Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff

The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm(-3) and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm(-3). Molal concentrations, x (mmol g(-1)) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm(-3), with regard to exchange capacity for particular ions, best exchanged are Na+ ions, followed by Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+ > Mg2+ > Ca2+ > K+). At ammonium concentrations from 0.2 to 1 mmol cm(-3) the order is Na+ > Ca2+ > Mg2+ > K+. At concentrations higher than 1 mmol cm(-3) the order is Na+ > Ca2+ > K+ > Mg2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm(-3) and indicate the importance of Mg2+ (besides Na+ ions) for the exchange between clinoptilolite cations and H+ ions, in contrast to K+ ions, whose participation in the reaction with H+ ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na+, Mg2+, and Ca2+ ions, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+, and Ca2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K+ ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na+, Mg2+, and Ca2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H+ ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H+ ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm(-3), from the acid-modified zeolite samples, Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+, and K+ ions. Further to the results, it is to be assumed that exchangeable Al3+ ions available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.     

Exchange and reduction of Cu(2+) ions in clinoptilolite

The ion-exchange and reduction processes for Cu(2+) ions in clinoptilolite from the Caimanes deposit (Moa, Cuba) were studied at different temperatures. The ion-exchange studies were done to determine the kinetic parameters of Cu(2+) removal from solution by this clinoptilolite modified previously to NH(+)(4) form, and thermodynamic parameters of Cu(2+) elution from zeolite using NH(4)Cl solution. The results show that temperature increase favors the exchange and that it is a reversible process. The external diffusion rate appreciably increases with temperature, while, the internal diffusion coefficient rises relatively little. This means that besides ion exchange other processes (such as precipitation of the low-solubility phase and/or salt adsorption) occur, which cause copper removal from solution and affect the intracrystalline diffusion of the ions. For steric reasons the exchange of [Cu(H(2)O)(6)](2+) ions from a solution must occur with a number of water molecules n smaller than 6 (6 > n > or = 0). Cu(2+) reduction by hydrogen and the formation of Cu-particles in the clinoptilolite were verified. The Cu(2+) reduction mechanism is complex, indirect, and sensitive to reduction temperature; consequently, Cu(+)(n) states intermediate between Cu(2+) and Cu(0) should be present in the reduced samples.     

The cation-chelation mechanism of metal-ion sorption by polyurethanes

The mechanism of sorption of ions by polyurethanes has been investigated through detailed studies of the extraction of cobalt(II) thiocyanate and the salts of several organic acids. Polyether-based polyurethanes. particularly those containing poly(ethylene oxide), were found to be distinctly superior to polyesters in the sorption of salts and performed much better than might be expected by analogy with monomeric liquid solvents. The results were judged to be inconsistent with several possible mechanisms, including adsorption, solvent extraction, weak or strong base anion-exchange, and complexation of metal anions by the polymer. A new proposal, termed the cation chelation mechanism (CCM), was advanced to account for the observations. In this view, a number of cations (including those of the alkali metals, alkaline earth metals, some transition metals, NH(+)(4), RNH(+)(3) and perhaps H(3)O(+)) may be multiply complexed (chelated) by portions of the polymer, thus facilitating the sorption of accompanying anions. As predicted by the mechanism, moderately strong and selective complexation of several cations was observed to occur with the following order of selectivity: Li(+) < Na(+) < Cs(+) < Rb(+) < K(+) approximately NH(+)(4) < Ag(+) approximately Tl(+) < Ba(2+) < Hg(2+) < Pb(2+). Such behaviour parallels that known for many crown and non-cyclic polyethers and is therefore identified with the polyether portions of the polymer, which are thought to adopt helical conformations surrounding the complexed cations. The cation-chelation mechanism may be widely applicable to the sorption of ions of several types by polyether-based polyurethanes, particularly when large, hydrophobic anions (such as anionic metal complexes) are accompanied by an excess of chelatable cations.     

The interaction mechanisms between aqueous solutions of137Cs and134Ba radionuclides and local natural zeolites for an deactivation scenario

¹³⁷Cs and¹³⁴Ba were removed from synthetic aqueous solutions by means of natural zeolites of Slovakian origin. The equilibrium sorption behavior of Cs and Ba ions onto clinoptilolite and mordenite were studied under static as well as dynamic experimental conditions. Both Freundlich and Langmuir isotherms describe satisfactory by Cs and Ba adsorption on the zeolites studied. The elution of Cs and Ba ions from zeolite columns after the loading cycle was undertaken additionaly, in order to compare column operating runs of various exchanged zeolite forms.     

