Silver nanoparticles impregnated zeolites derived from coal fly ash : effect of the silver loading on adsorption of mercury (II)

Removal of mercury (II) from aqueous phase is of utmost importance, as it is highly toxic and hazardous to the environment and human health. A promising method for the removal of mercury (II) ions from aqueous solutions is by using adsorbents derived from coal fly ash (CFA), such as synthetic zeolites. In this work we present the hydrothermal production of synthetic zeolites from CFA followed by a modification for impregnation of silver nanoparticles, in solid concentrations from 0.15 to 4.71 wt.%. All produced zeolites and parent materials are characterized by XRD, XRF, BET and PSA to obtain morphological and microstructural data. Moreover, mercury (II) ions removal from aqueous solutions with initial concentration of 10 ppm is studied. According to results, zeolites and Ag-nanocomposites demonstrate much higher removal than parent CFA (up to 98%). In addition to this, we could observe a distinct adsorption behavior depending on the loading of Ag NPs in nanocomposites. A possible removal mechanism for both zeolites and Ag-nanocomposites is discussed

A fractal-based correlation for time-dependent surface diffusivity in porous adsorbents

Fluid-solid adsorption processes are mostly governed by the adsorbate transport in the solid phase and surface diffusion is often the limiting step of the overall process in microporous materials such as zeolites. This work starts from a concise review of concepts and models for surface transport and variable surface diffusivity. It emerges that the phenomenon of hindered surface diffusion for monolayer adsorption, which is common in zeolites, and models able to fit a non-monotonic trend of surface diffusivity against adsorbate solid phase concentration, have received limited attention. This work contributes to the literature of hindered diffusion by formulating a time-dependent equation for surface diffusivity based on fractal dynamics concepts. The proposed equation takes into account the contributions of both fractal-like diffusion (a time-decreasing term) and hopping diffusion (a time-increasing term). The equation is discussed and numerically analyzed to testify its ability to reproduce the possible different patterns of surface diffusivity vs. time

Insights into the S-shaped sorption isotherms and their dimensionless forms

Isotherms are of paramount importance for the interpretation of adsorption and ion exchange mechanisms and the design of separation and catalytic processes. Although the literature on sorption isotherms is rich, most of experiments and models employed are limited to systems that obey simple equilibrium isotherms, such as linear, favorable (convex-upward) or unfavorable (concave-upward). This paper deals with the rather overlooked S-shaped isotherms and their dimensionless forms, which are of great importance for the modeling of separation processes and interpretation of equilibrium data. A review on the physical significance and applications of S-shaped isotherms in adsorption and ion exchange process is also presented

Mars in situ resource utilization (ISRU) with focus on atmospheric processing for near term application : a historical review and appraisal

The inspirational paper by Ash, Dowler and Varsi in 1978 proposing to utilize in situ re-sources on Mars (ISRU) rather than bringing them from Earth, originated the field of Mars ISRU that has been the subject of research ever since. In this paper we reviewed significant research re-ported on Mars ISRU since 1978 and reported briefly on accomplishments. We found that prior to 2014, progress on small tasks was sporadic and intermittent, always at low Technology Readiness Level (TRL). In 2014, the National Aeronautics and Space Administration (NASA) took a bold, im-aginative, unprecedented step to fund a major project in Mars ISRU: the so-called “MOXIE” (Mars Oxygen In Situ Experiment) in which an oxygen production plant based on solid oxide electrolysis (SOEC) was developed, and finally demonstrated on Mars in 2022 and 2023. While MOXIE leaves behind it a wealth of accomplishments, there remains the need to close remaining gaps with addi-tional laboratory and field work. Solid-oxide electrochemical cell (SOEC) technology has become a major area of worldwide investment for terrestrial energy and CO2 control. There is a very strong overlap between this terrestrial technology and Mars ISRU. NASA has already leveraged the terres-trial development work via MOXIE. NASA can leverage further advances with a comparatively small investment beyond 2023. Because NASA is engaged in a major program to return humans to the Moon, NASA’s focus is on lunar ISRU. Unfortunately, the mission impact and return on invest-ment for lunar ISRU does not compare to that for Mars ISRU. NASA’s concept for Mars ISRU is futuristic involving autonomous mining, transporting, and processing large amounts of Mars rego-lith. This might well occur long after initial human landings which could better profit in the near-term from MOXIE technology. By continuing further development of SOEC technology beyond MOXIE, while leveraging large investments in terrestrial applications, NASA can develop the Mars ISRU appropriate to nearer term human missions at modest investment. The goal of this paper is to place the relatively mature MOXIE technology advance and solid oxide electrolysis in general in perspective to the historical evolution of low TRL Mars ISRU technology

