Ores in a mine operation or port facility are required to be stacked in stockyards prior to handling or shipping since the arrival time is usually much shorter compared to their consumption time. Buffer storage and homogenization piles are also necessary to take care of disruptions and/ or variability of the operation. These stockpiles typically range from a 7- to 45-day capacity. An important disadvantage is moisture infiltration into the stockpile as a result of long lasting and continuous rainfall. This affects flowability of the ore and, in some cases, slope stability. Ores having high moisture content can present significant problems in process steps downstream of the stockpile, for instance: liquefaction and flooding, MC (Moisture Content) above TML (Transportable Moisture Limit)
Moisture seepage and drainage
Drainage is the unsaturated flow of water through a mass of solid particles stored at rest in a stockpile. As a result of gravity, water flows downward through the pile. If the pile base is impervious or nearly so, water accumulates at the bottom, the bulk material cannot contain any more liquid, and it becomes saturated. When fully saturated, seepage occurs through the sides of the pile near the toe, but the water level can rise inside the pile affecting its stability.
The water permeability of a partially-saturated porous material is a function of capillary pressure Pc. Functional relationships between saturation, capillary pressure and permeability must therefore be determined via laboratory tests to model unsaturated flow – saturated hydraulic conductivity and water retention and permeability properties.
Jenike & Johanson conducts effective moisture drainage analysis for stockpiles following our typical analysis approach:
- Material testing to determine intrinsic hydraulic properties of the ore and other important physical properties
- Computational analysis of drainage in stockpile to determine:
- Moisture profile in stockpile as a function of storage time
- Analysis of different stockpile configurations and its effect on drainage
- Water infiltration due to rainfall
- Effectiveness of subsurface drainage systems
- Computational analysis to determine moisture evaporation from stockpile surface coupled with drainage, when important. e.g, dusting
- Computational model validation when necessary
- Drainage pipes
- Wind tunnel and surface evaporation