Cesium exchange reaction on natural and modified clinoptilolite zeolites

Cesium cation exchange reaction with K, Na, Ca and Mg ions on natural and modified clinoptilolite has been studied. Batch cation-exchange experiments were performed by placing 0.5 g of clinoptilolite into 10 ml or 20 ml of 1·10⁻³M CsCl solution for differing times. Two type deposits of clinoptilolite zeolites from, Nižny Hrabovec (NH), Slovakia and Metaxades (MX), Greece were used for ion-exchange study. The distribution coefficient (K _d ) and sorption capacity (Γ) were evaluated. For the determination of K, Na, Ca and Mg isotachophoresis method, the most common cations in exchange reaction was used. Cesium sorption was studied using ¹³⁷Cs tracer and measured by γ-spectrometry.     

Effect of lead on the sorption of phenol onto montmorillonites and organo-montmorillonites

The effect of lead (Pb) on the sorption of phenol onto montmorillonite-based sorbents was studied using a batch equilibration method when phenol and Pb were sorbed simultaneously and either Pb or phenol was previously sorbed. The sorbents were Na(+)-, Ca(2+)-, hexadecyl trimethylammonium (HDTMA)-Na(+)-, and HDTMA-Ca(2+)-montmorillonites. Pb diminished the sorption of phenol largely onto Na(+)- or Ca(2+)-montmorillonites, while phenol had little effect on the sorption of Pb onto all sorbents. Pb had no effect on the sorption of phenol onto HDTMA-Na(+)- or HDTMA-Ca(2+)-montmorillonites either. The sorption capacity of phenol followed the order HDTMA-Na(+)- > HDTMA-Ca(2+)- > Na(+)- > Ca(2+)-montmorillonites. The pseudo-second-order equation described the kinetics of phenol sorption well. Sorption isotherms of phenol followed the Freundlich equation. Phenol sorption on HDTMA-Na(+)- and HDTMA-Ca(2+)-montmorillonites was linear, while that on Na(+)- and Ca(2+)-montmorillonites was nonlinear.     

Sorption of radioactive cobalt in natural Mexican clinoptilolite

The ability of a natural Mexican clinoptilolite to sorb radioactive cobalt from aqueous solution was studied. The zeolite was stabilized partially with sodium and the content of Na⁺ in the samples was determined by neutron activation analysis. Ion exchange experiments were performed with solution labeled with radioactive⁶⁰Co at pH 6.5. XRD patterns were used to verify if the crystallinity of the aluminosilicate was affected by ionic exchange. A fast sorption uptake was observed and it was found that 0.408 meq/g of zeolite of Na⁺ ions were replaced by cobalt ions, followed by a desorption process where the uptake decrease to 0.314 meq/g of zeolite. This behavior is a consequence of the partial dehydration of the zeolite.     

A study of the sorption properties of natural calcium clinoptilolite by using radioactive indicators

The sorption of monovalent ions (cesium, silver, thallium, mercury), bivalent ions (strontium, barium, lead, copper, cobalt, zinc) and polyvalent ions (cerium) on calcium clinoptilolite under dynamic conditions has been studied. Both the dynamic exchange capacities in the different break-through of the ions and the degree of the exchanging ions in sorption of different metal cations have been determined. The good selectivity of calcium clinoptilolite in relation to cesium and strontium is displayed in the presence of sodium. The influence of various factors on the sorption the thermal and radiation treatment of the sorbent, the pH and concentration of solutions, equilibration time, presence of alkali and alkali earth ions deactivating agents—EDTA, citric acid tartaric acid, and boric acid in solution has been studied. The optimum conditions of sorption have been determined. Experiments for the desorption of cesium and strontium have been carried out. The possibility to use calcium clinoptilolite for the purpose of deactivation of radioactive wastes is shown. The better sorption properties of that sorbent, compared to calcium clinoptilolite, can be explained by the higher aluminium content, as well as by a prevalence of calcium and magnesium in its ion exchange complex.     

Sorption of lanthanum ions by natural clinoptilolite tuff

The equilibrium and kinetics of sorption of lanthanum ions on natural clinoptilolite tuff are studied. It is demonstrated that sorption of lanthanum ions from diluted solutions occurs in micropores of clinoptilolite, and from concentrated solutions in the mesoporous structure of tuff. The main capacity of zeolite tuff is found in the secondary porous structure. The sorption of lanthanum ions is limited by diffusion in tuff grains. Lanthanum ions are regularly distributed in the tuff phase and interact with the Brønsted centers of large clinoptilolite cavities.     

Simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash as influenced by salt treatment

To develop an effective technique for enhancing the removal efficiency of ammonium and phosphate at low concentrations without losing potential removal capacity, Na-ZFA (zeolite synthesized from fly ash) was converted into Ca-, Mg-, Al-, and Fe-ZFA by salt treatment and the simultaneous removal of ammonium and phosphate by ZFA saturated with different cations was investigated. It was shown that Al3+-ZFA had the highest removal efficiencies (80-98%) for ammonium, followed by Mg2+ (43-58%), Ca2+ (40-54%), Na+ (<20%), and Fe3+ (<1%). Both alkaline pH values (in the cases of Na+, Ca2+, Mg2+) and acidic pH value (in the case of Fe3+) inhibited the sequestration of ammonium. At low initial phosphate concentrations, the efficiency of phosphate removal by Al3+- and Fe3+-ZFA approached 100%, followed by Ca2+ (60-85%), Na+ (<25%), and Mg2+ (<5%). The difference in phosphate removal efficiency was explained by the adsorption mechanisms. It was concluded that ZFA could be used in simultaneous removal of NH4+ and phosphate at low concentrations with presaturation by an appropriate cation such as Al3+ through salt treatment.     

Cerium uptake by zeolite A synthesized from natural clinoptilolite tuffs

Summary Natural clinoptilolite tuffs from the Semnan region in Iran was used for the synthesis of zeolite A. The tuffs and synthesized zeolites were characterized by XRD and XRF. The sorption behavior of the synthesized zeolite toward cerium was studied. Using the Lagergren’s equation, the absorption constant was calculated. The measured distribution coefficient values (K_d) indicated that cerium uptake is higher in lower initial concentrations, higher temperature and higher pH values. Thermodynamic parameters of the exchange were calculated through construction of ion-exchange isotherms at three temperatures of 298, 323 and 343 K. The dynamic absorption of cerium was also studied by passing the solution through a column in the presence and absence of sodium ions.     

Improved protonation, collision-induced decomposition efficiency and structural assessment for 'red tide' brevetoxins employing nanoelectrospray mass spectrometry

Brevetoxins are a group of natural neurotoxins found in blooms of red tide algae. Previous electrospray mass spectrometry (ES-MS) studies show that all brevetoxins have high affinities for sodium ions, and they form abundant sodium adduct ions, [M + Na]+, in ES-MS, even when trace contamination is the only source of sodium ions. Attempts to obtain informative product ions from the collision-induced decomposition (CID) of [M + Na]+ brevetoxin precursor ions resulted only in uninformative sodium ion signals, even under elevated collision energies. In this study, a nano-ES-MS approach was developed wherein ammonium fluoride was used to form cationic [M + NH4]+ adducts of brevetoxin-2 and brevetoxin-3; a significant increase in the abundance of protonated brevetoxin molecules [M + H]+ also resulted, whereas the abundance of sodium adducts of brevetoxins [M + Na]+ was observed to decrease. Under CID, both [M + NH4]+ and [M + H]+ gave similar, abundant product ions and thus underwent the same types of fragmentation. This indicated that ammonium ions initially attached to brevetoxins forming [M + NH4]+ easily lose neutral ammonia in a first step in the gas phase, leaving protonated brevetoxin [M + H]+ to readily undergo further fragmentation under CID.     

Effect of the acidic treatment on the adsorption and structural properties of the natural mineral sorbent M45C20

Adsorption and structural properties of the initial natural mineral sorbent M₄₅C₂₀ and the sorbent treated with 2.33 M H₂SO₄ were studied. The sorbent mainly consists of montmorillonite and clinoptilolite. Aluminum, calcium, magnesium, sodium, and potassium ions are removed from the structure under the action of the acid. The specific surface, porosity of the sorbent, and pore size increase during this process. The sorption of ammonium ions in the natural samples predominantly follows the ion-exchange mechanism (exchange to calcium, magnesium, sodium, and potassium ions). The acid treatment changes the composition of the cation-exchange complex and results in an increase in the sorption capacity to ammonium ions by a factor of ??1.3.     

13X分子筛去除水中重金属离子的研究

以人工合成的13X型分子筛为吸附剂,研究了水中Pb2 、Cd2 和Cu2 在分子筛上的吸附行为,讨论了Pb2 、Cd2 和Cu2 共存条件下的竞争吸附,并考察了水中存在的Na 、Mg2 、Ca2 等离子对分子筛吸附去除重金属的影响.实验结果表明,13X分子筛对Pb2 、Cd2 和Cu2 3种离子的吸附符合Langmuir模型,最大吸附量分别为2.47mmol/L、2.0mmol/L和1.78mmol/L.在竞争吸附条件下,13X分子筛对3种重金属离子的选择性依次为pb2 ＞Cd2 ＞Cu2 .水中存在的Na 、Mg2 、Ca2 等对分子筛吸附重金属效率有一定的影响,其中Ca2 对Cu2 在分子筛上的去除影响最为显著.     

On the influence of ion exchange on the local structure of the titanosilicate ETS-10

The effect of ion exchange with different monovalent cations (NH(4)(+), K(+), Na(+) and Cs(+)) on the local structure of the titanosilicate ETS-10 has been studied by (29)Si MAS NMR and Raman spectroscopy. Although X-ray diffraction shows no significant influence of ion exchange on the long range order, ammonium exchange is found to result in substantial damage to the local structure. Ion exchange experiments with alkali cations under significantly more acidic conditions clearly show that the structural damage brought about by ammonium exchange is not caused by the low pH of the exchange solution. The exchange with potassium and caesium ions also leads to significant changes in the (29)Si NMR and Raman spectra. However, these changes can largely be reversed by sodium back-exchange.     

