Rosa Cidu

Arsenic enrichment in waters and sediments of the Rio Loa (Second Region, Chile)

The Second Region of Chile (126,500 km2) is extremely arid, with a dramatic scarcity of water. The only water resource for the population (about 420,000 habitants) and the mining industry (the most important economic activity in the region) is the 440 km long Rio Loa. Moreover, this is highly enriched in As. In order to assess As concentrations and sources, and to evaluate the impact of mining activity on the water quality in the Rio Loa basin, water and sediment samples were taken at strategic points along the river and its major tributaries. The water in the whole basin is quite saline (total dissolved solids up to 11 g/l) and heavily enriched in As (average: 1400 μg/l) and B (average: 21,000 μg/l). These values are up to 300 and 100 times higher than the respective guidelines suggested by the WHO for drinking water. The quality of water is extremely poor along the tributary Salado, mainly fed by the El Tatio geothermal waters that are very rich in As (up to 27,000 μg/l) and other components. Sediments from the Rio Loa and its tributaries have As contents in the range of 26–2000 mg/kg (mean value of 60 samples: 320 mg/kg), and reach 11,000 mg/kg at El Tatio. Sequential extraction analyses show the As to be mainly associated with Fe–Mn oxy-hydroxides and residual phases, but part of the As (about 20%) is readily available being extracted from the exchangeable and carbonate phases. This result is in agreement with the correlation observed between As content in sediments and As concentration in waters in the area. The extreme arid conditions, high evaporation, and the lack of low-As tributaries contribute to maintain high concentrations of As and other components in the Rio Loa water to the mouth. Due to the oxidising conditions, neutral to alkaline pH, high salinity and high As concentrations, adsorption of As-species is not favoured. The main As source in the Rio Loa basin is considered to be natural, i.e. linked to the lithologies in the area. Smelter emissions and mining wastes, as well as the As-rich effluents from the water treatment plants, possibly represent additional sources.

Rare earth elements in waters from the albitite-bearing granodiorites of Central Sardinia, Italy

With the aim of contributing to the knowledge of the geochemical behaviour and mobility of the rare earth element (REE) in the natural water systems, the ground and surface waters of the Ottana–Orani area (Central Sardinia, Italy) were sampled. The study area consists of albititic bodies included in Hercynian granodiorites. The waters have pH in the range of 6.0–8.6, total dissolved solid (TDS) of between 0.1 and 0.6 g/l, and major cation composition dominated by Ca and Na, whereas predominant anions are Cl and/or HCO3. The pH and the major-element composition of the waters are the factors affecting the concentration of REE in solution. The concentrations of ∑REE+Y in the samples filtered at 0.4 μm vary between 140 and 1600 ng/l, with La of between 14 and 314 ng/l, and Yb of between <6 and 12 ng/l. A negative Ce anomaly, especially marked at high pH, is observed in the groundwaters. The surface waters show lower REE concentrations, which are independent of pH, and negligible Ce anomaly. Speciation calculations, carried out with the EQ3NR computer program, showed that the complexes with the CO32− ligand are the dominant REE species at pH in the range of 6.7–8.6. The REE3+ ions dominate the speciation at pH <6.7 and only in the light REE (LREE). The relative concentrations of REE in water roughly reflect those in the aquifer host rocks. However, when concentrations of REE in water are normalised relative to the parent rocks, a preferential fractionation of heavy REE (HREE) into the water phase can be observed, suggesting the greater mobility and stability of HREE in aqueous solution.

Antimony in the soil-water-plant system at the Su Suergiu abandoned mine (Sardinia, Italy): strategies to mitigate contamination.

This 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(-1), 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(-1), 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(-1), and dissolved organic carbon ≤2 mg L(-1). The waters collected upstream of the mine have Ca-bicarbonate dominant composition, and median concentration of Sb(tot) of 1.7 μg L(-1) (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(-1) 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(-1) Sb and 20 μg L(-1) Sb, respectively). The waters flowing in the mine area are characterized by Ca-sulfate dominant composition, and median concentrations of 7000 μg L(-1) Sb(tot). Extreme concentrations, up to 30,000 μg L(-1) 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(-1) 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(-1) Sb(tot) in the stream Rio Ciurixeda at 3 km distance, and 25 μg L(-1) 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(-1), 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. Major effects of contamination were observed on the water bodies located downstream of the Su Suergiu abandoned mine. The maximum load (16.6 kg Sb per day) to the Flumendosa, the main aquatic recipient, was observed after heavy rain events. Therefore, priorities of mitigation actions should be focused on minimizing the contact of rain and runoff waters on the heaps of mining wastes.

