Moisture absorption rates via capillary suction within packed beds-The effect of material and fluid properties with implications for heap leaching operations

Preferential flow has been identified as a key cause for failure to meet optimal metal recovery rates in dripirrigated leaching packed beds. In such systems, the lateral spread of solution is predominantly dependent on the strength of capillary forces within the bed. Capillary tests using the upward infiltration method were used to examine the effect of particle size distribution, porosity, wettability as well as the fluid viscosity on moisture absorption via capillary action. Tests were conducted on packed beds of different representative materials with unique physical properties: glass shards (irregularly shaped, non-porous), greywacke (irregularly shaped, porous, highly wettable) and malachite ore (irregularly shaped, highly porous, low wettability). Five size fractions were tested; 0.1-0.5 mm, 0.5-1.0 mm, 1.0-2.0 mm and 2.0-2.8 mm, including an equal mass mix of the four fractions (0.1-2.8 mm). Glycerol was used to formulate solutions with viscosities ranging from 0.8 to 2.2 cP, typical of irrigant solutions. The results indicate that particle size distribution was the main factor influencing the strength of capillary forces. However, higher levels of particle wettability and internal porosity also led to increased capillary action. A greater proportion of small to large sized pores within the beds' void networks at lower size fractions and at high porosities were deemed responsible for these effects. Increasing fluid viscosity led to slower moisture absorption rates with longer absorption times due to the higher resistance to fluid flow. The results highlight the importance of the inclusion of fines (< 1 mm particles) as well as the beneficial role high degrees of particle porosity and wettability play in aiding fluid transport via capillary action.

Automated summary

Preferential flow is a key factor in the failure to achieve optimal metal recovery rates in drip-irrigated leaching packed beds. Capillary tests were conducted to investigate the impact of particle size distribution, porosity, wettability, and fluid viscosity on moisture absorption via capillary action. The results showed that particle size distribution had the greatest influence on the strength of capillary forces. Higher wettability and porosity also contributed to increased capillary action.