A reactive transport model designed to predict the environmental footprint of an 'in-situ recovery' uranium exploitation.

Worldwide, most uranium production relies on the 'in situ recovery' (ISR) extraction technique. This consists of dissolving the ore using a leaching solution (acid or alkaline) directly within the deposit through a series of injection and extraction wells. Due to the nature of the injected ISR solutions, the water quality of the aquifer could be affected. Reactive transport modeling is a powerful tool for predicting fluid flow and geochemical reactions in ISR reservoirs. In this study we present a coupled 3D environmental geochemical model (EGM) (based on the HYTEC reactive transport software), capable of predicting the physico-chemical conditions in an acid-leaching ISR uranium mine and its environmental footprint on the aquifer in the years following the closure of the production block. The model was validated at the KATCO mine (Kazakhstan) on two different and independent production blocks, over 10 years after their closure. The model shows that incorporating two main geochemical processes, (1) cationic sorption on clay surfaces (smectite-beidellite) and (2) precipitation of gypsum (CaSO4.2H2O), successfully reproduces the measured well data (pH, acidity and SO4) over short- and long-term time scales. Clay surface sites remain mostly saturated in protons during the production phase. Simulations show that sorbed protons on the clay surfaces maintains the acid conditions for a longer period of time. The environmental impact model was also compared to a pre-existing model specifically developed for production simulation purposes: differences are observed as expected for the uranium production, but also for the impact distances, due to differences in the considered reactive mineralogical paragenesis. Thus, the choice of geochemical model should be made with due regard for the desired objectives. This work will assist the mine operator by providing a tool capable of assessing both the short- and long-term environmental footprints of the ISR production operation conditions and of identifying the best remediation strategy.

Reactive transport modelling to investigate multi-scale waste rock weathering processes.

Prediction of drainage quantity and quality is critical to reduce the environmental risks associated with weathering mine waste rock. Reactive transport models can be effective tools to understand and disentangle the processes underlying waste-rock weathering and drainage, but their validity and applicability can be impaired by poor parametrization and the non-uniqueness conundrum. Here, a process-based multicomponent reactive transport model is presented to interpret and quantify the processes affecting drainage quantity and quality from 15 waste- rock experiments from the Antamina mine, Peru. The deployed uniform flow formulation and consistent set of geochemical rate equations could be calibrated almost exclusively with measured bulk waste-rock properties in experiments ranging from 2 kg to 6500 tons in size. The quantitative agreement between simulated dynamics and the observed drainage records, for systems with a variety of rock lithologies and over a wide range of pH, supports the proposed selection of processes. The controls of important physicochemical processes and feedbacks such as secondary mineral precipitation, surface passivation, oxygen limitations, were confirmed through sensitivity analyses. Our work shows that reactive transport models with a consistent formulation and evidence-based parametrization can be used to explain waste-rock drainage dynamics across laboratory to field scales.

[A model for intracranial vasospasm in subarachnoid hemorrhage]. / Etude d'un modèle de vasospasme intra-crânien dans les hémorragies méningées expérimentales.

Cerebral vasospasm (V.S.P.) is a major complication of subarachnoid hemorrhage. In order to investigate this cerebral vasospasm, an intracisternal injection of autologous blood and topical application around the internal carotid artery was performed in the dog model. Thirty dogs were divided into five groups and a cerebral angiography was performed on D0, D2, D5, D7 and D9. In comparison with the control group (group 1), the angiography in group 2 (12 dogs) systematically exhibited severe V.S.P. In group 3 (intracisternal injection of venous blood: 5 dogs), the angiography exhibited no vasospasm at all. In group 4, a left frontoparietal flap was opened, allowing us to deposit blood around the carotid bifurcation. In these cases, a severe narrowing of cortical arteries was demonstrated. In group 5 (intracisternal injection of heparinated blood), no vasospasm was observed. These findings suggest that the vasospasm involves the circle of Willis' as well as the cortical arteries.