Ion Exchange to extract wealth from mine waters
For the IMWA 2016 conference we put together a paper that provides an overview of the potential for recovery of value from contaminated mine waters and waste streams. It discusses various metal ions commonly found in acid mine drainage and other mine waters (mainly Co, Ni, Zn, and U) and evaluates at what concentration they become attractive to investigate for recovery using ion-exchange technology. Waste streams are often treated to achieve compliance with environmental legislation before discharge, but recovery of valuable materials from acid discharge waters can result in economic benefits as well; in certain cases, the recovery of such metals can actually cover the cost of capital and operation and provide an additional revenue stream to the mine.
The economics depend on the nature of the valuable metals, their concentrations, and volumes required for treatment. Ion exchange is well established in mining and metallurgical processing as a primary purification technology, treating process streams in which the levels of valuable metals are relatively high. To recover these same metals from surface runoff, tailings, contaminated ground water or mine decant waters; they must be present at a certain level before it becomes worthwhile to fully investigate options for their recovery.
We reviewed a number of valuable metals that are likely to be found in mine waters and, based on the capital and running costs, determined the capital payback period for varying contamination levels. Technical issues were discussed and their effect on the economics explored. Using the model developed, it is possible to show early on in a feasibility assessment whether there is economic benefit to the processing of waste water of a given composition from a mining operation. The specific case studies that informed the model are discussed.