Cr6+ adsorption by modified vermiculite

This work aimed at investigating the adsorption of Cr6+ in water by exfoliated vermiculite. The adsorbant tested in this experiment was a vermiculite (from China) which has been subjected to heating at 1000 °C for 1 minute, resulting in an exfoliated vermiculite. Three effects were studied: 1) contact time; 2) initial concentracion of Cr6+; 3) adsorbent mass. Samples were analysed by X Ray Fluorescence (XRF), X Ray Diffraction (XRD) and the solutions with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to quantify the adsorbed Cr6+ by the vermiculite. Results from XRD diffraction showed a conversion of vermiculite into flogopite after heating at 1000°C for 1 minute because of: 1) high content of potassium, 2) dehydration and 3) structural re-ordering; after the contact of vermiculite with Cr6+, the mineral structure did not change. The adsorption of Cr6+ was studied by Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. DKR model, indicative of a cooperative process, described adsorption equilibrium better than the other two models and the maximum adsorption capacity obtained was of 2.81 mol/g. Kinetic was studied using pseudo-first and pseudo-second order kinetic models, with a better description of the process by pseudo-second order model with correlation coefficient almost unitary (R2=0.9984; other kinetic parameters were k2=0.0015 and the absorption initial rate of 0.2x10-8 mg g-1 h-1). The present study demonstrates the effectiveness of modified vermiculite adsorbents for the treatment of hexavalent chromium-contaminated waters and that its adsorption depends on the experimental conditions (such as contact time, initial concentracion of Cr6+ and adsorbent mass)

Ammonium adsorption by chabazite zeolite-tuff from swine manure for soil amendment

T he use of natural sorbent geomaterials, like zeolitites (rocks containing > 50% of zeolites) is recognized as a valid method to recover N in the form of ammonium ions (NH4 +) from Zootechnical Wastewaters (ZoWs). Using zeolite-rich tuff as N sorbent from ZoWs lead to varius advantages like the decrease in environmental impact of ZoWs (decreased N content) and the subsequent creation of a high-value soil amendment employable also in organic agriculture (NH4-charged zeolite-tuff). In order to understand the characteristics of NH4-charged zeolites (CZ) as sorbent, it is mandatory a deep investigation on their sorption dynamics when they react with ZoWs. Scientific literature is rich of studies about sorption in sintetic solutions (especially NH4CL) while it lacks studies about sorption in real ZoWs. The aim of this work was therefore to characterize the NH4 sorption dynamics of a chabazite zeolite tuff from swine manure. In particular, two grain sizes were selected, a micronized (< 125 μm, CHAμ) and a granular one (0.7-2.0 mm, CHAg). A series of batch experiments were performed to investigate the effects of temperature, contact time and grain size on sorption of NH4. Equilibrium data were fitted with appropriate isothermal models; kinetic models were also investigated to characterize the kinetik sorption reactions and the thermodinamic parameters like change in free energy (ΔG), enthalpy (ΔH) and entropy (ΔS). Results have shown a significant grain size effect with respect to the equilibrium loading (qe), with better performances for CHAμ in all the temperatures investigated; the isothermal data showed that the influence of temperature is less for CHAμ with respect to CHAg. The kinetic data differs from the two grain size investigated, in particular CHAg showed an initial external surface adsorption and macropore diffusion during the first 60 minutes of contact, then the diffusion occurs also inside the micropores. The Intraparticle Diffusion model (ID) for CHAμ showed that the diffusion in the macropores are much more fast than CHAg and the intercept indicates the formation of a boundary layer thicker than CHAg. Pseudo-second-order kinetic model well explained CHAg behavior but not that of CHAμ. Both grain sizes were well explained by Elovich equation wich is a model used to explain the sorption kinetics for energetically heterogeneous solids surfaces (as likely the surface of the zeolite-tuff employed). Thermodinamic data showed that the energy in the liquid-solid adsorption surfaces increased during adsorption (ΔH ˃ 0), thus the cation exchange reaction needs energy from the liquid phase. The free standard entropy change (ΔS) is also positive, indicating that the NH4 sorption is a directional process with no significant differences with respect to the tested temperatures and that the randomness at the solid-solution interface increased during adsorption. The negative values of Gibbs free energy (ΔG) indicates that the NH4 sorption is an exergonic process (spontaneous reaction)

