External Cation Exchange Capacity Research Articles

Facile and innovative application of surfactant-modified-zeolite from Austrian fly ash for glyphosate removal from water solution

This study highlights a pioneering approach in the development of an efficient, affordable, and economically feasible adsorbent specifically tailored for the removal of glyphosate (Gly) from contaminated water. To accomplish this objective, a low-cost and pure NaA Zeolite (NaAZ) was synthesized with 93% crystallinity from Austrian fly ash (AFA) as a precursor for the first-time. Taguchi design was employed to optimize critical parameters such as the SiO2/Al2O3 ratio, alkalinity concentration, time, and temperature. The cation exchange capacity (CEC) and external cation exchange capacity (ECEC) are determined as critical factors for the modification process. Subsequently, the pure NaAZ was modified with hexadecyl trimethyl ammonium chloride (HDTMAC), a cationic surfactant. The utilization of surfactant-modified zeolite (SMZ) for Gly removal demonstrates its innovative application in this field, highlighting its enhanced adsorption capacity and optimized surface properties. The AFA, NaAZ, and SMZ were characterized using analytical techniques including XRD, XRF, FTIR-ATR, SEM, TGA, BET, CHNSO analyzer and ICP-OES. The adsorbent exhibited effective Gly removal through its pH-dependent charge properties (pH 2–10), with an optimized pH 6 facilitating a significant electrostatic interaction between the adsorbent and Gly. SMZ demonstrated remarkable adsorption capacity and removal efficacy, surpassing most reported adsorbents with values of 769.23 mg/g and 98.92% respectively. Our study demonstrates the significant advantage of the SMZ, with a low leaching concentration of only 6 ppm after 60 days, ensuring environmental safety, long-term stability, and public health considerations. The kinetics of the adsorption process was well described by the pseudo-second order and the Freundlich isotherm. Pore diffusion and H-bonding were postulated to be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption. Consequently, SMZ provides a practical significance, broad applicability and promising solution for Gly removal, facilitating sustainable water treatment.

Characterization of Bentonites from the In Situ ABM5 Heater Experiment at Äspö Hard Rock Laboratory, Sweden

The Alternative Buffer Material ABM5 experiment is an in situ medium-scale experiment performed at Äspö Hard Rock Laboratory (HRL) conducted by SKB in Sweden with the aim of analysing the long-term stability of bentonites used as an engineering barrier for a high-level radioactive waste repository (HLWR). In this work, four different ring-shaped Ca- and Na-bentonite blocks, which were piled around a carbon steel cylindrical heater, subjected to a maximum temperature of 250 °C and hydrated with saline Na-Ca-Cl Äspö groundwater (0.91 ionic strength), were characterized after dismantling. This work allowed us to identify the main geochemical processes involved, as well as the modifications in the physico-chemical properties and pore water composition after 4.4 years of treatment. No significant modifications in mineralogy were observed in samples close to the heater contact, except an increase in Fe content due to C-steel corrosion, carbonate dissolution/precipitation (mainly calcite and siderite) and Mg increase. No magnetite and a low amount of Fe(II) inside the clay mineral structure were detected. No modifications were observed in the smectite structure, except a slight increase in total and tetrahedral charge. A decrease in external surface area and cation exchange capacity (CEC) was found in all samples, with lower values being detected at the heater contact. As a consequence of the diffusion of the infiltrating groundwater, a modification of the composition at clay mineral exchange sites occurred. Ca-bentonites increased their Na content at exchange sites, whereas Na-bentonite increased their Ca content. Exchangeable Mg content decreased in all bentonites, except in MX-80 located at the bottom part of the package. A salinity gradient is observed through the bentonite blocks from the granite to the heater contact due to anions are controlled by diffusion and anion exclusion. The pore water chemistry of bentonites evolved as a function of the diffusion transport of the groundwater, the chemical equilibrium of cations at exchange sites and mineral dissolution/precipitation processes. These reactions are in turn dependent on temperature and water vapor fluxes.

Fixed-Bed Modification of Zeolitic Tuffs and Their Application for Cr(VI) Removal.

