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Antimonate uptake by calcined and uncalcined layered double hydroxides: effect of cationic composition and M2+/M3+molar ratio
No full textThis study gives a contribution to assess the efficacy of some LDHs (layered double hydroxides) in Sb(V) uptake and understand the mechanisms involved in the removal process. Uncalcined nitrate Mg/Al LDHs and the mixed Mg-Al oxides derived from calcined carbonate Mg/Al LDHs mainly remove Sb(OH)6âfrom aqueous solution through the formation of a brandholzite-like phase (a non-LDH compound with general formula Mg[Sb(OH)6]2·6H2O), although with a different efficiency (< 50 and 90â100% of Sb(V) removed, respectively). The formation of a brandholzite-like compound highlights the fundamental role of Mg in the removal process. The Sb(OH)6âremoval capacity of uncalcined nitrate Mg/Al LDHs increases from 22 to 46% as the Mg/Al molar ratio decreases from 4 to 2 thanks to the increasing excess of positive charge of brucite-like sheets and the expanding interlayer thickness due to the different spatial orientations of nitrate groups (flat for Mg/Al = 4, perpendicular for Mg/Al = 2). The presence of Fe3+in the trivalent cationic site of carbonate LDHs (Mg/(Al + Fe) = 3/(0.5 + 0.5)) improves the Sb(OH)6âremoval capacity of their calcined products. When Mg is replaced by Zn in the divalent cationic site of carbonate LDHs and the sorption experiments are performed using the mixed Zn-Al oxides derived from calcination, Sb(OH)6âis mainly removed from the solution through the reconstruction of an antimonate LDH structure (i.e., a zincalstibite-like compound with general formula Zn2Al(OH)6[Sb(OH)6]). The removal efficiency of calcined carbonate Zn/Al LDHs is high and comparable to that of calcined carbonate Mg/Al LDHs; however, the mechanisms involved in the removal process are substantially different: entrance of Sb(OH)6âin the interlayer in the first case, adsorption of Sb(OH)6âonto the surface and formation of a new phase (a brandholzite-like compound) in the second case. In both cases, the removal processes are described with the pseudo-second-order kinetic model; the theoretical maximum adsorption capacity determined with the Langmuir isotherm results to be 4.54 and 4.37 mmol gâ1for calcined carbonate Mg/AlFe and Zn/Al LDHs, respectively
Antimony in the soil–water–plant system at the Su Suergiu abandoned mine (Sardinia, Italy): Strategies to mitigate contamination
No full textThis study was aimed to implement the understanding of the Sb behavior in near-surface environments, as a contribution to address appropriate mitigation actions at contaminated sites. For this purpose, geochemical data of soil (8 sites),water (29 sites), and plant (12 sites) samples were collected. The study area is located at Su Suergiu and surroundings in Sardinia (Italy), an abandoned mine area heavily contaminated with Sb, with relevant impact on water bodies that supply water for agriculture and domestic uses.
Antimony in the soil horizons ranged from 19 to 4400 mg/kg, with highest concentrations in soils located close to the mining-related wastes, and concentrations in the topsoil much higher than in the bedrock. The Sb readily available fraction was about 2% of the total Sb in the soil. Antimony in the pore water ranged from 23
to 1700 μg/L, with highest values in the Sb-rich soils.
The waters showed neutral to slightly alkaline pH, redox potential values indicating oxidizing conditions, electrical conductivity in the range of 0.2 to 3.7 mS/cm, and dissolved organic carbon ≤2mg/L. The waters collected
upstream of the mine have Ca-bicarbonate dominant composition, and median concentration of Sb(tot) of 1.7 μg/L (that is total antimony determined in waters filtered through 0.45 μm), a value relatively high as compared with the background value (≤0.5 μg/L Sb) estimated for Sardinian waters, but below the limits established by the European Union and the World Health Organization for drinking water (5 μg/L Sb and 20 μg/L Sb, respectively).
The waters flowing in the mine area are characterized by Ca-sulfate dominant composition, and median concentrations of 7000 μg/L Sb(tot). Extreme concentrations, up to 30,000 μg/L Sb(tot), were observed in
waters flowing out of the slag materials derived from the processing of Sb-ore. The Sb(III) was in the range of
0.8 to 760 μg/L and represented up to 6% of Sb(tot).
In the waters collected downstream of the mine, median Sb(tot) concentrations decreased as distance from the
mine area increases: 1300 μg/L Sb(tot) in the stream Rio Ciurixeda at 3 km distance, and 25 μg/L Sb(tot) in the main River Flumendosa 15 km further downstream. Attenuation of Sb contamination was mainly due to dilution. Results of modeling, carried out by both EQ3 and Visual MINTEQ computer programs, suggest that sorption of dissolved Sb onto solid phases, and/or precipitation of Sb-bearing minerals, likely give a minor
contribution to attenuation of Sb contamination. The slightly alkaline pH and oxidizing conditions might favor
the persistence of inorganic Sb(V)-bearing species at long distance in the studied waters.