Determination of gold at the ultratrace level in natural waters

Abstract Several methods for the preconcentration of dissolved gold in natural waters were evaluated for use with graphite furnace atomic absorption spectroscopy (GFAAS) or inductively coupled plasma mass spectrometry (ICP-MS). An anion exchange method prior to GFAAS, and a solvent extraction method prior to ICP-MS both proved to have similar recoveries, low limits of detection (0.4 and 0.2 ng l −1 , respectively, for a 2-1 sample) and good reproducibility. Parallel analyses of particulate gold were also carried out by instrumental neutron activation analysis (INAA) with detection limits between 0.04 and 0.5 ng l −1 depending on the volume of filtered water, to provide a complete evaluation of transported gold. These methods were subsequently tested on stream, spring and adit water samples, to check the accuracy of methods for natural waters. Results obtained by ICP-MS and GFAAS on natural water samples were comparable. The maximum dissolved gold concentration was 3 ng l −1 , and particulate gold formed less than 50% of the total amount of gold transported. No significant variation was found in the dissolved gold content of one spring water sample monitored monthly over a one year period.

Geochemistry of the high-PCO2 waters in Logudoro, Sardinia, Italy

Abstract A geochemical study of the high-PCO2 waters in Logudoro, northern Sardinia, was carried out starting from regional hydrogeochemical prospecting for geothermal energy, based on the major dissolved components and some minor elements. This preliminary investigation led to the identification of five different lithologies marking the different aquifers. The high-PCO2 waters can be divided into the less saline (TDS

The abandoned Pb-Zn mine of Ingurtosu, Sardinia (Italy)

Abstract The Ingurtosu Pb-Zn mine, situated in the southwestern part of Sardinia, has been in production from the beginning of the last century up to 1968. The orebody consists of galena/sphalerite/barite/siderite veins in Ordovician arenaceous and phyllitic sediments, near the contact with a Hercynian batholith. Abundant tailings were collected in a pond from which they were discharged during the winter months into the sea via the Rio Naracauli stream. Today this area of outstanding scenic beauty, is degraded by tailings and waste rock scattered all along the stream. Material derived from mining activities was studied for grain size, mineralogical and geochemical composition. The Rio Naracauli was sampled over a length of ten kilometers at regular intervals. The results can be summarized as follows: (a) tailings contain a varying, but often quite high, percentage of Pb; lower percentages were found for Zn and Cd; (b) a sharp increase in dissolved Zn, Cd and Pb was observed in the Rio Naracauli where it leached the tailings; and (c) tailings and waste rocks should be recycled or revegetated.

Hydrogeochemical exploration for gold in the Osilo area, Sardinia, Italy

A study to test the use of hydrogeochemical methods for gold prospecting was carried out in the Osilo area, northern Sardinia. The study area, covering about 30 km2 is characterised by Tertiary andesitic rocks. Gold concentrations up to several ppm, associated with abundant pyrite, arsenopyrite, stibnite, tetrahedrite and electrum, and subordinate galena, sphalerite and chalcopyrite, are present in quartz veins associated with a polyphase, incipient and pervasive alteration of the andesitic rocks. Forty-eight water samples (17 streams, 29 springs and 2 boreholes) were analysed for Au and a wide range of major and trace elements, both in solution (< 0.4 μm) and in suspension. Background values for dissolved Au were below the detection limit of the methods used (between 0.3 and 0.5 ng L−1 Au). Gold concentrations in solution up to 3 ng L−1 were found in waters draining the mineralised vein system. The observed dispersion of Au in surface waters was restricted to about 500 m from the auriferous veins. Dissolved Au anomalies do not vary significantly in water samples, taken monthly over a one year period, suggesting that the dispersion of Au is unaffected by seasonal conditions in the Osilo area. For samples where Au was detected both in solution and in suspension, the Au content of the suspended matter was usually lower than that in solution. The best indicators of Au mineralisation, apart from Au itself, both in solution and in suspension, were As and Sb which showed a dispersion clearly related to the known auriferous veins.

