Atmosphere Interaction and Capillary Barrier in Filtered Tailings

Abstract

The filtered tailings technology consists in reducing the water content of tailings ahead of their final disposal and later storing them in stacks with no containment structures. Since the stability of the waste storage facility (WSF) partly relies on the increase of strength due to suction, the unsaturated condition should be always preserved. Therefore, limiting the water content by the time of burying the tailings under the next lifts of the stack and preventing the infiltration of rainfall water into the already buried tailings becomes essential. This paper presents two field column tests performed with the Casposo Mine tailings material. The initial desiccation process and the effects of a number of rainfall events at the actual mine site conditions were observed during a period of 14 months. The columns were 1 m high and the water content was monitored at five different depths. In one of the columns, a gravel layer made of crushed waste rock was intercalated between tailings layers, simulating the layered structure of the actual WSF. In this case, capillary barrier effect developed at the tailings layer-waste rock interphase. This effect is availed in the WSF design for preventing the infiltration of rain water into the lower layers, keeping it close to the deposit top surface for ease of evaporation and preserving the unsaturated condition of the deposit. The water storage capacity of the top tailings layer is evaluated, both analytically and experimentally, in order to study how likely would be the infiltration of water into the deep layers of the deposit.