Effect of acid phosphate media on the stability of clinoptilolite-rich tuff

The stability of the clinoptilolite-rich tuff from Oaxaca (México) treated with acid phosphate solutions at pH values from 0 to 6 at 70 °C was investigated with base on the dealumination of the zeolitic material and the effective ion exchange capacity property. The aluminum of the natural zeolite was determined by both atomic absorption spectroscopy and near infrared spectroscopy developed in this work. The effective cation exchange capacity (EfCEC) of the clinoptilolite-rich tuff was determined based on the method described by Ming et al. According to the experimental data, the pH of the phosphate solutions influences the stability of the clinoptilolite-rich tuff. The dealumination of the zeolitic material at pH 0 follows a first order kinetic model. It was also found that the EfCEC is the lowest and the material loses crystallinity at the same pH. The presence of phosphorous in the zeolitic material is observed after the treatment with the acid phosphate solutions. Therefore, the treatments of clinoptilolite-rich tuff from Oaxaca with the acid phosphate solutions modify its characteristics depending on the acidity of the aqueous media and consequently its stability varies.     

Supplementary research of clinoptilolite-rich tuff composites after adsorption trials using the XPS technique

The paper deals with fabrication of carbonized and hydrophobized clinoptilolite-rich tuff using organic carbon rich substances, here particularly starch and waste vegetable residues, which were pyrolytically combusted and covered the external zeolite surface. Hydrophobization of the zeolite external surface was accomplished by octadecylammonium surfactant. Both surface modified clinoptilolite-rich tuffs were tested and compared with each other with regard to removal of organic (phenol) and inorganic (chromate, arsenate) pollutants from aqueous solutions. These elaborated composites with surface adsorbed pollutant species were analysed by X-ray photoelectron spectroscopy (XPS).     

Preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral and its evaluation for the sorption of cadmium and cobalt

The preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral as well as the evaluation of its sorption properties for cadmium and cobalt are presented. The mineral was modified with different concentrations of hexadecyltrimethyl-ammonium bromide (HDTMA), the resulting materials were characterized by electron microscopy, IR spectroscopy, BET surface analysis, X-ray diffraction and their cation exchange capacities were determined. The cobalt and cadmium uptake was carried out in different concentrations. Neutron activation was used to measure the sorption of cobalt and cadmium. Organo zeolitic mineral samples were obtained with different surface characteristics compared with the original material and it was found that the retention of cobalt and cadmium by the organo zeolite diminishes due to the presence of HDTMA.     

An approach to physical characterization of fundamental ion exchange and adsorption behaviours of tuffaceous minerals in aqueous solutions of some environmental pollutants

Adsorption was measured and compared for the uptake of zinc, iron, lead, copper and ammonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian and Chinese origin for both the natural and near homoionic Na form as well, using the radioanalytical and spectrometric determination. The higher quality of Slovakian clinoptilolite-rich tuff has been proven to be effective for a potential lead and ammonium removal in native form, while parent tuff in Na exchanged variety may be proposed for even Fe(III) species removal out of water. The raw and Na-exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity, however lower adsorption capacity. Chinese clinoptilolite-rich tuff has not proved any exceptional high adsorption performance towards Fe(III) species. The data obtained from the adsorption experiments at 7–75 °C were used for calculation of some thermodynamic parameters—Gibbs free energy, activation energy, standard enthalpy and entropy, too.     

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV-vis, cyclic voltammetry, ESR and M?ssbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe(2)O(3)-2.462, n(Fe)/n(Al)=0.19, n(Si)/n(Fe)=30.9 using FeCl(3), whereby the iron leachability was 0.1-0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 mug g(-1) arsenite (99% removal) from a 360 mug(As(III)) L(-1) and 6 mug g(-1) arsenate from a 230 mug(As(V)) L(-1). Adsorption of arsenite and arsenate reached practically a plateau at n(Fe)/n(Si)=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.     

Sorption of cobalt by two Mexican clinoptilolite rich tuffs zeolitic rocks and kaolinite

Summary The sorption of cobalt from aqueous solutions was studied for two Mexican clinoptilolite rich tuffs zeolitic rocks and kaolinite clay. The effects of pH and contact time on the sorption were examined. Cobalt was determined by neutron activation analysis of the exchanged aluminosilicates. The sorption of cobalt by the aluminosilicates was similar in the pH range from 4 to 7. Kinetic studies showed a rapid sorption in the first 5 hours and equilibrium in about 24 hours. Sorption kinetics was best described by the second-order Ritchie modified model. The experimental results obtained at different concentrations and room temperature for both zeolites were fitted to Freundlich, Langmuir and Freundlich-Langmuir isotherms. The sorption pattern was found to follow the Freundlich model.     

