| 1. |
- Bäckström, Mattias, 1974-, et al.
(author)
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Effects of a fulvic acid on the adsorption of mercury and cadmium on goethite
- 2003
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In: Science of the Total Environment. - Amsterdam, Netherlands : Elsevier. - 0048-9697 .- 1879-1026. ; 304:1-3, s. 257-268
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Journal article (peer-reviewed)abstract
- The effects of an aquatic fulvic acid on the pH-dependent adsorption of Hg(II) and Cd(II) to particulate goethite (a-FeOOH) were studied in batch systems. The ionic medium consisted of 0.01 M HClO and the total concentrations 4 of mercury and cadmium were maintained at 10y8 M with 203Hg and 109Cd as tracers. pH In the systems was varied in the range 3–10 by addition of HClO and NaOH.All commercial chemicals were of analytical grade or better. An 4 aquatic fulvic acid (20 ppm), previously isolated and characterised in detail, was used as a model for humic substances and its adsorption to goethite is included in this study. The adsorption of the fulvic acid (20 ppm) onto goethite decreased slowly from 90% at pH 3–7.5 to 10% at pH 10. In systems without fulvic acid the adsorption of mercury increased in a linear fashion from 10% at pH 3 to 70% at pH 10.In the presence of fulvic acid (20 ppm), the adsorption was almost quantitative in the intermediate pH range (pH 5–7), and exceeded 92% over the entire pH range. Thus, association between mercury and the fulvic acid enhanced adsorption in general although the largest impact was found at low pH.Adsorption of cadmium increased from nearly 0 to almost 100% at approximately pH 6. In the presence of fulvic acid, the adsorption increased below pH 7 and decreased above pH 7. The adsorption isotherm for mercury when the concentration was increased from 10y8 to 1.8=10y4 M showed a corresponding increase of K (lyg) up to a total concentration at 10y6 M.At higher mercury concentrations K was lowered. In the presence of fulvic acid the corresponding relationship of K was bi-modal, i.e. high values at low and intermediate concentrations of mercury. This behaviour suggests that in the absence of fulvic acid the adsorption follow the expected behaviour, i.e. adsorption sites with similar affinity for mercury. In the presence of fulvic acid, additional adsorption sites are available by the organic molecule (possibly sulfur groups) when it is associated to the goethite. The adsorption isotherm for cadmium indicates a lowering of K at 10y4 M. Cadmium had no competitive effect on mercury and vice versa. Zinc, however, affected the adsorption of cadmium but not the adsorption of mercury.
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| 2. |
- Chan, Wing Sze, et al.
(author)
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Metal accumulations in aquatic organisms and health risks in an acid mine-affected site in South China
- 2021
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In: Environmental Geochemistry and Health. - : Springer Nature. - 0269-4042 .- 1573-2983. ; 43:11, s. 4415-4440
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Journal article (peer-reviewed)abstract
- Metal contamination from base metal sulphide mines is a major environmental challenge that poses many ecological and health risks. We examined the metal concentrations in the Dabaoshan mine in South China in water, sediments, and aquatic organisms and their specific characteristics (i.e. size, body tissue, species, and habitat) along the Hengshi and Wengjiang River courses to assess acid mine drainage remediation efforts. Metal concentrations of arsenic, cadmium, chromium, copper, lead, nickel, thallium, and zinc were examined in tissues (i.e. gills, intestines, and muscles) of 17 freshwater species of fish, shrimps, and crabs. Metals in tissues followed the trend: intestines > gills > muscles; nearly all intestine samples exceeded the safe limits of metals analysed in this study. There is a positive correlation between distance from the mine and metal concentrations related to the flow of surface water and the habitat of aquatic organisms. The concentrations of arsenic, copper, and zinc were the highest in aquatic organisms, and the distribution was influenced by physical (distance from mine, currents, and seasonality), chemical (pH and competing ions), and biological (species, habitat, and predator-prey relation) factors. Large demersal fish and benthic fauna had higher concentrations of metals. Bioaccumulation and biomagnification of metals, as well as the high metal pollution index and target hazard quotient (arsenic, cadmium, copper, lead, thallium, and zinc), occurred in bottom feeders (C. aumtus, X. argentea) and fish belonging to higher trophic levels (P. fulvidraco, O. mossambicus). Lead and cadmium indicated the highest level of biomagnification from prey to predator. Health risks exist from the dietary intake of common aquatic species such as tilapia and carp besides crustaceans due to high arsenic, cadmium, lead, and thallium levels. Further reduction of metals is necessary to improve the effects of acid mine drainage in the catchment.
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| 3. |
- Dario, Mårten, et al.
