Gunter Faure

Removal of trace metals by coprecipitation with Fe, Al and Mn from natural waters contaminated with acid mine drainage in the Ducktown Mining District, Tennessee

Abstract This study examined the sorption of trace metals to precipitates formed by neutralization of 3 natural waters contaminated with acid mine drainage (AMD) in the former Ducktown Mining District, Tennessee. The 3 water samples were strongly acidic (pH 2.2 to 3.4) but had distinctively different chemical signatures based on the mole fractions of dissolved Fe, Al and Mn. One sample was Fe-rich (Fe=87.5%, Al=11.3%, and Mn=1.3%), another was Al-rich (Al=79.4%, Mn=18.0%, and Fe=2.5%), and the other was Mn-rich (Mn=51.4%, Al=25.7%, and Fe=22.9%). In addition, these waters had high concentrations of trace metals including Zn (37,700 to 17,400 μg/l), Cu (13,000 to 270 μg/l), Co (1,500 to 520 μg/l), Ni (360 to 75 μg/l), Pb (30 to 8 μg/l), and Cd (30 to 6 μg/l). Neutralization of the AMD-contaminated waters in the laboratory caused the formation of either schwertmannite at pH 4. Both phases were identified by XRD analyses of precipitates from the most Fe-rich water. At higher pH values (∼5) Al-rich precipitates were formed. Manganese compounds were precipitated at pH∼8. The removal of trace metals depended on the precipitation of these compounds, which acted as sorbents. Accordingly, the pH for 50% sorption (pH50) ranged from 5.6 to 7.5 for Zn, 4.6 to 6.1 for Cu, 5.4 to 7.7 for Ni, 5.9 to 7.9 for Co, 3.1 to 4.3 for Pb, and 5.5 to 7.7 for Cd. The pH dependence of sorption arose not only because of changes in the sorption coefficients of the trace metals but also because the formation and composition of the sorbent was controlled by the pH, the chemical composition of the water, and the solubilities of the oxyhydroxide-sulfate complexes of Fe, Al, and Mn.

Sorption of trace metals to an aluminum precipitate in a stream receiving acid rock-drainage; Snake River, Summit County, Colorado

The quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream. The purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water. The stream chosen for this purpose was the Snake River, Summit County, Colorado, which is affected by natural acid rock-drainage (ARD) containing SO4, Al, Fe, and various trace elements such as Zn, Cu, Pb, Ni, and others. Most of the Fe in the Snake River is removed from solution by the oxidation of Fe2+ to Fe3+ and the subsequent precipitation of Fe-oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river. Further downstream, the Snake River (pH=3.0) mixes with water from Deer Creek (pH= 7.0) thereby increasing its pH to 6.3 and causing SO4-rich precipitates of Al-oxyhydroxide to form. The precipitates and associated organic C complexes sorb trace metals from the water and thus have high concentrations of certain elements, including Zn (540–11,400 ppm), Cu (34–221 ppm), Pb (90–340 ppm), and Ni (11–197 ppm). The concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream. The trace element concentrations of the water in the mixing zone at the confluence with Deer Creek decrease by 75% or more and are up to 3 orders of magnitude lower than those of the precipitates. Sorption curves for Zn, Cu, Pb, Ni, and SO4 were derived by stepwise neutralization of a sample of Snake River water (collected above the confluence with Deer Creek) and indicate that the trace metals are sorbed preferentially with increasing pH in the general order Pb, Cu, Zn, and Ni. Sulfate is removed between pH 4 and 5 to form an Al-hydroxysulfate and/or by sorption to microcrystalline gibbsite. The sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace-metal concentrations in the precipitates. The results of this study demonstrate that the partitioning of trace metals in the Snake River is not only a function of pH, but also depends on the progressive removal of trace metals as the water of the Snake River flows through its confluence with Deer Creek. The chemical composition of the water also determines what compounds precipitate with increasing pH.

Strontium isotope composition and petrogenesis of the Kirkpatrick basalt, Queen Alexandra Range, Antarctica

