To develop more economical and efficient heavy metal adsorbents, natural bentonite was employed as a raw material, and triethoxyvinylsilane served as a grafting agent to achieve the grafting bonding of sodium polyacrylate and bentonite. Structural alterations in the modified bentonite were analyzed through thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The adsorption and desorption characteristics of SAPAS-Bentonite and raw bentonite were compared and tested under various conditions, including time, temperature, pH, and lead ion concentration. The adsorption and desorption properties of sodium polyacrylate-grafted bentonite (SAPAS-Bentonite) were compared under various conditions (time, temperature, pH, and lead ion concentration). The results revealed that the modified method successfully achieved nano-scale coating of bentonite particles with sodium polyacrylate, leading to an increase in the maximum adsorption capacity of lead ions by 47.5%, reaching 165.73 mg g. A greater adsorption affinity for lead ions was exhibited by the outer sodium polycarboxylate portion of SAPAS-Bentonite compared with the inner bentonite. The adsorption of internal bentonite was limited by blocking when the adsorption of sodium polyacrylate did not reach the upper limit. The adsorption isotherm shifted from the Langmuir monolayer characteristic of the original bentonite to the S-shaped isotherm, reflecting the sodium polycarboxylate properties of SAPAS-Bentonite. Both bentonites demonstrated strong retention capacity for lead, with SAPAS-Bentonite surpassing raw bentonite in performance. This study provides valuable insights into the potential of SAPAS-Bentonite in the treatment of heavy metal pollution.

The kinetics of the thermal decomposition of the kaolin: dimethylsulfoxide (kaolin: DMSO) and the kaolin: N-methylformarnide (kaolin: NMF) intercalates have been reexamined. Two different sample sizes (2 mg and 8 mg) and grain-size distributions (<45 μm and 45–63 μm were investigated using isothermal and dynamic gravimetry in the temperature range 100°–200oC. All sample configurations for the kaolin: DMSO intercalate (2 mg, <45 μm; 2 mg, 45–63 μm; 8 mg, <45 μm; 8 mg, 45–63 μm) followed the rate law -ln(1 - α) = kt to a value for α, the reaction fraction complete, of.6, yielding activation energies and standard deviations at the 99% confidence level of 85.5 ± 3.79 and 71.75 ± 8.75 kJ/mole for the isothermal and dynamic runs, respectively. The kaolin: NMF intercalate (2 mg, <45 μm) also followed the same rate law for α <.8, with activation energies and standard deviations at the 99% confidence level of 89 ± 5.05 and 79.25 ± 6.47 kj/mole for the isothermal and dynamic studies, respectively. In solution the rate law -ln(1 - α) = kt is known as first-order kinetics, but here it appears to represent the non-instantaneous nucleation of uniformly sized particles, followed by the inward movement of a reaction interface.

Samples of Na-saturated, Upton montmorillonite were prepared with different contents of water (H2O or D2O) by: (1) adsorption of water from the vapor phase at a specific value of p/p°, the relative humidity, (2) adsorption of water from the vapor phase at p/p° = 1.0 followed by desorption of the water into the vapor phase at a specific p/p° < 1.0, and (3) adsorption of water from the liquid phase followed by desorption of the water into the vapor phase at a specific p/p° < 1.0. Water adsorbed initially from the vapor phase was called V-adsorbed water, and water adsorbed initially from the liquid phase was called L-adsorbed water. The water contents of these samples were determined by gravimetric analysis, the c-axis spacings by X-ray powder diffraction, the O-D stretching frequencies by IR spectroscopy, and the heats of immersion by differential microcalorimetry. No difference was found between V-adsorbed and L-adsorbed water; however, if the final water content was established by adsorption, the system was in a different state than if the final water content was established by desorption. In particular, hysteresis was observed in the following properties: the relative humidity of the adsorbed water, the O-D stretching frequency in this water, and the degree of order in the stacking of the clay layers. The only property that did not exhibit hysteresis was the heat of immersion. Apparently, hysteresis occurred because the orderliness of the system was not reversible, and, thus, any property that depended on orderliness was hysteretic.

