Water recovery study for Pampa Pabellon tailings impoundment, Collahuasi, Chile

摘要

A water recovery study has been completed for the Pampa de Pabellon tailings impoundment at Minera Dona Ines de Collahuasi, in the high Andes of northeastern Chile. The main objective of this study was to develop a water balance model, which could be used for prediction of future water losses under different tailings management scenarios. The study included (ⅰ) a detailed field investigation to determine in-situ properties of the Collahuasi tailings and (ⅱ) calibration of an updated water balance model using water recovery data collected during the period July 2002 to February 2003. The field investigation indicated that the Collahuasi tailings are relatively fine-grained (55% average fines content) and do not show significant hydraulic segregation during placement. The initial void ratio of the Collahuasi tailings is about e_0 = 1.3 (±0.1) and the final void ratio (after full consolidation) is approximately e_f = 0.75 (±0.05). The Collahuasi tailings typically maintain a high degree of saturation in the order of 80-90% with significant desaturation (down to 50%) only occurring in the near-surface layers (maximum ～ 0.3 m) during the warm summer months. A simplified water recovery model was used to determine water losses as well as recoverable water quantities occurring from the active ("flooded") beaches during active discharge. With this approach the losses, which occur from inactive beaches (where no free water is available for recovery) need not be modeled (see Wels & Robertson, 2003). The total water losses during the 8-months monitoring period averaged 41,835m~3/day or 70% of all process water discharged into the impoundment. This represents an average "make-up" water requirement of 0.605 m~3/t of ore processed. The average water recovery was 17,143m~3/day (or 28.5% of all process water discharged with the tailings). The updated model was calibrated using the observed water losses and recovery rates. According to the model, entrainment losses represent the largest proportion of all losses (on average 74.7% of total water losses). Evaporation losses from active beaches represent the second largest component (on average 15.7% of total water losses). Water losses due to pond evaporation and rewetting represent a much smaller proportion of total water losses (5.4% and 4.2%, respectively). The modeling results suggest that there is only limited potential for improving water recovery rates due to the high initial entrainment losses of these fine-grained tailings.