Natural clinoptilolite tuff (CL) and chabazite-clinoptilolite tuff (CH) were modified in fixed-bed column by immobilization of hexadecyltrimethylammonium bromide (HDTMA-Br), then investigated as a sorbent for inorganic anions of Cr(VI). The proposed modification technique combined with surfactant solution batching allows minimizing the surfactant loses through foaming and crystallization and creation of stable organic coverage. The HDTMA loading depended on the mineral composition of the zeolitic tuff, the topology of its external surface, and process conditions. The maximum surface coverage was obtained by gradually dosing surfactant solution in the smallest volume of batches and corresponded up to 100% and 182% of external cation exchange capacity (ECEC) for mono and double layer coverage, respectively. In case of mono layer coverage, modification proceeds until the exhaustion of surfactant in supply solution, while in the double layer one, until equilibrium of HDTMA concentration in both zeolitic and liquid phases was established. The efficiency of Cr(VI) uptake by prepared surface modified zeolites (SMZs) increased with increasing of HDTMA loading. In the case of mono layer SMZs, the capacities of CH-HDTMA and CL-HDTMA were 10.3 and 5.4 mg/g, respectively, while in the case of double layer SMZs, the amount of Cr uptake on CH-HDTMA and CL-HDTMA were 16.8 and 15 mg/g, respectively. Ion exchange is the predominant mechanism of Cr(VI) sorption but it takes place only if modification resulted in at least partial double layer coverage. The XPS analysis reveals Cr(VI) reduction to a less-toxic Cr(III) by the electron donating N-containing groups and by reaction with Fe+2 ions on the zeolite external surface.

Modified zeolite as a sorbent for removal of contaminants from wet flue gas desulphurization wastewater

The aim of the present work was to prepare and investigate the sorption efficiency of unwashed cationic surfactant-modified natural zeolite (Cp) for the simultaneous removal of selected inorganic compounds (NH4+, SO42−, NO3−, Fe, Mn, Zn, and Ni) from wet flue gas desulphurization (WFGD) wastewater. The Cp was modified using hexadecyltrimethylammonium bromide (HDTMA-Br) salt in an amount not exceeding its external cation exchange capacity (1.0 ECEC). The present analysis showed that the modification process was completed by forming an incomplete monolayer by the uptaken HDTMA ions. Fourier transform infrared (FTIR) and textural analysis indicated that the adsorbed HDTMA ions formed a disordered, macroporous structure onto Cp surface. Batch adsorption experiments with different sorbent dosages revealed an increase in the sorption efficiency of NH4+ and NO3− with the increase in the amount of modified Cp. The highest removal efficiency was observed at adsorbent dosage of 150 g/L. The studies also revealed, that the SO42− removal did not change significantly regardless the sorbent dosage. The kinetic tests showed that a substantial amount of inorganic compounds was removed within 2 h, and the sorption kinetics of each compound were best fitted to the pseudo-second order model. The studies of adsorption mechanism revealed that cation exchange, anion exchange with Br− counterion, electrostatic interaction between the surfactant and inorganic ions, as well as precipitation of insoluble salts might be involved simultaneously in the immobilization of NH4+, SO42−, NO3−, Fe, Mn, Zn, and Ni.

Surface functionalized Philippine natural zeolite for arsenic adsorption in an aqueous solution

This study shows the effectiveness of the natural zeolite and its surface modified form in adsorbing arsenic from deep well water sources and irrigated waters in some rural areas in the Philippines. It aims to compare the arsenic adsorption efficiency between, pre-conditioned sodium modified natural [Na-Philippine natural zeolites (PNZ)] and surface-modified Na-PNZ (SM-PNZ) with varying concentrations of 100% and 330% of the external cation exchange capacity (ECEC) of the PNZ. Characterization of the adsorbents were conducted such as X-ray diffraction (XRD) (mineralogy using X-ray diffraction), XRF (chemical composition using X-ray fluorescence), Fourier-transform Infrared for functionalization test and wettability tests (contact angle and water penetration tests). Arsenic adsorption studies were conducted using the Atomic absorption spectroscopy to determine the arsenic uptake of the adsorbents at varying contact times. The results proved that the adsorbent modified with surfactant, cetyltrimethylammonium bromide, at 100% ECEC has the highest arsenic uptake compared with Na-PNZ.