Adsorption of Co2+ nitrilotriacetic acid (NTA) and equal-molar Co2+ and NTA by a low surface area (LSA) commercial gibbsite (3.5 m2 g−1) was investigated in batch as a function of pH (4.5 to 10.5), adsorbate (0.5 to 10 µM) and adsorbent (0.5 to 75 g L−1) concentrations and ionic strength (0.01 to 1 M NaClO4). The adsorption of Co2+ (Co-only) and the acid form of NTA (NTA-only) by gibbsite in 0.01 M NaClO4 exhibit cation-like and anion-like adsorption edges, respectively. For the equal-molar CoNTA chelate, Co and NTA adsorption edges were similar but not identical to the Co-only and NTA-only edges. Differences suggest the existence of a ternary CoNTA surface complex with the Co in the intact chelate coordinated to surface hydroxyls. NTA-only adsorption was insensitive to ionic strength variation, indicating weak electrostatic contributions to surface coordination reactions. This is consistent with the formation of inner-sphere surface NTA complexes and ligand exchange reactions in which monodentate, bidentate and binuclear NTA surface complexes form. Cobalt adsorption increases (edge shifts to lower pH by 1 pH unit) on LSA gibbsite as ionic strength increases from 0.01 to 1 M NaClO4. For the same ionic strength change, a similar shift in the Co-only edge was observed for another commercial gibbsite (16.8 m2 g−1); however, no change was observed for δ-Al2O3. Ionic strength shifts in Co2+ adsorption by gibbsite were described as an outer-sphere CoOH+ surface complex using the triple-layer model. Results suggest that, at waste disposal sites where 60Co and NTA have been co-disposed, NTA will not promote ligand-like adsorption of Co for acid conditions, but will reduce cation-like adsorption for basic conditions. Thus, where gibbsite is the dominant mineral sorbent, NTA will not alter 60Co mobility in acidic pore waters and groundwaters; however, NTA could enhance 60Co mobility where alkaline conditions prevail, unless microbial degradation of the NTA occurs.

Methods previously used to distinguish between water adsorbed on external surfaces and in the interlamellar space of Na-montmorillonite during adsorption and desorption of water vapor have been extended to a set of homoionic Li-, Na-, K-, Rb- and Cs-montmorillonite. The textural and structural features have been investigated at different stages of hydration and dehydration using controlled-rate thermal analysis, nitrogen adsorption volumetry, water adsorption gravimetry, immersion microcalorimetry and X-ray powder diffraction under controlled humidity conditions. During hydration, the size of the quasi-crystals decreases from 33 layers to 8 layers for Na-montmorillonite and from 25 layers to 10 layers for K-montmorillonite, but remains stable around 8–11 layers for Cs-montmorillonite. Each homoionic species leads to a one-layer hydrate, which starts forming at specific values of water vapor relative pressure. Li-, Na- and K-montmorillonite can form a two-layer hydrate. By comparing experimental X-ray diffraction patterns with theoretically simulated ones, the evolution of structural characteristics of montmorillonites during hydration or desorption can be described. Using structural and textural data, it is shown that during adsorption: (1) the rate of filling of interlamellar space of the one layer hydrate increases with the relative pressure but decreases with the size of the cations; and (2) the different hydrated states are never homogeneous.

The swelling of some well-defined Mg-, Ca-, Sr- and Ba- homoionic montmorillonites was studied in the domain of water relative pressures lower than 0.95. This involves the expansion of the crystal lattice itself, commonly known as the “interlamellar expansion” or “inner crystalline swelling”. The initial freeze-dried clays were characterized by nitrogen adsorption-desorption volumetry and controlled transformation rate thermal analysis. The evolution of the structural and textural properties of these different clays at different stages of hydration and dehydration was investigated using water adsorption gravimetry, immersion microcalorimetry at different precoverage water vapor relative pressures and X-raydiffraction (XRD) under controlled humidity conditions. Large textural variations are observed in the dry state depending on the exchangeable cations. The 2-layer hydrate exhibits the most ordered layer stacking. Water is mainly adsorbed in the interlamellar space. With increasing water pressure, each homoionic species leads to a 1-layer hydrate and, with the exception of Ba-montmorillonite, to a predominant 2-layer hydrate. The relative pressure corresponding to the formation of the 2-layer hydrate decreases with increasing hydration energy of the interlayer cation. For Ca-, Sr- or Mg-montmoriHonites, simulation of XRD patterns leads to the definition of successive homogeneous states corresponding to the 2-layer hydrate. Furthermore, it yields the water filling ratio corresponding to the different hydration states during adsorption and desorption of water vapor.

