its potential application in phosphate removal/recovery from wastewater

In this study, a novel and low-cost seawater-modified biochar (SBC) was fabricated via the pyrolysis of fir wood waste followed by co-precipitation modification using seawater as the Ca/Mg source. The co-precipitation pH was a vital factor during modification, and the optimal pH was 10.50 according to calculations using PHREEQC 2.5 and experiments. The characterizations indicated that Ca and Mg were loaded on the SBC as irregular CaCO3 and nanoflake-like Mg(OH)2, respectively, with the latter dominating. The SBC exhibited a high maximum adsorption capacity of 181.07 mg/g for phosphate, calculated using the Langmuir model, excellent adsorption performance under acidic and neutral conditions (pH = 3.00–7.00), and remarkable selectivity against Cl−, NO3−, and SO42−. The presence of HCO3− promoted adsorption. The mechanisms behind phosphate adsorption involved electrostatic attraction, ligand exchange, precipitation, and inner-sphere complexation. Mg, rather than Ca, was served as the main adsorptive sites for phosphate. Additionally, the feasibility of treating real-world wastewater was tested in batch (using SBC powders) and fixed-bed column (using SBC granules) experiments. The results indicate that the SBC powders could reduce the phosphate concentration from 1.26 mg P/L to below 0.5 mg P/L at a low dose of 0.50 g/L, and the SBC granules exhibited a high removal efficiency with excellent recyclability; the capacity still remained at 78.92% of the initial capacity after five adsorption–desorption runs. Furthermore, the modification process almost did not increase the production cost of the SBC, which was estimated to be 0.41 $/kg. Our results demonstrate that seawater is a low-cost and efficient modifier for biochar modification, and the resultant SBC demonstrates great potential for treating actual phosphate-containing wastewater.

Arsenic(V) Removal from Water by Resin Impregnated with Cyclodextrin Ligand

More rigorous environmental rules on hazardous metals release require the implementation of diverse methods to remove them from contaminated streams. The adsorption process is the most attractive method for removal of toxic metal ions from different aqueous solutions. In the present study, batch and fixed bed column experiments were carried out to investigate the performance of permethylated β-cyclodextrin impregnated resin for the removal of As(V) ions from aqueous solutions. Sorption of As(V) ions was performed in groups under a variety of pH and metal concentrations. It was noted that removal efficiency was the highest (98%) at pH 6.0, and at an initial As(V) concentration equal to 0.1 mg/L. Sorption model use for experimental data indicates that the removal mechanism of As(V) by the permethylated β-cyclodextrin impregnated resin was the physical sorption. The adsorption capacity of the cyclodextrin ligand immobilized onto Amberlite XAD-4 resin was 19 mg/g. In addition, the impregnated resin was regenerable, thus was able to be used over and over.

Facile fabrication of tannic acid functionalized microcrystalline cellulose for selective recovery of Ga(III) and In(III) from potential leaching solution

Selectively recovery Gallium (Ga) and Indium (In) is significant because of their low reserves and wide range of applications. In this work, tannic acid (TA) functionalized microcrystalline cellulose (MCC-g-GMA-TA) was successfully synthesized by radiation induced grafting polymerization. The selective separation and recovery of Ga(III) and In(III) from potential leaching solution were investigated using batch and fix-bed column experiments. The maximum adsorption capacity reached 26.55 for Ga(III) and 35.63 mg/g for In(III) at pH 3, respectively. Especially, MCC-g-GMA-TA could effectively separate Ga(III) from Ga(III)/As(III) mixing solution, and separate In(III) from In(III)/Zn(II) mixing even at the coexistence ions was 100 times of Ga(III) and In(III). The fixed-bed column experiments revealed that MCC-g-GMA-TA can effectively and selectively recover Ga(III) and In(III) from simulated leaching solution from Zn refinery residue or semiconductor waste. The ionic strength effect, FTIR and XPS analyses revealed that the adsorption of Ga(III) and In(III) by adsorbent was attributed to the formation of chelates between the hydroxyl groups and Ga(III) or In(III). Overall, MCC-g-GMA-TA was demonstrated to be a low cost, pro-environmental and potential adsorbent with excellent selectivity for Ga(III) and In(III) recovery from effluents and prospective sources.

Phosphate removal from actual wastewater via La(OH)3-C3N4 adsorption: Performance, mechanisms and applicability

In this study, La(OH)3 nanoparticles were immobilized on C3N4 to effectively restrict their aggregation and subsequently enhance the La utilization efficiency to promote phosphate adsorption. The prepared La(OH)3-C3N4 nanocomposite was characterized by SEM, XRD, FTIR, XPS, BET and Zeta potential analysis. Batch and continuously-fed (fixed-bed column) experiments to assess the adsorption performance of La(OH)3-C3N4 showed that the composite exhibits superior utilization efficiency, resulting to relatively quick adsorption with a short equilibrium time of 30 min. The theoretical maximum P adsorption capacity reached the 148.35 mg·g−1, efficiency that remained unaffected by the anions and HA present. The adsorption mechanism showed stability in a wide pH range (4.0–11.0) and is considered effective even after extensive use (five-cycles). The dynamics of the adsorption capacity and the half-penetration time values were estimated by ‘Thomas’ and ‘Yoon-Nelson’ models showed that are better represented from the experimental values obtained from the fixed-bed column trial. The adsorption mechanisms were attributed to surface precipitation, electrostatic attraction, and inner-sphere complexation via ligand exchange. Furthermore, La(OH)3-C3N4 demonstrated high efficiency in scavenging phosphate from both diluted and concentrated wastewater (natural pond and swine wastewater respectively). The above confirm that La(OH)3-C3N4 is a promising composite material for phosphate management in aqueous environments.