Leaching Practice

A few examples of leaching practice are presented with die aim of illustrating types of leaching processes rather than an extensive treatise of current practice. The general outline of ore types presented earlier will he followed. 

Channeling. Channeling of each liquor occurs as a result of compaction and salt precipitation. Fluid flow down channels essentially bypasses regions of the dump. It is enhanced if solution application is by surface ponding. 

Seep or Blowout. Compacted zones may cause entrapment of solutions, resulting in the formation of a perched water table within the dump. The buildup of hydrostatic pressure can cause surface seepage and even expulsion of solid material from the dump wall, 

Strat katkm. During the dumping of waste rock, the coarse material travels further down the slope or the dump than the fine material, causing stratification. Without appropriate ripping, stratification may affect the flow pattern within the dump. 

FIGURE 9.2-1 Cross section of copper leach dump illustrating physical and hydrological features. (Reproduced from Whiting.2) 

Aeration. Aeration is best nearthe face of the dump, providing optimal conditions of temperature and bacterial activiQr. Aeratkm by convection throu the dump is an essential part of the leaching mechanism. In r ions of high oxidation potential, iron is oxidized by bacterial activi to the ferric state resulting in the precipitatimi of ferric oxides and Jarosites. 

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Modem heap leaching practice has also made possible the treatment of extremely lean (ca 1 g/1) gold ores, which had been considered uneconomic... 

The leaching and precipitation of copper at Rio Tinto in Spain this century is described by Taylor and Whelan (Tl) and an extensive report on the present-day technology of copper leaching practices in the western United States is discussed by Sheffer and Evans (SIO). Modified practices have been successfully used throughout the world both in low- (SlO) and high-rainfall areas (B7). 

R. Pizarm, J. D. McBeth. and G. M. Potter, Heap Leaching Practice at the Carlin Gold Mining... 

M. B. Moiman, J. D. Miller, J. B. Hiskey, and A. R. Hendricksz, in Comparative of Process Alternatives for Gold Recovery from Cyanide Leach Solutions, Au and Ag Heap and Dump Leaching Practice (J. B. Hiskey, ed.), AIME, 1984, p. 93. 

Pinkney, E. T. A review of uranium leaching practice in South Africa, Symposium Uranium in South Africa. The Associated Sdentific Technical Societies of South Africa (1957). 

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