Leaching

	NATIONAL TECHNICAL UNIVERSITY OF ATHENS SCHOOL OF MINING AND METALLURGICAL ENGINEERING Section of Metallurgy and Materials Technology *Laboratory of Metallurgy*
	HYDROMETALLURGY UNIT

Laboratory and pilot-scale tests are almost invariably required before metallurgical development can proceed. Difficulties with sampling, as well as with classical chemical and physical scale-ups are normally anticipated and relatively well-understood, but more subjective factors also come into play, including misunderstandings of the operating scheme chosen.

The leaching section is equipped to process different kind ores. Firstly, the ore is crushed and grinded in ball mill. The fine product is delivered to leaching lab, where the quartering, sieve analysis and leaching operation is carried out by different methods depending on mineralogy and specification of the ore, to extract valuable elements.

Agitation leaching is a process where the soil is slurried with the extraction fluid for a period of time. When equilibrium between the metal on the soils surface and the metal contained by the solution is approached, the solubilization of the metal in the soil is slowed, and the extraction is considered to be complete.

At equilibrium, additional metal will not be extracted from the soils surface unless the soil is subjected to fresh extraction solution. Once the process is considered to be at equilibrium, the soil is separated from the extraction fluid using sedimentation, thickening, or clarification. The extraction process may be continued in a separate extraction vat with clean extraction solution to enhance extraction. An agitation vat coupled with a solid-liquid separation vessel (sedimentation or clarification) is considered to be a single stage

The purpose of a column leach test is not so much to duplicate in a laboratory test the results that can be expected from a commercial heap leaching operation but to collect kinetic information on the ore being evaluated so that scale-up equations can be validated which will allow the projection of the commercial heap leach operation's performance under different operating scenarios.

These different operating scenarios include variations in the particle size of the ore to be leached, different lift heights, different irrigation rates, and different leachate concentrations. When the laboratory tests are designed with this objective in mind the number of tests required are fewer than if the tests were designed to directly simulate the commercial heap's performance because scale-up equations can be used to calculate the commercial heap's performance eliminating the need for the more costly laboratory test.

Generally it is necessary to run no more than three column leach tests on each ore type in a deposit to validate a kinetic model for heap leaching of the ore being evaluated. Evaluation of the ore can then be directed at examining the different ore types within the deposit rather than evaluating the response of each ore type to changes in each of the operating parameters

Leaching of ore in a static or semi-static condition either by gravity flow downward through an open pile or by flooding a confined ore pile is, rather broadly termed heap leaching. Heap leaching is useful for the treatment of low-grade dumps, and for small ore bodies located at a considerable distance from conventional processing facilities.