Thermal treatment of zeolitic tuff

In this study, the zeolitic tuffs having clinoptilolite obtained from Bigadic region of western of Anatolia, Turkey were investigated as regards to whether it is possible to be transformed into amorphous phase from them. At first, the zeolite tuffs rich in clinoptilolite were characterized using XRD, DTA, TG, DSC, and FTIR standard methods. All the samples were heated at 110 °C for 2 h and then were expanded within 5 min between the temperatures 1200 and 1400 °C. In addition, porosity and density were determined. The resistance values of all the samples were measured in acidic and basic media. These samples were also analyzed. As a result of this study, zeolitic tuffs in clinoptilolite were transformed into amorphous phase, and especially in chemical industry were found convenient.     

Arsenic sorption by modified clinoptilolite–heulandite rich tuffs

Recent works show that modified natural zeolites improve the remotion of anionic or non-polar organic pollutants from water. In this work the arsenic sorption from aqueous solutions onto clinoptilolite–heulandite rich tuffs modified with lanthanum, hexadecyltrimethylammonium or iron was investigated considering the arsenic chemical species and the pH of the arsenic solutions. Clinoptilolite–heulandite rich tuffs were characterized by scanning electron microscopy and X-ray diffraction analysis. The elemental composition of the zeolitic samples was also determined. According to the Langmuir isotherm model the arsenic (V) sorption capacity of the zeolites was 75.4 μg As/g at pH 3, 3.9 μg As/g at pH 5 and 53.6 μg As/g at pH 6, for the lanthanum, HDTMA and iron modified clinoptilolite–heulandite rich tuff from Chihuahua (México), respectively. In general, the results suggested that the arsenic retention depends on the precedence of zeolitic material, the nature of arsenic chemical species, pH as well as the characteristics of modified natural zeolites. In this work the arsenic adsorption mechanisms are also discussed.     

天然沸石粉阳离子吸附性能分析方法的探讨

通过比较不同浓度的NH4Ac溶液对天然沸石粉所吸附的碱金属和碱土金属离子多次连续提取的效果,将由交换性K^ 、Na^ 、Ca^2 和Mg^2 加和所获得的阳离子交换量与由常规土壤阳离子交换量测定法获得的阳离子交换量进行比较,发现常规的土壤分析方法不适于测定天然沸石粉所吸附的交换性K^ 、Na^ 、Ca^2 和Mg^2 及阳离子交换量。建议用K^ 、Na^ 、Ca^2 和Mg^2 5次提取总量分别作为天然沸石粉所吸附的交换性K^ 、Na^ 、Ca^2 和Mg^2 的估算值,并把其提取量加和作为沸石粉阳离子交换量的估算值．     

Sorption of aqueous carbonic, acetic, and oxalic acids onto alpha-alumina

The presence of organic complexing agents can modify the behavior of a surface. This study aims to better understand the impact of carboxylic acids (acetic, oxalic, and carbonic acids) issued from cellulose degradation and equally naturally present in soils. First, evidence of two different kinds of sites for chloride adsorption onto alpha-alumina and another for sodium sorption was provided. Consequently, no competition between these cation and anion sorptions occurs on alpha-alumina. The associated exchange capacities and ionic exchange constants were measured. Second, the adsorption behavior of the carboxylic acids was studied as a function of aqueous -log[H(+)] and 0.01 to 0.1 M ionic strength (NaCl), and modeled by using mass action law for ideal biphasic systems. The carboxylic acids were found to be adsorbed on the same sites as chloride ions. The competition between organic ligands and chloride ions was satisfactorily accounted for by the model assuming the deprotonated form of the ligands was sorbed on alpha-alumina. The model also allowed us to interpret the adsorption of all species under various conditions without any extra fitting parameters.     