Differences in coating mechanism of structurally different aluminosilicates observed through the thermal analysis

Systematic modification of three structurally different minerals (zeolite, mica, and vermiculite) was carried out with the aim of determining the modification mechanism and exposing the hydrophobic surface that can be used as a sorbent for many organic compounds. Mechanism of modification with cationic surfactant depends strongly on the mineral type. In order to identify the influence of aluminosilicates structural differences on the modification process, adsorption experiments with organic matter and water vapor, supplemented with the DTA/TG analysis, were performed. The cation exchange capacity (CEC) value was 1454 > 560 > 28 meq kg−1 for zeolite (clinoptilolite), vermiculite, and mica (muscovite), respectively. Despite its CEC value, vermiculite adsorbed three times the amount of organic matter than did clinoptilolite due to the porous structure of zeolite, which acted to limit the adsorption only on the external exchangeable cations. If the loading amount is equal to the CEC or the external cation exchange capacity for clinoptilolite (ECEC ≈ 10% CEC), the monolayer will form while mineral surface will have hydrophobic character. Only one active center exists at the surface of the clinoptilolite that was identified by DTA curves with a sharp and defined peak around 300 °C and by the mass loss at the TG diagrams. Two significant and equal active centers were observed in vermiculite, one for the exchange of the surface cations and the other for the interlayer cations and H2O molecules. Muscovite CEC is negligible, and due to the absence of any other functional groups, the modification of this mineral was impossible.

Experimental Study on the Removal of VOCs and PAHs by Zeolites and Surfactant-Modified Zeolites

Synthetic zeolite Na-X and clinoptilolite (Cp) as well as their modifications with quaternary ammonium salts were used to remove volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. A novel procedure was developed for the synthesis of organo-zeolites which consisted of surface modification with hexadecyltrimethylammonium bromide (HDTMA) in amounts of 1.0 and 2.0 of external cation exchange capacity (ECEC). Modification of both zeolites with HDTMA improved sorption properties. p-Xylene and dibenz[a,h]anthracene were adsorbed in amounts of 6.82 and 0.65 mg/g, respectively. Ethylbenzene and naphthalene were the lowest-removed hydrocarbons (2.99 and 0.058, respectively). The removal efficiencies for BTEX followed the order p-xylene > toluene > benzene > ethylbenzene, and for PAHs they followed the order dibenz[a,h]anthracene > benzo[a]pyrene > anthracene > naphthalene. Efficiency of sorption depends on the chemical properties of the various organic compounds (d...

Investigations on humic acid removal from water using surfactant-modified zeolite as adsorbent in a fixed-bed reactor

Natural organic matter (NOM) is ubiquitous in aquatic environments and has recently become an issue of worldwide concern in drinking water treatment. The major component of NOM is humic acids (HA). In this study, a natural zeolite (mordenite) was modified employing hexadecyltrimethylammonium bromide (HDTMA) to enhance greater efficient sites for sorption of HA. The natural zeolite and surfactant-modified zeolite (SMZ) were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectrometer (FT-IR), N2 Adsorption–desorption isotherms and BET-specific surface area, thermographic analysis, derivative thermographic analysis (TGA-DTA) and Field emission scanning electron microscopy (FESEM). A fixed-bed reactor was used for the removal of HA and the effects of different experimental parameters such as HDTMA loading levels, HA solution flow rate, solution pH and eluent concentration were investigated. The results indicated that the SMZ bed with HDTMA loading of 75% of external cation exchange capacity (ECEC) at a flow rate of 2 BV/h and pH of 10 showed the greatest enhanced removal efficiency of HA while ethanol solutions (25%v/v) with feed flow rate of 2 BV/h were sufficient for complete regeneration of SMZ and desorption of HA. Measurements of surface area of SMZ indicated that a monolayer formation of the surfactant at those conditions allowed the optimum removal of HA.

Adsorption of the mycotoxin zearalenone by clinoptilolite and phillipsite zeolites treated with cetylpyridinium surfactant

In this study, organozeolites were prepared by treatment of the natural zeolites (clinoptilolite and phillipsite) with cetylpyridinium chloride (CP) equivalent to 50 and 100% of their external cation exchange capacities (ECEC). Organoclinoptilolites (ZCPs) and organophillipsites (PCPs) were characterized by FTIR spectroscopy, thermal analysis, determination of the point of zero charge and zeta potential. Adsorption of zearalenone (ZEN) by ZCPs and PCPs at pH 3 and 7 was investigated. Results showed that adsorption of ZEN increases with increasing amounts of CP at the zeolitic surfaces for both ZCPs and PCPs but the adsorption mechanism was different. Adsorption of ZEN by ZCPs followed a linear type of isotherm at pH 3 and 7 while ZEN adsorption by PCPs showed non linear (Langmuir and Freundlich) type of isotherm at both pH values. Different interactions between the ZEN molecule (or ion) and ZCPs and PCPs occurred: partition (linear isotherms) and adsorption in addition to partition (non linear isotherms), respectively. For the highest level of organic phase at the zeolitic surfaces, the maximum adsorbed amount of ZEN was 5.73mg/g for organoclinoptilolite and 6.86mg/g for organophillipsite at pH 3. Slightly higher adsorption: 6.98mg/g for organoclinoptilolite and 7.54mg/g for organophillipsite was achieved at pH 7. The results confirmed that CP ions at both zeolitic surfaces are responsible for ZEN adsorption and that organophillipsites are as effective in ZEN adsorption as organoclinoptilolites.