Concentrations of Sb in the plants Pistacia lentiscus and Asparagus ranged from 0.1 to 22 mg/kg, with maximum values in plants growing very close to the mining-related wastes. The P. lentiscus grows well on the soils highly
contaminated with Sb at Su Suergiu and might be used for revegetation of the Sb-rich heaps, thus contributing
to reduce the dispersion of contaminated materials
Molybdate sorption by Zn-Al sulphate layered double hydroxides
No full textThe efficacy of Zn–Al sulphate layered double hydroxides (LDHs) in removing molybdenum from aqueous
solution was tested through sorption of aqueous molybdate by synthetic samples in batch experiments. Up
to ~54% Mo is removed; the most efficient mechanism is sulphate–molybdate exchange within the LDH
interlayer, which preserves the layered structure, though with a partial loss of structural order. The Mo
uptake is influenced primarily by the [Zn2+]/[Al3+] ratio, which determines the ionic charge of the brucitelike
layer; high ratios facilitate the release of sulphate from the interlayer and the entrance of molybdate,
whilst for low ratios surface adsorption of molybdate becomes an important uptake mechanism. The Mo removing
potential shown by Zn–Al sulphate LDHs may prove useful for the treatment of moderately contaminated
waters
METODO DI SINTESI DELLA MOLECOLA OTTACALCIO FOSFATO
Full text linkL’invenzione è relativa ad un processo per la produzione di Ottacalcio fosfato a partire da carbonato di calcio e acido ortofosforico in cui il carbonato di calcio e l’acido ortofosforico sono posti a reagire in acqua secondo un rapporto molare compreso nell’intervallo 1,25-1,41, la massa di carbonato di calcio essendo compresa nell’intervallo 0,1-20 g per litro d’acqua, la temperatura di reazione essendo compresa nell’intervallo 55-85°C e la reazione essendo condotta per un intervallo di tempo fra 3 e 16 ore. Al termine della reazione, si recupera l’Ottacalcio fosfato dalla sospensione acquosa per filtrazione o decantazion
Antimony contamination of surface water at abandoned Sardinian mine sites
No full textThe element antimony raises much concern from both toxicological and
environmental viewpoints. The World Health Organization has established a guideline value of 20 μg/L Sb for drinking water, while the Italian legislation indicates a lower value (5 μg/L Sb). Antimony is ubiquitously present throughout the environment as a result of both natural and human processes. Particularly high concentrations of Sb may occur in water draining abandoned mining sites and in
adjacent soils.
This study is aimed to assess the Sb occurrence, and dispersion in aquatic systems
located in the Sarrabus-Gerrei mining district, south-eastern Sardinia (Italy). In
this area, Sb ores have been mined till the 1980s. Thereafter, mines were closed
and mining residues were abandoned without intervention to mitigate the
environmental impact. Surface waters downstream of the mine show high concentrations of Sb (up to 1500 μg/L) and As (up to 230 μg/L). Contamination extends several kilometers downstream of the mine and affects the Flumendosa river, which water is used for irrigation and domestic purposes. Antimony
concentrations in the Flumendosa water exceed 5 times the Italian standard for
drinking water.
The Regional Government has recently recognized this site as a priority in the
remediation plan for contaminated sites. The results derived from this study can
give a valuable contribution in the correct management and preservation of
aquatic bodies, and also in suggesting the appropriate actions able to mitigate
environmental effects in Sb-contaminated aquatic systems
Antimony dispersion at abandoned mines in Sardinia, Italy
No full textAqueous Sb may result from both natural and human processes. The World Health Organization established guideline values of 20 μg/L Sb for drinking water. Concentrations of Sb above drinking water standards may occur in water draining abandoned mines. The Sb occurrence in water and potential dispersion in the atmosphere were investigated in the Su Suergiu area (Sardinia, Italy). The Su Suergiu Sb ores were exploited since 1880 until 1980, with mining and processing residues abandoned on site. Surface waters downstream of the mine show high concentrations of Sb (up to 1500 μg/L). Contamination extends several km downstream of the mine and affects the Flumendosa river, which water is used for irrigation and domestic purposes. Dust materials deposited on leave samples collected in the mine area carry 70 μg/kg Sb, as compared to 7 μg/kg Sb observed on leaves collected on slopes upstream mine
Fate of antimony and arsenic in contaminated waters at the abandoned Su Suergiu mine (Sardinia, Italy)