双功能聚合物基质阳离子交换固定相的制备及其在离子色谱中的应用

离子色谱是分离分析阳离子型化合物的重要手段之一。高效阳离子交换固定相的制备研究对离子色谱技术的发展具有重要的意义。该文以丙烯酸和顺丁烯二酸酐为单体,2-巯基乙基磺酸钠为巯基改性剂,提出了聚合物基质微球巯基改性自由基聚合修饰方法,用以制备新型双功能的阳离子交换固定相。该固定相以羧基和磺酸基为功能基,仅用简单的强酸淋洗液便可以实现常规阳离子的基线分离。利用色谱学模型,对金属离子和有机胺的保留行为进行了研究。采用梯度淋洗模式,可在24 min内实现10种阳离子的分离,表明固定相具有优异的色谱性能。“巯基-烯”修饰方法简单、高效。此外,通过调节巯基改性剂的比例能够实现对固定相交换能力的调控。     

载铜球形活性炭的制备及其吸附脱硫性能的研究

以122型弱酸性酚醛系阳离子交换树脂为炭前驱体,经过Cu²⁺交换、炭化和CO₂活化等过程制备得到负载金属铜的球形活性炭,对其进行了SEM、XRD、AAS和BET表征,采用动态吸附实验研究了其对模拟汽油中噻吩类硫化物的吸附性能,并且考察了甲苯和环己烯对其吸附性能的影响,对吸附脱硫机理进行了初步研究。结果表明,载铜球形活性炭上Cu以单质形态存在,并主要与硫原子产生配位作用,提高了对噻吩类硫化物的吸附性能,对噻吩(T)、3-甲基噻吩(MT)、2,5-二甲基噻吩(DMT)和苯并噻吩(BT)的饱和硫容依次为0.938、1.230、1.581和3.744 mg/g,吸附选择性依次为T < MT < DMT < BT。模拟汽油中加入甲苯和环己烯后,饱和硫容分别下降了77%和56%,这是甲苯和环己烯通过π电子与Cu发生作用,从而与硫化物产生竞争吸附导致的。     

Adsorption and thermodynamic behavior of uranium on natural zeolite

Adsorptive behavior of natural clinoptilolite-rich zeolite from Balikesir deposites in Turkey was assessed for the removal of uranium from aqueous solutions. The uranium uptake and cation exchange capacities of zeolite were determined. The effect of initial uranium concentrations in solution was studied in detail at the optimum conditions determined before (pH 2.0, contact time: 60 minutes, temperature: 20 °C). The uptake equilibrium is best described by Langmuir adsorption isotherm. Some thermodynamic parameters (ΔH°, ΔS°, ΔG°) of the adsorption system were also determined. Application to fixation of uranium to zeolite was performed. The uptake of uranium complex on zeolite followed Langmuir adsorption isotherm for the initial concentration (25 to 100 μg/ml). Thermodynamic values of ΔG°, ΔS° and ΔH° found show the spontaneous and exothermic nature of the process of uranium ions uptake by natural zeolite. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of electrochemical oxidation of activated carbon fiber on competitive and noncompetitive sorption of trace toxic metal ions from aqueous solution

A viscose-rayon-based activated carbon cloth (ACC) was electrochemically oxidized to enhance its cation sorption capacity for comparison with as-received ACC. The ACCs were characterized by sodium capacity measurement, pH titration, zeta potential measurement, elemental analysis, Brunauer-Emmet-Teller surface area, and pore size distribution. Batch sorption experiments showed that electrochemically oxidized ACC (EO) is more effective for the removal of lead and copper ions compared to unoxidized ACC (UO) for both competitive and noncompetitive sorption. For electrochemically oxidized fibers the copper and lead sorption capacities of ACC increased 17 and 4 times, respectively, for noncompetitive sorption and 8.8 and 8.6 times, respectively, for competitive sorption. However, reduction in the sorption capacities for both metals was observed for the competitive sorption. The sorption of lead and copper onto EO was by ion exchange, while that onto UO was likely to be due to surface complex formation. The affinity order of the two metal ions sorbed by UO and EO is Pb(2+)>Cu(2+). The effect of pH on sorption isotherms indicated that metal uptake increased with an increase in solution pH.     

Selective ion exchange onto Slovakian natural zeolites in aqueous solutions

Ion exchange isotherms have been measured and plotted for the uptake of cesium, barium, cobalt, zinc, silver and amonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian origin selectively for both the natural and near homoionic Na form as well, using the radioanalytical determination. The higher quality clinoptilolite-rich tuff has been proven to be effective for a potential radionucleides removal in native form according to the following selectivity sequence: Ag⁺,Ba²,Cs⁺>NH₄ ⁺>Co²⁺, while parent tuff in Na exchanged variety exhibited a little different sequence according to: Ag⁺?>?NH₄ ⁺?>?Ba²⁺?>?Cs⁺. The raw and Na exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity : Ag⁺?>?Zn²⁺?>?Cs⁺, Ba²⁺?>?Co²⁺ and Ag⁺?>?Zn²⁺.     

