Theoretical Exchange Capacity Research Articles

Novel pre-treatment of zeolite materials for the removal of sodium ions: potential materials for coal seam gas co-produced wastewater.

Coal seam gas (CSG) is the extraction of methane gas that is desorbed from the coal seam and brought to the surface using a dewatering and depressurisation process within the saturated coalbed. The extracted water is often referred to as co-produced CSG water. In this study, co-produced water from the coal seam of the Bowen Basin (QLD, Australia) was characterised by high concentration levels of Na+ (1156 mg/L), low concentrations of Ca2+ (28.3 mg/L) and Mg2+ (5.6 mg/L), high levels of salinity, which are expected to cause various environmental problems if released to land or waters. The potential treatment of co-produced water using locally sourced natural ion exchange (zeolite) material was assessed. The zeolite material was characterized for elemental composition and crystal structure. Natural, untreated zeolite demonstrated a capacity to adsorb Na+ ions of 16.16 mEq/100 g, while a treated zeolite using NH4+ using a 1.0 M ammonium acetate (NH4C2H3O2) solution demonstrated an improved 136 % Na+ capacity value of 38.28 mEq/100 g after 720 min of adsorption time. The theoretical exchange capacity of the natural zeolite was found to be 154 mEq/100 g. Reaction kinetics and diffusion models were used to determine the kinetic and diffusion parameters. Treated zeolite using a NH4+ pre-treatment represents an effective treatment to reduce Na+ concentration in coal seam gas co-produced waters, supported by the measured and modelled kinetic rates and capacity.

Mercury removal from wastewater using a poly(vinylalcohol)/poly(vinylimidazole) complexing membrane

Removal of Hg(II) ions from aqueous solutions by a novel complexing membrane was investigated by performing sorption and filtration experiments. The membrane, prepared by the technique of semi-interpenetrated polymer networks, consists in a matrix of poly(vinylalcohol), crosslinked by gaseous dibromoethane, that immobilizes chains of poly(vinylimidazole), a complexing polymer synthesised for this purpose. The morphology of the membrane was observed by scanning electron microscopy, showing an homogeneous structure, but surface unevenness. The dissolution of the membrane in water was slow and limited to 8% in 2 months, showing the efficiency of the crosslinking process. Efficient retention of Hg(II) was observed at pH 2.5. The kinetics of sorption were studied. The sorption equilibrium was satisfactorily represented by the Langmuir model. Isotherms performed at different temperatures allowed the calculation of the thermodynamical parameters. The sorption of mercury was endothermic, with a large positive entropy change that was ascribed to proton release. The effects of parameters such as water hardness, and the presence of complexing chloride anions were investigated, showing little influence on the retention ratio. Fast and efficient regeneration of the membrane was performed with a 0.5 M HNO 3 solution. The maximum capacity of the membrane was 120 mg Hg g −1, whereas the theoretical exchange capacity was 853 mg Hg g −1, showing that most internal complexing sites of the membrane were not accessible to mercury ions in sorption experiments. When used in the filtration mode, the elimination ratio of Hg(II) was ≥99.4% for solutions containing 91.6 or 17.5 mg Hg L −1.

A Simple Mechanochemical Route to Layered Double Hydroxides: Synthesis of Hydrotalcite‐Like Mg‐Al‐NO3‐LDH by Manual Grinding in a Mortar

AbstractHydrotalcite‐like Mg‐Al‐NO3‐layered double hydroxide (LDH) was successfully prepared in a mortar by manually grinding the hydrated magnesium and aluminum nitrate salts with sodium hydroxide. Various techniques, including XRD, MAS NMR, FTIR, SEM; thermogravimetric and differential thermal analyses (TGA,DTA), surface area and zeta potential measurements were used to establish a correlation between the LDH samples prepared in the mortar and by co‐precipitation. The LDH prepared in the mortar showed all the characteristics of a layered structure but with a lower crystallinity. This product was tested for its anion exhange property with tetraborate anions and 52 % of the theoretical exchange capacity was reached. The mortar route does not require heating/refluxing treatment, CO2‐free atmosphere and solvent as in the conventional preparation methods and allows obtaining LDHs in a short reaction time.

Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na + ions had almost completely replaced the interlayer K +. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs + exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr 2+ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs + when the equivalent exchange capacity of Cs + in the exchanger phase ( X¯ Cs) was < 0.66 and selective for Sr 2+ when X¯ Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs + equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr 2+ and Cs +, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.