The initial 87Sr/86Sr ratios of twelve basalt flows of Jurassic age on Storm Peak in the Queen Alexandra Range are anomalously high and range from 0.7094–0.7133. The average value is 0.7112±0.0013 (1σ). The concentrations of rubidium and strontium have arithmetic means of 60.6±19.4 ppm and 128.8±11.9 ppm, respectively. The corresponding average Rb/Sr ratio is 0.47 which is also anomalously high for rocks of basaltic composition. In addition, these rocks have high concentrations of SiO2 (56.50%) and K2O (1.29%) and are depleted in Al2O3 (12.92%), MgO (3.44%) and CaO (7.91%) compared to average continental tholeiites. They are nevertheless classified as basalts on the basis of the composition of microphenocrysts.The initial 87Sr/86Sr ratios and all of the chemical parameters of the flows exhibit systematic stratigraphic variations. These are interpreted as indicating the occurrence of four eruptive cycles. In a typical cycle the initial 87Sr/86Sr ratios of successive flows and their concentrations of SiO2, FeO (total iron), Na2O, K2O, P2O5, Rb and Sr decrease in ascending stratigraphic sequence while the concentrations of TiO2, Al2O3, MgO, CaO and MnO increase upward. The initial 87Sr/86Sr ratios of the flows show a strong positive correlation with the strontium concentration. Similar correlations are observed between the initial 87Sr/86Sr ratios and all of the major oxide components. These relationships are incompatible with the hypothesis that these flows are the products of crystal fractionation of a-34 magma at depth under closed-system conditions. It is suggested that the flows resulted from the hybridization of a normal tholeiite basalt magma by assimilation of varying amounts of granitic rocks in the Precambrian basement which underlies the entire Transantarctic Mountain chain.Mixtures of two components having different 87Sr/86Sr ratios and differing strontium concentrations are related to each other by hyperbolic mixing equation. Such an equation was fitted by least squares regression of data points to a straight line in coordinates of initial 87Sr/86Sr and the reciprocals of the concentrations of strontium. This equation and plots of strontium versus other oxides were then used to estimate the chemical composition of the parent basalt magma and of the granitic contaminant by substituting reasonable estimates of their 87Sr/86Sr ratios. The chemical composition of the parent basalt (87Sr/86Sr=0.706) is generally compatible with that of average continental tholeiite, but is distinctive by having a low concentration of strontium (117 ppm). The chemical composition of the contaminant (87Sr/86Sr=0.720) is enriched in strontium (173 ppm), SiO2, FeO (total iron) and the alkalies but is depleted in Al2O3, MgO and CaO. The data for strontium indicate that the lava flows on Storm Peak contain between 20 and 40% of this granitic contaminant. The contamination of basalt magma is not a local event but is characteristic of the Jurassic basalt flows and diabase sills throughout the Transantarctic Mountains and in Tasmania.

The isotopic composition of strontium in surface water from the North Atlantic Ocean

Abstract The isotopic composition of strontium in surface water from ten localities in the North Atlantic Ocean has been determined. The results support the conclusion that the Sr 87 Sr 86 ratio of the ten samples is constant within experimental errors. Eight of the ten samples came from the western half of the North Atlantic from the Bahamas to the Northumberland Straits of Nova Scotia. Two samples originated from the vicinity of the West African coast. The mean SrSr 87 Sr 86 ratio is 0.7093 ± 0.0005 (σ), relative to Sr 86 Sr 88 = 0.1194 . This value is in agreement with determinations of most previous analysts. A model is proposed which describes the isotopic composition of strontium in the oceans as a mixture of three isotopic varieties of strontium originating as weathering products of three types of rocks on the continents and in the ocean basins.

Some aspects of the geochemistry of strontium and calcium in the Hudson Bay and the Great Lakes

Abstract The ratio Sr 87 Sr 86 in samples of water and shells of the peleoypod Mytihis edulis, Linne, from the Hudson Bay was found to be 0.7093 ± 0.0003 which is identical to the value of this ratio in the northern Atlantic Ocean. The concentrations of strontium and calcium in four water samples from the eastern Hudson Bay vary linearly with salinity and are appreciably lower than in the open ocean. The ratio Sr × 103/Ca in the Hudson Bay was found to be equal to 18.7 ± 0.3 and does not differ significantly from values obtained for surface water from the Atlantic Ocean. Concentrations of strontium and calcium in Lake Superior are uniform throughout and average Sr = 21.8 ± 0.4 ppb, Ca = 14.3 ± 0.5 ppm. The ratio Sr × 10 3 Ca is 1.53 ± 0.04. Concentrations of the same elements in Lake Huron exhibit regional variations and are significantly higher than in Lake Superior. The Sr × 10 3 Ca ratio is approximately 3.5. The distribution coefficient for Sr+2 for Mytilus edulis in the Hudson Bay ranges from 0.14 to 0.20 and is significantly lower than experimentally determined values in carbonates composed of a mixture of aragonite and calcite. The average distribution coefficient for Sr+2 in the aragonitic shells of Lamposilis is 0.256 ± 0.027 (σ). The concentration of strontium in shells of Lampsilis fluctuates widely, but appears to be controlled, to a first approximation, by the distribution coefficient of Sr+2 in calcium carbonate and water. Attention is drawn to the discrepancy between the Sr × 10 3 Ca ratios of surface run-off water and the modern ocean. The apparent enrichment of strontium over calcium in the oceans is an important aspect of the marine geochemistry of strontium and calcium.