Use of surface modified natural zeolite (SMNZ) in pharmaceutical preparations. Part 2. A new approach for a fast functionalization of zeolite-rich carriers

Main purpose of the research was to define an operative protocol, applicable at industrial scale, optimizing the functionalization of natural zeolites with surfactants, especially in pharmaceutical and environmental sphere.Three zeolite-rich samples from Italy (PHI_SAV), Slovakia (CLI_SK) and California (CLI_CA) were used for preparation of SMNZ. Two different protocols allowed to carry out surfactant adsorption equilibrium runs and surfactant sorption kinetics by varying different parameters: mixing speed (4000, 6000, and 8000 rpm); contact time (15 ÷ 90 min) and initial surfactant concentration (from 25% to 200% of the external cation exchange capacity - ECEC) at a constant solid/liquid ratio (1 g/50 mL). Zeolite-rich materials were treated with solutions of cetylpiridinium chloride (CP-Cl). The functionalization of SMNZ was obtained by using a high-speed disperser.The amount of absorbed surfactant onto two carriers (CLI_SK and PHI_SAV) was evaluated through kinetic experiments under the following conditions: the initial CP-Cl concentration of 150% of the ECEC and a disperser speed of 8000 rpm. Results showed that after 15 min, equilibrium was attained with the adsorbed amount of about 0.14 meq/g of CP-Cl (equivalent to the ECEC of the investigated zeolitic support), confirming formation of monolayer (emi-micelle). The functionalization (micelle formation) of two samples occurred after 70 min of solid/liquid interaction with a total yield equal to 150% of the ECEC, thus indicating formation of a patchy bilayer.By contrast, CLI_CA behaves completely differently since the formation of emi-micelle was achieved only at much higher speed (18000 rpm) and not earlier than 90 min of mixing.

Sorption of organic compounds by organo-zeolites [abstract

Organic compounds such as BTEX and PAHs are one of the most common contaminants in water system. These contaminants would take decades to degrade and they have harmful effects on human health (Qin et al., 2008). Several treatment methods have been developed to remove those contaminants from industrial wastewater. They include ion-exchange, filtration, adsorption and the use of various types of sorbents for example zeolites (Kibazohi et al., 2004; Mathur et al., 2007; Aivaliotiet al., 2012; Almeida et al. 2012). Natural clinoptilolite (Cp) from the Bystre deposit in Slovakia and zeolite Na-X synthesized from fly ash has been modified with a hexadecyltrimethyl ammonium bromide (HDTMA) in amounts of 1.0 and 2.0 of external cation exchange capacity (ECEC) of the zeolites (Szala et al., 2013). The sorption properties of unmodified zeolites and organo-zeolites in terms of aqueous solutions of benzene, ethylobenzene, toluene, p-xylene (BTEX) and their mixtures as well as anthracene, naphthalene, benzo[a]pyrene, dibenzo[a,h]anthracene (PAHs) and their mixtures at different concentrations were evaluated. The results showed that the modification of the zeolite Na-X and Cp with HDTMA improves the sorption properties. Modification in the amount of 1.0 ECEC proved to be the best in terms of p-xylene, anthracene, naphthalene, benzo[a]pyrene, dibenzo[a,h]anthracene. On the other hand benzene, ethylobenzene and toluene were adsorbed the most effectively by 2.0 ECEC modification of Na-X and Cp. Based on experimental data, the removal efficiencies for BTEX follows the order: p-xylene > toluene > benzene > ethylobenzene, for POHs: dibenzo[a,h]anthracene > benzo[a]pyrene > anthracene > naphthalene. P-xylene and naphtalene were adsorbed in the greatest quantity and benzene and anthracene in the lowest quantity from the mixtures of BTEX and PAHs, respectively. The sorption efficiency depends on the physicochemical properties of the organic compounds (dipole moment, molar mass, molecule structure and the time of the sorption process) as well as natural Cp and synthetic zeolite Na-X properties, such as Si/Al ratio, texture parameters and external cation exchange capacity. With an increasing concentration of the hydrocarbons in the solution the sorption capacity increases (Szala et al., 2015). Natural Cp is a better sorbent than synthetic zeolite Na-X in case of BTEX sorption, while PAHs are adsorbed more effectively by zeolite Na-X and its modifications. The mechanism of the sorption consists on the dissolving of the organic compounds into the organic layer of the surfactant (on the zeolites’ surface) as well as on the organic compounds’ penetration into the mesopores.

