K. Håkansson

Speciation of heavy metals in road runoff and roadside total deposition

The concentrations of Cd, Co, Cu, Pb, W and Zn were measured in road runoff and total deposition at two Swedish field sites during one year. It was found that the concentrations of most elements increased significantly during the winter, up to one order of magnitude. For cobalt and tungsten, it was found that around 90% of the total mass transport occurred during the winter, whereas for Cu, Pb, Cd, Zn and Na, the corresponding figures were 70–90, 40–80, 60–90, 50–70 and ≥99% depending on site specific conditions. The deicing salts (rock salts) did not significantly contribute to the increase in trace element concentrations. Instead, the increased concentrations were due to more intense wearing of the pavement during the winter because of the use of studded tires in combination with the chemical effects caused by the use of deicing salts. New potential elemental markers for roads and traffic are suggested.

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.

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.

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.

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.

Fractionation of trace metals in surface water with screen filters

Abstract Size fractionation of solid particulate phases serving as carriers of trace elements (e.g. Al, Cd, Cu, Fe, Mn and Zn) in surface waters was conducted by pressure filtration using screen filters with defined pore sizes in the range 5-0.015 μm. The particle size distribution in solution was determined by Photon Correlation Spectroscopy. The accumulation of solids on the filter surface was demonstrated, leading to a successive reduction of the efficient pore size (‘clogging’). Thus, filters with a defined pore size of 0.40 μm and a diameter of 47 mm had an apparent separation efficiency corresponding to a pore size of 0.015 μm after filtration of 100 ml containing approximately 100 mg/l of suspended solids. Aluminium and iron were almost exclusively present in the particle size range 5-0.20 μm. Copper and manganese were retained to 45% and zinc and cadmium to 30% by the 0.015-μm pore size filter.

Simultaneous dissolution of organic acids in sequential leaching of sediment bound trace metals

Inorganic metal-solid associations can somewhat arbitrarily be characterized in various extraction procedures. The simultaneous extraction of organics (humic and fulvic acids, HFA, characterized by their UV absorbance) has been studied in the sequential leaching of sediment bound trace metals (Cd, Cu, Fe, Mn and Zn). Typically 2-5% of the total HFA would follow the ion exchangeable fraction, 4-10% the carbonate/hydroxide fraction and 7-13% the hydrous oxide fraction. Essentially no HFA remains after wet oxidation with H/sub 2/O/sub 2//HNO/sub 3/. From the distribution of the metals and the HFA between the various leaching steps it appears that organics can constitute a significant structural component of the amorphous hydrous oxide phase (iron and manganese) which partly prevent the distribution of this fraction in reducing acidic media (NH/sub 2/OH-HCl).

A field study of diffusion controlled migration of copper, zinc and cadmium in a clay formation

The distribution of Cu, Zn and Cd within an illitic clay formation located beneath a ca 150 yr old deposit of sulfidic mine tailings was studied. Total concentrations of metals have been quantified as a function of depth. The distribution between the pore water and the solid phase has been measured. Qualitative information was obtained by an operational leaching procedure. Field measurements were validated with batch adsorption experiments. The results suggest that transport of metals originating from the tailings is diffusion controlled. Apparent diffusivities as well as distribution coefficients were estimated.

Effects of weathering on metal releases from an engineered deposit for alum shale leaching residues

A pile of ca 15,000 t of crushed alum shale leaching residues from uranium refining was deposited in Ranstad, Sweden, in 1972 as a part of a pilot study of various waste storage concepts. A field study has been performed in order to evaluate the efficiency of the engineered barriers (bentoniteltill or crushed limestone) for the prevention of weathering of the leaching residues and subsequent release of metal rich leachates. The concentration levels of Fe (from pyrite in the alum shale) as well as metals associated with the pyrite (e.g. Cu and Ni) indicate that the weathering of leaching residues underneath the cover has progressed to less than 4 cm in 15 yr. No breakthrough of precipitation is indicated from the composition of the percolation water coming from the deposit. Thus, the weathering rate is reduced by ca 3 orders of magnitude in comparison with leaching residues freely exposed to air and precipitation.