Metal Cation Exchange Research Articles

Selective adsorption and ion exchange of metal cations and anions with silico-titanates and layered titanates

Metal ions may be removed from aqueous wastes from metal processing plants and from refineries. They may also be used in concentrating radioactive elements found in dilute, aqueous, nuclear wastes. A new series of silico-titanates and alkali titanates are shown to have specific selectivity for cations of lead, mercury, and cadmium and the dichromate anion in solutions with low and high pH. Furthermore, one particular silico-titanate, TAM-5, was found to be highly selective for Cs + and Sr 2+ in solutions of 5.7 M Na + and 0.6 M OH −. A high potential exists for these materials for removing Cs + and Sr 2+ from radioactive aqueous wastes containing high concentrations of Na + at high and low pH.

Competitive Adsorption of Para‐Xylene and Water Vapors on Calcium, Sodium, and Lithium‐Saturated Kaolinite

AbstractVapor‐phase adsorption of volatile organic chemicals (VOC) on soils and clay minerals has been shown to be greatly reduced in the presence of water. Exchangeable metal cations are known to interact strongly with water, and thus may influence the competitive adsorption of water and organic vapors. Flow‐equilibration experiments were conducted to measure the concentration of water and p‐xylene vapors adsorbed on oven‐dried Ca‐, Na‐, and Li‐saturated kaolinite from single and binary vapor systems. Li‐saturated kaolinite adsorbed significantly less water than Ca‐ and Na‐kaolinite. This was attributed to a 50% reduction in cation exchange capacity (CEC) of Li‐kaolinite following heating at 110°C. The adsorption of p‐xylene vapors on Ca‐, Na‐, and Li‐kaolinite at 0% relative humidity (RH) was also related to the CEC and exchangeable cation species, which suggests that specific interactions occurred between exchangeable cations and p‐xylene molecules. When the RH was increased to 10 and 20%, p‐xylene adsorption decreased in small, but successive, increments. The competitive adsorption of both water and p‐xylene on Ca‐, Na‐ and Li‐kaolinite was underestimated by two‐component adsorption equations based on the Brunauer, Emmett, and Teller (BET) model. At low RH's, water adsorption on kaolinite was hypothesized to occur primarily at cation exchange sites, allowing for the continued adsorption of p‐xylene on exposed mineral surfaces. Thus, the assumption of complete monolayer coverage prior to the onset of multilayer formation, upon which the BET model is based, may limit the ability of these equations to accurately predict the competitive adsorption of polar and nonpolar vapors.

Oxidative and immersional heating on low rank coal surfaces

The low temperature heating of low rank coal was examined by both differential thermal/thermogravimetric analysis (DTA/TGA) and immersional calorimetry. The effect of surface composition was examined by modifying the oxygen-containing functional groups and the exchangeable metal cation contents. It was seen that a smooth decline in the heat of immersion resulted from a reduction in surface polarity. The heat of immersion was related to a generalized expression that demonstrated the relative contributions of exchangeable metal ion, carboxylic acid and phenolic groups. It was found that brown coals produced highly characteristic heat release profiles on DTA/TGA analysis and that the initial lowest temperature peak and the second exothermic peak could be correlated to the cation content. Removal of a large part of the cations in the high cation Morwell coal transformed it into a coal with a low temperature heating profile almost identical to the low cation Loy Yang coal.

Reactions of Water and Dinitrogen Monoxide Adsorbed on Cation-Exchanged Zeolite with Excess Electrons Generated by Gamma-Radiation

Abstract Hydrogen formation from water and nitrogen formation from dinitrogen monoxide adsorbed on a zeolite during gamma-irradiation have been studied in order to clarify the role of the metal cation contained in the zeolite and the effect of the pore size; Molecular Sieve 4A, 5A, 13X, and cation-exchanged 13X were used for that purpose. The hydrogen yield from water was observed to increase with increasing amount of adsorbed water. The dependence of G(H2) on the amount of adsorbed water was affected by the exchange of metal cations and the pore size of the zeolite. For nitrogen formation from dinitrogen monoxide in cation-exchanged 13X, the saturation behavior of G(N2) could be roughly classified into two categories, namely one approaching ca. 3 and the other around 6. The results indicate that the metal cation participates in the reaction of an excess electron with an adsorbed water molecule, at least in the range of small amounts of water.

