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

<p>The 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 (NH<sub>4</sub><sup>+</sup>) from Zootechnical Wastewaters (ZoWs).</p><p>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 (NH<sub>4</sub>-charged zeolite-tuff).</p><p>In order to understand the characteristics of NH<sub>4</sub>-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 NH<sub>4</sub>CL) while it lacks studies about sorption in real ZoWs.</p><p>The aim of this work was therefore to characterize the NH<sub>4</sub> 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 NH<sub>4</sub>. 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).</p><p>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.</p><p>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).</p><p>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.</p><p>The free standard entropy change (ΔS) is also positive, indicating that the NH<sub>4</sub> 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.</p><p>The negative values of Gibbs free energy (ΔG) indicates that the NH<sub>4</sub> sorption is an exergonic process (spontaneous reaction).</p>

Surface-modified apricot pits as biochar feedstock and phosphate sorbent

<p>Pits from fruit like apricots, peaches and cherries are an under-utilized resource. If there is any use at all, they may be extracted for special vegetable oils. Mostly the pits are combusted or left to rot. However, they are also an appropriate feedstock for pyrolytic carbonization. This study investigated the biochar produced from apricot pits for its potential to sorb phosphate from liquid media and from artificial wastewater.</p><p>Shredded apricot pits were pyrolyzed at 450 °C in a lab-scale screw reactor (Pyreka 3.0). Additionally, the impregnation of the feedstock with Mg(OH)<sub>2</sub> before pyrolysis was studied to test the hypothesis that phosphate sorption to biochar takes advantage of metal bridges on the biochar surface.</p><p>The results of isotherm sorption experiments showed that the pre-pyrolysis Mg-surface modification of the pits improved the sorption capacity of the biochar up to 42 mg PO<sub>4</sub>-P/g whereas the unmodified biochar adsorbed only about one tenth. When KH<sub>2</sub>PO<sub>4</sub> was used as the only sorbate, EDX-mapping showed the formation of K-struvite-crystals in the pores of the biochar. Desorption experiments showed a major release of the adsorbed phosphate within a few hours. Sorption competition experiments with phosphate and nitrate showed no negative effect of nitrate on phosphate sorption. Feedstock impregnation with Ca(OH)<sub>2</sub> resulted in more variable sorption dynamics.</p><p>The results could be confirmed by deploying the surface-modified apricot pit biochar for the reduction of the phosphate load in artificial wastewater.</p>

Water vapor sorption dynamics in different compressions of eelgrass insulation

Eelgrass shows potential in meeting the rising demands towards new, sustainable materials. It hosts a range of characteristics that benefits its application as a building material, such as thermal and acoustic insulating properties that can compete with conventional mineral wool insulation. However, as a porous bio-based building material, the moisture performance of eelgrass must be assessed to ensure its practical application. In this study, experimental investigations are conducted by a new automated vapor sorption analyzer (VSA) to measure adsorption and desorption of water vapor on different compressions of eelgrass insulation, ranging from loose strands to densely compacted insulation batts. Overall, higher sorption dynamics are observed in eelgrass insulation compared to conventional mineral wool insulation. Loose strands of eelgrass depict higher dynamics (including hysteresis) for the full range of relative humidity in comparison to insulation batts, potentially due to additional binder. Increasing the compression of eelgrass insulation batts results in lower sorption dynamics in the >70% relative humidity range. A Guggenheim-Anderson-deBoer model is applied that shows good fit with the experimental data and may be applied in moisture transfer calculations. This study furthers the potential of compressing eelgrass for application in passive design strategies through its moisture buffering capabilities.