Ionic-liquid-crafted zeolite for the removal of anionic dye methyl orange

In this study a clinoptilolite zeolite was modified by an ionic liquid 1-hexadecyl-3-methylimidazolium chloride monohydrate to 1.0 and 2.0 times its external cation exchange capacity (ECEC). The ionic-liquid-crafted zeolite (ILCZ) was tested for its removal of anionic dyes from solution using methyl orange (MO) as an example. The uptake of MO was fast and followed a pseudo-second-order kinetics with MO adsorption capacities of 45 and 116 mmol/kg on ILCZ modified to 1.0 and 2.0 ECEC, respectively. Stoichiometric desorption of counterion chloride accompanying MO uptake suggested an anion exchange mechanism of MO uptake on ILCZ modified to 2.0 ECEC. Solution pH in the range of 2–11 and ionic strength in the range of 0.001–0.01 M of background salt concentrations of varying charges had minimal effects on MO uptake, suggesting higher affinity of MO for ILCZ in comparison to other inorganic anions. As the MO adsorption capacity on ILCZ modified to 2.0 ECEC was about the same as the ECEC of the zeolite, the mechanism of removal of anionic dyes was attributed to surface anion exchange resulted from the positively charged ILCZ surfaces due to a bilayer IL formation on zeolite after being modified to 2.0 ECEC. In contrast, patchy admicelles of IL would form on zeolite after being modified to 1.0 ECEC, resulting in reduced MO uptake. The contrasting behaviors of IL modification on zeolite and subsequent MO adsorption on ILCZ suggested that modification of ILCZ to 2.0 ECEC was necessary for ILCZ to serve as a sorbent material for the removal of anionic dyes from solution.

Removal of chromium(VI) from aqueous solutions using zeolites modified with HDTMA and ODTMA surfactants

AbstractThe removal of Cr(VI) from aqueous solutions under various conditions was investigated using a natural clinoptilolite and a synthetic zeolite derived from fly-ash (Na-P1), modified either with hexadecyltrimethylammonium bromide (HDTMA) or octadecyltrimethylammonium bromide (ODTMA). The study was focused mainly on the impact of the properties of the zeolite on the sorption capacity, the sorption mechanism, the influence of pH and the durability of the immobilization. The zeolites were modified with HDTMA and ODTMA surfactants up to 100% and 120% of their external cation exchange capacity. Batch and column studies were conducted to evaluate the influence of pH and the initial Cr(VI) concentration on their efficiencies for removing chromates. The organo-zeolites show a significant ability to remove Cr(VI) from aqueous solutions. The amount of Cr(VI) removed by organo-clinoptilolite and organo-zeolite Na-P1 is greater at low pH values, whereas the sorption efficiency decreased with increasing pH. Sorption of Cr(VI) was more efficient with the HDTMA-modified organo-clinoptilolite (150 mmol Cr(VI)/kg) than the ODTMA-modified clinoptilolite (132 mmol Cr(VI)/kg). The maximum sorption capacity was obtained with the 1.2 × ECEC ODTMA-modified clinoptilolite (237 mmol Cr(VI)/kg). The organozeolites Na-P1 adsorbed Cr(VI) from aqueous solutions more effectively and were much more durable than the organo-clinoptilolites.