Reduction of Nitrogen Load in a Zootechnical Wastewater Using a Natural Chabazite Zeolite: An Investigation on Sorption Mechanisms

The use of zeolite-rich tuffs is a valid method for recovering nitrogen from wastewaters. This paper aims at describing the NH4+ adsorption processes of an Italian chabazite zeolite tuff used for the treatment of raw liquid swine manure. The effects of temperature, grain size and contact time were investigated. The isothermal analysis showed a multilayer adsorption behavior, well explained by the Harkins–Jura model, while kinetics was explained by pseudo-second-order, Elovich and intraparticle diffusion models. This study highlighted the complexity of the adsorption process from raw liquid manure, as well as the significant differences between tested particle sizes of the same zeolite tuff

Exploring the Combined Effects of Different Nitrogen Sources and Chabazite Zeolite-Tuff on Nitrogen Dynamics in an Acidic Sandy-Loam Soil

Volcanic tuffs rich in chabazite zeolites have been extensively examined for their potential to enhance soil properties and increase fertilizer efficiency, both in their natural state and when enriched with nitrogen (N). However, there is a scarcity of data regarding their utilization in acidic sandy soil, particularly when used alongside organic fertilizers. This paper presents the findings of a 50-day laboratory incubation study that investigated the dynamics of N pools in an acidic sandy-loam agricultural soil treated with various N sources. These sources included urea, N-enriched chabazite zeolite tuff, and pelleted composted manure applied at a rate of 170 kg N/ha. Additionally, the N sources were tested in combination with chabazite zeolite tuff mixed into the soil to assess its role as a soil conditioner. The results revealed distinct behaviours among the tested N sources, primarily impacting soil pH and N dynamics. Soil fertilized with manure exhibited slow N mineralization, whereas N-enriched zeolite displayed a more balanced behaviour concerning net NO3−-N production and NH4+-N consumption. Both N-enriched zeolite and urea temporarily altered the soil pH, resembling a “liming” effect, while pelleted manure facilitated a prolonged shift towards neutral pH values. Considering the water adsorption capacity of zeolite minerals, caution is advised when adjusting water content and employing combustion methods to measure soil organic matter in zeolite treated soil to avoid potential inaccuracies. In summary, N-enriched chabazite zeolite tuff emerged as a valuable N source in acidic sandy-loam soil, offering a promising alternative to synthetic fertilizers and showcasing a sustainable means of N recycling

Reducing Nitrogen Fertilization in Olive Growing by the Use of Natural Chabazite-Zeolitite as Soil Improver

In order to improve the sustainability and productivity of modern agriculture, it is manda tory to enhance the efficiency of Nitrogen (N) fertilizers with low-impact and natural strategies, without impairing crop yield and plant health. To achieve these goals, the ZeOliva project conducted an experiment using a zeolite-rich tuff as a soil amendment to improve the efficiency of the N fertiliz ers and allow a reduction of their inputs. The results of three years of experimentation performed in three different fields in the Emilia-Romagna region (Italy) are presented. In each field, young olive trees grown on zeolite-amended soil (−50% of N-input) were compared to trees grown on unamended soil (100% N-input). Soils and leaves were collected three times every year in each area and analyzed to monitor the efficiency of the zeolite treatment compared to the control. Vegetative measurements were performed along with analysis of pH, Soil Organic Matter and soluble anions in soil samples, whereas total C and N, C discrimination factor and N isotopic signature were investigated for both soils and leaves. Besides some fluctuations of nitrogen species due to the sampling time (Pre-Fert, Post-Fertilization and Harvest), the Total Nitrogen of leaves did not highlight any difference between treatments, which suggest that plant N uptake was not affected by lower N input in the zeolite treatment. Results, including vegetative measurements, showed no significant differences between the two treatments in all the observed variables, although the control received twice the N-input from fertilization. Based on these results, it is proposed that zeolite minerals increased the N retention time in the soil, allowing a better exploitation by plants which led to the same N uptake of the control notwithstanding the reduction in the N inputs. The use of zeolite-rich tuff in olive growing thus allows a reduction in the amount of fertilizer by up to 50% and improves the N use efficiency with many environmental and economic benefits

