Adsorption of heavy metals on silica-supported hydrophilic carbonaceous nanoparticles (SHNPs).

This paper reports experimental results on the removal of Cd(II), Ni(II) and Pb(II) ions using hydrophilic carbon nanoparticles (HNPs) supported over silica beads to enhance their separation from treated water. The supported HNPs (SHNPs) exhibit high removal efficiencies especially at neutral pH and low temperature (10 °C), conditions that commonly occur for natural water remediation and for some types of industrial wastewater. The maximum adsorption capacity of the SHNPs at a reference concentration of 0.2 mM is 0.042 mmol g-1, 0.027 mmol g-1 and 0.055 mmol g-1 for Cd(II), Pb(II) and Ni(II) ions, respectively. Modelling analysis on the adsorption isotherms revealed that the free Gibbs' energy of interactions between the sorbent and Ni(II) and Pb(II) ions is higher than that of Cd(II) ions indicating that the sorbents are more affine to intermediate acids, as Ni(II) and Pb(II) ions, than to soft acids, as Cd(II) ions. The sorbents exhibit appreciable adsorption capacities per gram of active phase (0.54 mg g-1 for Cd(II) ions, 13.48 mg g-1 for Ni(II) ions and 8.87 mg g-1 for Pb(II) ions) at the corresponding quality limit admitted by Italian regulations on wastewater, suggesting their possible use in water treatment plants.

Dataset of wet desulphurization scrubbing in a column packed with Mellapak 250.X.

Flue-Gas Desulphurization (FGD) is a fundamental process commonly adopted for the treatment of exhausts deriving from both stationary and mobile sources. The removal of SO2 from flue gasses can be made through different technologies and absorption offers the highest versatility for a large spectrum of applications. The data presented in this paper derive from FGD experiments carried out in a pilot wet scrubber equipped with a structured packing (Hastelloy C-22, Mellapak 250.X). The experiments aim to determine the SO2 removal efficiency from a simulated flue-gas in different operating conditions, similar to those observed in common wet FGD processes. Experimental data are reported in terms of gas velocity, concentration of SO2 in the flue-gas, liquid/gas feed ratio, fluids temperature and pressure. The dataset also includes the measurements of several working parameters, i.e. pressure drops in the column, wash water pH, relative humidity of the outlet gas and temperatures of gas and liquid flowing out of the FGD unit. The collection of these data could be useful in future studies and in the analysis of FGD units, also to design/improve large-scale absorption columns with structured packing, using various scrubbing liquids and in different operating conditions.

Experimental and modelling analysis of As(V) ions adsorption on granular activated carbon.

In this work the adsorption of pentavalent arsenic on a granular activated carbon (GAC) has been experimentally studied. The effects of arsenic concentration, pH, temperature and salinity on equilibrium adsorption capacity have been investigated. Experimental results show that the adsorption capacity is the highest at neutral pH conditions, low salinity levels and high temperatures. A model for the description of the arsenic adsorption mechanism is reported. This is based on the multicomponent Langmuir adsorption theory applied to the ionic species in solution. The model points out that the adsorption capacity is proportional to the concentration of arsenic anions in solution and decreases by increasing the concentration of competitive ions such as hydroxides and chlorides, allowing a correct interpretation of the pH and salinity effects on the adsorption capacity. Finally, one of the main goals of the proposed model is to preserve the exothermicity of the adsorption phenomena despite the observed trend of experimental results: the increase of adsorption capacity with temperature appears to be related to a higher arsenic dissociation.

Groundwater protection from cadmium contamination by permeable reactive barriers.

This work studies the reliability of an activated carbon permeable reactive barrier in removing cadmium from a contaminated shallow aquifer. Laboratory tests have been performed to characterize the equilibrium and kinetic adsorption properties of the activated carbon in cadmium-containing aqueous solutions. A 2D numerical model has been used to describe pollutant transport within a groundwater and the pollutant adsorption on the permeable adsorbing barrier (PRB). In particular, it has been considered the case of a permeable adsorbing barrier (PAB) used to protect a river from a Cd(II) contaminated groundwater. Numerical results show that the PAB can achieve a long-term efficiency by preventing river pollution for several months.

