Monitoring and operation of internal drainage systems within bauxite residue deposits

Alcoa has been operating tailings dams for the past thirty years at four locations within the southwest of Western Australia. During this period a number of different methods of liquor recovery have been used to maximise the operational and final tailings densities, to maximise soda recovery from the deposits and to minimise seepage potential through the base seals. Drainage systems employed to date include eductors, windmills and perforated pipe underdrainage. Significant data has been collected over the period which will be used to compare the effectiveness of the various systems against design expectations. Monitoring data collected includes flow measurements via magnetic flow meters, sparling meters, weirs and flumes; in situ tailings densities via in situ sampling and mass balance; internal water levels via standpipes, pneumatic piezometers and vibrating wire piezometers; and soda recovery via sampling of recovered liquor concentrations and in situ liquor concentrations. This paper will comment on Alcoa's experience in the use of internal drainage systems, their effectiveness and efficiency with respect to time.