To better predict the fate and mobility of surfactants in the environment, sorption and desorption of a nonionic polyoxyethylene lauryl ether surfactant (Brij 35) by two smectites (Wyoming montmorillonite and Panther Creek smectite) and two interstratified mica-vermiculites (IMVs) were investigated by batch techniques, X-ray diffraction, and infrared spectroscopy. Maximum surfactant sorption by smectites ranged from 196 to 256 g kg−1, whereas the maximum sorption by the IMVs was indeterminate over the range of concentrations employed. Sorption by smectites was best described by the Langmuir model, but sorption by the IMVs showed an S-shaped isotherm, suggesting that cooperative sorption occurred. The surfactant was more readily desorbed from the IMVs than from the smectites in an initial wash with water. After two water washes, 65–75% of the initially sorbed surfactant was retained by the smectite, and 44–51% of the surfactant sorbed to the IMVs remained with the solid phase. In this study, basal spacing of the smectites increased to ≈17.5 Å near the sorption maximum, suggesting intercalation of surfactant molecules in the interlamellar regions of the clay. X-ray data also suggested that the surfactant molecules were oriented horizontally in the interlayer spaces. Greater surfactant sorption by the Casmectites gradually diminished the intensity of the 1630 cm−1 infrared band dues to hydration water, indicating that some water had been displaced by the surfactant. The surfactant was also sorbed by the IMV clays, but only on external surfaces and probably via interactions of micelles with the solid phase.

Results from earlier laboratory and field experiments were interrogated for the possibilities of sequestration, or long-term accumulation, of carbon from excess greenhouse gases in the atmosphere. In the laboratory study, samples of three (top) soils dominated by kaolinite and illite (together), smectite, and allophane were examined for the adsorption and desorption of dissolved organic carbon (DOC). Adsorption and desorption of DOC were carried out on clay fractions extracted physically and after first native organic matter and then iron oxides were removed chemically. Labeled organic material was added to the soils to assess the priming effect of organic carbon (OC). In the field, changes in OC were measured in sandy soils that had been amended by additions of clay for between 3 and 17 years, both through incorporation of exogenous clay and delving of in situ clay. The laboratory experiments demonstrated that a portion of DOC was held strongly in all soils. The amount of DOC adsorbed depended on clay mineral types, including Fe oxides. Much adsorbed DOC was lost by desorption in water and a substantial amount of native OC was lost on priming with new OC. Addition of clay to soils led to increased OC. Therefore, addition of clay to soil may enhance net sequestration of C. Organic carbon close to mineral surfaces or within microaggregates is held most strongly. Carbon sequestration may occur in subsoils with unsaturated mineral surfaces. However, incorporation of carbon into macroaggregates from enhanced plant growth might be most effective in removing excess carbon from the atmosphere, albeit over the short-term.

Desorption processes of low-molecular-weight compounds from the surface of smectites into the gas phase determine a number of processes, e.g. those involved in drug delivery and the release of herbicides. The desorption has not been investigated thoroughly and is not well understood. The present study was undertaken in order to understand better the factors influencing these desorption mechanisms. Starting with a very pure standard (Na+-rich) montmorillonite (Kunipia-F), which was exchanged against cations with different hydration properties (Ca2+, Li+, phenyltrimethylammonium, hexyltrimethyl-ammonium), the experiments explored the rate of desorption of volatiles with different chemical functionalities (water, ethanol, ethyl acetate, and toluene). The desorption was monitored by thermogravimetry and differential scanning calorimetry under isothermal conditions, and by ramping the temperature at a constant rate. The experiments were compared with numerical calculations based on finite-element methods and with analytical models. These data point to a two-step mechanism where the desorption follows the curve of the equilibrium desorption isotherms of those molecules on the montmorillonite. The bulk-like volatiles (i.e. volatiles with release kinetics close to that of the bulk liquids) were desorbed in a first step. With a decrease in the degree of coverage of the volatile on the montmorillonite, the desorption was increasingly dominated by the strength of interaction between the volatile and the interlayer cations of the montmorillonite.

