Economy of the Process

The lixivaition on heap leaching, being a simple operation which does not require of a fine grinder of the material and with minor energetic necessities and of water, it has economical advantages concerning the methods by agitation. In this manner, thanks to its low costs of capital and of operation, it is possible to commercially process resources of marginal law and more limited reserves to those permissible by conventional procedures. Some estimates show that for the process of lixiviation in heap leaching, adsorption with activated carbon and electro-obtaining, the costs of the capital are situated approximately between a 20% and 30% of those of a plant by agitation, between a 30% and 65% (2, 23). The ample fluctuation of these last mentioned is explained by the diverse sizes and conditions of operation which is capable of carrying the lixiviation in heap leaching, which impossibilitates a more precise general estimation.

The information available above these real costs is relatively antique, besides being scarce and dispersed. In some plants in activity, the State of nevada, the direct costs of lixiviation in heap leaching, adsorption with activated carbon and compiled electro-obtaining for operations which go from 220,000 up to2’000,000 TC of mineral per year, they vary between US$ 1.70 (1979), and US$ 5.32 (1980) by processed TC, including in some cases crushing up to – ½” or – ¾” (14); these prices, actualized in the mid 1983 according to the index CE (j) and converted, would be of the order of US$ 2.50 and US$ 7.10 by TM, respectively. In a plant of New Mexico (8) with annual capacity for 34,000 TC, the total cost of operation with this same process, including the mining labors too, crushing to – ¼” and fixed payment of the machinery, was calculated in US$ 10.41/TC (1978), some US$ 16.60 actual by TM; the capital invested in this operation was of US$ 600,000 in the same year.older data which was proportioned in 1974 by Pizarro (21) and Mc Quinston (19) allow to calculate an actualized cost of operation of US$ 2.54/TM of mineral in the lixiviation in heap leaching of 9,000 TM monthly practiced initially in Carlin Gold Mining Co.. Nevada. Due mainly to the minimal consumption of reactives and to the use of the infrastructure of crushing and of precipitation with zinc in the plant of agitation, this value appears as being too low, due to the fact that it is comparable to the one of the present operation of 200,000 TM per year, US$ 2.50/TM actualized (14), which uses adsorption of activated carbon and electro-obtaining.