Removal of chromium ions from [corrected] aqueous solutions by adsorption on activated carbon and char.

Adsorption isotherms of chromium ions in aqueous solution have been experimentally measured on a granular activated carbon (GAC) and on a char of South African coal (CSAC). Experimental results show that the adsorption capacity for the GAC strongly depends on solution pH and salinity, with maximum values around 7mg/g at neutral pH and low salinity levels. On the contrary, the CSAC shows a smaller adsorption capacity, near 0.3mg/g, which slightly decreases by increasing pH and salinity levels. Chromium adsorption mainly depends on the availability of chromium ions in solution and on the occurrence of redox reactions between the surface groups and the Cr(VI) which lead to the formation of Cr(III). The reduction of Cr(VI) and the following sorption of Cr(III) cations appears as the leading mechanism for chromium uptake on the CSAC. A similar behaviour can be observed for the GAC at pH below 3. On the contrary, at pH>7, the multicomponent competitive adsorption of Cr(VI), OH(-) and Cl(-) has to be considered.

Capture of mercury ions by natural and industrial materials.

In this paper the technical feasibility of various adsorbents for mercury removal from contaminated waters has been studied. Adsorption isotherms of mercury ions in aqueous solution have been experimentally measured on a granular activated carbon (Aquacarb 207EA), a char, a pozzolana and a yellow tuff. The experimental evidences show that the mercury capture capacity of yellow tuff and char is of few tenths of milligrams per gram of sorbent while for the pozzolana and the activated carbon this value is of the order of 1mg/g of sorbent. Moreover, for a mercury concentration as high as 3000 microg/l the pozzolana shows the highest adsorption capacity. This result seems to be quite interesting, especially in consideration of the extremely low cost of this natural sorbent.

Equilibrium and dynamic study on hexavalent chromium adsorption onto activated carbon.

In this work, the results of equilibrium and dynamic adsorption tests of hexavalent chromium, Cr (VI), on activated carbon are presented. Adsorption isotherms were determined at different levels of pH and temperature. Dynamic tests were carried out in terms of breakthrough curves of lab-scale fixed bed column at different pH, inlet concentration and flow rate. Both the adsorption isotherms and the breakthrough curves showed non-linear and unconventional trends. The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions. Equilibrium tests were interpreted in light of a multi-component Langmuir model supported by ion speciation analysis. For the interpretation of the adsorption dynamic tests, a mass transfer model was proposed. Dynamic tests at pH 11 were well described considering the external mass transfer as the rate controlling step. Differently, for dynamic tests at pH 6 the same model provided a satisfying description of the experimental breakthrough curves only until a sorbent coverage around 1.6mgg(-1). Above this level, a marked reduction of the breakthrough curve slope was observed in response to a transition to an inter-particle adsorption mechanism.

Desorption of arsenic from exhaust activated carbons used for water purification.

This work aims to the analysis of arsenic desorption from an exhaust activated carbon used for the purification of a natural water. This last was used to mimic the properties of common groundwater or drinking water. Different low-cost and harmless eluting solutions were considered, including distilled water, natural water, saline (NaCl, CaCl2 and NaNO3) and basic (NaOH) solutions. Experimental results showed that, for 1g of activated carbon with arsenic loading close to the maximum value available for the model natural water (ω ≈ 0.1 mg/g), it is possible to recover more than 80% of the arsenic using 20 ml of 0.1 M sodium chloride solution. A temperature variation within 20 and 40 °C has scarce effect on desorption efficiency. A comparison between desorption data and adsorption isotherms data suggests that arsenic adsorption is actually a reversible process. Therefore, it is virtually possible to increase arsenic recovery efficiency close to 100% by increasing the NaCl concentration or the volume of the desorption solution, but a preliminary cost benefit analysis lead to consider a NaCl 0.1M solution as an optimal solution for practical applications.

Mercury adsorption on granular activated carbon in aqueous solutions containing nitrates and chlorides.