Hydrothermal synthesis of zeolite production from coal fly ash : a heuristic approach and its optimization for system identification of conversion

Commercialization of synthetic zeolites has given considerable impetus to optimization of its production routes. The preferred production route involves hydrothermal treatment of coal fly ash in a strong alkali solution. The process involves several parameters, such as reaction temperature, time, the concentration and amount of alkali solution, and silica content in the fly ash, all of which strongly and non-monotonically affect the conversion. We herein perform several experiments with the Kazakhstani fly ash, and obtained a highest conversion of zeolites of 78% using 3 M NaOH at 110 °C. Further, we propose a conversion model using zero-order Takagi-Sugeno fuzzy system to analyze the effect of individual process parameters on conversion, and thereby, the reaction mechanism(s) of zeolite formation. The model is designed and developed, using the data, both from literature and our experiments on Kazakhstani fly ash. The obtained results clearly illustrate that the model accurately predict the conversion percentage of zeolite for a given set of reaction parameters. The model is further optimized to provide accurate inferences and an average deviation between the model predictions and experimental values for zeolite yield is observed to be less than 5%

Photochemical degradation of organic pollutants in wastewaters

In the present work, the photochemical treatment of a synthetic wastewater in a batch recycle photochemical reactor using ultraviolet irradiation (254 nm, 6 W), hydrogen peroxide and ferric ions was studied. Reactor volume was 250 mL with 55.8 mL of irradiated volume in the annular photoreactor. The synthetic wastewater was composed mainly of organic carbon. The effect of initial total carbon (136-1080 mg L-1), initial H2O2 amount (1332-5328 mg L-1), pH, and Fe(III) presence (2-40 ppm), on total carbon (TC) removal was studied. Each experiment lasted 120 min, and the process was attended via pH and TC concentration. Direct photolysis in the absence of any oxidant had practically no effect on TC removal. Regarding the effect of initial TC concentration in the wastewater keeping the same initial hydrogen peroxide concentration (2664 mg L-1), it was observed that for 136-271 mg L-1 TC, around 60% TC removal was achieved, while when initial TC was increased at 528 mg L-1, the TC removal observed decreased to 50%. For a further increase in TC at 1080 mg L-1, TC removal dropped to 14%. Initial pH adjustment of the wastewater resulted in slight variations of the TC removals achieved. Finally, adding Fe(III) in the process was beneficial in terms of TC removal obtained. Particularly, the addition of 40 ppm Fe(III) in the presence of 2664 mg L-1 H2O2 and initial TC equal to 528 mg L-1 increased the TC removal from 50% to 72%

Removal of Cd2+ from water by use of super-macroporous cryogels and comparison to commercial adsorbents

In this study amphoteric cryogels were synthesized by the use of free-radical co-polymerization of acrylate-based precursors (methacrylic acid and 2-acrylamido-2-methyl-1-propansulfonic acid) with allylamine at different ratios. The physico-chemical characteristics of the cryogels were examined using SEM/EDX, FT-IR, XPS and zeta potential measurements. The cryogels were tested toward Cd 2+ removal from aqueous solutions at various pH and initial concentrations. Equilibrium studies revealed a maximum sorption capacity in the range of 132–249 mg/g. Leaching experiments indicated the stability of Cd 2+ in the cryogel structure. Based on kinetics, equilibrium and characterization results, possible removal mechanisms are proposed, indicating a combination of ion exchange and complexation of Cd 2+ with the cryogels’ surface functional groups. The cryogels were compared to commercially available adsorbents (zeolite Y and cation exchange resin) for the removal of Cd 2+ from various water matrices (ultrapure water, tap water and river water) and the results showed that, under the experimental conditions used, the cryogels can be more effective adsorbents