(author)
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Effects of cement additives on radionuclide mobility
- 2004
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In: Scientific basis for radioactive waste management XXVII. - Warrendale, Pa : Materials Research Society. - 1558997520 ; , s. 639-644
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Conference paper (other academic/artistic)
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| 4. |
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| 5. |
- Dario, Mårten, 1970-
(author)
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Metal distribution and mobility under alkaline conditions
- 2004
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Doctoral thesis (other academic/artistic)abstract
- The adsorption of an element, expressed as its distribution between liquid (aquatic) and solid phases in the biogeosphere, largely determines its mobility and transport properties. This is of fundamental importance in the assessment of the performance of e.g. geologic repositories for hazardous elements like radionuclides. Geologic repositories for low and intermediate level nuclear waste will most likely be based on concrete constructions in a suitable bedrock, leading to a local chemical environment with pH well above 12. At this pH metal adsorption is very high, and thus the mobility is hindered. Organic complexing agents, such as natural humic matter from the ground and in the groundwater, as well as components in the waste (cleaning agents, degradation products from ion exchange resins and cellulose, cement additives etc.) would affect the sorption properties of the various elements in the waste. Trace element migration from a cementitious repository through the pH- and salinity gradient created around the repository would be affected by the presence and creation of particulate matter (colloids) that may serve as carriers that enhance the mobility. The objective of this thesis was to describe and quantify the sorption of some selected elements representative of spent nuclear fuel (Eu, Am) and other heavy metals (Zn, Cd, Hg) in a clay/cement environment (pH 10-13) and in the pH-gradient outside this environment. The potential of organic complexing agents and colloids to enhance metal migration was also investigated. It was shown that many organic ligands are able to reduce trace metal sorption under these conditions. It was not possible to calculate the effect of well-defined organic ligands on the metal sorption in a cement environment by using stability constants from the literature. A simple method for comparing the effect of different complexing agents on metal sorption is, however, suggested. The stability in terms of the particle size of suspended colloidal matter (clays and an iron hydroxide) was measured by photon correlation spectroscopy. In the absence of large amounts of organic material, the present colloids will, in most cases, not enhance metal migration in a cementitious environment due to agglomeration of the colloidal phase at high pH and salinities.
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| 6. |
- Dario, Mårten, et al.
(author)
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Sorption of Cd to colloidal ferric hydroxides : impact of pH and organic acids
- 1997
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In: Chemical speciation and bioavailability. - 0954-2299 .- 2047-6523. ; 9:1, s. 3-14
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Journal article (peer-reviewed)abstract
- The sorption (both ad- and desorption) of Cd to or from colloidal ferric hydroxides as a function of pH, the concentration of organic acids (acetic acid (AA), EDTA, fulvic acid (FA) and malonic acid (MA)), the precipitation procedure for the ferric hydroxide as well as the contact time were investigated in the present study. The concentrations of Cd, colloids and organic acids were chosen to be representative of natural surface waters. The ferric hydroxide were either precipitated in presence of FA or the acid was mixed with the colloids after the purification steps. The presence of FA during the precipitation of ferric hydroxide, had an impact on the size distribution of the solid phase, but it did not have any influence on the sorption behaviour of Cd. The adsorption process was found to be relatively fast and largely pH-dependent. It was fully reversible when the pH was decreased, however, with somewhat slower kinetics. The addition of up to 1 mmol L-1 AA or MA did not cause any measurable desorption of Cd, probably due to the relatively weak complexes formed between Cd(II)-ions and the anions of the acids. Thermodynamic calculations of the distribution between different soluble Cd-species indicated that EDTA and FA would form stronger complexes with Cd. This was indicated in the experiments as enhanced adsorption at low pH-values due to the adsorption of Cd(II)-organic species, and an increase in the soluble fraction at high pH-values caused by competition for Cd(II)-ions between complex forming groups on the surfaces and the soluble organic ligands.
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| 7. |
- Dario, Mårten, et al.
(author)
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Sorption of europium on TiO2 and cement at high pH in the presence of organic ligands
- 2006
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In: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 270:3, s. 495-505
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Journal article (peer-reviewed)abstract
- Organic substances present in radioactive waste lower the sorption of metal ions at the high pH in cement matrices and, hence, enhance their possible migration. The aim of this study was to develop a method to compare organic substances or their degradation products with respect to what extent they affect metal sorption. Batch sorption studies were performed with cement or TiO2 as solid phase and Eu(III) as a model element for trivalent lanthanides and actinides at pH 12.5 (representative of a cement waste matrix during the first approximately 100,000 years). Different kinds of ligands were studied in a broad concentration range, e.g., organic acids, cement additives, cleaning agents and degradation products from ion-exchange resin.
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