Ion exchange properties of natural clinoptilolite: lead–sodium and cadmium–sodium equilibria

Abstract In the present work, ion exchange of lead and cadmium on the sodium form of Western Anatolia clinoptilolite is examined at 25 °C and 0.1 total normality. Its total theoretical cation exchange capacity was 2.3 meq/g. But only the sodium was exchanged during the equilibrium experiments. On this basis, the theoretical exchange capacity is 1.74 meq/g. According to the equilibrium studies, the selectivity sequence can be given as Pb 2+ >Na + >Cd 2+ . The maximum exchange levels expressed as the percentage of the theoretical exchange capacity were 100% for lead and 54% for cadmium. Using the equilibrium data, the thermodynamic analysis of the system was carried out. The solution non-ideality correction factor has almost no effect on the Kielland plot and so on the numerical values of the thermodynamic equilibrium constant. The thermodynamic equilibrium constant ( K a ) and the standard free energy of exchange (Δ G °) were calculated as 16.6 and −3.48 kJ/eq. for lead–sodium system; and 0.16 and +2.27 kJ/eq. for cadmium–sodium system, respectively. Comparing the results of the present work with the data in literature, it can be concluded that the ion exchange capacities and cation selectivities of clinoptilolites with different cationic compositions are different. So, one should carry out cation exchange experiments on representative samples from the deposit before using it as cation exchanger for any practical application.

Ion-exchange capacity

Publisher Summary This chapter explains the ion exchange capacity in zeolites. In a traditional aluminosilicate zeolite the source of the ion exchange capacity is the extent of isomorphous substitution of Al for Si in the tetrahedral framework. The theoretical exchange capacity thus can be derived from the elemental composition. To estimate the CEC (cation exchange capacity, meq/g) in a natural zeolite it is usual to observe the uptake of the ammonium cation at room temperature when equilibrium conditions are known to have been attained in the presence of a IM ammonium salt solution. When synthetic materials are to be characterized, prior careful elemental analysis will provide the expected, theoretical cation capacity. The most sensitive analytical technique available is to use radioisotopes to prelabel the A cation and follow its replacement by increase in solution activity with time. (Isotope dilution technique). This will be possible for the as synthesized cations Na, K, Rb, Cs, Ca, Sr and Ba. In the absence of radiochemical facilities, flame photometry, atomic absorption are perfectly adequate.

Thorium equilibria with the sodium form of clinoptilolite and mordenite

A study has been performed in order to examine the iron exchange behavior of tetravalent thorium ions using natural sodium clinoptilolite and mordenite. The free energy values, ΔG0, were calculated and found to be 3.33 kJ/g eq for the Th/Na-CLI system, and for Th/Na-MOR 3.94 kJ/g eq. Despite the fact that the overall preference of the zeolites is for the sodium ions, thorium uptake was quite significant for mordenite, covering 30% of its theoretical exchange capacity at the equilibrium point, while for clinoptilolite only 10% was occupied.

Comparative studies between synthetic and natural zeolites for ammonium uptake

Abstract Studies have been performed in order to obtain information related to the ammonia removal using natural zeolites, clinoptilolite, mordenite and ferrierite in their sodium forms as well as synthetic zeolite A in its sodium, potassium and calcium forms. Experimental results indicate that natural zeolites show higher selectivity for ammonium ions despite the much higher theoretical exchange capacity of zeolite A. Clinoptilolite of Greek origin shows the best performance regarding selectivity for the ammonium ion, ion exchange rate and quantities taken. This performance is very promising for the possible use of clinoptilolite for water and wastewater treatment.

Lead and Cadmium Removal by Ion Exchange

The ion exchange properties of the zeolites can be used to remove certain ions from the effluents. In this work a natural clinoptilolite has been examined systematically in order to evaluate whether this low cost mineral can be employed for the removal of the metals lead and cadmium which are very toxic, even at very low concentrations. Studies were performed under various conditions such as presence of different cations (Pb, Cd, Na), zeolite grain size, solution temperature. The results obtained indicate that the size of the zeolite does not affect the actual metal uptake at the equilibrium point, but the metal removal is greatly affected when the contact of the solid/liquid phases is short, a very essential parameter for the waste water treatment. For a short contact time the metal quantities removed using small grain size is nearly doubled. The same pattern is followed at higher temperatures, though a slight increase is observed for both zeolite grain sizes and both metals, lead and cadmium. At equilibrium half of the theoretical exchange capacity of the zeolite is used, approximately 1.4 meq/g for lead and 1.1 meq/g for cadmium. The kinetic curves show very clearly the selectivity of the zeolite for the Pb ions but also significant amounts of cadmium are removed as well.