Leach Resistance Properties and Release Processes for Salt-Occluded Zeolite A

ABSTRACTThe pyrometallurgical processing of spent fuel from the Integral Fast Reactor (IFR) results in a waste of LiCI-KCI-NaCI salt containing approximately 10 wt% fission products, primarily CsCI and SrCI2. For disposal, this waste must be immobilized in a form that it is leach resistant. A salt-occluded zeolite has been identified as a potential waste form for the salt. Its leach resistance properties were investigated using powdered samples. The results were that strontium was not released and cesium had a low release, 0.056 g/m2 for the 56 day leach test. The initial release (within 7 days) of alkali metal cations was rapid and subsequent releases were much smaller. The releases of aluminum and silicon were 0.036 and 0.028 g/m2, respectively, and were constant. Neither alkali metal cation hydrolysis nor exchange between cations in the leachate and those in the zeolite was significant. Only sodium release followed t0.5 kinetics. Selected dissolution of the occluded salt was the primary release process. These results confirm that salt-occluded zeolite has promise as the waste form for IFR pyroprocess salt.

Alkali metal cation exchange of HZSM-5 and the catalytic properties of the alkalized zeolites

Ion-exchange of HZSM-5 with dilute KCl (or NaCl) solutions leads to partially exchanged zeolites, KHZSM-5. The degree of exchange was also found to be a function of the type of cation used. With increasing aluminium content of the zeolites, 0.70 to 1.60 mass-%, the K/Al molar ratio decreased from 0.68 to 0.38. The catalytic properties of the samples were compared using n-hexane cracking as the test reaction. For the HZSM-5 zeolites and under the appropriate reaction conditions, the percentage conversion was proportional to the aluminium content. The KHZSM-5 samples, on the other hand, exhibited an almost complete loss of catalytic activity. The effective degree of poisoning as evaluated in terms of the test reaction is therefore considerably higher than that determined from the K/Al molar ratio. The catalytic and ion-exchange results are interpreted as indicating that, depending on the aluminium content, a potassium cation is influencing between one and three acid sites, thereby implying that the aluminium tetrahedra in ZSM-5 are not in an isolated state.

Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden

The upper C-horizon was analyzed in 19 beech and oak stands in southern Sweden over a period of 40 years. The results confirmed a study of ten other stands of the same period. The exchangeable base and metal cations had decreased, on average, in the following order: Na>Mn>Zn>Ca>, Mg>K and 20–70% was recovered in 1988. Exchangeable Al had doubled. In spite of soil acidification, which according to earlier results should also have occurred in the upper soil horizons, many field-layer species had increased in cover. Among these were several nitrophilous species. However, a few species had decreased in cover, especially in the most-acid pH range. The yield of beech and oak has been measured since 1945. Beech had increased more than expected in both basal area and site index (height) in 1976–1985, while oak showed no stable changes in yield. The simultaneous increase of nitrogen deposition and decrease of soil macronutrients leads to the conclusion that the higher availability of N has been of greater influence on the ground flora and yield of beech than the loss of other macronutrients.

ChemInform Abstract: Organic Anions. Part 10. Hard Sphere Electrostatic Calculations on Group 1 Organometallic Compounds.

A point charge electrostatic treatment of tetrameric organolithium compounds predicts a quotient of lithium–lithium to carbon–carbon bond lengths of 0.78, which compares with an average experimental value of 0.75. A hard sphere electrostatic (HSE) treatment of hexameric organolithium compounds predicts quotients characterising the shapes and sizes of the carbon and lithium trigonal antiprisms of 1.23, 1.23, and 1.00. The corresponding (average) experimental quotients are 1.13, 1.27, and 0.88. The HSE method is further developed for predicting the structures of group 1 Organometallic ion pairs in which a single delocalised anion is associated with several mutually interacting mobile cations. In doing so it is stressed that the critical energy surface (termed the ion-pair surface) is that described by the nucleus of the cation as it rolls over the surface of the anion. The quantitative information obtained from such calculations is crude but it is sufficient to make predictions of a general type. For example a clear division is seen between those anions that will and those that will not form solvent-separated ion pairs. In tetrahydrofuran (THF) all ion pairs R2–, Li+ will be contact-ion pairs, and most ion pairs of R2–, 2Li+ will also be contact-ion pairs but in some one of the lithiums may be solvent separated. In triple ions R–, 2Li+, on the other hand, both lithiums will be of the solvent-separated type. Calculations on various metal-ion-exchange reactions accord well with experimental findings. In the case of dianions it is predicted that mixing R12–, 2M1+ with R22–, 2M2+ will sometimes result in an exchange of both metal cations but in other cases only one will be exchanged. The dominant HSE bonding term for 1 : 1 ion pairs R–, M+(where R– is a delocalised anion) is that for the atoms immediately in contact with the metal ion and significant delocalisation (in the HSE sense) is that which removes charge from those atoms. Hence in the HSE sense the degree of charge delocalisation in methyl, allyl, and U-pentadienyl anions is the same. The W-conformer of the pentadienyl anion is, however, more charge delocalised and the metal ion is less tightly bound. Throughout this work, HSE calculations are shown to provide a useful first-order guide to the properties of group 1 organometallics.

