Halka Bilinski

Trace metal adsorption on inorganic solid phases under estuarine conditions

The adsorption of trace metals (Pb, Zn, Cu, Cd and Hg) on calcite, kaolinite and bentonite has been studied in Krka river water of various salinities (S = 3, 20 and 38‰). n nModel experiments were performed at pH 8 in natural water and in UV-irradiated water samples to determine the importance of natural soluble organic matter. Cold vapour atomic absorption spectrometry was used for the Hg determination, and a differential pulse anodic stripping voltammetry (DPASV) method for determination of other trace metals, using either a hanging mercury drop electrode or a mercury-coated glassy carbon working electrode. The following results have been obtained on calcite: n1. n(1) a powerful absorption of Pb and Zn was observed for both natural and UV-irradiated waters at S=20‰; n n2. n(2) a strong adsorption of Hg was observed in natural water, and significantly lower adsorption in UV-irradiated water at all three salinities, particularly at low salinity; n n3. n(3) Cd adsorption was of medium intensity in both waters at S=20‰; n n4. n(4) Cu was practically not adsorbable in both waters at S=20‰ if the total Cu ion concentration was lower than the copper complexing capacity value; n n5. n(5) Cu adsorption was of a medium intensity at S=38‰. It has not influenced by the EDTA model ligand. n n nTrace metals Pb, Zn and Cu are adsorbable on kaolinite and bentonite at S=38‰, whereas Cd is practically not adsorbed. The Krka River is a calcareous river, which supplies the sea with calcite and aluminosilicates. In the light of our model experiments, we suggest that the self-purification of the Krka River is remarkable in respect to Pb, Zn and Hg; this occurs to a lesser extent for Cu, and is negligible in the case of Cd.

Formation of some manganese minerals from ferromanganese factory waste disposed in the Krka River Estuary

Abstract The identification, characterisation and formation of managanese minerals takanelite and kutnahorite calcian found in the Krka River Estuary, is described. These minerals originated from the hydrochemical transformation of waste disposed from a ferromanganese factory. Industrial slag, dust settled inside a chimney, and marine sediments in the vicinity of the ferromanganese plant “Crnica”, situated in the suburb of the city of Sibenik were analysed in details. The samples of slag and dust were equilibrated with estuarine waters for 20 d. In marine sediment, calcite is predominant, while quartz, aragonite, kutnahorite calcian and dolomite were found as minor components. Iron is present in all samples as an amorphous phase. Strontium, titanium, copper, zinc, lead and rubidium were found as microcomponents. It was found that slag and dust particles partly dissolve in contact with estuarine water of different salinities, and present renewable supply of manganese, iron and numerous trace elements. A possible way of the formation of manganese minerals takanelite and kutnahorite is discussed. Takanelite mineral was obtained in laboratory by partial disolution of slag containing bustamite ferroan. For kutnahorite calcian it is suggested that it forms in the process of dolomitization. With respect to aqueous environment of the Krka River Estuary, the slag and dust from a ferromanganese industry upon contact with water transform into scavengers (gypsum, calcite, quartz, takanelite) which help purifying the water column from other micro-impurities.

Adsorption of lead and cadmium ions on calcite in the Krka estuary

Abstract The adsorption of Pb 2+ and of Cd 2+ ions from calcareous Krka river water of various salinities (3, 14, 20 and 38 psu) on calcite (CaCO 3 , Merck p.a.) was investigated. Simultaneous adsorption of Pb 2+ and Cd 2+ ions was studied as well. The results suggest that the two ions are adsorbed at different calcite surface sites; Pb 2+ remained firmly bound to calcite at all salinities, whereas Cd 2+ was firmly bound at low salinities and released at high salinities. Dissolved natural organic ligands at the freshwater-seawater interface (FSI; at 14 psu) promoted and below the FSI (at 20 psu) decreased the adsorption of Cd 2+ . The experiments were performed at metal concentrations of 8 × 10 −8 mol l −1 and at natural pH values around pH 8. Adsorbed amounts of trace metal ions were determined in filtered samples by differential pulse anodic stripping voltammetry (DPASV) with a three-electrode system, after 24 h of equilibration with calcite. Several adsorption models were tested, such as Freundlichs, Langmuirs and Schindler-Stumms surface coordination model. Adsorption isotherms belong to S-1 class of empirical adsorption isotherms. None gave reasonable values of adsorption constants. The fractional partitioning of adsorbent to the solid phase when normalized to the quantity of adsorbent present ( K d ) declined as solid concentration increased. It was found that the surface charge is not responsible for the observed effect. Instead, aggregate size increased, which effected a loss in surface area. This is a reasonable explanation for the observed S-shaped adsorption isotherms curves.

