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The adsorption of humic acid (HA) and 152 Eu onto bentonite, kaolin, montmorillonite and quartz in the presence of HA has been studied as a function of pH (2 to 10). HA adsorption onto the mineral surfaces decreased with increasing pH, probably due to both electrostatic and specific site interactions. The zeta potentials of the clay systems were also investigated and the results showed that the zeta potentials decreased with increasing pH due to deprotonation and that the mineral surfaces were negatively charged across the pH range. HA only affected the zeta potential of the montmorillonite system, conferring a more negative charge on the surface. 152 Eu (1 X10" 9 mol Γ 1 ) adsorption to HA free mineral surfaces generally increased with increasing pH. The mechanism appeared not to be purely electrostatic, but due to metal speciation and the nature of the surface, i.e. specific site binding. In the presence of HA, Eu adsorption generally increased or stayed similar at pHs up to 5. This was due to adsorption of EuHA complexes on the mineral surface. At higher pH, adsorption was decreased, reaching a minimum at around pH 6 to 7 and then increasing again up to a pH of around 10. This was probably due to both the desorption of EuHA complexes from the mineral surface and possibly because inorganic Eu species were being blocked from adsorbing to the colloid surface by adsorbed HA. It may be concluded that if mineral surfaces, either colloidal or stationary, are to be included in metal speciation and transport codes, a thorough understanding of the ternary interactions of natural organic matter (NOM) with toxic metals and minerals must be gained.Ternary metal interactions may also occur. For example, the possibility of mixed complexes of humic acid, europium and low molecular weight organics have been examined [7], Previous work has suggested that both colloidal and non-colloidal mineral surfaces in the environment may be coated to some extent by natural organic matter (NOM) [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], conferring a more negative surface charge to the mineral [24] and influencing colloidal stability [25,26] and mobility [27]. If such HA coatings do exist on mineral surfaces then ternary NOM-metal mineral interactions must be considered and understood if they are to be included in metal speciation and migration codes. However, at present, this information is still limited to a few ternary systems which have been investigated under a limited range of conditions [28][29][30][31][32][33][34][35][36][37][38].Inorganic surfaces in the environment often occur as colloidal and non-colloidal oxy/hydroxides of Mn, Fe, Al and Si, as well as carbonates and clays [39][40][41], In this paper we report investigations on the adsorption of humic acid (HA) to a range of minerals (quartz, bentonite, kaolin and montmorillonite), over a range of pH and report the effect this has on the zeta potential of the clays. The influence of humic acid on the adsorption of europium to these minerals is also reported, ...

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Water samples have been extracted from inside (from standpipes) and from outside (from boreholes) of the trenches at the low level radioactive waste disposal site at Drigg in Cumbria, UK. The samples were taken anaerobically from between 8.5 and 10.0 m below the surface using a submersible pump at low flow rates to ensure that the waters in the standpipes and boreholes were maintained at constant levels. To ensure representative samples, the Eh, pH. conductivity, temperature, iron and dissolved oxygen concentrations of the waters were taken during initial purging and during sampling. The gross tritium, gross non-tritium beta, gross alpha and gamma activities of each sample were determined using suitable sample preparation and counting techniques. Samples were then anaerobically, sequentially filtered through 12 microm, 1 microm, 30 kDa and 500 Da filter membranes. The filtrates were analysed for gross alpha, gross non-tritium beta and gamma activities. SEM and STEM analyses were used to determine the colloid population. An energy dispersive analyser on the SEM was used to determine the major elements present in the colloids. UV-visible spectrophotometry, fluorescence spectrophotometry and high performance size exclusion liquid chromatography were used to analyse the waters before and after treatment with ion exchange materials to determine whether natural organic matter was present in the waters. Results showed that two major types of colloids (iron containing colloids and silicon containing colloids) were present in the waters. There were also a small number of other colloids that contain, as major elements, aluminium, calcium and chromium. Organic colloids were also present. The majority of the radioactivity in the waters was due to tritium. Waters taken from outside the trenches contained low levels of non-tritium beta activities and alpha activities which were lower than the minimum detectable amount. Waters taken from the trenches contained non-tritium beta activities and low levels of alpha emitters. Filtration of the trench waters showed that some of the alpha activity was retained by the 30 kDa and 500 Da membranes suggesting that this activity was associated with small colloids. Radioactivity was not found to be associated with colloids present in the waters taken from outside the trenches. Possible reasons for this observation could be that radionuclide bearing colloids have not yet reached the far-field or that the radionuclide concentration is diluted to below the minimum detectable amount. After concentrating two of the samples by factors of x20 and x 16 respectively, 2.4+/-0.1 and 0.6+/-0.1 Bq dm(-3) of 137Cs were measured.