Adsorption is an effective process to remove mercury from polluted waters. In spite of the great number of experiments on this subject, the assessment of the optimal working conditions for industrial processes is suffering the lack of reliable models to describe the main adsorption mechanisms. This paper presents a critical analysis of mercury adsorption on an activated carbon, based on the use of chemical speciation analysis to find out correlations between mercury adsorption and concentration of dissolved species. To support this analysis, a comprehensive experimental study on mercury adsorption at different mercury concentrations, temperatures and pH was carried out in model aqueous solutions. This study pointed out that mercury capture occurs mainly through adsorption of cationic species, the adsorption of anions being significant only for basic pH. Furthermore, it was shown that HgOH(+) and Hg(2+) are captured to a higher extent than HgCl(+), but their adsorption is more sensitive to solution pH. Tests on the effect of temperature in a range from 10 to 55 °C showed a peculiar non-monotonic trend for mercury solution containing chlorides. The chemical speciation and the assumption of adsorption exothermicity allow describing this experimental finding without considering the occurrence of different adsorption mechanisms at different temperature.

A descriptive model for metallic ions adsorption from aqueous solutions onto activated carbons.

The design of adsorber units is mainly dependent on the equilibrium adsorption capacity of the sorbent in the working conditions. At the moment, these data are available in a limited number of experimental conditions and, for the case of activated carbon, there are no predictive models to assess the adsorption capacity as a function of the process parameters. This makes the adsorber design a complex and approximated task. In this work, a model for the description of metallic ions adsorption onto activated carbon is presented. The model starts from an evaluation of ion speciation and it considers the approach of the multi-component Langmuir model to correlate the metal uptake to the ion concentration in solution. The model has been used to analyse available experimental data on the adsorption of As(V), Cd(II), Cr(III) and Cr(VI) ions on activated carbon. A good matching between experimental results and model predictions has been obtained for all the investigated conditions.

[Characterization of the convoluted seminiferous tubule wall. II. Ultrastructural alteration after testis retention in the abdominal cavity]. / Caratterizzazione della parete del tubulo seminifero contorto. II) Modificazioni ultrastrutturali dopo ritenzione del testicolo in cavita' addominale.

An ultrastructural analysis has been carried out on the seminiferous tubules after different periods of stay of the rat testis in the abdominal cavity. With respect to control rats, no changes are detectable after 5 days, while after 15 and 30 days considerable modifications take place. A number of cellular features are modified, such as the nuclear shape and the perinuclear vesicles, while the cytoplasmic filaments show a less ordered appearance. In addition, the extracellular amorphous matrix undergoes a large increase, due either to an enhanced production or to a reduced turnover related with a lowered cell activity.

[Characterization of the convoluted seminiferous tubule wall. I. Ultrastructural aspects after the ligation of the vas deferens and the efferent tubules]. / Caratterizzazione della parete del tubulo seminifero contorto. I) Aspetti ultrastrutturali dopo legatura del condotto deferente e dei tubuli efferenti.

The structure of the wall of the rat seminiferous tubules has been studied by electron microscopy. No significant modifications have been revealed after the ligature of the vas deferens while on the contrary the ligature of the efferent ductules produces a reduction of the contractile filaments and of the pinocytosis vesicles, as well as an increase of the amount of collagen fibers in the basal membrane.

Does chronic hypoxia increase rat carotid body nitric oxide?

The carotid body plays an important role in ventilatory adaptation during chronic hypoxia. Nitric oxide (NO) may act as a regulator in neurotransmission, influencing the carotid body chemosensory discharge. The aim of the study was to understand if NO could contribute to the adaptation process during chronic hypoxia. The rats were kept in chronic hypoxia (10-11% inspired oxygen) for 12 days, while the controls were kept in room air (21% O2). The distribution for diaphorase activity and immunohistochemistry for nitric oxide synthase (NOS) showed that chronic hypoxia induces an increase in NOS activity in the carotid body. It was concluded that NO release increased during chronic hypoxia and causes an inhibitory effect on carotid chemosensory discharge of the rat carotid body.