Abstract
Separation of target elements or minerals from their host rock or ore is essential to successful mining operation. The inevitable loss of a portion of the desired material that accompanies each step in the extraction process must be documented to develop the operational protocol. Superposition of the characteristic X-ray fluorescence spectra of head (crushed rock ore particles, pre-processing) and tail (post-processing particles) samples provides a direct visual comparison of relative peak sizes, and thereby the relative concentrations, of elements of interest. If the head and tail peaks are identical, none of the element was recovered in the extraction process. At the other extreme if the tail peak “flat lines”, i.e., there is no peak, there was 100% recovery of that element. Standardless visual comparison is valid if the same mass of identical starting material is incorporated into the head and tail sample analysis pucks, and XRF analytical conditions are identical. The considerable time and expense of acquiring and calibrating the standards associated with XRF analysis of 75 or more elements are avoided, a significant advantage during initial broad screening of an experimental extraction procedure. Full quantitation by XRF or an alternate technique can proceed at a later project stage, if desired. The approach retains and presents all features of the original data, thus eliminating questions about data quality, standards and their calibration, and data manipulation in processing from raw counts to concentrations in printout tables. This form of display is ideal for both the mining professional and such less technical groups as corporate staff, investors, regulators, and the public. Examples presented herein are for heap leaching; the protocol can be applied as well to any of the other traditional ore processing and beneficiation procedures, e.g., gravity concentration, magnetic and electrical separation, froth flotation, and ore sorting.
Highlights
The mining process involves a number of steps that route the raw material of economic interest from the ground to a concentrated or purified target element or compound (e.g., Li2CO3)
Separation of target elements or minerals from their host rock or ore is essential to successful mining operation
Examples presented are for heap leaching; the protocol can be applied as well to any of the other traditional ore processing and beneficiation procedures, e.g., gravity concentration, magnetic and electrical separation, froth flotation, and ore sorting
Summary
The mining process involves a number of steps that route the raw material of economic interest from the ground to a concentrated or purified target element (e.g., gold or silver metal) or compound (e.g., Li2CO3). For low-grade, high-volume open pit mining operations, e.g., copper porphyry or Carlin-type gold deposits, heap leaching preferentially releases the target material from a stack of finely crushed base rock via irrigation with an appropriate chemical solution [8]-[13] To design such a process, extensive initial bench-scale testing is required to determine, from an economic standpoint, the ideal combination of grain size, solvent, solvent-rock volume ratio, reaction time, evaporation potential, etc. A significant advantage of the XRF over our laboratory’s high resolution magnetic sector ICP-MS was no requirement to dissolve each sample, a tedious and time-consuming multi-step procedure in a silicate rock such as our rhyolite Dissolution of such resistate minerals as the zircon (ZrSiO4) found in the rhyolite presented an additional challenge. Because the same mass of material is incorporated into the head and tail pucks, and analytical conditions are identical, such direct comparison proves valid
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