In Laboratory, on Site, in Situ Sampling and Characterization of Grimsel Colloids - Phase I

Summary

The characterisation of Grimsel colloids has been carried out after sampling the natural colloids by pulsed diaultrafiltration in situ/on site i.e. in the NAGRA Felslabor Grirasel or in laboratory i.e. EIR Wurenlingen after transfer of water samples. In the first phase, colloid speciation, size distribution and concentration are reported from SEM/EDX investigations on dry flat ultrafiltration membranes, in addition colloid species are estimated by running a thermodynamic code. The parameters from the water analytical survey have been very constant (e.g. T=285K, pH=9.7) for more than one year. Calculation of saturation indices indicates that from the most concentrated elements i.e. Ca, Si, C, F, S; quartz, calcite and fluorite should precipitate in “in situ” conditions (i.e. log PCO2 =-5.5), while in laboratory (atmospheric conditions pH=8) calcite is dissolved. In laboratory and on site/in situ sampling by pulsed diaultrafiltration yields the production of microsamples of colloids investigated by SEM/EDX. The colloid concentration is 2-5 10E10 particles per litre, the size distribution reported from 40 to 1000 nm is a continuous decay starting from small size e.g. 40-80 nm (120 items per 200 umE2) and decreasing for the larger e.g. 720-760 nm (1 item per 200 umE2). EDX analysis indicates that Si is present as colloidal material, however, its small concentration yields the conclusion that composite colloids including silica have been generated e.g. with part of the 350ppb DOC.