Adsorption Capacity Of Column Research Articles

Fabrication of melamine formaldehyde/graphene oxide composite for efficient static and dynamic adsorption of lead ions from aqueous medium.

The present work discusses the synthesis, characterization, and environmental applications of graphene oxide (GO), melamine formaldehyde resin (MF), and melamine formaldehyde/graphene oxide composite (MGO) for the efficient removal of Pb2+ from aqueous medium via batch and column procedures. TGA, XRD, TEM, zeta potential, nitrogen adsorption/desorption, ATR-FTIR, and other characterization techniques revealed that MGO is characterized by a greater surface area (609 m2/g), total pore volume (1.0106 cm3/g), pHPZC (6.5), and the presence of various surface chemical functional groups. The synthesized solid adsorbents were used in both static and dynamic adsorption processes to remove Pb2+, with varying application parameters such as pH, starting concentration, adsorbent dosage, and shaking time in the case of static adsorption method. While through the column adsorption process the effects of column bed height, flow rate, and starting Pb2+ were taken into consideration. Results of the batch adsorption demonstrated that MGO had the highest Langmuir adsorption capacity (201.5 mg/g), and the adsorption fit the nonlinear Langmuir adsorption model and Elovich kinetic models. The adsorption of Pb2+ onto all prepared solid materials is endothermic, spontaneous, and physical in nature, as demonstrated by thermodynamic studies. Column adsorption of Pb2+ well fitted by Thomas and Yoon Nelson nonlinear adsorption models. MGO showed a maximum column adsorption capacity of 168 mg/g when applying 4 cm, 15 mL/min, and 150 mg/L as bed height, flow rate, and initial Pb2+, respectively. With only a 12.6% reduction in its adsorption capacity, column regeneration showed that MGO exhibited a high degree of reusability even after five cycles of adsorption/desorption studies.

Harnessing carboxymethyl cellulose and Moringa oleifera seed husks for sustainable treatment of a multi-metal real waste

This study aimed to evaluate effective treatment strategies for laboratory waste with an initial pH of 1.0, containing Cr6+, Mn2+, Co2+, Fe3+, Ni2+, Cu2+, Zn2+, Sr2+, Hg2+, and Pb2+ ions, focusing on flocculation, precipitation, and adsorption techniques. The study utilized microparticles derived from Moringa oleifera seed husks (MS), cryogels of carboxymethyl cellulose (CMC), and hybrid cryogels combining CMC and MS (CMC-MS25 and CMC-MS50) as adsorbents. The optimal strategy involved raising the pH to 7 using NH4OH, leading to the partial precipitation of metal ions. The remaining supernatant was then passed through columns packed with the aforementioned adsorbents. Utilizing CMC-MS25 and CMC-MS50 adsorbents resulted in the simultaneous removal of over 90% of the targeted metal ions. The adsorption of Cu2+ ions onto the adsorbents was facilitated by electrostatic interactions between Cu2+ ions and carboxylate groups, as well as Cu–OH chelation, as confirmed by X-ray photoelectron spectroscopy. Under optimized conditions, the fixed-bed column adsorption capacity was determined as 88.2 mg g−1. The CMC-MS25 adsorbents proved reusable at least 5 times, with the recovered Cu2+ ions potentially suitable for other processes. The scalability and feasibility of producing these novel adsorbents suggest a promising, cost-effective solution for treating complex matrices and recovering high-value metals, as copper.

Fabrication and characterization of Araucaria gum/calcium alginate composite beads for batch and column adsorption of lead ions

In this work, we developed five solid adsorbents such as calcium alginate beads (CG), Araucaria gum (AR) extracted from Araucaria heterophylla tree by chemical precipitation procedures, and Araucaria gum/calcium alginate composite beads (CR21, CR12, and CR11) prepared with different calcium alginate: Araucaria gum ratios (2:1, 1:2, and 1:1, respectively). The synthesized solid adsorbents were characterized utilizing TGA, XRD, nitrogen adsorption/desorption analysis, ATR-FTIR, pHPZC, swelling ratio, SEM, and TEM. Through the batch and column adsorption strategies, we evaluated the effect of adsorbent dose, pH, initial Pb (II) concentration, shaking time, bed height, and flow rate. The data of batch technique indicated that CR11 demonstrated a maximum batch adsorption capacity of 149.95 mg/g at 25 °C. Lead ions adsorption was well fitted by pseudo-second order and Elovich according to kinetic studies, in addition to Langmuir and Temkin models based on adsorption isotherm studies onto all the samples. Thermodynamic investigation showed that Pb (II) adsorption process is an endothermic, physical, and spontaneous process. The highest column adsorption capacity (161.1 mg/g) was achieved by CR11 at a bed height of 3 cm, flow rate of 10 mL/min, and initial Pb+2 concentration of 225 mg/L with 68 min as breakthrough time and 180 min as exhaustion time. Yoon-Nelson and Thomas models applied well the breakthrough curves of Pb (II) column adsorption. The maximum column adsorption capacity was decreased by 11.4 % after four column adsorption/desorption processes. Our results revealed that CR11 had an excellent adsorption capacity, fast kinetics, and good selectivity, emphasizing its potential for its applications in water treatment.

