(4)Leaching of coarse caliche ore

摘要

Heap leaching of caliche is carried out using particles of different sizes,from fine material up to particles with several decimeters. Lab-scaleexperiments are usually performed using small particles, but due to the factthat particle size is a critical variable in heap leaching, experiments withlarger particles were carried out in a transparent column with a square base.The empty space was filled with small glass-stones and the column wasirrigated initially with an average rate of 0.004 m3/m2/h, which was reducedto half after a while. Outlet concentrations for several ions were determined.The maximum values were lower than those observed for leachingexperiments using small particles. However, the concentrations weremaintained high during longer times.For determining if liquid flow takes place through the caliche or only onthe particle surface or as a combination of both, prior to loading the calichein the column, some stones were cut to obtain a plane face that was putagainst one of the column walls to observe the liquid flow in the stone. Theupper border was sealed to avoid liquid flow between the stone and thewall. The observations showed that the liquid is introduced into the stoneby capillary forces, but no flow is observed through the caliche stone.Additional experiments were performed to physically characterize thecaliche, which showed that capillary forces are large, but that thepermeability is very small. This implies that flow through caliche stoneswould be very small.