The citrate-induced desorption kinetics of pre-adsorbed Se from montmorillonite (Mt) and its complexes with hydroxyaluminum (HyA-Mt) and hydroxyaluminosilicate (HAS-Mt) were studied. The mole fraction of pre-adsorbed Se released in 24 h from different clays followed the trends of Mt>> HAS-Mt> HyA-Mt with a significant increase with elevated citrate concentration in the desorbing solution. In contrast, the amount of Se adsorbed per unit mass of different clays followed a clear-cut opposite trend of HyA-Mt>HAS-Mt>>Mt. The Se desorption kinetics in different systems indicated multiple rate characteristics; where an initial fast reaction (0.25–2 h) was followed by a slow reaction (2–16 h). Of the six different kinetic models tested (zero-, first-, and second-order; power function, Elovich, and parabolic diffusion), the second-order rate equation showed the overall best fit to the fast and slow desorption kinetic data from the clays. Based on second-order rate constants, the rates of the mole fraction of Se desorption by citrate from different clay systems at 298 K followed the order Mt > HAS-Mt >> HyA-Mt. For both fast and slow reaction, the rates of desorption increased proportionally with the level of citrate. Replicate experiments conducted across a range of temperature (288–318 K) yielded Arrhenius parameters that followed the order HyA-Mt > HAS-Mt >> Mt. Considering that a lower mole fraction of Se desorption after a particular reaction period, slower desorption kinetics, and a greater activation energy of desorption are the indices of increased adsorption bond strength, the results clearly indicate that HyA- and HAS-interlayering and coatings on Mt not only augmented its Se adsorption affinity and capacity, but also increased the adsorption bond strength. Silication in HyA not only reduced the Se adsorption capacity, but also weakened the adsorption bond strength. This establishes a significant role of HyA/HAS-interlayering and coating on Mt in influencing the rate of citrate-induced release of Se. Reduction in surface-positive potential following citrate adsorption on the clay surface, a direct ligand exchange between Se and citrate, and structural dissolution are possible mechanisms responsible for citrate-induced Se desorption in the present study.

There is a clear gap in the understanding of the desorption patterns of metals sorbed on soils and clays, despite their importance in the mobility, transport and fate of metals in natural environments. In this study, we investigated the desorption behavior of Cd, Zn and Pb sorbed on montmorillonite (Mt) and on hydroxyaluminum (HyA)- and hydroxyaluminosilicate (HAS)-Mt complexes. At pH 6.5, 2.5 g L–1 of HyA-Mt and HAS-Mt sorbed almost all of the 10–6 M Cd, Zn or Pb, while Mt under the same condition sorbed ~48, 49 and 55% of the added Cd, Zn and Pb, respectively. Based on pH50 values, the selectivity of metal sorption on Mt was Pb > Zn > Cd, and on the complexes, it was Pb ≫ Zn = Cd. In general, larger fractions of sorbed metals were remobilized from Mt than from the complexes. Again, in comparison with Pb, larger fractions of sorbed Cd and Zn were remobilized from different clays. Reducing the pHs of the equilibrium sorption systems from a fixed point (6.5) to different points (6.0, 5.5, 5.0, 4.5, and 4.0) and from different points (6.5, 6.0, 5.5, 5.0, and 4.5) to a fixed point (4.0) both yielded hysteretic metal desorption patterns. The fractions of Cd and Zn desorbed through Na and Cu exchange from the clays, especially from the complexes, were very different, indicating the existence of cation exchangeable metal sorption sites of weak and strong affinities on the complexes. Based on the EDTA-extractable fractions of Cd and Zn from HAS–Mt and HyA-Mt, it appeared that HyA–metal bonds are stronger than the HAS–metal bonds. Compared with other agents, acetic acid remobilized the highest fractions of all metals irrespective of the type of clays, with a concomitant release of Al or Al + Si. The Pb-HyA/HAS-Mt bonds were, however, still much too strong to be broken substantially by this mechanism. The results accomplished in this study suggest further attention to the fundamental understanding of the mobility, fate, bioavailability and toxicity of the concerned metals in soils and related environments.

Polymers maintain colloidal stability by adsorbing onto the surface of sepiolite particles, and changes in temperature and salinity can affect this process. We chose three typical polymers to investigate their interactions with sepiolite under high-salinity (15 wt.% NaCl) conditions at >180°C. Sepiolite samples were characterized using infrared testing, X-ray diffraction testing, contact angle testing, thermogravimetric testing, filtration loss testing and rheological testing. The experimental results showed that the desorption of the polymers under high-temperature and high-salinity conditions reduces the stability and filtration control of the suspension significantly. Adding polymers to sepiolite suspensions can maintain good stability even after thermal ageing at 240°C. In terms of drilling fluid regulation, sepiolite can play a role in regulating rheological properties, and the interactions between various polymers and sepiolite can be utilized to maintain the stable colloidal state of the drilling fluid. Studying the adsorption behaviour of various types of polymers on the surface of sepiolite under high-temperature and high-salinity conditions has important implications for the design and selection of sepiolite drilling fluid treatment agents.