Removal of Malachite Green Using Hydrochar from PALM Leaves

Biochar was prepared by the hydrothermal carbonization (HTC) of palm leaves, characterized, and utilized as an adsorbent for Malachite Green dye (MG). The Higher Heating Value (HHV) of biochar depends on the carbonization temperature and has a maximum value of 24.81 MJ/kg. Activation using H2O2 oxidation of HTC biochar prepared at 208 °C produced AHTC with improved capacity. The optimum pH was found to be in the range 7–8. Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich adsorption isotherms were used to study MG adsorption data. The Langmuir isotherm provided the best fit for experimental data. Experiments conducted using activated biochar AHTC at 25 °C resulted in an adsorption capacity of 62.80 mg/g, far greater than what was observed for HTC biochar (45.59 mg/g). The maximum adsorption capacity was 88% when the concentration of MG solution was 66 ppm. The free energy change in adsorption DG° indicated that the adsorption process was spontaneous. Adsorption followed pseudo-second-order kinetics. Fixed-column adsorptions models, namely, Thomas, Yan et al. and Yoon–Nelson models, were investigated for AHTC. The column adsorption capacity determined by the Thomas model was 33.57 mg/g. In addition, a computational investigation has been carried out to determine the structural and electronic features, as well as the quantum chemical parameters of HTC and MG. Moreover, the interaction between the HTC and MG is investigated, which is further elaborated by performing non-covalent interaction (NCI) through the reduced density gradient (RDG) analysis. Thus, the easily prepared hydrochar from abundant waste palm leaves can be used as a high-value biocoal and efficient adsorbent of the cationic dye malachite green.

Water Cleaning by a Continuous Fixed-Bed Column for Cr(VI) Eco-Adsorption with Green Adsorbent-Based Biomass: An Experimental Modeling Study

In this study, chromate adsorption onto red peanut skin (RPS) was investigated in a fixed-bed column; FTIR, PZC, SEM, DLS, and BET were used to evaluate its adsorption properties. The experiments were conducted to determine the effect of physical parameters, including the inlet initial Cr(VI) concentration (100–500 mg L−1), bed height (10–20 cm), and feed flow rate (13.59–23.45 mL min−1). They were carried out to predict breakthrough curves. The adsorption capacity coefficients were determined using the most widely used Bohart–Adams model. It was tested to fit experimental data, for a better understand the dynamic behavior, and for further optimize column performance. It was found that the Cr(VI) uptake decreases when increasing the flow rate and that high chromate concentration and bed height consequently increase the column’s life span. A high column adsorption capacity can be achieved with a higher Cr(VI) concentration due to the higher driving force. The results indicated that the Bohart–Adams model provides a good description (R2 > 0.98) of the experimental data of the Cr(VI)’s removal from the aqueous solution on the RPS suggesting that the surface diffusion is the rate-limiting step in the continues adsorption process.. Breakthrough adsorption capacity is crucial for comparing RPS with other similar materials. Indeed, possible mechanisms have been suggested for illustrating adsorption onto RPS. The obtained results showed significant potential of 26.23 mg g−1 of RPS on Cr(VI) elimination at a natural pH of 5.35. Furthermore, this global investigation allowed for the design of a promising low-cost material for the future scale-up of cleaning wastewater polluted by metal and determine the properly conditions for operating column adsorption. This material provides an economical, efficient means of eliminating pollutants, thus meeting the main aims of the UN Sustainable Development Goals (UN SDGs).

