Stefan Karlsson

Metal speciation in a humic surface water system polluted by acidic leachates from a mine deposit in Sweden

Abstract A speciation study of some metals (Al, Fe, Cu, Zn and Cd) was performed in the surface water downstream from a deposit with sulphidic mine waste where acidic leachates were neutralized by mixing with well buffered groundwater and surface run-off. The water was rich in humic and fulvic acids (HFA). The chemical forms of the metals were characterized with respect to their cationic and anionic exchange properties. In the present pH range (5–8) Al and Fe precipitated as solids that were partly retained by both cation and anion exchangers. Zinc and cadmium were dominated by cationic forms but for cadmium anionic forms were always present in minor amounts under the conditions of the study. Copper was predominantly anionic (as HFA-complex) except at low pH and high concentrations of Al and Fe, which evidently occupied all available complexing sites on the HFA. Conditional stability constants were estimated for the corresponding metal-HFA complex entirely from field data. The values obtained with this empirical method (logβ∗ at pH 7; 4.7 Cu; 3.2 Zn; 4.0 Cd) are in reasonable agreement with measurements in controlled model systems.

Measurements in situ of concentration and size distribution of colloidal matter in deep groundwaters by photon correlation spectroscopy

Abstract Photon correlation spectroscopy (PCS) was applied for the characterization (concentration and size distribution) of colloidal matter in a deep groundwater. The measurements were performed on-line and in situ at the Aspo underground Hard Rock Laboratory, Oskarshamn, Sweden. The colloidal concentration in the rather saline groundwater was not above 0.1 mg/l and probably below 0.03 mg/l, according to the field measurements and with calibrations of the PCS-instrument with well-defined reference colloids of α-Fe2O3, γ-Al(OH)3 and SiO2. The results clearly demonstrated that the stability and concentration of a colloidal-size suspended phase in an anoxic groundwater with high Fe(II) content, like the one in Aspo (0.3 mg/l), is sensitive to exposure to atmospheric conditions during the handling of the sample. Diffusion of air into the closed measuring cuvette was enough to alter the colloidal content significantly within 6 h. A particle fraction with a size distribution range of 170–700 nm was formed within 45 min when air was allowed to diffuse into the aqueous phase from the air-filled upper part of the cuvette. The corresponding time to generate a significant colloidal precipitate was less than 1 min (size distribution range 100–600 nm) when a stream of air (1.5 ml) was bubbled through the water samples. The precipitating colloidal phase was a mixture of ferric hydroxide and calcium carbonate in all three cases.

Applicability of photon correlation spectroscopy for measurement of concentration and size distribution of colloids in natural waters

Abstract The suitability of proton correlation spectrosocpy (PCS) for the determination of concentration and size distribution of colloidal matter was tested in a surface water and in a deep groundwater. Well-defined colloids (sizes predominately in the range 50–500 nm) of α-Fe2O3, γ-Al(OH)3, SiO2, kaolinite, illite and humic acid in aqueous solutions were used as references for calibration of the PCS-instrument (signal vs. concentration). The intensity of the scattered light was dependent on the composition of the colloid. The concentration ranges, where a quantitative determination of the colloid could be achieved, were 0.03–2 mg/1, 0.1–2 mg/1, 0.1–7 mg/1, 0.5–10 mg/1, 0.5–50 mg/1 and 0.5–75 mg/1 for α-Fe2O3, γ-Al(OH)3, SiO2, kaolinite, illite and humic acid, respectively (in homogeneous systems). The colloidal populations in the surface waters (inlet and outlet of a lake) had a size distribution in the range 100–500 nm. The measured count rates were around 330 kcps and 30 kcps at the inlet and outlet, respectively, which correspond to totally 2.8 mg/1 and 0.9 mg/1 of colloidal matter according to gravimetric determinations (collected on clogged 0.015 μm filters). Comparisons of concentrations estimated from measurements of reference colloids with PCS and gravimetric determinations of the colloidal showed that a combination of the two methods would be needed. The measurements of a deep groundwater were performed on-line and in situ with a PCS technique. The content of colloidal matter in the groundwater was below the detection limit for the PCS-equipment, which corresponds to a concentration not above 0.5 mg/1 and probably below 0.1 mg/1 in the present system. The feasibility and advantages of using PCS for non-disturbing size characterisation and concentration measurements of colloids in aquatic systems have been demonstrated, as well as some limitations of the method.

Effects of pH on the accumulation and redistribution of metals in a polluted stream bed sediment

Abstract The accumulation of metals (Al, Fe, Cu, Zn, Cd, Pb) in the bottom sediments of a stream that serves as a drainage for a mine waste deposit has been studied. Data have been collected describing the water chemistry of the stream (major components as well as heavy metals), the formation and composition of suspended particulate matter in the stream and some qualitative data on the composition of the sediments (at three locations). Qualitative information on metal speciation and mechanisms for the association with solid phases as well as on the accumulation in sediments has been obtained from sequential leaching studies of both the suspended particulate phase and the stationary sediments. Combined effects of primarily pH, presence of organics and the presence and formation of sparingly soluble carrier phases (aluminum and iron hydroxides) on the redistribution of metals from the deposit are indicated.