Equilibrium aluminium hydroxo-oxalate phases during initial clay formation; H+-Al3+-oxalic acid-Na+ system

Abstract The conditions necessary for initial clay formation have been studied in different model systems comprising different organic acids besides Si and Al. In the present paper the solid phases and the precipitation boundary characterizing the subsystem H+-Al3+-oxalic acid (H2L) are discussed. pH and tyndallometric measurements were performed in an ionic medium of 0.6 M Na(Cl) at 25 °C. The two phases Al3(OH)7(C2O4) · 3H2O (phase I) and NaAl(OH)2(C2O4) · 3H2O (phase II) determine the precipitation boundary. The following formation constants for the two phases were deduced: lgβ1 = lg([Al3+]−3[H2C2O4]−1[H+]9 = −21.87 ± 0.08 and lgβ11 = lg([Al3+]−1[H2C2O4]−1[H+]4 = −5.61 ± 0.06. Phase I exists in the range [Al]tot≥ 10−4.4 mol dm−3,[H2C2O4]tot ≥ 10−4.9 mol dm−3 and at pH The solid phases have been characterized by X-ray analysis of powders, TGA and IR spectra, and tentative structures are proposed. Phase I seems to be an octahedral layer structure, in which 3 5 of the octahedral sites between two close packed oxygen sheets are occupied by Al3+ and the oxalate ion acts as a bridge ligand between two aluminium atoms. Phase II forms a more open sheet structure and has ion exchange properties. Powder data for a phase crystallized from the studied solution after a year are also presented. This phase, Na4Al2(OH)2(C2O4)4 · 10H2O, supports the results from the equilibrium analysis of recent solution data by Sjoberg and O hman (1985), who have found the dinuclear complex Al2(OH)2(C2O4)44− to exist in a solution in which the ligand is in excess.

Mercury distribution in the water column of the stratified Krka river estuary (Croatia) : importance of natural organic matter and of strong winds

Abstract Estuarine water samples were collected at the vertical profile on one selected station in the Krka river estuary (Croatia) during the period from September 1995 to July 1998. The concentrations of reactive and total mercury (in the UV-irradiated samples) were measured in unfiltered and acidified samples by atomic absorption and show non-conservative behavior. The location of the mercury maximum found in the region, 2−12.5 ngl −1 , changes and is not always at the freshwater/seawater interface (FSI) as suggested in earlier estuary studies. The proportion of reactive to total mercury, two operational species, also changed, depending on salinity, seasonal and weather changes not only in fresh water and at the FSI but in some cases in seawater down to the bottom. Maximal apparent mercury complexing capacity was determined as 2.7 ngHgl −1 . Information about surfactant activity in the same vertical profile was obtained using a hanging mercury drop electrode (HMDE), by a.c. out of phase voltammetry at two fixed potentials (−0.2 and −0.6xa0V). Continuous variation of hydrophylic and hydrophobic substances was observed. No correlation with the mercury maximum was found. In samples showing the total mercury maximum, hydrophobic heterodispersed substances (>0.7xa0 μ m) were found, giving evidence that mercury is partly bound to particulate organic carbon having hydrophobic properties. Submicron colloids and aggregates (10xa0nm–1xa0 μ m) were directly proved using electronmicroscopy. Characteristic estimated time for the coagulation/sedimentation process in the Krka river estuary (about 8 days) can be influenced by the strong northerly Bura wind. Removal of mercury from the water column was evidenced in winter, when extremely low (less than 1 ngl −1 ) mercury concentrations were found in the water column after the very strong Bura wind. During the Jugo wind the outflow of brackish water decreases. The current going from sediment to FSI accumulates mercury at FSI (12.5 ngl −1 ), predominantly in inorganic form.

The influence of organics on the adsorption of copper (II) on γ-Al2O3 in seawater, model studies with EDTA

Abstract The natural “complexing capacity” of aquatic systems was determined using titration with cupric ions. It was compared with “complexing capacity” determined in the presence of both EDTA, used as a model for organic substances, and of EDTA and γ-Al 2 O 3 . The γ-Al 2 O 3 was used as a model for solid particles of hydrous oxide in natural waters. The adsorption isotherm of copper in seawater on γ-Al 2 O 3 particles was determined with and without EDTA. For EDTA alone and for the Cu—EDTA complex, it was found that they are not adsorbed on γ-Al 2 O 3 in the natural seawater. However, by adsorption on solid particles, the labile ionic Cu-complex can be removed from the seawater.

