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Delft University of Technology (2014)

Designing a treatment system for the underground effluent at Loulo Gold mine (Mali, West Africa)

Diarra, H.B.

Titre : Designing a treatment system for the underground effluent at Loulo Gold mine (Mali, West Africa)

Auteur : Diarra, H.B.

Université de soutenance : Delft University of Technology (TU Delft)

Grade : Master Thesis 2014

Résumé
Water monitoring and analysis results have shown that the current underground water discharge into the adjacent Faleme river is substandard, indicating that the existing settling ponds are not suitable to bring the effluent into compliance with the Malian discharge limits prior to discharge. Since the identification of the problem, the mine has undertaken a number of studies to find the best possible solution to the discharge quality issue. This study puts all the different studies into perspectives and uses the available data to assess the impact of the effluent on the receiving environment and to develop a constructed wetland which is believed to be a more adequate treatment solution than the existing settling ponds. The study is divided into three main parts. The first part assesses the impact of the mine effluent on the Faleme river by characterizing the discharge water quality since mining commenced (i.e. from 2010) up to date ; then by evaluating the current ecological status of the Faleme river and finally by attempting to draw conclusions as to the potential sources of the issues identified in the Faleme with the mine discharge quality and other activities in and along the river (e.g. artisanal mining activities, agriculture, and others). Even though the quality of the mine discharge is substandard, the current issues associated with the Faleme river ecosystem are caused by the artisanal mining activities and aggregate mining by the clandestine sand miners. The second part of the report deals with the designs of a thickening system to remove the solids from the effluent prior to entering a constructed wetland which design also is proposed to remove the nitrate from the effluent. A 10 m diameter thickener was designed assuming a 160m3/h maximum flow rate, a 5%m solid concentration in the feed and a 2m/h critical rise to achieve a settling rate of 20 t0 30 m/h. the overflow of the thickener will enter a subsurface horizontal flow type wetland with an inlet, macrophyte zone and an outlet. Due to the complex nature of the processes in the wetland and the difficulty in modelling it, a number of design options was proposed to be trial tested. Since the final wetland should be at least 100 m wide and 300m long, the proposed pilot scale size is 10m x 30m. Cyperus papyrus and Typha will be tested as the plants to be used. If the uncertainties around the design of the wetland can be reduced and a model developed through the pilot scale test, this can be used in other mines in Mali and even in other countries with similar climatic conditions and similar problems.

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