Radiation synthesis of binary poly(ionic liquid) functionalized silica-based materials for selective adsorption of ReO4− as analogue of TcO4− from simulated radioactive wastewater

Binary ionic liquid functionalized silica-based adsorbents for the treatment of TcO4− in radioactive wastewater was synthesized and evaluated. The column adsorption capacity of adsorbents increased with increasing hydrophobicity of the ionic liquid.

Enhanced adsorption and recyclability of surface modified hydrophobic silica aerogel with triethoxysilane: removal of cefixime by batch and column mode techniques.

Amine modified pumice-derived silica aerogel (AMPDSA) was synthesized and grafted up to 6.52 [Formula: see text] with (3-aminopropyl) triethoxysilane for cefixime antibiotic adsorption. Using Response surface methodology, at the pH of 3, the maximum removal of cefixime of 80.42% for an initial concentration of 3.56mg L-1 was achieved at an equilibrium time of 150min. The compliance of various kinetic and isotherm models for the batch sorption system was corroborated from the correlation coefficient (R2) values. The maximum adsorption capacity of 19.76mgg-1 and 49.63mgg-1 was calculated for Langmuir and Khan isotherm models, respectively. The removal by fixed-bed column as a function of flow rate, initial cefixime concentration, and bed height was also performed. The maximum adsorption capacity of column with the bed height of 15cm was found to be 31mgg-1 at the flow rate of 10mLmin-1 for the initial concentration of 20mg L-1. The compliance of Thomas model with the column sorption was observed. The characterization using SEM, BET, and XRD was carried out for the virgin and regenerated AMPDSAs. The regeneration experiments confirmed the ability of AMPDSA for its cefixime removal efficiency of 80% up to eight cycles.

Ultra-high selective removal of CR and Cr(VI) from aqueous solutions using polyethyleneimine functionalized magnetic hydrochar: Application strategy and mechanisms insight

Herein, a novel polyethyleneimine (PEI) functionalized magnetic hydrochar (MHTCP-5) adsorbent with low cost and easy recovery is unveiled, which exhibits excellent adsorption capacity for CR and Cr(VI) from aqueous solution. And the maximum adsorption capacities are respectively 1019.2 and 287.7 mg/g, exceeding those of most previously reported biochar-based adsorbents. Surprisingly, MHTCP-5 possesses ultra-high selectivity for both CR and Cr(VI) from mixed solutions, which was the first time proposed in this study. In addition, a series of adsorption experiments are conducted under different conditions to investigate the adsorption behavior of MHTCP-5. The results suggest that the adsorption of CR and Cr(VI) onto MHTCP-5 followed Elovich and Freundlich models, and the surfactants have a significant influence on the adsorption capacity due to electrostatic interactions. Moreover, MHTCP-5 exhibits extremely fast adsorption rate for Cr(VI) ions, which can reduce the Cr(VI) concentration below WHO allowable value (0.05 mg/L) for drinking water within only 5 min, and the cycle experiments manifest that MHTCP-5 still exhibits excellent Cr(VI) adsorption capacity after 17 cycles. The adsorption-reduction mechanisms of CR and Cr(VI) onto MHTCP-5 are systematically investigated based on FT-IR and XPS. Additionally, the outstanding removal efficiency of CR and Cr(VI) in simulated wastewater as well as the superior reusability and fixed-bed column adsorption capacity of MHTCP-5 adsorbent indicate that the adsorbent has great potential in the treatment of actual wastewater containing CR and Cr(VI).

Simultaneous nitrate and phosphate abatement using calcium silicate hydrate adsorbent: Fixed bed column adsorption study

Nitrate and phosphate are the main nutrients that cause eutrophication and thus remedial measures have to be taken. In this work, Calcium Silicate Hydrate (CSH) synthesized from Alum Factory solid waste residue was used to simultaneously remove nitrate and phosphate by fixed-bed column adsorption. The effect of fixed-bed column operating parameters, namely flow rate (5, 7.5, and 10 mL/min.) and bed depth (6, 9, and 12 cm) on the breakthrough curves were examined. Fixed-bed column adsorption models namely Thomas, Yoon-Nelson, Adams-Bohart, and bed depth service time (BDST) were fitted to the experimental data. The observed data demonstrated that Thomas and BDST models were fitted well with the experimental data and thus are suitable to predict the breakthrough curve parameters for both nitrate and phosphate. The column adsorption capacity estimated by the Thomas model for binary-component, mono-component, and municipal wastewater were 1.74 mg/g, 2.13 mg/g and 1.63 mg/g for nitrate, and 4.93 mg/g, 5.61 mg/g, and 3.37 mg/g for phosphate, respectively. The high R2 value of 0.973–0.997 for nitrate and 0.917–0.999 for phosphate indicated that the BDST model could be used to estimate the breakthrough time required for selected depth without conducting extra experiments. Moreover, the fractional value of 0.82 and 0.88 for nitrate and phosphate, respectively calculated using (qm binary)/(qm mono) for simultaneous adsorption of nitrate and phosphate indicated the antagonism (competitive) nature of adsorption. The observation of this work concluded that CSH could be used for the simultaneous removal of nitrate and phosphate from an aqueous solution.

Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests

The co-contamination of metals and organic pollutants, such as Pb and methyl tert-butyl ether (MTBE), in groundwater, has become a common and major phenomenon in many contaminated sites. This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier (PRB) packed with mixed zeolites (clinoptilolite and ZSM-5) using fixed-bed column tests and breakthrough curve modeling. The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite. The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold. The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules (130.6 mg/g versus 45.3 mg/g) due to higher specific surface areas. The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5% of granular clinoptilolite was mixed with 5% ZSM-5 and 90% sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite. This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs.

Ingenious ambient temperature fabrication zirconium-metal organic framework laden polysaccharide aerogel as an efficient glyphosate scavenger

Developing superior adsorbents to remove pollutants from aqueous solution is increasingly becoming urgent with respect to grave water pollution and public health consequences. Herein, a metal organic framework (MOFs)-decorated shapeable aerogel (CS-CNC@UiO-66-NH2) prepared by in situ growth of Zr-MOF (UiO-66-NH2) on chitosan/cellulose nanocrystal (CS-CNC) hybrid aerogel at room temperature was developed to remove glyphosate (Gly) from water. The aerogel possessed highly porous structure and excellent water stability upon introduction of cellulose nanocrystals extracted from cotton. Besides, the loading ratio of UiO-66-NH2 of the proposed ambient growth strategy (37.72%) was higher than conventional solvothermal method (10.91%) because of the structure integrity of polysaccharide aerogels at room temperature. Further, the BET area and porosity of CS-CNC@UiO-66-NH2 aerogel increased from 21.65 m2 g−1 to 231.60 m2 g−1 and 87.47–93.03% due to the synergy of UiO-66-NH2. Owing to these virtues, the separation-free aerogel exhibited a high adsorption capacity of 133.7 mg/g in batch adsorption and displayed high recyclability over four consecutive adsorption-desorption cycles. Moreover, the Zr-OH/oxygen-containing moieties of the aerogel, electrostatic attraction and hydrogen-bonding accounted for driving Gly adsorption. Considering practical application, the aerogels were packed in glass column for fixed-bed test which revealed that the aerogels could decontaminate Gly with column adsorption capacity of 44.99 mg/g. Consequently, the CS-CNC@UiO-66-NH2 aerogel with highly porous structure exhibited good Gly adsorption and simple separation, offering a novel strategy to synchronously improve adsorption capacity of polysaccharide-based adsorbent and MOFs shaping for pollutant removal.

Application of amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite in fixed-bed column for phosphate removal from water

BACKGROUND AND OBJECTIVES: Fixed-bed column has been considered an industrially feasible technique for phosphate removal from water. Besides the adsorption capacity, the effectiveness of an adsorbent is also determined by its reusability efficiency. In this study, phosphate removal by a synthesized amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite in a fixed-bed column system was examined. METHODS: The effects of flow rate, bed height, phosphate concentration, solution pH, and adsorbent particle size on the phosphate adsorption ability were examined through a series of continuous adsorption experiments. The appropriate breakthrough curve models, phosphate adsorption from real anaerobic sludge and synthetic seawater, column regeneration and reusability, and adsorption mechanism were also investigated for practical application feasibility. FINDINGS: The results showed that the increased bed height and phosphate concentration, and reduced flow rate, pH, and adsorbent particle size were found to increase the column adsorption capacity. The optimum adsorption capacity of 25.15 mg-P/g was obtained at pH 4. The coexistence of seawater ions had a positive effect on the phosphate adsorption capacity of the composite. Nearly complete phosphate desorption, with a desorption efficiency of 91.7%, could be effectively achieved by 0.1 N NaOH for an hour. Moreover, the initial adsorption capacity was maintained at approximately 83% even after eight adsorption-desorption cycles, indicating that the composite is economically feasible. The high phosphate adsorption capacity of the composite involves three main adsorption mechanisms, which are electrostatic attraction, inner-sphere complexation, and anion exchange, where the amorphous zirconium hydr(oxide) on the surface of the layered double hydroxides likely increased the number of active binding sites and surface area for adsorption. CONCLUSION: The amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite, with its high adsorption capacity and superior reusability, has the potential to be utilized as an adsorbent for phosphorus removal in practical wastewater treatment. This study provides insights into the design of amorphous zirconium (hydr)oxide/MgFe layered double hydroxides composite for phosphorus removal and recovery in a practical system.

