Chilean Zeolite Research Articles

Sequential Nitrification—Autotrophic Denitrification Using Sulfur as an Electron Donor and Chilean Zeolite as Microbial Support

Sequential nitrification–autotrophic denitrification (SNaD) was carried out for ammonium removal in synthetic wastewater (SWW) using sulfur as an electron donor in denitrification. Four reactors were operated in batch mode, two with zeolite (1 mm size) used as microbial support and two without support, to assess the effect of the zeolite addition in the SNaD. Aeration, anoxic, and anaerobic cycles were established, where 96% removal of NH4+-N (oxidized to nitrite or nitrate) was achieved in nitrification, along with 93% removal of NO3−-N in denitrification for the SNaD with zeolite. It was observed that the use of zeolite assists in buffering reactor load changes. Inhibition caused by nitrite accumulation in the denitrification stage was minimized by increasing the nitrogen concentration in the SWW. The results obtained in this study are the basis for the development of ammonium removal by simultaneous nitrification–autotrophic denitrification using a single reactor.

Influence of Chemical Surface Characteristics of Ammonium-Modified Chilean Zeolite on Oak Catalytic Pyrolysis

The influence of chemical surface characteristics of Chilean natural and modified zeolites on Chilean Oak catalytic pyrolysis was investigated in this study. Chilean zeolite samples were characterised by nitrogen absorption at 77 K, X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The nature and strength of zeolite acid sites were studied by diffuse reflectance infrared Fourier transform (DRIFT), using pyridine as a probe molecule. Experimental pyrolysis was conducted in a quartz cylindrical reactor and bio-oils were obtained by condensation of vapours in a closed container. Chemical species in bio-oil samples were identified by a gas chromatography/mass spectrophotometry (GC/MS) analytical procedure. Results indicate that after the ionic exchange treatment, an increase of the Brønsted acid site density and strength was observed in ammonium-modified zeolites. Brønsted acids sites were associated with an increment of the composition of ketones, aldehydes, and hydrocarbons and to a decrease in the composition of the following families (esters; ethers; and acids) in obtained bio-oil samples. The Brønsted acid sites on ammonium-modified zeolite samples are responsible for the upgraded bio-oil and value-added chemicals, obtained in this research. Bio-oil chemical composition was modified when the pyrolysis-derived compounds were upgraded over a 2NHZ zeolite sample, leading to a lower quantity of oxygenated compounds and a higher composition of value-added chemicals.

Ethylene adsorption onto natural and transition metal modified Chilean zeolite: An operando DRIFTS approach

Abstract Ethylene is a plant growth regulator that induces accelerated softening and ripening of fruits during transport and storage. Among the most applied methods for ethylene control, adsorption appears as a cheap and efficient technique. In this work, the effect of the incorporation of transition metals into natural Chilean zeolite on ethylene adsorption is investigated. Natural zeolite mainly composed of clinoptilotite and mordenite is modified using copper and zinc nitrate solutions and calcined under oxygen flow at 623 K, generating different transition metal modified zeolites. Parent and modified zeolites were characterised by X-ray diffraction, X-ray fluorescence spectroscopy and nitrogen adsorption. Zeolite surface modifications were assessed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Experimental results reveal the incorporation of Cu2+ and Zn2+ as new compensating cations into the zeolite framework. Ethylene adsorption isotherms show an enhancement on the adsorption capacity of Cu-exchanged zeolite. This result is not only associated to the higher micropore surface area of this sample, but also to the higher affinity of ethylene molecules to copper cations incorporated on this zeolite. DRIFTS operando experiments of ethylene adsorption in the absence and in the presence of moisture reveal a competitive mechanism of water and ethylene molecules toward hydroxyl sites. Si-OH-Al and Si-OH sites are rapidly occupied with water, reducing the adsorption of ethylene.

DEVELOPMENT OF AN ACTIVE FILM WITH NATURAL ZEOLITE AS ETHYLENE SCAVENGER

Ethylene (C 2 H 4 ) acts as a plant hormone, growth regulator that has a number of effects on the growth. Ethylene accelerates respiration, leading to maturity and also softening and ripening of many kinds of fruits. Although ethylene has some positive effects, it is often hazardous to the quality and shelf-life of fruits and vegetables. The removal of ethylene and/or inhibition of the effect of ethylene in stored environments is fundamental to maintaining postharvest quality of climacteric produce. In this study, the efficiency of a Chilean natural zeolite (NZ-Ch) against a commercial Na + montmorillonite (Cloisite Na+) was studied. The aluminosilicate characterization (XDR, FTIR, EGME, CEC, chemical composition) indicates that natural Chilean zeolite belongs to mordenite group. Elemental chemical analysis indicated that compensating ions, were sodium for MTNa+ and calcium, sodium and potassium for NZ-Ch, and in both aluminosilicates copper was present in their composition. Ethylene adsorption kinetics were fitted to a pseudo-second order model. The rate constant of the ethylene adsorption was nearly double for NZ-Ch compared with MtNa+. Langmuir-Freundlich isotherm allowed to determine maximum adsorption capacity that reached values of 5.4 µl g-1 for NZ-Ch and 1.28 µl g-1 for MtNa+. Films of low density polyethylene (LDPE) were obtained with different NZ-Ch concentrations. After 50 hours, a removal of 37% of ethylene present on headspace was achieves with 10% of ZN-Ch in LDPE active films.

