Ion exchange equilibria of arsenic in the presence of high sulfate and nitrate concentration

The aim of this work was to develop a quantitative description of the ion exchange equilibria of arsenic on a strong anionic resin, in the presence of nitrates and sulphates. First, the ion exchange equilibrium data of As(V) and NO3- on a strong anionic resin in chloride form were obtained and described with a model based on the mass action law. Namely, assuming ideal behaviour for both solution and resin phase, the thermodynamic constant of the As(V)/Cl- and NO3-/Cl- ion exchange equilibria were estimated by fitting of experimental data. Then, these equilibrium constants were used to predict the ion exchange behaviour of the ternary system As(V)/NO3-/Cl-, providing a rather good agreement with experimental results. The ion exchange equilibria involving sulphate ions were also studied, showing,a very high affinity to the resin phase. This behaviour did not allow a quantitative robust modelling of the equilibrium pattern. The results discussed in this paper represent a first step toward the development of a comprehensive modelling of the ion exchange process for the removal of As(V) from surface and groundwater in the presence of competitive, naturally occurring anions

Mineral carbonation process for CO2 sequestration

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Analysis of the effect of temperature, pH, CO2 pressure and salinity on the olivine dissolution kinetics

AbstractThe dissolution kinetics of olivine has been extensively studied under several temperatures, CO2 pressures, and solution compositions. Dissolution is an important mechanism in the aqueous mineral carbonation process. The overall carbonation reaction consists of dissolution of mineral silicate, e.g. olivine, serpentine and wollastonite, followed by carbonate precipitation, thus fixing CO2 into naturally occurring stable solids, such as magnesite and calcite. The slowness of the dissolution kinetics hinders the overall carbonation reaction and in order to make the process technically and economically feasible, such a reaction should be sped up by finding the optimum operating conditions. Experiments were performed in a flow-through reactor at 90–120–150 ∘C. The pH was adjusted by adding either acids (e.g., HCl, citric acid) or LiOH, and by changing PCO2. The salinity was changed by adding NaCl and NaNO3. From the experimental data, the dissolution rate was estimated by using the population balance equation (PBE) model coupled with a mass balance, and the obtained values were regressed with a linear model log(r)=−npH−B, where r is the specific dissolution rate (mol s−1 cm−2)

Biodegradation of 3-chlorophenol in a sequencing batch reactor

The present paper shows the results obtained through a study on the biodegradation of 3-chlorophenol (3-CP) in a Sequencing Batch Reactor (SBR). To such a purpose a lab-scale SBR was fed a synthetic wastewater containing 3-CP and nutrients (nitrogen and phosphorus) diluted in tap water. The operating strategy, in terms of both the duration of either the cycle or the react phase, was changed throughout the experimental activity in order to find out the optimal one allowing to ensure constant and high removal efficiency despite the increasing 3-chlorophenol concentration in the feed. Biomass collected from a full-scale continuous flow activated sludge facility treating domestic wastewater was used as seed, after being acclimated to 3-CP by means of several batch tests. The results showed that a periodically operated activated sludge system can be successfully used for the biodegradation of chlorophenol compounds, after the needed members of the microbiological consortium are selected and enriched

Granulation–carbonation treatment of alkali activated steel slag for secondary aggregates production

In view of the EU’s circular economy strategy, there is a need to develop treatments that may allow to improve the management of industrial residues such as steel manufacturing slag, for example by producing secondary products that may be used for different applications. This work evaluates the performance of a combined carbonation and granulation treatment applied to basic oxygen furnace (BOF) steel slag with the aim of producing secondary aggregates and of storing CO2 in a solid and stable form. In order to improve the mechanical properties of the product, a solution of sodium silicate and sodium hydroxide was tested as binder instead of water in both the granulation and combined granulation–carbonation tests. The results showed that the granules produced using the alkali activator with or without CO2 addition, presented a mean size ranging from 1 to 5 mm and adequate mechanical properties for use in civil engineering applications. The maximum CO2 uptake attained was of 4% wt. for the alkali activated and carbonated granules after 60 min of treatment and 7 days curing. As for the leaching behaviour of the produced granules, an increase in the release of Cr and V was found for the product of the granulation–carbonation treatment with alkali activation. Instead, granulation with alkali activation or granulation with carbonation showed to decrease the release of Ba and Cr with regard to the untreated residues

