1. The Field of the Invention
The present invention relates to minerals processing. More particularly, the present invention relates to an improved method for distributing chemical reagents, bacteria, or bacterial nutrients into mineral ore. In particular, the present invention relates to a method of distributing reagents onto ore prior to heaping and heap processing thereof.
2. Background
Heap leaching is the leaching of crushed ore, mine strip waste material mill tailings or mine dump material that has been stacked onto an impervious drainage pad to prevent solution losses and pollution of ground waters. Interest in heap leaching, particularly heap and dump leaching has increased in recent years.
During the last two decades, the process of heap leaching of gold and silver has evolved into an efficient method of treating deposits once considered uneconomical. This process has also been used extensively throughout the world to leach oxide copper values from mine strip material from open pit mining of disseminated porphyry copper deposits. Additionally, producers of U.sup.308 have applied heap leach technology since the late 1950s for extracting uranium from sub run-of-mill grade ores.
Heap leach cyanidation of precious metal ores is a comparatively new development. The U.S. Bureau of Mines metallurgists in 1967 developed this method as a potential low-capital means for processing sedimentary ores containing submicron particles of gold occurring in northern Nevada, USA. Conventional operations well known to those skilled in the art and for purposes of brevity will not be described in detail herein. Such methods are described in: "Silver and Gold Recovery from Low-Grade Resources" by Gene McClelland and S. D. Hill, Mining Congress Journal, 1981, pages 17-23.
Various physical and chemical methods have been employed to increase the distribution of the leach solution as it passes through the heaped ore to minimize blinding and channeling. Channeling occurs when fine ore particles migrate and segregate to an area in the heap, blind off that area of the heap, and force the leach solution to "channel" around that area of the heap. Blinded areas in the heap and the channeling that it causes are undesirable because leaching solution makes no contact with a significant fraction of the heap that resides beneath the blinded area. The agglomeration of fine particles is said to prevent channeling of the leach solution and migration of the fine particles into the channels. U.S. Pat. No. 4,898,611 to Gross, U.S. Pat. No. 5,186,915 to Polizzotti, U.S. Pat. No. 5,472,675 to Polizzotti, et al., and U.S. Pat. No. 5,512,636 to Polizzotti, et al., illustrate the use of high molecular weight polymers and varying ratios of cement/lime for agglomeration of fine ore particles. However cement causes a buffering action which increases the detoxification/reclamation rinsing costs of the heap to return pH levels to original environmental levels. Additionally, the high molecular weight polymers present costly operational problems associated with high water addition requirements, conveyor mudding, and high equipment maintenance cost. U.S. Pat. No. 4,080,419 to Englemann teaches passing a reagent-carrying foam through the already heaped ore in order to leach minerals with decreased amounts of leach solution.
Various physical and chemical methods have been employed to increase the interaction of leach lixiviants or bacteria with heaped ore particles. Some prior art utilizes chemical polymers for agglomeration of ore particles and agglomeration of particles with bacteria. However, as with leaching operations, the polymers present costly operational problems associated with high chemical costs, high water addition requirements, and crusher and conveyor equipment mudding and freezing complications. Other prior art methods of agglomeration utilize cement, lime, and chemical polymers in varying combinations and ratios. However, cement slows down the resumption of pH levels of the heaped ore, back to required environmental levels.
What is needed in the art is a method of agglomerating ore particles without the problems of the prior art. What is also needed in the art is a method of agglomerating ore that does not interfere with biological activity during heap leach treatment. What is also needed in the art is a method of facilitating enhanced ore-lixiviant contact in heap leach treatment. What is also needed in the art is a method of agglomerating ore particles that increases the percolation rate during processing. What is also needed in the art is a method of agglomerating ore particles that improves reagent-ore, and/or bacteria-ore contact for a more efficient process. What is also needed in the art is a method of agglomerating ore particles that avoids the expense of decommissioning a heap that is known in the prior art.