Invasive winter annual grass infestations on rangeland accumulate large quantities of litter on the soil surface, as plants senesce yearly and decompose slowly. It has been speculated that winter annual grass litter can adsorb soil-active herbicides and reduce overall performance. Three experiments were conducted from 2017 to 2018 at the Colorado State University Weed Research Laboratory to evaluate interception and subsequent desorption of herbicides applied to litter from three invasive winter annual grass species with simulated rainfall. Imazapic, rimsulfuron, and indaziflam were applied to medusahead [Taeniatherum caput-medusae (L.) Nevski], ventenata [Ventenata dubia (Leers) Coss.], and downy brome (Bromus tectorum L.) litter at two amounts (equivalent to 1,300 and 2,600 kg ha−1). Rainfall was simulated at 3, 6, 12, and 24 mm at 0, 1, and 7 d after herbicide application. Herbicide concentration from the collected rainfall was measured using liquid chromatography–tandem mass spectrometry. At 2,600 kg ha−1, B. tectorum herbicide interception was 84.3%, while V. dubia and T. caput-medusae averaged 76% herbicide interception. There were no differences in desorption among the three litter types. Simulated rainfall at 0 d after application recovered 100% of the intercepted rimsulfuron and imazapic from B. tectorum litter, while recovery decreased to 65% with rainfall at 1 or 7 d after application. Only 54% of indaziflam could be recovered at 0 d, and recovery decreased to 33% when rainfall was applied at 1 or 7 d after application. Applying soil-active herbicides before forecasted rain or tank mixing with a POST herbicide to provide initial control could potentially increase the amount of herbicide reaching the soil and provide more consistent invasive winter annual grass control.

The influence of Zn on the adsorption and desorption of Cry1Ab toxin from Bacillus thuringiensis (Bt) on palygorskite and montmorillonite was studied. The adsorption of the toxin gradually increased with increasing Zn concentration from 0 to 1.0 mmol L–1, and then decreased with further increase in Zn concentration. The adsorption isotherms of the toxin in the absence and presence of Zn were well described by the Langmuir equation (R2 > 0.9810–0.9991). The separation factor (RL) decreased with increase of Zn concentration, suggesting that the irreversibility of the adsorption increases. The XRD results showed that the treatment by Tris buffer or Zn(NO3)2 solution caused an expansion of the interlayer space of montmorillonite but did not affect palygorskite. The IR spectra suggest that Zn was likely to be combined with amino groups on the surface of the toxin. The presence of Zn during the adsorption of the toxin decreased desorption, suggesting that the residual risk of toxin would be exacerbated if soil is polluted by zinc.

The adsorption and desorption of Hg(II) by humic acid (HA) previously adsorbed on kaolin was studied. In the range of HA concentration investigated (0.0 –26.9 mg g–1), the Hg(II) adsorption capacity of kaolin at pH 4 is enhanced by the presence of HA. For the complexes with the highest HA concentration and for low Hg(II) initial concentrations, adsorption was lower, i.e. as HA concentration on the complexes increases, Hg(II) equilibrium concentration also increases. This behaviour is due to the increasing presence of dissolved organic matter as the HA concentration on the complexes increases. The dissolved organic matter is able to form a soluble complex with Hg, thus decreasing adsorption. Hg(II) adsorption from a 2.5×10–5 MHg(II) solution was influenced by pH. For kaolin, a pHmax (pH where maximum adsorption occurs) of 4.5 was observed. At pH values >pHmax retention decreased with increasing pH. This same behaviour was observed for the kaolin- HA complex containing the lowest HA concentration (6.6 mg g –1). For the other kaolin-HA complexes there was little effect of pH on Hg(II) adsorption between pH 2.5 and pH 6.5. The presence of HA increased the adsorption of Hg(II) on kaolin all along the pH range studied. Desorption experiments showed that the amount of Hg(II) desorbed was quite low (<1%) for all the HA and Hg(II) concentration range studied, except for the kaolin at acid pH (pH 2.5) where the Hg(II) released was >50% of Hg(II) previously adsorbed. The presence of HA dramatically reduced this percentage of desorption to values of <3%, indicating reduced risk of toxicity problems in surface and subsurface waters. The addition of Cu(II) did not favour any Hg(II) desorption, even though Cu exhibits a strong affinity for organic matter.