Removal of fluoride from groundwater using MnO2 bentonite-smectite rich clay soils composite

A clay based composite adsorbent for fluoride was fabricated by blending the locally available smectite rich clay and MnO2 coated bentonite clay. The efficiency of the material towards fluoride adsorption was evaluated using fixed-bed column experiments. The results from column experiments showed that increasing parameters such as bed height and initial fluoride concentration increases the adsorption capacity whereas increasing flow rate decreases the column adsorption capacity. The paramount adsorption capacity of obtained at breakthrough point 0.6 mg/g when flow rate of 0.65 mL/min, bed height 2.5 cm and adsorbate concentration of 3.75 mg/L were used. The prepared composite was successfully regenerated using 0.01 M Na2CO3 and reused for up to 2 cycles. Thomas breakthrough model confirmed that fluoride adsorption by the prepared composite involves chemical interaction and transfer of ions into the internal layers of the adsorbent particles. The obtained results showed that MnO2 bentonite-smectite rich clay composite has potential for use in groundwater defluoridation.

Ultrahigh and selective adsorption of Au(III) by rich sulfur and nitrogen-bearing cellulose microspheres and their applications in gold recovery from gold slag leaching solution

• A novel adsorbent with high-density functional groups was prepared. • NS-CM exhibited ultrahigh capacity of 4656.9 mg/g in batch experiments. • The column adsorption capacity of NS-CM reached a significant breakthrough. • NS-CM can effectively recover trace Au(III) from gold slag leaching solution. • The adsorption mechanism was ion exchange, coordination and oxidation-reduction. In this work, we combined a powerful radiation grafting method that yields high-density functional groups containing rich sulfur and nitrogen with microcrystalline cellulose microspheres (MCCs) to achieve a novel functionalized cellulose microsphere (NS-CM) as a Au(III) adsorbent. It was found that high-density functional groups containing around 37.4 wt% sulfur and nitrogen in total on the NS-CM exhibited a maximum capacity of 4656.9 mg/g in batch experiments, which is the highest level recorded in comparison with other reported literatures. Meanwhile, the column adsorption capacity of NS-CM reached 3110 g/L in simulated acidic waste effluent, which is a significant breakthrough in Au(III) uptake. Finally, the NS-CM could selectively capture trace Au(III) from the actual gold slag leaching solution with an excellent adsorption efficiency of 95.17%. A well-designed adsorbent (NS-CM) with ultrahigh adsorption ability and excellent selectivity provided a very efficient, sustainable, and industrially feasible way for Au(III) to be recovered in leaching solution of gold slag, electronic waste, and other prospective sources.

High phosphate removal using La(OH)3 loaded chitosan based composites and mechanistic study

Our present study was to prepare a biomass-supported adsorbents with high adsorptive capacity and high selectivity to prevent the accelerated eutrophication in water body. To this end, different metal hydroxide (La, Zr and Fe) first was successfully loaded on chitosan microspheres. Then the quaternary ammonium group with different content was introduced into the adsorbent by polymerization. By comparison of adsorption properties, chitosan-La(OH)3-quaternary ammonium-20% (CS-La-N-20%) has strong adsorption to phosphate (160 mg/g) by immobilizing nano-sized La(OH)3 within a quaternary-aminated chitosan and it maintain high adsorption in the presence of salt ions. The pH results indicated that the CS-La-N-20% would effectively sequestrate phosphate over a wide pH range between 3 and 7 without significant La3+ leaching. What's more, adsorption capacity on the introduce of positively charged quanternary-aminated groups was significantly higher than that of the unmodified adsorbents at alkaline conditions. The column adsorption capacity reached 1300 bed volumes (BV) when phosphate concentration decreased until 0.5 mg/L at 6 BV/hr. The column adsorption/desorption reveals that no significant capacity loss is observed, indicating excellent stability and repeated use property. Characterizations revealed that phosphate adsorption on CS-La-N-20% through ligand exchange (impregnated nano-La(OH)3) and electrostatic attraction (positively charged quanternary-aminated groups). All the results suggested that CS-La-N-20% can serve as a promising adsorbent for preferable phosphate removal in realistic application.

