Effects of Pregnant Leach Solution Temperature on the Permeability of Gravelly Drainage Layer of Heap Leaching Structures

In copper heap leaching structures, the ore is leached by an acidic solution. After dissolving the oremineral, the heap is drained off in the acidic solution using a drainage system (consisting of a networkof perforated polyethylene pipes and gravelly drainage layers) and is, then, transferred to the leachingplant for copper extraction where the copper is extracted and the remaining solution is dripped overthe ore heap for re-leaching. In this process, the reaction between the acidic solution and copper oxideore is exothermal and the pregnant leach solution (PLS), which is drained off the leaching heap, has ahigher temperature than the dripped acidic solution. The PLS temperature variations cause somechanges in the viscosity and density which affect the gravelly drainage layer's permeability. In thisresearch, a special permeability measuring system was devised for determining the effects of the PLStemperature variations on the permeability coefficient of the gravelly drainage layer of heap leachingstructures. The system, consisting of a thermal acid resistant element and a thermocouple, controls thePLS temperature, which helps measure the permeability coefficient of the gravelly drainage layer. ThePLS and gravelly drainage layer of Sarcheshmeh copper mine heap leaching structure No. 1 were usedin this study. The permeability coefficient of the gravelly soil was measured against the PLS and purewater at temperatures varying between 3°C to 60°C. Also, the viscosity and density of the PLS andpure water were measured at these temperatures and, using existing theoretical relations, thepermeability coefficient of the gravel was computed. A comparison between the experimental andtheoretical results revealed a good conformity between the two sets of results. Finally, a case (Taftheap leaching structure, Yazd, Iran) was studied and its gravelly drainage layer was designed based onthe results of the present research.

Keywords:

heap leaching structure , gravelly drainage layer , permeability coefficient , pregnant leach solution , temperature , viscosity