Geochemistry of thermal waters from Morocco

Thermal waters from the Rif (Northern Morocco) have temperatures in the 31‐528C range, near-neutral pH (6.3‐7.0), variable redox conditions (fromˇ0.2 to 0.5 V) and a wide range of total dissolved solids (<1‐27 g/l). The D/H and 18 O= 16 O isotopic ratios of the water suggest a meteoric origin for the thermal waters. The main chemical composition is sodium-chloride, resulting from the interaction of water with marine sediments. Highsalinity waters show high concentrations of B, Li, and Sr, while other minor components and metals (e.g., Fe, Mn, Zn, Cd, Pb, Cu, Co, Ni, As, Sb and Hg) are usually very low. At Oulmes (Massif Central) the water shows 428C, a pH of 5.9, TDS of 1.5 g/l, sodiumbicarbonate chemical composition, and high P-CO2. This water flows out of granite rocks and is characterised by high concentrations of SiO2, Li, Rb, Cs, Fe, Mn, Be and As. Chemical equilibrium studies show that the thermal waters are close to equilibrium with respect to calcite, dolomite, chalcedony and kaolinite, while equilibrium with respect to gypsum and barite occurs in the sulphate-rich waters. Chemical geothermometers suggest deep temperatures close to 1008C for the warmest water in the Rif (My Yacoub: 528 Ca t the emergence), and about 1308C at Oulmes. 7 2000 CNR. Published by Elsevier Science Ltd. All rights reserved.

Natural Biomineralization in the Contaminated Sediment-Water System at the Ingurtosu Abandoned Mine

The Ingurtosu Pb–Zn mine (S-W Sardinia) was exploited for about a century until 1968. Huge amounts of tailings were abandoned, resulting in long-term heavy metal dispersion processes in both soils and waters. Zn and Pb concentration in tailings and soils attains values up to thousands of mg per kilogram. The maximum Zn concentration in water attains several hundreds of mg per liter, whereas Cd and Pb concentrations are in the order of thousands of μg per liter. Heavy metal concentration in waters of Rio Naracauli, the main stream of the area, is abated by seasonal biomineralization processes. Precipitation of hydrozincite [Zn5(CO3)2(OH)6] and of a Zn-rich amorphous phase results in a decrease of Zn concentration down to a few mg per liter. Other metals such as Pb, Cd, Cu, and Ni are coprecipitated with the Zn phases. This chapter reports the state of our knowledge on the Naracauli biomineralization process.

Geochemistry and stable isotope composition of surface waters from the Ravenna plain (Italy): implications for the management of water resources in agricultural lands

This paper examines the issues related to salinization and water quality in the complex drainage system of the historical land reclamation of Lamone basin (Ravenna coastal plain, northern Italy), with the aim of guiding ongoing agricultural-related decisions. Major and trace element concentration and O–H–B–Sr isotope-ratios were measured on surface water from a network of canals and ditches. Sampling was carried out during the winter period and in summer, to assess the effects of agricultural water management on the aquatic system. Results show widespread salinization of waters over the entire crop, due to both the direct saltwater inland flushing through the canals in proximity of the mouths, and sea salt leaching from soils. During winter, salinization is partly mitigated by rainfalls, while in summer dilution processes are due to freshwater input from outside the watershed, planned to assist the agricultural water demand. In the winter season, the concentration of some elements such as Fe, Mn, Al, and Cu in waters exceeds the maximum permissible limits imposed by the Italian regulations, while during summer the concentration of these elements is significantly reduced. A seasonal cycling is established, where the bottom sediments of canals and ditches act as sinks of harmful elements, mostly through adsorption by Fe–Mn–Al oxy-hydroxide solid phases. The irrigation practice, although improving the water quality, increases water turbidity by re-mobilization of sediments which act as transport agents of contaminants, with detrimental effects that may become significant over the years.