Sustainable treatment method of a high concentrated NH3 wastewater by using natural zeolite in closed-loop fixed bed systems

The aim of this study is to investigate ammonium removal from a wastewater resulted after homogenization and anaerobic digestion of a mixture of wastes and wastewater from animal processing units and sewage sludge, by using natural zeolite clinoptilolite. Batches as well as closed loop fixed bed system (CLFB) are studied, offering an alternative to conventional fixed bed systems. The experimental results showed that the optimum pH is in the vicinity of 6.48, where the achieved removal in the batch system reached 46%. The CLFB system, under the same experimental conditions and relative flow rate of 2.56 BV h−1, reached a removal of 55%, which is almost 22% higher. In the CLFB the removal of ammonia could be further increased by diluting the initial solution by 1/8, reaching the level of 96%. The achieved zeolite loading, for all studied systems, is between 2.62 and 13 mg g−1. This kind of operation is very useful for relatively high concentration and small volumes of wastewater and in systems that there is no need for continuous flow operation

Photocatalytic treatment of a synthetic wastewater

This work aimed at investigating the photocatalytic treatment of a synthetic wastewater using UV light (254 nm, 6 W), TiO2 catalyst and H2O2 in a batch recycle annular photoreactor. The total volume of the solution was 250 mL while the irradiated volume in the annular photoreactor with 55.8 mL. Each experiment lasted 120 min and samples were sent for Total Carbon and HPLC analysis. The stock wastewater had initial total carbon 1118 mg L-1. The effect of the presence of phenol in the wastewater on total carbon (TC) removal was also studied. It was shown that the photocatalytic treatment was effective only when initial TC was decreased to 32 mg L-1, whereas the optimum TiO2 concentration was 0.5 g L-1, leading to a TC removal up to 56%. For the same initial carbon load, the optimum H2O2 concentration was found to be 67 mg L-1 resulting in 55% TC removal. Combining, however, TiO2 and H2O2 did not lead to better performance, as 51% TC removal was observed. In contrast, when initial carbon in the wastewater was partially substituted by phenol, the combination of catalyst and hydrogen peroxide was beneficial. Specifically, when 10 ppm of phenol were added keeping the same initial TC concentration, UV/TiO2 treatment resulted in 46% TC removal and 98% phenol conversion, whereas using additionally H2O2 led to 100% phenol conversion after 45 minutes and 81% TC removal

Essentials of endorheic basins and lakes: a review in the context of current and future water resource management and mitigation activities in Central Asia

Endorheic basins (i.e., land-locked drainage networks) and their lakes can be highly sensitive to variations in climate and adverse anthropogenic activities, such as overexploitation of water resources. In this review paper, we provide a brief overview of one major endorheic basin on each continent, plus a number of endorheic basins in Central Asia (CA), a region where a large proportion of the land area is within this type of basin. We summarize the effects of (changing) climate drivers and land surface-atmosphere feedbacks on the water balance. For the CA region we also discuss key anthropogenic activities, related water management approaches and their complex relationship with political and policy issues. In CA a substantial increase in irrigated agriculture coupled with negative climate change impacts have disrupted the fragile water balance for many endorheic basins and their lakes. Transboundary integrated land and water management approaches must be developed to facilitate adequate climate change adaptation and possible mitigation of the adverse anthropogenic influence on endorheic basins in CA. Suitable climate adaptation, mitigation and efficient natural resource management technologies and methods are available, and are developing fast. A number of these are discussed in the paper, but these technologies alone are not sufficient to address pressing water resource issues in CA. Food-water–energy nexus analyses demonstrate that transboundary endorheic basin management requires transformational changes with involvement of all key stakeholders. Regional programs, supported by local governments and international donors, that incorporate advanced adaptation technologies, water resource research and management capacity development, are essential for successful climate change adaptation efforts in CA. However, there is a need for an accelerated uptake of such programs, with an emphasis on unification of approaches, as the pressures resulting from climate change and aggravated by human mismanagement of natural water resources leave very little time for hesitation