The contamination of water bodies in urban areas is a serious problem, which may increase when wastewater is discharged without complete remediation. Due to their high adsorption capacity and ion-exchange properties, zeolites, such as clinoptilolite, can be used successfully to detoxify the wastewater before discharging it into the water body. In this study, experimental use of clinoptilolite is presented for water remediation. A static flow (A) and a laminar flow (B) method were applied in order to evaluate the efficiency of clinoptilolite for reducing different contaminants in the outflow wastewater of an old municipal treatment plant in Bologna District (Northern Italy). Mesocosm experiments were performed in order to achieve reduction of the microbial faecal indicators and of the excess nutrients and heavy metals in the effluent. During the experiments, pathogenic microorganisms, ammonium and heavy metals were reduced by as much as between 78 and 95% within 24 h, highlighting the great efficiency of this low-cost material for water remediation.

The sorption of ibuprofen by modified natural zeolite composites at three concentration levels (10, 20 and 30 mmol/100 g) of cationic surfactants – benzalkonium chloride and cetylpyridinium chloride, in a buffer solution (pH 7.4), was studied. Characterization of the composites before and after ibuprofen sorption was performed by drug sorption and isotherm studies, zeta potential and Fourier Transform infrared spectroscopic analysis. The biopharmaceutical performance of cationic surfactant-modified zeolites as drug formulation excipients was evaluated by in vitro dissolution experiments from the composites with medium surfactant contents. The drug sorption was influenced by the surfactant type and amount used for the zeolite modification. Prolonged drug release over a period of 8 h (up to ~40%) was achieved with both groups of samples. The kinetic analysis showed that the drug release profiles were best fitted with the Higuchi and the Bhaskar models, indicating a combination of drug diffusion and ion exchange as the predominant release mechanisms.

Phillipsite was crystallized from a high siliceous aluminosilicate mixture containing Zn cations and methylene blue (MB). The presence of MB did not affect the crystallization, but it resulted in a substantial amount of dye being anchored to the zeolite, despite its narrow channels. Dye-free synthetic phillipsite modified with MB solution showed markedly lower dye content, which, however was considerably higher than those in the MB-treated natural phillipsite and mordenite. The ultra violet/visible (UV-vis) spectra of the dye-modified synthetic phillipsites indicated the presence of MB monomers and oligomers, whereas the spectra of the modified natural zeolites showed protonated MB also. The electron spin resonance spectra of samples crystallized with MB indicated the presence of paramagnetic species.

The removal of gaseous mercury from flue gases from coal-fired power plants is currently an environmental challenge under investigation. Therefore, the main aim of this paper was to evaluate the suitability of faujasite group zeolites (Na-X) to adsorb mercury compounds. Previous, initial tests showed negligible Hg0 uptake by Na-X zeolite, but silver impregnation improved adsorption markedly. Therefore, the testing of mercury adsorption from flue gases into Ag+- impregnated Na-X synthetic zeolite (Ag-X zeolite) derived from coal fly ash was carried out. This material was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, X-ray fluorescence and nitrogen adsorption/desorption before being evaluated for mercury removal from exhaust gas. After preliminary mercury adsorption tests (fixed bed) under a nitrogen atmosphere, the adsorbent was examined with a simulated flue gas composition under various conditions, i.e. weight of zeolite, temperature of experiment and zeolite in powder and granulated forms. The removal of mercury was shown to depend on the sorbent texture (powder or granulate), exhaust gas flow rate and contact time, as well as the temperature of the experiment. The Ag-X zeolite tested reduced the level of mercury in the flue gas and, depending on the experimental conditions, long-time mercury breakthrough ranges from 15 to 40% were obtained. The best results for mercury capture were obtained for granulated material.

Zn-exchanged natural clinoptilolite was studied by powder X-ray diffraction and positron annihilation lifetime spectroscopy. The original clinoptilolite tuff was subjected to size fractionation by sedimentation and dissolution of cristobalite (opal-C). After Zn2+-exchange the purified clinoptilolite sample contained 2.2 Zn2+ ions per unit cell. Structural details obtained by Rietveld refinement showed that the Zn2+ cations are located in three sites (Zn1, Zn2 and Zn3) in the channels of the clinoptilolite. Site Zn1 is located in the centre of channel-A (Mg2+-M4 site). Site Zn2 is in channel-B, next to the calcium M2 position. A new Zn3 site is located in channel-A, in imminent proximity to Zn1. Positron Annihilation Lifetime Spectroscopy (PALS) was employed to assess the Zn exchange. As the cation content influences the free volume of the channels, the ionexchange process can be monitored by PALS. The results suggest the existence of two sizes of cavities, in accordance with the structural refinement.