A comparative study of immobilizing ammonium molybdophosphate onto cellulose microsphere by radiation post-grafting and hybrid grafting for cesium removal.

Ammonium molybdophosphate (AMP) exhibits high selectivity towards Cs but it cannot be directly applied in column packing, so it is necessary to prepare AMP-based adsorbents into an available form to improve its practicality. This work provided two AMP immobilized cellulose microspheres (MCC@AMP and MCC-g-AMP) as adsorbents for Cs removal by radiation grafting technique. MCC-g-AMP was prepared by radiation graft polymerization of GMA on microcrystalline cellulose microspheres (MCC) followed by reaction with AMP suspension, and MCC@AMP was synthesized by radiation hybrid grafting of AMP and GMA onto MCC through one step. The different structures and morphologies of two adsorbents were characterized by FTIR and SEM. The adsorption properties of two adsorbents against Cs were investigated and compared in batch and column experiments under different conditions. Both adsorbents were better obeyed pseudo-second-order kinetic model and Langmuir model. MCC-g-AMP presented faster adsorption kinetic and more stable structure, whereas MCC@AMP presented more facile synthesis and higher adsorption capacity. MCC@AMP was pH independent in the range of pH 1-12 but MCC-g-AMP was sensitive to pH for Cs removal. The saturated column adsorption capacities of MCC@AMP and MCC-g-AMP were 5.4g-Cs/L-ad and 0.75g-Cs/L-ad in column adsorption experiments at SV 10 h-1. Both adsorbents exhibited very high radiation stability and can maintain an adsorption capacity of >85% even after 1000kGy γ-irradiation. On the basis, two AMP-loaded adsorbents possessed promising application in removal of Cs from actual contaminated groundwater. These findings provided two efficient adsorbents for treatment of Cs in radioactive waste disposal.

Graphene nickel silica supported nanocomposites as an efficient purifier for water treatment

This work reports the preparation of graphene nickel silica GCNi@SiO2 (1) and GCNi@1/2SiO2 (2) adsorbents in high yield. The preparation is a simple pyrolysis of readily prepared Ni(2,2′-bipyridine)Cl2.H2O complex with cheap abundant silica support and an extra carbon source anthracene, at 850 °C. The nanocomposites showed rough porous carbon microstructures over silica particles with some nickel nanoparticles forming rods, cubes, octahedron, pyramids, and cuboids within 5 μm size. The agglomerated nickel nanoparticles bursting out of graphitic sheets caused increase in surface porosity and noticeable electroactivity. The current density for electrode coated with (2) is three time greater than in (1) when testing K4Fe(CN)6. TEM of GCNi (3) indicated the presence of 15 to 45 nm nanoparticles made up of graphitic shell and nickel cores, graphene flakes and bamboo-like multiwall carbon nanotubes MWCNT. Although in (2), graphene and MWCNT were condensed on silica. Raman and EDX indicated higher carbon to silica ratio in (2) compared to (1), as expected. The presence of Ni(0) and Ni2+ in nanocomposites is evidenced by XPS and Xrd. The nanocomposites were applied as adsorbent of aromatic cationic dyes for water treatment. Langmuir adsorption capacity qmax of (1) for methylene blue was 39.5 mg/g. While qmax of (1) and (2) for crystal violet were 23.9 and 26.0 mg/g, respectively. The mechanism of adsorption is the best described as π–π interactions between graphitic carbon and aromatic cationic dyes. The column adsorption capacity of (2) for crystal violet was 9.8 mg/g, and the data was best fitted with Thomas model. The column was recycled three times with no clogging.