Gross Ammonification and Nitrification Rates in Soil Amended with Natural and NH4-Enriched Chabazite Zeolite and Nitrification Inhibitor DMPP

Using zeolite-rich tuffs for improving soil properties and crop N-use efficiency is becoming popular. However, the mechanistic understanding of their influence on soil N-processes is still poor. This paper aims to shed new light on how natural and NH4+-enriched chabazite zeolites alter short-term N-ammonification and nitrification rates with and without the use of nitrification inhibitor (DMPP). We employed the 15N pool dilution technique to determine short-term gross rates of ammonification and nitrification in a silty-clay soil amended with two typologies of chabazite-rich tuff: (1) at natural state and (2) enriched with NH4+-N from an animal slurry. Archaeal and bacterial amoA, nirS and nosZ genes, N2O-N and CO2-C emissions were also evaluated. The results showed modest short-term effects of chabazite at natural state only on nitrate production rates, which was slightly delayed compared to the unamended soil. On the other hand, the addition of NH4+-enriched chabazite stimulated NH4+-N production, N2O-N emissions, but reduced NO3-N production and abundance of nirS-nosZ genes. DMPP efficiency in reducing nitrification rates was dependent on N addition but not affected by the two typologies of zeolites tested. The outcomes of this study indicated the good compatibility of both natural and NH4+-enriched chabazite zeolite with DMPP. In particular, the application of NH4 +-enriched zeolites with DMPP is recommended to mitigate short-term N losses

Natural zeolitites in combination with struvite precipitation technology for the recovery of nutrients from agricultural wastewaters

