Reactive Transport Modelling of the contaminant release from Uranium Tailings using PhreeqC/Excel-coupIing

摘要

Between the early 1950's and 1990, uranium mining and processing produced large quantities of radioactive mill tailings in Eastern Germany. Presently, the tailings sites are remediated according to the strategy of dry in-situ stabilization. Due to recontouring of the tailings, pore water is squeezed out resulting in a significant contaminant release. A multi-layer type soil cover will finally minimize the water infiltration, gas transport and seepage in the future.The release of contaminated seepage water into ground and surface waters cannot be completely avoided due to lack of base sealing. For planing and monitoring of the remediation works geochemical models are essential in order to evaluate the long-term development of the contaminant release and to forecast future challenges for the water management and treatment at the site. In fact, the geochemical conditions within the tailings are highly complex due to the history of processing and discharge regime which resulted in a large heterogeneity of hydraulic and geochemical properties within the tailings impoundments.This paper summarizes the current state of the development of a geochemical transport model in order to identify the geochemical processes responsible for the contaminant release in seepage water based on available lab-test data. For this purpose a 1-dimensional multi-component transport model was developed using the hydro-geochemical transport code PhreeqC and the spreadsheet program Microsoft Excel~R. The coupling was realized using a Microsoft COM (component object model) enabling the simple manipulation of the PhreeqC input via Visual Basic for Applications (VBA) macro. Two infiltrative column experiments with tailings material from the tailings management facility (TMF) Culmitzsch (Seelingstadt) were used to validate the model approach by computing the effluent water composition of the columns.