Organic anions. Part 10. Hard sphere electrostatic calculations on group 1 organometallic compounds

A point charge electrostatic treatment of tetrameric organolithium compounds predicts a quotient of lithium–lithium to carbon–carbon bond lengths of 0.78, which compares with an average experimental value of 0.75. A hard sphere electrostatic (HSE) treatment of hexameric organolithium compounds predicts quotients characterising the shapes and sizes of the carbon and lithium trigonal antiprisms of 1.23, 1.23, and 1.00. The corresponding (average) experimental quotients are 1.13, 1.27, and 0.88. The HSE method is further developed for predicting the structures of group 1 Organometallic ion pairs in which a single delocalised anion is associated with several mutually interacting mobile cations. In doing so it is stressed that the critical energy surface (termed the ion-pair surface) is that described by the nucleus of the cation as it rolls over the surface of the anion. The quantitative information obtained from such calculations is crude but it is sufficient to make predictions of a general type. For example a clear division is seen between those anions that will and those that will not form solvent-separated ion pairs. In tetrahydrofuran (THF) all ion pairs R2–, Li+ will be contact-ion pairs, and most ion pairs of R2–, 2Li+ will also be contact-ion pairs but in some one of the lithiums may be solvent separated. In triple ions R–, 2Li+, on the other hand, both lithiums will be of the solvent-separated type. Calculations on various metal-ion-exchange reactions accord well with experimental findings. In the case of dianions it is predicted that mixing R12–, 2M1+ with R22–, 2M2+ will sometimes result in an exchange of both metal cations but in other cases only one will be exchanged. The dominant HSE bonding term for 1 : 1 ion pairs R–, M+(where R– is a delocalised anion) is that for the atoms immediately in contact with the metal ion and significant delocalisation (in the HSE sense) is that which removes charge from those atoms. Hence in the HSE sense the degree of charge delocalisation in methyl, allyl, and U-pentadienyl anions is the same. The W-conformer of the pentadienyl anion is, however, more charge delocalised and the metal ion is less tightly bound. Throughout this work, HSE calculations are shown to provide a useful first-order guide to the properties of group 1 organometallics.

Fate of Heavy Metals in Sludge Disposal Landspread Operation – A Case History

Land treatment of waste biological solids (sludge) has been practiced many years and there have been many studies conducted to determine the applicability of this disposal technique. This paper is based upon an investigation which was conducted to determine if the heavy metals which are associated with sludge are stabilized and contained within a landspread area where no agricultural crops are grown. Sludge/soil mixture samples were analyzed for heavy metal concentrations and cation exchange capacity (CEC) on a routine basis to determine if the heavy metals were remaining in an insoluble form. Groundwater samples and rainfall runoff samples were also analyzed for heavy metals to determine if the metals were solubilizing and being transported into either the groundwater or back to the wastewater treatment process in the rainfall runoff. Analytical results indicate that most of the heavy metals in sludge applied to this landspread area are in a stable form and those that do enter solution are absorbed by the native clay soils and do not contaminate groundwater or upset the biological wastewater treatment process when rainfall runoff is treated.

Pyrolysis of a lignite in an entrained flow reactor: 1. Effect of cations on total weight loss

The role of exchangeable metal cations (Ca, Mg, Na, K, Sr and Ba) in the rapid pyrolysis of a Montana lignite has been studied. The effects of variation of the cations present, and cation concentration, on weight loss and pyrolysis kinetics are presented. The reactor utilized was a dilute-phase entrained flow reactor. The reactor conditions decrease the degree of secondary reactions occurring to the primary volatile species and allow a clearer view of the fundamental pyrolysis processes. A model of the heat and momentum transfer in the reactor has been employed to estimate the particle time-temperature history. The results of pyrolysing the lignite samples display a significant role of metal cations. At 1173 K, the presence of metal cations resulted in a decrease in total weight loss at maximum residence time (0.25 s) from 50% (dry inorganic constituent free basis, dicf) for 0 wt% metal cations (acid washed) to 30% (dicf) (raw lignite, 2.8 wt% cations). Data are also presented concerning the maximum weight loss when only calcium, sodium or magnesium exchangeable cations were present. The apparent activation energy obtained from a first-order Arrhenius kinetic treatment is shown to be dependent on the presence of cations.