The geochemistry of Jurassic dolerites from Portal Peak, Antarctica

Geochemical and isotopic analyses have been performed on a suite of samples from a Jurassic quartz tholeiite sill of the Ferrar Group at Portal Peak, Queen Alexandra Range, near the Beardmore Glacier in Antarctica. The data include major and trace element (XRF and INAA) concentrations, as well as Sr and Nd isotopic compositions, and are combined with the results of other studies on samples from Antarctica. It is demonstrated that despite differences in the pre-intrusion (or eruption) evolution of the Ferrar Group magmas, the similarity in isotopic and chemical compositions for these rocks supports the existence of a remarkably uniform mantle source with unusual signature over a distance of thousands of kilometres. The favoured origin of this source involves the subduction of terrestrial sedimentary material into a depleted mantle reservoir.

A study of strontium isotopes in lakes and surficial deposits of the ice-free valleys, southern Victoria Land, Antarctica☆

Abstract The ice-free valleys of southern Victoria Land, Antarctica, contain saline lakes including Lake Vanda in Wright Valley and Lake Bonney in Taylor Valley. The source of the salts dissolved in the brines has not yet been identified. Strontium in water-soluble salts of soil samples in Wright Valley has 87 Sr 86 Sr ratios ranging from 0.7119 to 0.7157 with an average of 0.7144 ± 0.0008 (1 σ). This value is very similar to the 87 Sr 86 Sr ratio of brines in Lake Vanda ( 87 Sr 86 Sr = 0.7149 ± 0.00017 ), but differs significantly from the 87 Sr 86 Sr ratios of seawater (0.7094 ± 0.00012) and basaltic rocks of the McMurdo Volcanics (0.7044 ± 0.00046). The Sr in Lake Vanda therefore could not have originated from seawater or from volcanic rocks of the area, but may have been derived by chemical weathering of the igneous and metamorphic rocks exposed in Wright Valley. The 87 Sr 86 Sr ratios of Lake Bonney are invariant with depth and average 0.7130 ± 0.00014 (1 σ), whereas the Sr concentrations increase from 0.7345 ppm near the surface to a maximum of 39.92 ppm at a depth of 25 m. The Sr concentrations at greater depth decrease slightly to 35.88 ppm at 30 m. The Sr in water-soluble soil salts near Lake Bonney and of the Taylor Red Cone is similar isotopically to the Sr in the lake. The 87 Sr 86 Sr ratios of soil salts and of meltwater in Taylor Valley decrease systematically from Lake Bonney toward the coast. The water in Lake Fryxell, which is closest to the coast, has an 87 Sr 86 Sr ratio of 0.7090 and is identical to that of seawater. The evidence from this and similar studies in other parts of the world indicates that the 87 Sr 86 Sr ratios of saline brines in closed continental basins are representative of the Sr in the rocks underlying the basin. The Sr in carbonate and sulfate minerals precipitated from such brines preserves the 87 Sr 86 Sr ratios that existed at the time of deposition. Because of these relationships we suggest that stratigraphic variations of the 87 Sr 86 Sr ratios of non-marine carbonate or sulfate rocks reflect changes in the geology of the drainage basin. The isotopic composition of Sr of such rocks may therefore provide useful information about the geologic histories of continental basins.

Origin of the salts in Lake Vanda, Wright Valley, Southern Victoria Land, Antarctica

Abstract Measurements of the isotopic composition of strontium suggest that the salt content of Lake Vanda, Wright Valley, Antartiica, is derived mainly by chemical weathering of bedrock. No evidence was found for a direct marine or volcanic source for the salts.

Petrogenesis of the Kirkpatrick Basalt, Solo Nunatak, northern Victoria Land, Antarctica, based on isotopic compositions of strontium, oxygen and sulfur

Chemical and isotopic compositions of Jurassic tholeiites of the Kirkpatrick Basalt Group from Solo Nunatak, northern Victoria Land, indicate that these rocks are contaminated with crustal material. The basalts are fine grained and contain phenocrysts of augite, pigeonite, hypersthene and plagioclase. The flows on Solo Nunatak are chemically more similar to average tholeiite than flows from Mt. Falla and Storm Peak in the Central Transantarctic Mountains (TAM) which appear to be more highly differentiated. Initial 87Sr/86Sr ratios of the flows on Solo Nunatak are high (>0.710) and are similar to those reported for the Kirkpatrick Basalt in the Central TAM. Whole-rock δ18O values are also high, ranging from +6.0 to +9.3‰ and correlate positively with initial 87Sr/86Sr ratios, similar to the Kirkpatrick Basalt in the Central TAM. The correlation between initial 87Sr/86Sr ratios and δ18O values is explained as the result of simultaneous fractional crystallization and assimilation of a crustal contaminant. Sulfur isotope compositions vary between limits of δ34S= -4.01 to +3.41‰ Variations in (δ34S probably resulted from outgassing of SO2 under varying oxygen fugacities.

DIFFERENCES BETWEEN BARITES OF MARINE AND CONTINENTAL ORIGINS.

Uranium, thorium and strontium concentrations and strontium and sulphur isotopic ratios have been determined on a group of barites. The isotopic analyses and the uranium and thorium concentrations appear to be especially diagnostic in distinguishing between marine and continental origins of the mineral. These critiques have been applied to some barites recovered off the California coast.