sequestration of organometallic compounds by synthetic and naturally occurring polycarboxylate ligands binding of monomethylmercury ii by polyacrylic and alginic acids

AbstractThe sequestering capacity of synthetic and naturally occurring polycarboxylate ligands towards mono-methylmercury(II) was evaluated by stability quantitative data on the interaction of CH3Hg+ with different molecular weight synthetic polyacrylates (2 and 20kDa average M.wt) and alginate (70–100 kDa) extracted from brown algae Macrocystis pyrifera. The influence of ionic medium was evaluated by measurements on the CH3Hg+-polyacrylate systems in NaNO3 medium at different ionic strengths (0.10, 0.25, 0.50 and 0.75 mol L−1), and a Debye-HiJckel type equation was used for the dependence of complex formation constants on ionic strength. Measurements on the CH3Hg+ - alginate system were carried out at l = 0.10 mol L−1 in NaNO3 medium. By using the stability data, the sequestering capacity of both ligands towards monomethylmercury(II) was determined at different pH values. Results obtained show that the binding ability of polyacrylic ligands (PAA) is stronger than the alginate (AA), following the trend PA..

Hydrocarbons removal from wastewater by adsorption onto biochar from Posidonia oceanica

Environmental pollution by petroleum derivatives is a very current topic. In particular, low concentration of this kind of pollutants can seriously compromise the life of animals and plants of aquatic ecosystems [1]. For this reason, recent environmental legislation imposes severe restriction to oil-in-water content for overboard discharge with concentration limits from 15 to 5 ppm [2]. The shipping industry is trying to adapt to these directives by equipping ships with cleaning treatment devices in which there are several oil removal steps. Usually, the last step of bilge water treatment is based on adsorption onto suitable adsorbent materials that must be able to remove the last and most dispersed oil fraction reducing its concentration within legal limits. In this work, a biochar obtained from pyrolysis of Posidonia oceanica, a Mediterranean sea plant, has been tested as adsorbent material of a synthetic bilge water. The pristine biochar (BCP) was tested as it was and after two chemical activation treatments with sulfuric acid (BCA) and potassium hydroxide (BCB). The adsorbent materials have been characterized by using different techniques (TGA, SEM-EDAX, FT-IR, etc) and their adsorption capacity was studied by batch and column experiments. Oil concentration measurements were performed by using: HPLC-FLD and TOC techniques

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures

The acid-base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol -1 ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L-1 and T = 298.15 K was also performed for other three Zn2+/Lz- systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn2+/ligand species, while computational molecular simulations allowed information to be gained on the metal-ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye-Hückel model, the classical specific ion interaction theory, and the van't Hoff equations, respectively

Evaluation of the purity of magnesium hydroxide recovered from saltwork bitterns

Magnesium has been listed among the 30 critical raw materials by the European Union. In recent years, many green and sustainable alternative Mg2+ sources have been sought to satisfy the EU’s demand and to avoid mineral ore consumption. In this context, saltwork bitterns, the by-products of solar sea salt production, have attracted much attention thanks to their high Mg2+ concentrations (up to 80 g/L) and low Ca2+ and bicarbonate contents (95% (w/w). This work presents a comprehensive experimental effort of reactive precipitation tests with NaOH solutions at stoichiometric and over-stoichiometric concentrations to: (i) assess the technical feasibility of Mg2+ recovery from real bitterns collected in saltworks of the Trapani district (Italy) and, (ii) for the first time, conduct an extensive purity investigation of the precipitated magnesium hydroxide powders as brucite. This experimental investigation demonstrates the possibility of extracting highly valuable compounds from saltwork bittern waste, embracing the water valorization and resource recovery approach.Peer ReviewedPostprint (published version

Sorption of Pd(II) ion by calcium alginate gel beads at different chloride concentrations and pH. A kinetic and equilibrium study

A kinetic and thermodynamic study on the sorption ability of calcium alginate gel beads towards Pd(II) ion was made in aqueous solution at different pH and chloride concentrations. The experimental conditions adopted in the sorption experiments were established on the basis of a speciation study on the Pd2+-AA system in which all the side reactions, such as the hydrolysis of Pd(II), the protonation of alginate and the interactions of the ligand and the metal ion with ions of ionic medium were taken into account. In the pH range 2–5 and at chloride concentration in the range 0 ⩽ CCl-/mmol L−1 ⩽ 10 the gel beads showed good sorption ability towards Pd(II) ion as confirmed by kinetic and thermodynamic data calculated by a pseudo second order equation and using Langmuir and Freundlich models. The comparison between qe values related to the kinetics of Pd(II) sorption and Ca(II) release in solution by gel beads indicated that the ion exchange is one of the main sorption mechanisms of the sorbent material. Similarities were found between the trends of sequestering (% PdAA species, pL0.5) and the sorption (qe, qmax) parameters as function of pH and chloride concentration. It confirms a close relation between the behaviour of alginate as sequestering agent for Pd(II) ion in aqueous solution and of calcium alginate gel beads as sorbent material for the removal of the metal ion

Chemical Speciation of Organic and Inorganic components of Environmental and Biological Interest in Natural Fluids: Behaviour, Interaction and Sequestration