No full textWe investigated the fate of Sb and As downstream of the abandoned Su Suergiu mine (Sardinia, Italy) and surrounding areas. The mined area is a priority in the Sardinian remediation plan for contaminated sites due to the high concentrations of Sb and As in the mining-related wastes, which may impact the Flumendosa River that supplies water for agriculture and domestic uses. Hydrogeochemical surveys conducted from 2005 to 2015 produced time-series data and downstream profiles of water chemistry at 46 sites. Water was sampled at: springs and streams unaffected by mining; adits and streams in the mine area; drainage from the slag heaps; stream water downstream of the slag drainages; and the Flumendosa River downstream from the confluence of the contaminated waters. At specific sites, water sampling was repeated under different flow conditions, resulting in a total of 99 samples. The water samples were neutral to slightly alkaline. Elevated Sb (up to 30 mg L−1) and As (up to 16 mg L−1) concentrations were observed in water flowing from the slag materials from where the Sb ore was processed. These slag materials were the main Sb and As source at Su Suergiu. A strong base, Na-carbonate, from the foundry wastes, had a major influence on mobilizing Sb and As. Downstream contamination can be explained by considering that: (1) the predominant aqueous species, Sb(OH)6− and HAsO4−2, are not favored in sorption processes at the observed pH conditions; (2) precipitation of Sb- and As-bearing solid phases was not observed, which is consistent with modeling results indicating undersaturation; and (3) the main decrease in dissolved Sb and As concentrations was by dilution. Dissolved As concentrations in the Flumendosa River did not generally exceed the EU limit of 10 μg L−1, whereas dissolved Sb in the river downstream of the contamination source always exceeded the EU limit of 5 μg L−1. Recent actions aimed at retaining runoff from the slag heaps are apparently not sufficiently mitigating contamination in the Flumendosa River
Antimonate Removal from Polluted Mining Water by Calcined Layered Double Hydroxides
Full text linkAbstract: Calcined layered double hydroxides (LDHs) can be used to remove Sb(V), in the Sb(OH)6 − form, from aqueous solutions. Sorption batch experiments showed that the mixed MgAlFe oxides, obtained from calcined hydrotalcite-like compound (3HT-cal), removed Sb(OH)6 − through the formation of a non-LDH brandholzite-like compound, whereas the mixed ZnAl oxides, resulting from calcined zaccagnaite-like compound (2ZC-cal), trapped Sb(OH)6 − in the interlayer during the formation of a Sb(V)-bearing LDH (the zincalstibite-like compound). The competition effect of coexistent anions on Sb(OH)6 − removal was HAsO4 2− >> HCO3 − ≥ SO4 2− for 2ZC-cal and HAsO4 2− >> HCO3 − >> SO4 2− for 3HT-cal. Considering the importance of assessing the practical use of calcined LDHs, batch experiments were also carried out with a slag drainage affected by serious Sb(V) pollution (Sb = 9900 μg/L) sampled at the abandoned Su Suergiu mine (Sardinia, Italy). Results showed that, due to the complex chemical composition of the slag drainage, dissolved Sb(OH)6 − was removed by intercalation in the interlayer of carbonate LDHs rather than through the formation of brandholzite-like or zincalstibite-like compounds. Both 2ZC-cal and 3HT-cal efficiently removed very high percentages (up to 90–99%) of Sb(V) from the Su Suergiu mine drainage, and thus can have a potential application for real polluted waters
Determination of traces of Sb(III) using ASV in Sb-rich water samples affected by mining
No full textChemical speciation [Sb(V) and Sb(III)] affects the mobility, bioavailability and toxicity of antimony. In
oxygenated environments Sb(V) dominates whereas thermodynamically unstable Sb(III) may occur. In
this study, a simple method for the determination of Sb(III) in non acidic, oxygenated water contaminated
with antimony is proposed. The determination of Sb(III) was performed by anodic stripping voltammetry
(ASV, 1–20 mg L1 working range), the total antimony, Sb(tot), was determined either by inductively
coupled plasma mass spectrometry (ICP-MS, 1–100 mg L1 working range) or inductively coupled plasma
optical emission spectrometry (ICP-OES, 100–10,000 mg L1 working range) depending on concentration.
Water samples were
filtered on site through 0.45 mm pore size
filters. The aliquot for determination of Sb
(tot) was acidified with 1% (v/v) HNO3. Different preservatives, namely HCl, L(+) ascorbic acid or L(+)
tartaric acid plus HNO3, were used to assess the stability of Sb(III) in synthetic solutions.
The method was tested on groundwater and surface water draining the abandoned mine of Su Suergiu
(Sardinia, Italy), an area heavily contaminated with Sb. The waters interacting with Sb-rich mining
residues were non acidic, oxygenated, and showed extreme concentrations of Sb(tot) (up to
13,000 mg L1), with Sb(III) <10% of total antimony. The stabilization with L(+) tartaric acid plus
HNO3 appears useful for the determination of Sb(III) in oxygenated, Sb-rich waters. Due to the instability
of Sb(III), analyses should be carried out within 7 days upon the water collection. The main advantage of
the proposed method is that it does not require time-consuming preparation steps prior to analysis of Sb
(III)
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