Pragmatic strategy for the removal of ammonia from gold mine effluents using a combination of electro-coagulation and zeolite cation exchange processes: A staged approach

Considerable amount of water is frequently used in gold mine for dust suppression and ore processing. The generated effluent mainly contains heavy metals, suspended solid and ammonia. This paper investigates the ammonia removal from mine effluent by a natural zeolite-adsorption process. Preliminary experiments showed that the fresh zeolite has a higher ammonia removal efficiency. Based on the results of adsorption isotherm, Langmuir isotherm model was found to be well fitted with the experimental data with a maximum adsorption capacity of 8.7 mg N g−1 zeolite. As the ammonia concentration in the mine effluent was not exceeding 30 mg L−1, column adsorption capacity was around 0.85 mg g−1; however, the regeneration of zeolite by 0.6 M NaCl was ineffective after third adsorption/regeneration cycle. To overcome this challenge, electrocoagulation process was introduced as a pre-treatment step to remove suspended solids and metal cations. With current density of 1.14 mA cm−2 and 20 min of reaction time, more than 90 % of suspended solid, turbidity and total metal cations were precipitated. For an optimal scenario, the adsorption capacity of zeolite increased up to 2.3 mg.g−1. Electrocoagulation for raw effluent significantly prolongs the life span of zeolite because the adsorption of trivalent metal cations on zeolite is irreversible.

Utilisation of cobalt doped Iron based MOF for enhanced removal and recovery of methylene blue dye from waste water

In the present study attempts have been made to improve the adsorption performance of Fe-Benzene dicarboxylic acid metal organic framework for the removal of methylene blue dye from waste waters through cobalt doping. The removal efficiency of Co doped Fe-BDC MOF improved from 8.56 to 23.92 mg/g. Batch and column methods have been used to evaluate removal efficiency of the Co doped Fe-BDC MOF for removal of methylene blue. Effect of various parameters such as pH, amount of adsorbent, dye concentration, temperature, and contact time on dye removal has been studied. It has been observed that extent of adsorption increases in acidic medium and dye removal decreases on increasing pH of dye solution. Langmuir adsorption isotherm has been found to best fit the adsorption process. Thermodynamic parameters, evaluated for the dye-adsorbent system, revealed that the adsorption process is endothermic in nature. Experimental data were modeled by using pseudo-first, pseudo-second and intraparticle diffusion models. Pseudo-second-order kinetics was found to describe the adsorption of methylene blue on MOF. Column operations were made to achieve bulk removal of the dye. Column adsorption capacity has been found to be greater than the batch adsorption capacity. The improved maximum adsorption capacity of the Co doped Fe BDC MOF in comparison to the previously developed Fe BDC MOF establishes the significance of the present investigation.

Tuning the crosslink structure of cationic hydrogel for enhanced chromium(VI) removal: The covalent and electrostatic co-crosslinked effects and adsorption mechanism

Elevated chromium(VI) (Cr(IV)) concentrations in drinking water or ground water can pose a public health concern. In this study, layered double hydroxides-isethionate (LDH-ise) assisted covalent and electrostatic co-crosslinked cationic hydrogel (CH-LDH-ise) was prepared as a potential adsorbent for Cr(VI) removal from aqueous solution. The scanning electron microscopy and X-ray diffraction results indicated that the LDH-ise sheets were exfoliated and crosslinked with the 3-(Acryloylamino) propyltrimethylaminium chloride (APTMACL) polymer chains. The adsorption of Cr(VI) onto the CH-LDH-ise was highly pH-dependent, and the removal efficiency by CH-LDH-ise composites was much higher than the CH (no crosslinker). The adsorption kinetic followed a pseudo-second-order, and reached equilibrium within 2 h. The corresponding maximum Cr(VI) adsorption capacity of CH-LDH-ise was 408.4 mg/g at the equilibrium concentration of 364.4 mg/L. The enhanced adsorption of Cr(VI) was also achieved in the presence of competing anions (including Cl−, NO3−, SO42−, HCO3−, SiO44−, and HA). Moreover, the in situ regeneration/recycle results implied the column adsorption capacity of CH-LDH-ise was 2250 bed volumes as the concentration of Cr(VI) decreased from 2.5 mg/L to 0.1 mg/L (The US drinking water standard for total chromium) at empty bed contact time = 6 min, and slightly decreased in the second recycle. The combination analysis of in situ Fourier transform infrared, in situ Raman, X-ray photoelectron spectra, and electron paramagnetic resonance revealed that the Cr(VI) capture mechanism was dominated by the electrostatic interactions and hydrogen bonding effect - the sources of the –N+(CH3)3 and –NH groups in CH-LDH-ise, respectively.