Field studies of the leachability of aged brown coal ash

The environmental management of ash produced from the brown coal Fewer stat ions of the Latrobe Valley region of Australia has been studied. Current pr actice consists of slurrying fly and bottom ash, a short distance to an ash disposal pond. However, storage facilities are approaching capacity and al ternative ash management strategies are required in the near future. Initia lly, the ash produced within the power stations is known to possess a large soluble mass, which can leach rapidly to generate a saline leachate with m inor trace metal content. After slurrying and deposition within the ash pon d, it has been demonstrated that the soluble mass is significantly lower an d the ash can be considered as aged or "leached" ash - a more benign waste that meets the criteria for fill material. In order to assess the lung-term behaviour of the leached ash and its suitability for co-disposal in engine ered sites within overburden dumps, two field cells were constructed and mo nitored over a period of 1 year. Each cell was 5 X 5 m in area, 3-m deep an d HDPE lined with a coarse drainage layer and leachate collection pipe, The first cell only collected natural rainfall and was known as the Dry Cell. The second cell had an external tank of 5000 1 installed (200-mm rainfall e quivalent) and water was spray-irrigated regularly to simulate higher rainf all and accelerate the leaching process. The cumulative inflow and outflow for each cell has been calculated using a linear relationship and the leach ate quality was monitored over time. The results demonstrate that the ash b ehaves as an unsaturated porous material, with the effect of evaporation th rough the profile being dominant and controlling the production of leachate . The leachate quality was initially moderately saline in both cells, with the concentration dropping by nearly 95% in the Wet Cell by the end of the field study. The leachate chemistry has been analysed using the PHREEQC geo chemical model. The log activity plots of various species suggest the miner alogical controls on these species in leachate. The full results from this study are presented. (C) 2000 Elsevier Science B.V. All rights reserved.