Voltammetric study of adsorption of cu(II) species on solid particles added to seawater

The adsorption on solid particles of natural organic ligand in seawater of Cu(II) ions, and of the inert Cu(II) complexes has been studied. Model solids, γ-Al2O3, Na+-0.392-γ-Al2O3, ‘Aerosil 200’, chrysotile, northupite and CaCO3 were added to seawater. It was observed that at pH 8 natural organic matter was strongly adsorbed on chrysotile and was not adsorbed on Na+ -0.392-γ-Al2O3; it was also adsorbed on γ-Al2O3 over the range of 3 < pH < 7. In this pH range, the complexing capacity and adsorption of Cu is at a minimum because Cu(II) is not adsorbed on γ-Al2O3 and natural organic matter is adsorbed. Inert CuL complexes were adsorbed at pH 8.0 on γ-Al2O3, ‘Aerosil 200’, CaCO3, and chrysotile but they were not adsorbed on northupite. The voltammetric method can be recommended for use in natural waters for distinguishing between metal ionic and metal inert complex species which are adsorbed from solution onto various solid particles.

The role of the aluminosilicate matrix in the gamma-irradiation energy transfer to the oxalate molecule

Abstract Three types of aluminosilicate matrices, prepared from oxalate solutions, were γ-irradiated and investigated by ESR spectroscopy. In the aluminosilicates with Al:Si = 1:1 that can be considered as the end member of allophane series upon γ-irradiation at room temperature in the presence of air, no stable paramagnetic species were formed, even if the aluminosilicate was precipitated in the presence of oxalate. On the other hand, in the evacuated sample upon γ-irradiation at room temperature a single line ESR spectrum at g = 2.0036 was detected that was ascribed to oxalate radical Oxalate radical was observed in the other two types of aluminosilicates even in the presence of air. Upon γ-irradiation at 77 K, in addition to the described oxalate radical, primary irradiation sites were observed and identified as paramagnetic centres derived from chlorides and hydrogen atoms. Radicals from chlorides were observed in all samples except in NaAl(OH) 4 (H 4 SiO 4 ) 2 (hydrous feldspathoid), the same as were found recently in protoimogolite allophane. Hydrogen atoms were found in Al(OH) 3 · H 4 SiO 4 and NaAl(OH) 4 (H 4 SiO 4 ) 7 . The results suggest that oxalate acts as a trap for γ-irradiation energy.

Interactions between calcite, NaDBS, Pb(II) and Cd(II) ions in seawater

Abstract It was demonstrated by a Coulter counter method in combination with photomicrographs that the commercially used anionic surfactant sodium dodecylbenzene sulfonate (NaDBS) forms solid crystals with major seawater cations as Na + , Mg 2+ , Ca 2+ and Sr 2+ and thus can be removed from seawater to sediments. In the presence of calcite particles suspended in seawater with variable concentrations of NaDBS, complicated mutual interactions occur resulting in partial calcite dissolution, and consequently in surface area diminuation. Namely, from Coulter counter kinetic measurements simultaneous decrease of the total number and total volume of particles was observed. Partial dissolution of calcite was also confirmed by the weight loss in the presence of c t (NDBS) = 1.6 × 10 −3 mol l −1 . Remobilization of lead and cadmium ions from calcite particles occurs up to c t (NaDBS) = 1 × 10 −3 mol l −1 . At concentrations above that value, an increased removal of these ions can be explained with their adsorption on a reprecipitated calcium salt (either with DBS − or with SO 2− 4 from SW).

Paramagnetic molecular centers in the gamma-irradiated novel compound of aluminum and leucine, Al6O4(OH)10(leucine)2·5H2O

Abstract A new microcrystalline compound Al 6 O 4 (OH) 10 (leucine) 2 ·5H 2 O of possible biological and biochemical interest has been prepared and characterized by chemical analysis, i.r. spectrum, X-ray diffraction and thermogravimetric analysis. It was exposed to γ-irradiation at 77 K and at room temperature. Paramagnetic species formed were studied by ESR spectroscopy. The leucine radical has been identified which seems to be stabilized in the aluminium leucine compound by crystalline water. Coordinated leucine molecule in aluminium hydroxide acts as a trap for γ-irradiation energy.