Denitrification via Nitrite in a Modified UASB reactor using Chilean zeolite as Microbial Support

The general objective of this study was to develop a highly efficient, economical andintegrated technology for the removal of nitrogen compounds through denitrification via nitrite. Toachieve this, a modified UASB reactor was designed, set-up and operated using Chilean zeolite asmicrobial support. The results were compared to a conventional UASB reactor used as control. Thevolume of each reactor was 2 L. The reactors operated with synthetic wastewater under the sameoperating conditions (with superficial velocities, vs, of up to 1 m/h) in the first part of the experiment.Later, during the second part of the experiment, only the modified UASB was used, with vs of up to5.5 m/h. In the first part of the experiment, a higher velocity of denitrification in the reactor withzeolite was obtained. Nitrogen removal at the end of this experimental set for both reactors, with a vslower than 1 m/h, was 87%. In the second stage, the modified UASB reactor operated at vs ofbetween 1.5 and 5.5 m/h. Here, it was observed that the removal of nitrite increased significantly.Specifically, at vs values of 2.5, 4.0 and 5.5 m/h, a value of the nitrogen loading rate (NLR) of 1.22 kgN-NO2 -/m3/d was kept constant, achieving nitrogen removal efficiencies of 50%, 65% and 95.5%respectively. This last value proves how highly effective the modified UASB reactor is when operating with vs as high as 5.5 m/h.

BTX abatement using Chilean natural zeolite: the role of Brønsted acid sites

In wastewater treatment facilities, air quality is not only affected by conventional unpleasant odour compounds; toxic volatile organic compounds (VOCs) are also found. In this study, the adsorptive capacity of Chilean natural zeolite toward VOC removal was evaluated. Moreover, the influence of zeolite chemical surface properties on VOC elimination was also investigated. Three modified zeolite samples were prepared from a natural Chilean zeolite (53% clinoptilolite, 40% mordenite and 7% quartz). Natural and modified zeolite samples were characterised by nitrogen adsorption at 77 K, elemental analyses and X-ray fluorescence (XRF). Chemical modifications of natural zeolite showed the important role of Brønsted acid sites on the abatement of VOCs. The presence of humidity has a negative effect on zeolite adsorption capacity. Natural zeolites could be an interesting option for benzene, toluene and xylene vapour emission abatement.

Adsorption of sodium dodecyl benzene sulfonate from aqueous solution using a modified natural zeolite with CTAB

This paper describes studies of surface modification of a natural Chilean zeolite with cetyl trimethylammonium bromide (CTAB), to investigate the adsorption efficiency for the removal from aqueous solution of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), at bench scale. Modification of the zeolite with CTAB (named ZMS) was based on the external cation exchange capacity (ECEC) of 0.11 meq g −1. The medium pH influences the SDBS ions adsorption rate onto ZMS and the adsorption followed the pseudo-second-order kinetic model. Equilibrium data showed excellent correlation with the Langmuir isotherm model. The adsorption capacities depended on maximum uptakes followed the CTAB concentration or coverage ranging from 40% to 660% of the ECEC. The maximum adsorption capacity of 30.7 mg SDBS g −1 was obtained at 660% of ECEC value. These data contribute for the understanding of mechanisms involved in zeolite modification and provide same practical clues to improve the adsorption efficiency (uptake capacity) of anionic surfactants. Results were discussed in terms of interfacial and solution chemistry phenomena.

On the removal of Mn 2+ ions by adsorption onto natural and activated Chilean zeolites

This paper describes studies of preparation, activation and physical characterization of a Chilean zeolite (Ch-zeolite) employed as adsorbent for manganese ions from aqueous solutions. The zeolite sample, composed mainly of clinoptilolite and mordenite, had a specific surface area of 118 m 2 g −1 (N 2 adsorption), the particles were negatively charged in a wide pH range and presented a cation-exchange capacity of 1.09 meq NH 4 + g - 1 . The medium pH influenced significantly the Mn 2+ ions adsorption capacity and best results were obtained at pH 6–6.8 . The adsorption onto the activated zeolite followed the pseudo-second-order kinetic model and activation of the Ch-zeolite with NaOH resulted in the highest reaction rate. The equilibrium data showed excellent correlation with the Langmuir isotherm model. Ch-zeolite modification by treating it with NaCl (0.77 meq Mn 2+ g −1), NaOH (0.76 meq Mn 2+ g −1), Na 2CO 3 (0.72 meq Mn 2+ g −1) and NH 4Cl (0.67 meq Mn 2+ g −1) increased its uptake ability when compared with the natural Ch-zeolite (0.26 meq Mn 2+ g −1). These data contribute to the understanding of mechanisms involved in zeolite activation and provide some practical clues to improve the adsorption efficiency (uptake capacity and kinetics) of manganese ions.

Characterization and environmental application of a Chilean natural zeolite

The use of natural zeolites for environmental applications is gaining new research interests mainly due to their properties and significant worldwide occurrence. The present work describes the characterization of a natural Chilean zeolite and the results as adsorbent for ammonia from aqueous solutions. The zeolitic-rich tuff sample, mainly composed of clinoptilolite and mordenite, consisted of 13 μm mean volumetric particle diameter, 55 m 2 g −1 (methylene blue adsorption) and 177 m 2 g −1 (nitrogen adsorption) of specific surface area. Particles were negatively charged over a broad pH range (with or without ammonia) and 1.02 meq NH 4 + g −1 cation-exchange capacity. The ammonia removal appears to proceed through ion-exchange and rapid kinetics (rate constant of 0.3 min −1) at neutral pH value, with removal capacities up to 0.68 meq NH 4 + g −1. The Langmuir isotherm model provided excellent equilibrium data fitting ( R 2=0.97). Results indicate a significant potential for the Chilean natural zeolite as an adsorbent/ion-exchange material for wastewater treatment and water reuse applications.