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Performance evaluation of cover systems constructed of Paste Rock material Miskolczi, Jozsef

Abstract

Soil covers are accepted by the mining industry as being a possible solution for the long-term environmental problems associated with Acid Rock Drainage during operations as well as post-mining. But given the wide differences between geographical and climatic conditions in which mines operate, it is impossible to create a universally usable recipe. To overcome the challenges posed by site specific temperature and precipitation regimes several types of covers were developed. The cover discussed in the present paper is of the "barrier covers" type. Following the example of success of a soil cover constructed of glacial till at Equity Silver mine in BC (Weeks and Wilson 2005, 1615-1630) the decision was made to simulate the composition of the glacial till by blending together waste rock, tailings and crushed slag. The mixture is referred to as Paste Rock. The initial laboratory testing was conducted at UBC and reported by (Fines and Wilson, 2002) while the filed testing was devised and constructed at Inco's Central Tailings Facility in Copper Cliff, Ontario. The field scale experiment is described by the current thesis. A five-pad lysimeter was constructed in 2004 in the R2 area of the Central Tailings Facility in Copper Cliff, ON and the cells were filled with tailings collected on site. Four of the cells were subsequently covered with covers constructed of Paste Rock material according to four different recipes determined during lab testing. One cell was filled up with tailings only and used as control. The scope of this phase of the experiment was the installation of field instruments and subsequent data collection and data analysis. Precipitation, infiltration, run-off, and net solar radiation data was collected between the beginning of April and mid-November 2006, over a period of 227 days. The conclusion of the data analysis is that Paste Rock covers are effectively reducing infiltration into the underlying tailings while maintaining low values of matric suction, and reducing oxygen ingress to zero. A threefold decrease in the infiltration volumes was observed in the case of the uncompacted covers, whereas the compacted covers reduced infiltration by as much as two orders of magnitude.

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