The World Health Organization has emphasized the importance to start turning the perception of “nutrient-rich wastewaters”, from “wastes” to dispose of, to “resources”, useful for plant nutrition, but, despite this, 80% of municipal wastewaters globally produced are still discarded in the environment, without having been subjected to any treatment. On the other hand, the thoughtless use of excreta and derived materials for fertilization practices threatens the environmental systems, leading to pollution, soil degradation, and water contamination. The question of “how to efficiently dispose of nutrient-rich wastewaters” or, in other words, “how to improve the recycling of nutrients in agro-ecosystems”, remains thus a crucial topic for the sustainability of human activities. A promising technology consists in the precipitation of struvite crystals for the recovery of both nitrogen (N) and phosphorous (P). But, even if these processes are starting to scale up at industrial levels, the unbalance between the struvite components in wastewaters, as Mg2+, NH4+ and PO43-, remains one of the main issues for its implementation. The possibility to recover the excess of NH4+ before struvite precipitation may potentially increase the efficiency of struvite technologies. Within this thesis work, it was investigated a wastewater treatment process that uses natural zeolitites (rocks containing more than 50% in zeolite minerals) in combination with struvite precipitation, for the removal and recovery of N and P, in the form of struvite crystals and NH4+-N-enriched zeolitites. Before the wastewater treatment experiment, the NH4+-N adsorption properties of the applied zeolitite were characterized (experiment A) in terms of isotherms, kinetic models, and thermodynamic parameters, from livestock wastewater (pig manure), and two different grain sizes have been investigated: a granular zeolitite and a micronized one. Even if both showed interesting features, the micronized zeolitite demonstrated to reach higher adsorption capacities, with better temperature stability. This material was thus chosen for experiment B, where different treatment strategies have been investigated for the recovery of struvite from anaerobically digested wastewater. The investigated treatments were composed of two distinct steps: the 1st phase (zeolitite adsorption batch) tested the natural micronized zeolitite and a modified one (K+-enriched) for the reduction of NH4+-N loads. In the 2nd phase (struvite precipitation), 2 different Mg:NH4:PO4 molar ratios were tested, in particular, a condition of NH4+ excess (MR1) and another with Mg2+ in excess (MR2). Both these conditions were described in the literature as the best for struvite precipitation. The outcomes of experiment B suggested that the most feasible practice consists in the use of the natural zeolitites, in combination with the MR1 condition. This treatment showed indeed the highest nutrient removal efficiency, highest efficiency in struvite precipitation, and less alteration of the treated wastewater. The precipitate obtained was 89.9 mass % composed of struvite, poor in hazardous heavy metals, with 3.5% of nitrogen. The materials obtained, as the N-charged zeolitites, the struvite precipitates and the nutrient-depleted wastewater may potentially be used in agriculture, for crop nutrition, and/or as soil amendment. Even if the treatment described within this thesis work used livestock wastewaters and a derivate one, the methodology proposed may be appliable to any other nutrient-rich wastewater, as municipal ones.L' Organizzazione Mondiale della Sanità (WHO) ha sottolineato l'importanza di iniziare a percepire le acque reflue animali e umane, come “risorse” invece che “rifiuti”. Nonostante questo, l'80% delle acque reflue municipali prodotte a livello globale vengono ancora gettate nell'ambiente senza essere state sottoposte ad alcun trattamento. D'altra parte, anche l'utilizzo sconsiderato come fertilizzanti minaccia i sistemi ambientali, portando a inquinamento, a degrado del suolo e alla contaminazione delle acque. La questione riguardo a "come smaltire in modo efficiente le acque reflue " o, ancora meglio, "come migliorare il riciclaggio dei nutrienti negli agro-ecosistemi", rimane quindi un argomento cruciale, la cui soluzione è necessaria per garantire la sostenibilità delle attività umane. Una promettente tecnologia consiste nella precipitazione di struvite per il recupero di azoto (N) e fosforo (P) dal refluo, ma lo sbilanciamento tra gli ioni costituenti (Mg2+, NH4+ e PO43-) all’interno delle acque reflue, è uno dei problemi principali per la sua implementazione, in particolare rispetto al forte eccesso di NH4+ che tali materiali presentano. È quindi spesso necessario incrementare Mg2+ e PO43-, andando ad incidere sui costi di produzione e alterando la qualità del refluo trattato. La possibilità di recuperare in maniera controllata l'NH4+ in eccesso, prima della precipitazione di struvite, può potenzialmente aumentare l'efficienza di questa tecnologia, diminuendo considerevolmente la necessità nell’utilizzo di reagenti. È stato quindi studiato un processo di trattamento di acque reflue agricole che utilizza zeolititi naturali (rocce contenenti > 50% di minerali zeolitici) in combinazione con la precipitazione di struvite, per la rimozione e il recupero di N e P. Preliminarmente sono state caratterizzate le proprietà di adsorbimento di NH4+ della zeolitite (esperimento A). Lo studio è stato eseguito su un refluo da allevamento suinicolo, studiando l’effetto della granulometria del materiale tramite due diverse granulometrie: zeolitite granulare e micronizzata. La zeolitite micronizzata ha dimostrato di raggiungere capacità di adsorbimento più elevate, con una migliore stabilità rispetto alla temperatura. Questo materiale è stato scelto per l'esperimento B, dove sono state studiate diverse strategie di trattamento per il recupero di struvite da un digestato. Il trattamento prevedeva due fasi: nella prima fase è stata applicata la zeolitite micronizzata, sia naturale che arricchita in K+, per la riduzione controllata del carico di NH4+ del refluo. Nella seconda fase, sono stati testati 2 diversi rapporti molari (Mg:NH4:PO4) per la precipitazione di struvite, in particolare, una condizione di eccesso di NH4+ (MR1) e un'altra caratterizzata da Mg2+ in eccesso (MR2). I risultati dell'esperimento B hanno suggerito che la metodologia più promettente consiste nell'uso di zeolitite naturale, in combinazione con il rapporto molare MR1 (NZT-S MR1). Questo trattamento ha infatti mostrato maggiore efficienza nella rimozione dei nutrienti, per la precipitazione di struvite e una minore alterazione finale del refluo trattato. Il precipitato ottenuto era composto per l'89,9% da struvite, povero di metalli pesanti potenzialmente pericolosi, e con un contenuto di azoto totale pari al 3,5%.I materiali ottenuti (zeolititi cariche in NH4+, precipitati di struvite e il refluo trattato) sono potenzialmente utilizzabili in agricoltura come fertilizzanti/ammendanti.La metodologia proposta può essere applicabile a qualsiasi acqua reflua ricca in nutrienti, come le acque reflue municipali

Effects of natural and NH4-enriched Zeolitite on nitrogen leaching from a reclaimed agricultural soil of the Ferrara province (Italy)

natural zeolites, nitrate, agricultur