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The main aim of this work was to assess the potential of in situ carbonation as a treatment to modify the properties of alkaline materials such as industrial soil in terms of leaching behaviour and mineralogy and to store the CO2 generated by specific treatments applied in the context of Brownfield regeneration. The process was investigated through lab-scale column carbonation experiments, in which 100% CO2 was fed through humidified stainless steel slag under ambient temperature and pressure for set reaction times. The reaction kinetics and the maximum CO2 uptake attained (5.5%), corresponding to a Ca conversion yield of 15.6%, after 4 h treatment proved slightly lower than those resulting from batch tests carried out on the same particle size fraction at enhanced operating conditions. The mineralogy of the material showed to be affected by column carbonation, exhibiting a higher calcite content and the decrease of Ca hydroxide and silicate phases. As a result of carbonation, the material showed a decrease in pH and Ca release as well as an increase in Si mobility. Furthermore, a reduction of Cr and Ba leaching, up to 63% and 96% respectively, was achieved after 2 h of reaction. However, carbonation was observed to lead to an increased leaching of V and Mo. The effects of carbonation on the leaching behaviour of the material were also investigated performing pH-dependence leaching tests and the results indicated that in situ carbonation appears to be a promising treatment to improve the properties of alkaline materials in view of their reuse on-site

Storage of carbon dioxide captured in a pilot-scale biogas upgrading plant by accelerated carbonation of industrial residues

AbstractThis work reports the preliminary evaluations obtained within the UPGAS-LOW CO2 project (LIFE08 ENV/IT/000429) concerning innovative methods for biogas upgrading through CO2 capture and storage. One of the methods studied in this project is chemical absorption of the CO2 contained in landfill gas with a KOH solution followed by carbonation of the spent solution with selected industrial residues to regenerate the alkaline solution and store CO2 in a solid phase (calcite). This paper presents the main results of the lab scale experiments carried out to evaluate the effects o f the main operating parameters on the carbonation reaction so to identify the conditions that allow to maximize the CO2 uptake of the solid residues and the percentage of KOH that can be regenerated for the absorption process. These results provide the dataset for the design of a pilot plant unit to be built and operated in the follow-up of the project

Pilot-Scale Investigation of an Innovative Process for Biogas Upgrading with CO2 Capture and Storage

Abstract In this work an innovative carbon dioxide removal method that, differently from the currently employed commercial techniques, allows also to capture and store the separated CO 2 is investigated. This process, Alkali absorption with Regeneration (AwR), consists in a first step in which CO 2 is separated from the biogas by chemical absorption with an alkali aqueous solution followed by a second step in which the spent absorption solution is regenerated for reuse in the first step and the captured CO 2 is stored in a solid and thermodynamically stable form. The latter process is carried out contacting the spent absorption solution, rich in carbonate and bicarbonate ions, with a waste material characterized by a high content of calcium hydroxide and leads to the precipitation of calcium carbonate and to the regeneration of the alkali hydroxide content of the solution. The proposed processes were first investigated by preliminary laboratory and simulation analysis. On the basis of the results of these tests, air pollution control (APC) residues from Waste-to-Energy plants were selected as the material to use for the regeneration step and a pilot-scale regeneration plant was designed, built and installed in a landfill site downstream of the already existing absorption column. In this paper the sizing and design of the regeneration plant and the results of the preliminary AwR pilot- plant tests are reported. This study was carried out within the framework of the UPGAS-LOWCO2 (LIFE08/ENV/IT/000429) Life+ project

Long-range potential fluctuations and 1/f noise in hydrogenated amorphous silicon

We present a microscopic theory of the low-frequency voltage noise (known as "1/f" noise) in micrometer-thick films of hydrogenated amorphous silicon. This theory traces the noise back to the long-range fluctuations of the Coulomb potential produced by deep defects, thereby predicting the absolute noise intensity as a function of the distribution of defect activation energies. The predictions of this theory are in very good agreement with our own experiments in terms of both the absolute intensity and the temperature dependence of the noise spectra.Comment: 8 pages, 3 figures, several new parts and one new figure are added, but no conceptual revision