Effects of pH, ionic strength and a fulvic acid on size distribution and surface charge of colloidal quartz and hematite

Size distribution of colloidal quartz and hematite (initial diameter 140–190 nm and 70–360 nm, respectively) were determined by Photon Correlation Spectroscopy (PCS) in well-defined laboratory systems. Effects on the mean diameter and the size distribution were measured at various values of pH (2–12) and ionic strength (0.001–0.7 mol/l) in an inert medium (NaClO4). The effect of an aquatic fulvic acid on the stability of the colloids was included in the study. In the absence of fulvic acid the colloids flocculate at a pH close to pHzpc of the respective mineral. This increase in mean diameter is due to electrostatic interactions. Hematite colloids are also destabilised at a pH much below pHzpc. The quartz colloids are stabilised in the presence of fulvic acid. The hematite/fulvic acid systems are stable at high pH, but flocculate at low pH. Increasing ionic strength induces agglomeration of the quartz colloids at 0.1 mol/l, independently of the presence of fulvic acid (2 mg/l). Hematite is destabilised at 0.02 mg/l in the absence of fulvic acid, while in the presence of fulvic acid the colloids aggregate at ionic strength 0.07mol/l.

Determination of nitrate and other water quality parameters in groundwater from UV/Vis spectra employing partial least squares regression

The use of UV/Vis spectroscopy in combination with partial least squares (PLS) regression for the simultaneous prediction of nitrate and non-purgeable organic carbon (NPOC) in groundwaters was evaluated. A model of high quality was obtained using first order derivative spectra in the range 200-300 nm. Inclusion of non-UV-absorbing constituents in the modeling procedure, i.e., chloride, sulfate, fluoride, total carbon (TC), inorganic carbon (IC), alkalinity, pH and conductivity was also evaluated. This model seemed to be useful for prediction of chloride, TC, IC, alkalinity and conductivity, while its ability to predict sulfate, fluoride and pH was poor. In conclusion, application of PLS regression, which requires neither filtration of samples nor addition of chemicals, is a promising alternative for fast interpretation of geochemical patterns of groundwater quality.

Chemical characterization of stream-bed sediments receiving high loadings of acid mine effluents

Abstract Sediments from the bottom of a stream that receives acidic metal-rich effluents from a mine tailings deposit have been sampled and characterized. The distribution of metals (Mg, Al, Ca, Fe, Mn, Cu, Zn, Cd and Pb) between porewater phase and solid phase has been determined. The adsorbed fractions have been characterized by a sequential leaching procedure. The solubilities of Al and Fe are controlled by their respective hydroxides while concentrations of dissolved Cu, Zn, Cd and Pb are governed by adsorption and coprecipitation. The metals Ca, Cd, Mg and Zn are mainly exchangeable and to a less extent bound in hydrous oxides. The associations of both Cu and Pb with the solid phases are related to the presence of organic matter.

Characterization of suspended solids in a stream receiving acid mine effluents, Bersbo, Sweden

Abstract Suspended particulate matter was recovered by filtration (0.40 μm) of water from a stream receiving acidic effluents from a mine tailings deposit. This solid phase formed rapidly as pH increased from 3.5 at the release point to 6.5, approximately 2 km downstream. The suspended solid was present in concentrations that ranged from 10–20 mg/l for anoxic conditions (winter) to 30–120 mg/l for oxic conditions (early spring). The solid consisted of FeOOH + Fe(OH)3(am) and AlOOH + Al(OH)3(am), as well as silicates. The organic content (of natural origin) was up to 30% (dry wt). Most of the Fe and Al from the leachate was precipitated in the particulate phase, approximately 98% of total metal content in the aqueous phase, as well as ∼50% of Mn, Cu, Zn, Cd and Pb. These elements were predominantly adsorbed on the hydrous oxide precipitate, or to some extent (Mn and Pb) coprecipitated, as indicated from a sequential leaching procedure and powder X-ray diffractometry. All the elements, particularly Cu, were to a significant degree associated with organic matter.

Influence of filtration, preservation and storing on the analysis of low molecular weight organic acids in natural waters

Abstract The suitability of three filter materials (polycarbonate, cellulose acetate and glass fibre) for trace organic acids analysis (acetic, butyric, β-hydroxy-butyric, formic, lactic, maleic, methyl-succinic, malonic, oxalic, succinic and valeric) was tested by determining leached components and sorption/desorption properties. Analysis of the organic acids was made with capillary zone electrophoresis (CZE). Polycarbonate membranes were easily cleaned by leaching with Milli-Q water and showed limited adsorption of the acids. Cellulose acetate filters required a more elaborate washing before use and had a higher retention capacity. Glassfibre filters are not recommended due to severe contamination of organic compounds and release of colloids. Preservation of natural water samples (eutrophic, dystrophic) by addition of chloroform, sterile filtration and freezing (−20°C) were quantitatively evaluated, after spiking with the organic acids (500xa0μg/l each) and storing for 11xa0weeks. Freezing was the only treatment where the added acids were quantitatively recovered after 4xa0weeks. Sterile filtration in combination with storing of the samples in the dark at 4°C can be suitable for short time preservation (less than 30xa0days). However, these conditions resulted in a high variation of recovered amounts among the replicates. Storing of untreated samples at room temperature or in a refrigerator, as well as addition of chloroform should be avoided.

Light induced changes of Fe(II)Fe(III) and their implications for colloidal forms of Al, Mn, Cu, Zn and Cd in an acidic lake polluted with mine waste effluents

Abstract The photo induced reduction of ferric (hydr)oxides stabilises the ferrous state in acidic (pH 4) lake water, at light intensities higher than 7 W/m2 and despite equilibrium with atmospheric oxygen. Precipitation of ferric (hydr)oxides occurred at lower light intensities, particularly at water depths constantly below this light intensity and with contributions of Fe(II) from the bottom sediments. No specific reducing agent could be identified, but the low concentrations of dissolved organic carbon and humic substances indicate that inorganic components could be involved in the reduction. A maximum of 20% of the copper and zinc concentrations and up to 50% of the cadmium were associated with colloidal matter. These distributions were observed at depths in the lake where the ferrous state was stable and with a fairly constant solid/solution distribution of the trace metals.