Chemical and Mineralogical Properties of Some Gambian Soils

Abstract Chemical properties and clay mineralogy of 6 samples from the Republic of The Gambia have been studied. The samples were collected from sites with different drainage conditions. Chemical analyses show low contents of exchangeable metal cations and organic matter. The pH measured in water suspensions is also relatively low. In all six investigated samples kaolinite is the dominant clay mineral, indicating a high degree of chemical weathering. In places of poorer drainage other clay minerals have also been detected, but they are represented only in moderate to small amounts, or traces.

Rapid determination of the total amount of exchangeable metal cations in acidic soils

The application of bromophenol blue to the spectrophotometric determination of the total amount of exchangeable metal cations in acidic soil is described. The results of the determination are found to be satisfactory.

Sodium‐Calcium‐Magnesium Exchange Reactions on a Montmorillonitic Soil: I. Binary Exchange Reactions

AbstractThe binary cation exchange processes, Na → Ca, Na → Mg, and Ca → Mg, were investigated at 298 K for a montmorillonitic soil separate (principally clay and silt) suspended in a 50 mol m−3 perchlorate background at pH 6, 6.6, or 7. The resulting exchange isotherms indicated some preference on the soil for Ca and Mg over Na, and for Ca over Mg. These preferences were attributed primarily to organic matter associated with the soil separate, since previous studies had shown that pure montmorillonite exhibits essentially no preference among the three cations under the same conditions as in the present experiments. The exchange isotherms at pH 6, 6.6, and 7 were congruent for all three binary exchange reactions, showing that, at these pH values, proton competition did not affect the exchange selectivity of the soil. The total adsorbed metal charge, Q0, however, increased with the pH value, as expected from the presence of organic matter in the soil, and varied with the surface composition of the exchanger. This variation was rationalized as a net effect of the ionic potential and Lewis acid softness properties of the exchangeable metal cations. Greater ionic potential was considered to result in greater proton displacing power, whereas greater Lewis acid softness was considered to result in stronger complex formation between a metal cation and organic functional groups. Thus, increasing ionic potential could produce an increase in Q0, but increasing Lewis acid softness could produce a decrease in exchangeability and consequent decrease in Q0. Ionic potential was the dominant consideration in Na → Mg exchange, whereas Lewis acid softness played the principal role in Na → Ca and Mg → Ca exchange.

Sphagnum -dominated peat bog: a naturally acid ecosystem

Sphagnum -dominated peat bogs are naturally acid and cover perhaps 1 % of the Earth’s land surface. The tem poral and spatial variations of pH in a peat-bog in the northern Pennines are used to illustrate the relative im portance of different sources of acidity. At this site, where the pH of rain in summer was 4.0-4.2, rain and cation exchange of metal cations in the rain for H + in the newly grown Sphagnum were of about equal im portance, though cation exchange probably dom inated on hummocks in summer. Strongly acid ‘events’ are likely to follow heavy rain that follows a dry spell. The effects of interconversion of sulphur- and nitrogen-containing compounds on acidity is obscure.

Application of risk and uncertainty analysis techniques to a heavy metal speciation model

In every model there is a degree of uncertainty associated with every coefficient that controls the flow of material from one state variable to another. Because of this source of uncertainty, many simulations, each with different (but reasonable) estimates of coefficient settings should be made so as to approximate the probable behavior space of the system of interest. Deterministic models do not account for variability in output response caused by uncertain estimates of coefficients. This can cause their predictions to be of limited value in certain instances. One such instance occurs when trying to simulate the potential risk to the environment that might be incurred as a result of toxic metal inputs. If the uncertainty in coefficients that govern the kinetics of metal sorption and cation exchange reactions with particulate and dissolved substrates is accounted for, a range of values for endpoint concentrations of unbound (toxic) metal species would be expected. Each individual endpoint concentration from the range of simulated values can be tested against a pre-specified threshold concentration level that if exceeded is said to constitute a risk to the environment. If the threshold concentration is not exceeded, then no risk can be said to have occurred. By noting the number of times out of the total number of simulations that a risk threshold level is exceeded, the probability of risk can be calculated. Conversely, making an assessment of risk based on one endpoint concentration from a deterministic model gives little insight into the probability of a risk occurring. The degree of risk should be expected to change as our certainty in coefficient estimates increases or decreases.