Sorption of the polar insecticide imidacloprid on organic-saturated octadecylammonium (C18) and dioctadecyldimethylammonium (DOD) and inorganic- (Fe- ) saturated Wyoming (W) and Arizona (A) montmorillonites has been investigated. Sorption isotherms were fitted to the Freundlich equation. Imidacloprid-montmorillonite complexes were studied by X-ray diffraction and FT-IR techniques. Imidacloprid sorption coefficients, Kf, decreased in the order WC18> AC18> WFe> WDOD≥ ADOD. The low layer charge and saturation by primary alkylammonium cation facilitates sorption of imidacloprid in the interlayer of the smectite, corroborated by the increase in basal spacing observed in X-ray diffraction patterns and by the presence of absorption band shifts in FT-IR spectra. Imidacloprid sorbs in the interlayer space of smectite mainly by hydrophobic interactions with the alkyl chains in organic smectites and with the uncharged siloxane surface in Fe(III)-smectite. Further polar bonds between the NO2 group of imidacloprid and the NH of the primary alkyl cations and protonation of imidacloprid in Fe-smectites enhanced sorption in these cases.

The purpose of this study was to determine whether a bentonite from the Gafsa deposit (western Tunisia) could be used to remove the Foron Blue 291 (FB) azo dye from wastewater. Batch adsorption and desorption experiments were conducted using untreated and purified bentonite and the influence of contact time, pH, adsorbent mass and temperature of the dye solution on the adsorption of FB was evaluated. Kinetic and isotherm data were fitted using two non-linear kinetic and two non-linear isotherm equations. In addition, the fits were evaluated using the coefficient of determination (R2) and the RMSE. The percentage of dye removal increased with increasing amount of adsorbent until total discolouration was achieved. The adsorption isotherms followed the Langmuir model, with the purified bentonite having a higher adsorption capacity than the raw material due to its higher specific surface area. In addition, the FB molecules were removed from the liquid medium by physical adsorption. Batch desorption experiments were conducted to study the desorption kinetics and the characteristics of the desorption isotherms as well as to quantify the portion of the FB (by mass) that was irreversibly fixed on the solid. Overall, the desorption kinetics were similar to the adsorption kinetics, which indicated that the adsorption-desorption process of azo dye is non-singular; irreversibility occurred that was underlined by an observed thermodynamic index of irreversibility (TII) of 0.69–0.94. The desorption isotherms of the FB depended on the mass of the FB that was initially adsorbed on the bentonite sample, suggesting hysteresis. The amount of irreversibly retained FB was between 46 and 68% of the initial adsorbed mass.

This study focused on the mineralogical and physico-chemical properties of heulandite/clinoptilolite (Heu/Cpt)-rich zeolitic tuffs SE of Ankara (Turkey) and evaluated their potential for use as adsorbents. The main Heu/Cpt minerals correspond to the intermediate type and the Cpt-type of the heulandite series. Minor chabazite, erionite and rarely analcime and accessory feldspars, mica, smectite, and quartz were also detected. Three types of Heu were recognized according to their thermal behaviour. Cpt (type-III Heu) was thermally stable at 600°C, whereas type-I Heu collapsed and type-II Heu partially collapsed. The Si/Al ratios of the Hul/Cpt ranged from 3.54 to 5.03, the Γ parameter (Γ = Ca/Al + 0.115*Al) varied between 0.78 and 1.85 and Al + Fe3+ varied between 6.27 and 8.00. The Na, K and Ca contents of Heu/Cpt varied widely and the Heu had an intermediate composition between types II and III. The Mg + Ca content is greater than the Na + K content in Heu-type II and smaller in Heu-type III zeolites. The BET surface area and the pore-size of the samples varied between 10.15 and 194.27 m2/g, and between 1.41 and 12.42 nm, respectively. The N2 adsorption and desorption isotherms were comparable, but the adsorption/desorption capacity is greater in type III than in type II Heu zeolites. The cation exchange capacities of the Heu/Cpt-rich samples ranged from 185 to 280 meq/100 g.

The sorption properties of iron-modified zeolite (IMZ) and the kinetics of zinc and cadmium uptake by the IMZ were investigated by the batch method. Two kinetic stages were observed, fast uptake up to 240 min, followed by slow uptake up to equilibrium. Kinetic results were fitted to the reaction and diffusion kinetic models, which indicated that intra-particle diffusion was the rate-limiting step. The Vermeulen’s approximation model was used to predict the quantity of Zn and Cd ions removed per gram of IMZ. The results of the successive sorption and desorption of Zn and Cd ions, with different electrolyte solutions, showed the best desorption efficiency with sodium salt solutions. Four successive repetitions of the sorption/desorption cycles showed a small difference between the amount of sorbed and desorbed Zn and Cd ions from the second to the fourth cycle. This indicates excellent sorption/regeneration properties of the IMZ.