MINERALOGICAL AUDITS OF GRINDING AND FLOTATION CIRCUITS WITH THE QemSCAN MINERAL ANALYZER

W. Baum, J. Marsden, J. Vanderbeek (Phelps Dodge Mining Company, USA) and G. Wilkie (CSIRO, AUSTRALIA)

E-mail for Correspondence: wbaum@phelpsdodge.com

IntroductionOptimization of grinding and flotation plants has traditionally been hampered by the lack of quantitative mineralogical data. With the availability of the QemSCAN automated mineral analyzer, concentrator operations can now be subjected to size-by-size mineralogical analyses. QemSCAN capabilities can assess every metallurgically pertinent mineralogical parameter on a statistically reliable basis. The QemSCAN results are material-balanced against conventional chemical analyses.

The QemSCAN mineral analyzer consists of a modern LEO SEM combined with software and hardware developed by CSIRO to perform fully automatic mineralogical analyses. The QemSCAN can analyze all mineralogical features related to rock composition, metals deportment, comminution, flotation, hydro- and pyrometallurgy. For concentrator audits, it has specific capabilities for analysis of modal composition, liberation/locking, particle size and metals deportment. Currently, there are 15 QemSCANs operating worldwide. Phelps Dodge installed the first two commercial QemSCAN operations in the United States and has been dedicating them to its copper mining operations.

Mineralogical Plant AuditsThe major objectives of mineralogical audits are to (a) establish a size-by-size mineralogical profile of all pertinent process streams, (b) identify mineralogical features critically important to plant operation and (c) provide recommendations for circuit optimization.

Also, an integral part of successful concentrator optimization depends on better quantification of the process mineralogical characteristics of the plant's ore types. Therefore, a QemSCAN-based ore characterization program constitutes a vital part of concentrator performance and, ultimately, an essential tool for lowering mining and metallurgical operating costs.

Ore Characteristics and Circuit PerformanceAs variances in mineralogical ore feed characteristics will impact the metallurgical treatment, base line analyses of all important ore types will be of paramount significance in assisting the conclusions and recommendations of the QemSCAN circuit audit. Therefore, any concentrator audit should include an analysis of the major ore types in order to monitor bulk modal mineralogy, sulfide particle size and liberation/locking characteristics. The presence and concentrations of clay minerals warrant close attention due to their profound impact on flotation.

QemSCAN Analysis of Grinding and Flotation CircuitsThis presentation will provide a condensed overview of a "QemSCAN Plant Audit" in copper concentrators. Such a QemSCAN analysis typically encompasses the following major steps:1. Plant sampling campaign.2. Concurrent sampling of all major ore types.3. Sample preparation for assays, bench-scale flotation tests and QemSCAN measurement.4. Assays and metallurgical balances.5. Bench-scale flotation tests on ore types.6. QemSCAN measurements of samples.7. QemSCAN data processing/interactive off-line analysis.

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Size Fraction

Chalcopyrite in Rougher Tailings

Liberated (90-100%)

Middling (30-90%)

Locked (0-30%)

Following the QemSCAN measurement of all size fractions, the acquired images are processed and the results collated for metallurgical interpretation. The QemSCAN work focused on the following mineralogical and metallurgical issues:a) Feed mineralogy.b) Chalcopyrite liberation in the feed.c) Copper recoveries to the concentrate.d) Copper losses to tailings.e) Specific attention is devoted to certain parts of the circuit such as the primary grinding cyclones, the rougher circuit

and the regrind circuit.The attached Figures 1 and 2 illustrate some of the typical information obtained from a QemSCAN audit. Figure 1 shows a 3 dimensional graph that quantifies the size-by-size loss of three different classes of chalcopyrite-bearing particles these being

Liberated particles that are composed of more than 90% chalcopyrite, Middlings that are composed of between 30% and 90% chalcopyrite, and Locked particles that are composed of less than 30% chalcopyrite.

Analysis of Figure 1 shows two clearly distinct populations of chalcopyrite particles lost out of the rougher tailings. Locked chalcopyrite particles account for over 50% of the losses to (and predominate in) the coarse +106 micrometer size fractions. Conversely, liberated particles represent a smaller loss, i.e. 39% of the chalcopyrite lost to tailings. Liberated chalcopyrite losses predominate in the fine –25 micrometer size fractions and represent the best target for improved copper recovery.

Figure 1: Size-by-size liberation of chalcopyrite in a porphyry copper rougher tailings stream

Figure 2 shows a size-by-size mineralogical view of a rougher concentrate stream before and after re-grinding. This quantitative assessment shows that the action of the regrind circuit is to:a) Enrich chalcopyrite into intermediate and fine fractionsb) Enrich gangue into fine and ultra-fine size fractionsc) Selectively re-grind liberated pyrite into fine and ultra-fine size fractions.

Figure 2: Size-by-size mineral analysis of re-grind stream.

In addition to mineral abundances and textural information, routine QemSCAN analyses also quantify elemental abundances based upon the measured portion of each mineral and their chemical composition. These calculated QemSCAN assays are then compared with independently derived chemical assays (i.e. assay reconciliation) to assess the quality of the QemSCAN information. Thus, the objective of the QemSCAN audit is to obtain a statistically reliable mineralogical and metallurgical benchmark of the concentrator while it was operating within normal metallurgical parameters. Case studies from two copper concentrators will illustrate the use of the QemSCAN technology and will document that QemSCAN-based Process Mineralogy is an essential tool for a) Predictive ore characterization.b) Flow sheet development.c) Plant surveying.It provides the framework for matching the ore (Nature) with the desired process (Nurture).

Rougher Concentrate-Size by size mineralogy

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Gypsum

Calcite/Dolomite

Chlorite

Biotite

Muscovite

Smectite/Kaolinite

Plagioclase

K-feldspar

Quartz

Molybdenite

Pyrite

Chalcopyrite

Regrind Cyclone O/F - Size by size mineralogy

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Gypsum

Calcite/Dolomite

Chlorite

Biotite

Muscovite

Smectite/Kaolinite

Plagioclase

K-feldspar

Quartz

Molybdenite

Pyrite

Chalcopyrite

Re-grind