Vapor phase sorption and desorption of monomethylhydrazine by homoionic-exchanged clays

Isotherms were obtained at 298, 308, and 318 K for the sorption and desorption of monomethylhydrazine (MMH) by sodium-exchanged montmorillonite and kaolinite clays, and by an iron(III)exchanged kaolinite preparation. Isotherm data were analyzed in conjunction with data from X-ray diffraction and infrared spectroscopy in order to investigate the sorbate-sorbent interactions mechanisms. Similar isotherm analyses were carried out for the sorption of water vapor, which could be expected to compete with MMH for sorption sites. Type II isotherms were obtained for all systems. Sorption by Na +-kaolinite was essentially reversible but some hysteresis was evident in desorption from the ironclay. A marked hysteresis was observed on desorption from the montmorillonite because a monolayer of sorbate held between the clay layers was not removed under the experimental conditions used. Coordination to the exchangeable metal cation, or “hydrazination” of the cation, and weak hydrogen bonding to the clay surfaces were the principal binding mechanisms involved.

Ideal Behavior in Na+-Trace Metal Cation Exchange on Camp Berteau Montmorillonite

AbstractThe conditions under which an exchanger phase will behave as an ideal mixture are established from thermodynamic principles. It is shown that, if a stoichiometric cation-exchange reaction is reversible, the exchanger phase will exhibit ideal behavior if the Vanselow selectivity coefficient is independent of the exchanger composition. This criterion is applied to some recently published data for Na+-trace metal cation exchange on Camp Berteau montmorillonite. An analysis of the data suggests that, so long as the exchange process is reversible, Na+-trace metal cation exchange produces an exchanger phase that behaves as an ideal mixture.

On the mechanism of ion exchange in zirconium phosphates—XXVI Irreversible exchange of alkaline earth cations

Ion exchange of alkali metal cations and Cu 2+ with α-zirconium phosphate has been found to be irreversible. This is attributed to strong site binding. The cations are coordinated by water molecules and negative lattice oxygens in a stable arrangement. Site binding is also suggested as an explanation for the failure to produce fully exchanged alkali metal cation phases when α-zirconium phosphate is titrated with mixed metal chloride-metal hydroxide solutions.

Sources and sediment associations of heavy metals in polluted coastal regions

Vertical profiles and lateral distribution patterns of heavy metals in Recent sediments are increasingly employed in the assessment of the major sources of pollution in coastal regions, including estuaries and marginal seas. After a general review of studies from typical locations, examples from New Bedford Harbor, Mass./U.S.A., and from the southern German Bight in the North Sea are described in more detail. Chemical extraction procedures are used to evaluate different forms of metal associations in aquatic sediments: (i) heavy metals are transported and deposited as major, minor and trace constituents in the natural rock detritus, mostly in inert positions; (ii) slight alkalinity in sea water results in the formation and precipitation of hydroxides, carbonates, sulphides and phosphates of heavy metals; (iii) sorption and cation exchanges takes place in particular on fine-grained substances with large surface areas, e.g. on manganese dioxide, humic acids, hydrous iron oxides and clay minerals; (iv) organic substances play an important role in the transfer of metals between dissoved and solid phases, particularly by the process of flocculation; (v) under oxidizing conditions, the redox-sensitive Fe- and Mn-hydroxides and -oxides are significant “sinks” of heavy metals in aquatic systems. The characteristic rise in the residual content of lead, copper and cadmium in the polluted samples points toward the strong influence of atmospheric dust particles. Heavy metals immobilized in the bottom sediment constitute a potential hazard to water quality and aquatic life since they may be released as a result of chemical changes. In relation to the marine environment, the following mechanisms should be taken into account: (i) increased salinities at the inflow of rivers into the sea water will affect the partial exchange of metal cations sorbed onto the surface of suspended particles; (ii) oxygen deficiency in the bottom sediments may lead to the dissolution of hydrous iron and manganese oxides and to a release of co-precipitated heavy metals; (iii) complexing substances of both natural and synthetic origin increases the solubilization of metals; (iv) microbial activities can convert inorganic metal compounds to organic molecules and may thereby increase toxicity, as exemplified in organo-mercurial transformations.