The International Union of Pure and Applied Chemistry (IUPAC) defines the term “speciation” as the distribution of an element amongst defined chemical species in a system, while the process leading to quantitative estimation of the content of different species is called speciation analysis. The chemical speciation of elements in natural waters and biological fluids is a key topic, essential for discussing the chemical reactivity of constituents in these systems. It is well understood that it is the chemical form of a metal or metalloids that determines its reactivity, lifetime, and fate in the environment. Chemical speciation now involves various sectors of the sciences, from chemistry to biology, biochemistry, and environmental sciences, since—as is well known—the total concentration, alone, of an inorganic or organic component (metal or ligand) in a multicomponent natural system (fresh water, sea water, biological fluids, soil, etc.) is insufficient for a comprehensive understand of its behavior in those contests

Sequestration of Pd2+ by polyamino-polycarboxylic ligands

The increase of the worldwide demand of “Platinum group elements” (PGE) for application in several fields such as industry, medicine, jewellery and, especially, in catalyst converter production, caused a noticeable increasing of PGE concentration in the environment. Though palladium, among the anthropogenic PGE, is not the most abundant one, it is the most hazardous since it undergoes easily and quickly oxidation to palladium(II) when in contact with soils, with a consequent increase of its mobility in the environment. The presence of complexing agents, which form soluble complex species with palladium(II), favours the mobility of the ion with an increase of its availability to plants, animals and humans. Among anthropogenic complexing molecules, an important role is played by synthetic aminopolycarboxylic chelating agents (usually called with the acronym APC) whose concentration in the environment is progressively increasing owing to their considerable use in several fields (agriculture, industry, medicine) and a low biodegradability of most of them. The interaction of these ligands with palladium(II) ion leads to the formation of soluble complex species whose stability influences strongly the availability of palladium(II) in the environment. With the aim to assess the strength of interaction of Pd2+ with aminopolycarboxylic ligands, here we report the results of a systematic study, , on the formation of palladium(II) complex species with five APCs [ethylenediamine-N,N,N’,N’-tetraacetate (EDTA), (S,S)-Ethylenediamine-N,N′-disuccinic acid (S,S-EDDS), Nitrilotriacetate (NTA) and diethylenetriamine-N,N,N’,N’’,N’’-pentaacetate (DTPA) and triethylenetetraamine-N,N,N’,N’’,N’’’,N’’’-hexaacetate (TTHA)]. Owing to the high stability of the Pd2+ - APC complex species, the calculation of their stability constants was very difficult and was possible only by combining the results obtained from two series of ISE-H+ potentiometric titration (in NaNO3 and in mixed NaNO3 /NaI ionic medium) and from ISE-H+ potentiometric /spectrophotometric titrations (in NaClO4). As expected, the stability of Pd-APC complex species is function of the number of carboxylic and amino groups present in the ligand molecules (e.g., logKPd(APC) = 37.00, 36.31, 23.60, 23.07 and 17.82 for TTHA, DTPA, EDTA, S,S-EDDS and NTA in Na+ ionic media, at I = 0.1 mol L-1 and T = 25°C). Results obtained on the stability of species in the Pd- S,S-EDDS show that this ligand, which is the most biodegradable APC ligand, can be used successfully as environmental friendly chelating agent in substitution of the other less degradable APCs in all their application fields. From the stability data of the Pd2+ - APCs the sequestration capacity [expressed as pL50, i.e. the –log (APC concentration] necessary to bind the 50% of the metal ion) of the ligands under investigation towards palladium(II) ion was determined in the pH range considered. The pL50 is easily correlated to important physico-chemical parameters (pH, ionic strength, temperature, etc.) as shown in the Figure, were the dependence on pH of pL50 of the APCs towards Pd2+ ion is reported. As can be seen, TTHA and DTPA show almost the same sequestering ability in the pH range 2 – 10, clearly higher than that of EDTA, S,S-EDDS and NTA where a minor number of amino and carboxylic groups is present in the molecule

Interaction of Dioxouranium(VI) ion with aspartate and glutamate in NaClaq at different ionic strengths

The formation of complexes species of the dioxouranium(VI) ion with aspartic and glutamic acids was studied in the pH range of 3 to 6 at 25 °C by potentiometric measurements (H+-glass electrode). Results gave evidence for the formation of the following species: (UO2)A0, (UO2)AH+, and (UO2)2A(OH)2 0 (A2- ) a glutamic or aspartic ligand). Investigations were carried out in a NaCl ionic medium at I (0.1, 0.25, 0.5, and 1.0) mol L-1. The dependence on ionic strength of the formation constants was analyzed by the specific ion interaction theory (SIT) model. The formation constants at infinite dilution, obtained using this model, are log â110 ) 8.53 ( 0.03, 8.37 ( 0.05; log â111 ) 13.60 ( 0.05, 13.42 ( 0.02; and log â21-2 ) 3.31 ( 0.05, 2.98 ( 0.03 for glutamate and aspartate, respectively, where indexes for the overall formation constant âpqr refer to the equilibrium pUO22+ + qA2- + rH+ ) (UO2)p(A)qHr(2p - 2q + r). The specific interaction coefficients are also reported. A mononuclear hydroxo species (UO2)A(OH)-, of great interest for very low naturally occurring concentrations of uranium(VI), was hypothesized, with equilibrium constant log K [(UO2)A0 + H2O ) (UO2)A(OH)-])-5.4 at t ) 25 °C and I ) 0 mol L-1. Speciation profiles for different concentrations of UO22+ in the presence of both amino acids are discussed