The Kinetics of Sorption of Lead Ions on Clinoptilolite in the H-Form

The kinetics of ion exchange of lead ions on clinoptilolite in the H-form was studied experimentally. The kinetic parameters of sorption of lead ions by the natural zeolite were calculated as depending on zeolite dispersity and solution concentration.     

Solid phase extraction�Cinductively coupled plasma spectrometry for adsorption of Co(II) and Ni(II) from radioactive wastewaters by natural and modified zeolites

Natural and modified clinoptilolite as low-cost adsorbents have been used for adsorption of Co(II) and Ni(II) from nuclear wastewaters both in batch and continuous experiments. Zeolite X was also synthesized and its ability towards the selected cations was examined. Kinetic and thermodynamic behaviors for the process were investigated and adsorption equilibrium was interpreted in term of Langmuir and Freundlich equations. The effect of various parameters including the initial concentration, temperature, ionic strength and pH of solution were examined to achieve the optimized conditions. The clinoptilolite was shown good sorption potential for Co(II) and Ni(II) ions at pH values 4?C6. Based on desorption studies, nearly 74 and 85% of adsorbed Co(II) and Ni(II) were removed from clinoptilolite by HCl. The Na⁺ and NH₄ ⁺ forms of clinoptilolite were the best modified forms for the removal of investigated cations. It is concluded that the selectivity of clinoptilolite is higher for Co(II) than Ni(II). The synthesized zeolite showed more ability to remove cobalt and nickel ions from aqueous solution than the natural clinoptilolite. The microwave irradiation was found to be more rapid and effective for ion exchange compared to conventional ion exchange process.     

Kinetics of the sorption of metal ions from sea water on clinoptilolite

Based on a study of the sorption kinetics of metal ions from sea water onto granular clinoptilolite and powdered clinoptilolite incorporated into a grain of a highly permeable inert support it has been shown that the rate of the sorption processes is limited principally by diffusion in the microgranules of zeolite. For the Tedzami clinoptilolite studied the characteristic dimensions of the microgranules are 15–20 m and are commensurate with the dimensions of microcrystals determined independently.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 263–267, February, 1990.We thank E. V. Venetsianov, L. S. Kamenetskii and M. V. Veksler for assistance in the investigation.     

The study of thiophene adsorption onto La(III)-exchanged zeolite NaY by FT-IR spectroscopy

Zeolites NaY and LaNaY (ion-exchanged with aqueous lanthanum nitrate solution) were used as adsorbents for removing organic sulfur compounds from model gasoline solutions (without and with toluene) and fluid catalytic cracked gasoline in fixed-bed adsorption equipment at room temperature and atmosphere pressure. The adsorptive selectivity for organic sulfur compounds was significantly increased when Na(+) ions in zeolite NaY were exchanged with lanthanum ions. IR spectra of thiophene adsorption indicate that thiophene is adsorbed onto La(3+) ions via direct S-La(3+) interaction and Na(+) ions via pi-electronic interaction for La(3+)-exchanged zeolite NaY, but only via pi-electronic interaction with Na(+) ions for NaY. The amount of adsorbed thiophene on La(3+)-exchanged zeolite Y was slightly decreased by coadsorption of benzene, but greatly reduced on NaY. The adsorption of thiophene via interaction with La(3+) on La(3+)-exchanged zeolite Y is hardly replaced by benzene coadsorption. The direct S-La(3+) interaction might be the essential reason for the evidently improved adsorptive selectivity of LaNaY for removing organic sulfur compounds from solutions containing large amount of aromatics.     

13C NMR study of the ion-binding selectivity of a new ammonium ionophore

A bicyclic peptide, cyclo (L-Glu(1)-D-Leu(2)-Aib(3)-L-Lys(4)-D-Leu(5)-D-Ala(6))-cyclo-(1gamma-4epsilon) (I), was designed and synthesized to provide an ammonium ion complexation site in a tetrahedral geometry. Molecular modeling, dynamics and electrostatic studies for I indicated that it exhibits some selectivity for ammonium ions over potassium and sodium ions. NMR measurements in CDCl(3)/CD(3)OD (1:1) show that for those carbonyl groups involved in cation binding, (13)C resonances shifted downfield with increasing cation concentration. The resonance that exhibited the largest change in chemical shift between uncomplexed and complexed forms was used to determine the selectivity. Selectivity values obtained were logK(NH(4) (+), Na(+) ) = - 2.4 and logK(NH(4) (+), K(+) ) = - 0.6.