BTX sorption on Na-P1 organo-zeolite as a process controlled by the amount of adsorbed HDTMA

The main objective of the study was to utilize fly ash by transforming it into Na-P1 zeolite. The obtained synthetic zeolite has been modified with a HDTMA surfactant in amounts of: 0.2, 0.4, 0.6, 0.8 and 1.0 of external cation exchange capacity (ECEC). The process reported hereunder was designed at room temperature (20°C) and a low solid/solution ratio (1:2). Infrared spectroscopy (FTIR) was used to determine the quantity of the adsorbed surfactant on the crystallites’ surface. The normalized intensity of the selected bands was compared with CHN results. The results revealed a very strong correlation between spectroscopic and chemical analyses and enabled the preparation of calibration curves. The sorption properties of organo-zeolites towards benzene, toluene, p-xylene (BTX) were evaluated. The results showed that the modification of the Na-P1 zeolite by HDTMA improves the sorption properties in terms of benzene and toluene and that 1.0 ECEC modification proved to be the best sorbent of those compounds. Xylene was adsorbed in the greatest quantity, however, sorption efficiency from aqueous solutions does not depend on the amount of surfactant used. Experiments proved that it is possible to remove more than 95% of toluene and xylene and more than 85% of benzene contaminants from aqueous solutions.

Antibacterial activity of CTAB-modified zeolite NaY with different CTAB loading

The antibacterial activity of cetyltrimethyl ammonium bromide (CTAB) –Modified Zeolite NaY against Escherichia coli and Staphylococcus aureus was examined in agar disk diffusion (Kirby-Bauer) method. The diameter of the inhibition zones for E. coli and S. aureus, increased from 1.5 to 1.7 cm and 1.9 to 2.0 cm, respectively, with the increasing concentrations of CTAB adsorbed on Zeolite NaY from percent coverage of the External Cation Exchange Capacity of Zeolite NaY: 0.5 to 5.0. CTAB-Modified Zeolite NaY showed effective antimicrobial activity against S. aureus compared to E. coli.________________________________________GRAPHICAL ABSTRACT

Studies of anions sorption on natural zeolites

This work presents results of FT-IR spectroscopic studies of anions–chromate, phosphate and arsenate – sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorption has been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite, ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammonium cations (HDTMA+) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17mmol/100g for chabazite, 4mmol/100g for mordenite and ferrierite and 10mmol/100g for clinoptilolite. The used initial inputs of HDTMA correspond to 100% and 200% ECEC of the minerals. Organo-modificated sorbents were subsequently used for immobilization of mentioned anions.It was proven that aforementioned anions’ sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variations are due to bands corresponding to the characteristic Si–O(Si,Al) vibrations (occurring in alumino- and silicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrations have also been observed. Systematic changes in the spectra connected with the anion concentration in the initial solution have been revealed.The amounts of sorbed CrO42–, AsO43– and PO43– ions were calculated from the difference between their concentrations in solutions before (initial concentration) and after (equilibrium concentration) sorption experiments. Concentrations of anions were determined by spectrophotometric method.

Adsorption of chromate from aqueous solutions by HDTMA-modified clinoptilolite, glauconite and montmorillonite

Adsorption of chromate on natural clinoptilolite (Cp), glauconite (Gl), and montmorillonite (Mt) treated with hexadecyl trimethylammonium (HDTMA) bromide at amounts equivalent to 1.0 and 2.0 of their cation-exchange capacities (CEC) was investigated by batch study. In the case of the Cp and Gl, adsorption of HDTMA took place on the zeolite and clay mineral surfaces only and thus relates to the external CEC (ECEC). The amount of chromate removed from the solution by the organo-silicates continuously decreased with increasing pH in the range 1.3–10. The highest values were obtained at pH between 1.3 and 6, and decreased rapidly above pH6. At an initial chromate concentration of 6.25mmol/L, its amounts bound to the Cp, Gl and Mt modified using 1.0 CEC loadings of the surfactant were 47, 102, and 168mmol/kg, respectively. When amount of HDTMA used was equivalent to 2.0 CEC of the silicate, these values increased to 182, 240, and 285mmol/kg, respectively. The results obtained suggest that the surfactant molecules, bound beyond the CEC to the external surfaces of the Cp and Gl, show a greater chromate adsorption ability in comparison with such molecules located in the interlayer spaces of the Mt. It is also evident that an excess of the surfactant, not adsorbed on the silicate surfaces, participated in the removal of chromate from the solution by formation of a precipitate of alkylammonium chromate.