The sorption of Sr2+ ions by natural clinoptilolite was investigated using the batch method. The effects of pH, contact time and strontium concentrations were tested and the optimal conditions for sorption were determined. The process was very fast initially and equilibrium was reached within 24 h. Kinetic sorption data were fitted to pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The simple pseudo-second-order rate model provides good agreement with the experimental data for Sr2+ uptake. The respective rate constants, k2, calculated at different initial Sr2+ concentrations, were obtained. The equilibrium data were analysed by applying the Langmuir, Freundlich and Dubinin–Raduchkevich isotherm models. The Langmuir model describes the observed Sr2+ uptake most accurately and the value of the monolayer sorption capacity is 32.81 mg Sr2+/g. The effect of Na+ ions and the effectiveness of uptake from low saline groundwater simulated solutions were also studied and discussed.

In this study, a clinoptilolite modified with apolaccase was used to adsorb Reactive Black 5 (RB5) dye from aqueous solution using the batch procedure. The influences of pH, contact time, temperature and absorbent dosage on the adsorption were investigated. The optimum adsorption was obtained at pH = 6, contact time = 60 min, temperature = 25ºC and adsorbent dosages of 1.62 and 1.59 mg/50 mL per gram of clinoptilolite and of apolaccase-modified clinoptilolite (LMC), respectively). The adsorption experimental data fitted both the Langmuir and Freundlich isotherm models well. In addition, pseudo-first-order and pseudo-second-order kinetics were used to study the kinetics of RB5 dye adsorption onto natural clinoptilolite and LMC. Adsorption appears to follow pseudo-second-order kinetics with a high correlation coefficient. Thermodynamic parameters such as changes in the free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption were calculated. The thermodynamic parameters indicate that the adsorption of RB5 dye onto LMC was less spontaneous, feasible and endothermic. The LMC can be used as an alternative low-cost adsorbent for the dye removal from aqueous solutions.

Non-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20°C/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30–200°C suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54±1.18, 30.99±1.14 and 27.79±1.42 kJ/mol by the Flynn–Wall–Ozawa, the Kissinger–Akahira–Sunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.

The removal of lead and zinc from a binary solution by fixed bed depths (40, 80 and 120 mm) of a natural zeolite was examined at a flow rate of 1 mL/min. The results obtained were fitted to the Bed Depth Service Time (BDST) model and the parameters of the model (q and k) were used to design a column system for flow rates of 2 and 3 mL/min at a bed depth of 80 mm. The experimental results were in excellent agreement with those predicted and experimental breakthrough curves for the binary systems were obtained. This approach facilitates the design of effective binary column processes without additional experimentation. Two major design parameters, the Empty Bed Contact Time (EBCT) and the zeolite usage rate, were calculated. The highest EBCT value of 13.56 min represents the optimal conditions for the binary (Pb+Zn) solution.

The removal of Cr(VI) from aqueous solutions under various conditions was investigated using a natural clinoptilolite and a synthetic zeolite derived from fly-ash (Na-P1), modified either with hexadecyltrimethylammonium bromide (HDTMA) or octadecyltrimethylammonium bromide (ODTMA). The study was focused mainly on the impact of the properties of the zeolite on the sorption capacity, the sorption mechanism, the influence of pH and the durability of the immobilization. The zeolites were modified with HDTMA and ODTMA surfactants up to 100% and 120% of their external cation exchange capacity. Batch and column studies were conducted to evaluate the influence of pH and the initial Cr(VI) concentration on their efficiencies for removing chromates. The organo-zeolites show a significant ability to remove Cr(VI) from aqueous solutions. The amount of Cr(VI) removed by organo-clinoptilolite and organo-zeolite Na-P1 is greater at low pH values, whereas the sorption efficiency decreased with increasing pH. Sorption of Cr(VI) was more efficient with the HDTMA-modified organo-clinoptilolite (150 mmol Cr(VI)/kg) than the ODTMA-modified clinoptilolite (132 mmol Cr(VI)/kg). The maximum sorption capacity was obtained with the 1.2 × ECEC ODTMA-modified clinoptilolite (237 mmol Cr(VI)/kg). The organozeolites Na-P1 adsorbed Cr(VI) from aqueous solutions more effectively and were much more durable than the organo-clinoptilolites.

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.

This contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.