Understanding and Managing the Processes to Reduce Long-Term Environmental Liabilities
Abstract
At the present time, heap leaching is widely used as a part of normal copper recovery operations. The usual way to close an operation is to turn off the irrigation, wait until draining stops, and rehabilitate the dump. Tails go to a reservoir. It is supposed that the reservoir will remain chemically stable, and it should be so, but it depends on the way the closing operation was done.
In this paper, it is shown that when the lixiviation loop, defined by the transport of solution among Heap - PLS pond - SX plant - EW - Raffinate pond – Heap, has a high concentration of metals such as aluminium, magnesium and iron, there exists a high probability that their sulphate salts crystallize and stay in the tails reservoir.
Chemically, sulphate salts in contact with water and under special but natural conditions, can become sulphuric acid. For this reason leaving metal sulphate salts in dumps can create an environmental risk and from this, an environmental liability.
The paper explains how the metals appear in the heap leaching loop. The role of sulphuric acid reactions and the ionic shape of those reactions are also described. A detailed description of how the heap crystallization occurs, based on solid – liquid acid aqueous phase diagrams, developed specially for the analysis of this issue, is provided and their use is explained. An estimate of the magnitude of the crystallization event is provided and it is shown how this issue is not partial, and leaching operators should be aware of this phenomenon in order to avoid the creation of an enormous environmental liability.
Finally, a possible solution to the problem is introduced and some practical applications are suggested.
Author
S. Rivera, SKMMinmetal, Chile
A. Ramirez, SKMMinmetal, Chile
P. Pinto, SKMMinmetal, Chile
J. Rosales, SKMMinmetal, Chile
C. Gonzalez, SKMMinmetal, Chile