Comparative adsorption behavior between phenol and p-nitrophenol by Na- and HDTMA-clinoptilolite-rich tuff

A comparison of phenol (Phen) and p-nitrophenol (p-NPhen) sorption between sodium (ZCh-Na) and surfactant-modified (ZCh-HDTMA) clinoptilolite-rich tuffs is presented using kinetic and the isotherm parameters to describe the selectivity of the sorption processes. The clinoptilolite-rich tuff (ZCh) used in this work was obtained from a new deposit located in the state of Chihuahua (Mexico). The effective and external cation exchange capacities (EfCEC and ECEC) of the ZCh were evaluated previous surface modification with HDTMA. The clinoptilolite-rich tuff was characterized by X-ray diffraction and electron microscopy. A batch system was used to evaluate the kinetics and the isotherms of Phen and p-NPhen sorption. The results show that EfCEC and ECEC were 112 and 17 meq/100 g, respectively. The clinoptilolite is the major mineral phase although mordenite and quartz are minor components. The pseudo-second order kinetic model better fitted the adsorption data and Langmuir model best describes the isotherms for both Phen and p-NPhen using ZCh-HDTMA. p-NPhen is adsorbed by both ZCh-HDTMA and ZCh-Na; however, ZCh-HDTMA exhibits superior performance which reflex a major selectivity. Therefore, the surfactant-modified clinoptilolite-rich tuff could be used for p-NPhen wastewater treatment.

Chitosan modified zeolite as a versatile adsorbent for the removal of different pollutants from water

With the goal to develop a coal fly ash-based versatile material toward a broad range of pollutants in water, a zeolite (ZFA) was synthesized from coal fly ash and subsequently modified by chitosan. The chitosan modified zeolite (CMZFA) was examined for its capability to sequester cationic (ammonium), anionic (phosphate) and organic (humic acid) pollutants from water. The cation exchange capacity in the internal pores was regarded as the retention capability for cationic ammonium. From the difference between the total and external cation exchange capacity, it was estimated to be 0.90mmol/g (16.2mg/g). Results showed an improved adsorption of CMZFA for phosphate when compared with ZFA, and a maximum adsorption capacity of 4.05mg/g was obtained for CMZFA from the Langmuir model. Though ZFA presented little affinity for humic acid, modification by chitosan largely enhanced the adsorption performance with a Langmuir maximum of 31.6mg/g. The negative charge in the internal pores of zeolite, the oxides of CaO, Al2O3 and Fe2O3 in the non-zeolite fraction, and the monolayer chitosan on the external surface of zeolite were interpreted as the binding bodies for the retention of cationic ammonium, anionic phosphate, and organic humic acid, respectively.

Sorption of Chromate and Arsenate by Surfactant Modified Erionite (E-SMZ)

In recent years, growth of various industry has led to the introduction of pollutants in nature, especially heavy metal ions such as Cr(III) and As(V), which are usually present in wastewater. Heavy metals containing waste are generated from metallurgical, mining, chemical, leather, distilleries, sugar, battery, electroplating, and pigment industries, to name a few. Chromium is found in natural water in oxidation states, Cr(III) and Cr(VI). The former is an essential element for mammals whereas the latter is reported to be toxic. Similarly, arsenic is an ubiquitous contaminant that can be found in high concentrations in natural waters and wastewaters. Arsenic containing waste streams are generated mainly by the microelectronic industry and by pesticide and pharmaceutical facilities. It occurs in two oxidation states that form oxyanions, arsenate As(V), and arsenite As(III); arsenite is more mobile and toxic than . As arsenic is a major hazardous contaminant for human health, its removal is an issue of increasing concern. Zeolites are crystalline, hydrated aluminosilicates containing exchangeable alkaline and alkaline earth cations in their structural frameworks. Since zeolites have a permanent negative charge on their surfaces, they have no affinity for anions. However, recent studies have shown that modification of zeolite with certain surfactants or metal cations yield sorbents with a strong affinity for many anions. Zeolite has high internal and external surface areas and high internal and external cation exchange capacities suitable for the surface modification by cationic surfactant (HDTMA). When the initial surfactant concentration is less than the critical micellar concentration (CMC), the sorted surfactant molecules primarily form a monolayer; limited chromate and arsenate sorption indicates that the patchy bilayer may also be formed. When the surfactant concentration is greater than the CMC and enough surfactant exists in the system, the sorbed surfactant molecules form a bilayer, producing maximum chromate and arsenate sorption. Quantitative sorption of chromate and arsenate and desorption of bromide ions indicate that the sorption of oxoanions is primarily due to surface anion exchange.