Application of linear regression analysis for iron and copper removal process using natural zeolites

Natural zeolites (zeolitic volcanic tuffs) cropped out from three regions of Transilvania, Vultureni (V), Pagli?a (P) and M?cica? (M), were evaluated in the process of iron (V, P, M) and copper (M) removal from wastewaters. Iron and copper removal process was studied using a fixed bed column, when equilibrium and kinetic data were acquired. Four isotherms, Langmuir, Freundlich, Langmuir?CFreundlich and Redlich?CPeterson, were used to fit the experimental data obtained for each natural zeolite sample. Parameters of the adsorption isotherms were estimated from the experimental equilibrium data using MATLAB. Using these data the best fit with one of the chosen isotherm can be found. Isotherm constants were determined by linear regression analysis of the experimental data. We concluded that the mathematical model based on Freundlich isotherm is the most appropriate to describe the iron and copper exchange on our natural zeolite samples.     

Organomineral Sorbents Based on Clinoptilolite-Containing Tuffs and Polyethylenimime

Low-swelling sorbent with weakly basic anion-exchange properties was prepared from clinoptilolite-containing tuffs and polyethylenimine using epichlorohydrin cross-linking agent. The properties of this sorbent (total anion-exchange capacity, swellability, etc.) were studied as influenced by the concentrations of the modifying and cross-linking agents, their ratio, period after sorbent preparation, and number of sorption-desorption cycles. The optimal conditions for modifying clinoptilolite-containing tuffs were developed and elemental composition of the resulting sorbent (with respect to C, H, and N) was determined.     

Development of Kinetic Mechanism for the Esterification of Acrylic Acid with Hexanol Catalyzed by Ion‐Exchange Resin

The heterogeneous esterification reaction of acrylic acid with hexanol over three different cation‐exchange resins, Amberlyst 131, Amberlyst 15, and Dowex 50Wx‐400, was investigated. Surface area, pore volume, average pore diameter, and acid capacity analyses were carried out for these three catalysts. Amberlyst 131 gave the highest conversion, and therefore, further experiments were performed catalyzed by Amberlyst 131. The absence of external and internal mass transfer resistances was investigated for the esterification of acrylic acid with hexanol. Experiments showed that the reaction is controlled by chemical step rather than external and internal mass transfer steps. The effects of temperature, catalyst loading, and alcohol to acid molar ratio on the conversion of acrylic acid were determined. The activation energy and kinetic and adsorption constants were determined according to the Langmuir–Hinshelwood–Hougen–Watson mechanism.     

Zeolitic adsorption in course of pollutants mitigation and environmental control

The review focuses on the adsorption and selectivity properties of the inland natural zeolites clinoptilolite and mordenite towards a broad spectrum of environmental pollutants incl. radioactive and compare some of them partially to selected foreign samples. A series of elution experiments into a broad spectrum of individual isomolar metal solutions by means of NH₄ ⁺—exchanged clinoptilolite—and mordenite-rich tuffs was done to prove the affinity sequence of both minerals untill the steady-state approaching. Among the all recorded breakthrough profiles onto mordente-rich tuff the ammonium exchanged tuff yielded the best uptake performance towards Cs. Three various clinoptilolite-rich tuff samples (Hungarian, American and Slovakian) were compared to each other in order to evaluate the iodide removal in dynamic regime by using the Ag exchanged tuff.     

SORPTION OF OXYANIONS BY SURFACTANT-MODIFIED ZEOLITE

Zeolite has high internal and external surface areas and high internal and external cation exchange capacities suitable for surface modification by cationic surfactants. When the initial surfactant concentration is less than the critical micelle concentration, the sorted surfactant molecules primarily form a monolayer. Limited chromate sorption indicates that patchy bilayer may also form. When the initial surfactant concentration is greater than the critical micelle concentration and enough surfactant exists in the system, the sorbed surfactant molecules form bilayers, producing maximum chromate sorption. On a meq/kg basis, planar nitrate sorbs more on surfactant-modified zeolite surfaces than tetrahedral chromate. In the presence of sulfate or nitrate, chromate sorption is hindered due to competition for sorption sites. Quantitative sorption of nitrate and chromate and desorption of bromide indicate that the sorption of oxyanions is primarily due to surface anion exchange.