Copper in Ore Analysis Using the FAST Flame Sample Automation System

One of the major challenges in the mining industry is finding the exact location for digging. One way to gain this knowledge is to map an area for preferred elements which is usually done by drilling exploratory holes in a particular pattern and then qualitatively collecting the ore from the individual drill holes and analyzing for the elements of interest.

Because this procedure requires drilling a large number of holes, a large quantity of samples are produced which have to be analyzed to establish where to dig. Hence, fast, precise and repeatable analyses are needed. This article describes the testing of copper ore samples collected from different drill patterns to address these needs.

Experimental Procedure

In this analysis, copper ore samples were prepared using a proprietary sample preparation process, which results in solutions comprising 10 to 15% acids with dissolved solid contents of up to 4000 mg/L.

PerkinElmer’s AAnalyst™ 400 Atomic Absorption (AA) spectrometer, working in flame mode, was then used to examine the digested samples. The spectrometer is integrated with PerkinElmer’s FAST Flame 2 sample automation accessory which includes dual peristaltic pumps, an SC-4 autosampler, and a 1 mL sample loop. Table 1 shows the operating conditions of the AAnalyst 400 spectrometer.

Table 1. AAnalyst 400 operating conditions for Cu

Parameter Value
Wavelength 216.51 nm
Slit 1.8/1.35 mm
Burner Head 10 cm titanium
Flame/Flow Rates Air (10.00 L/min) / Acetylene (2.50 L/min)
Lamp Cu Hollow Cathode Lamp (Part Number N3050121)
Lamp Current 15 mA
Background Correction Deuterium (D2)

With the help of the FAST Flame 2 accessory, in-line dilution, high sample throughput, and fast sample washout can be realized - all of which are essential when studying bulk amounts of samples. SU-1b Nickel-Copper-Cobalt Ore is a geological reference material which was utilized as a quality control check for tracking both the stability and precision of the analyses.

This material was analyzed once during the course of an analytical run that included calibration verification solutions, a calibration blank and standards, and digested copper ore samples. All measurements were done against external calibration curves containing a blank, 1, 6, 20, 30, and 40 mg/L Cu in 15% acid.

It was observed that all calibrations exhibit correlation coefficients of 0.999 or better. To verify that the calibration remained steady, an independent calibration verification solution of 30 mg/L Cu was run for each 12 ore samples, and calibrations were again made after every 60 samples.

Results and Discussion

In order to evaluate the method precision, the SU-1b reference material containing 1.185% copper was examined during the course of analytical runs. Following sample preparation, the Cu concentration being read in the reference material was 47.4 mg/L.

Figure 1. Copper recoveries in SU-1b from 16 runs over seven days, both with and without autodilution.

Figure 1 illustrates the Cu recoveries obtained in the SU-1b reference material from 16 independent runs performed over a period of one week, for diluted as well as undiluted samples.

It was found that most of the recoveries were within 10% of the certified value, thus demonstrating both day-to-day stability and accuracy of the methodology. Also, since there is agreement in the recoveries of the diluted and undiluted samples, the system’s autodilution capability is shown to be accurate.

The main benefits of the FAST Flame 2 accessory are in-line sample dilution and improved sample throughput when utilizing the autosampler for studying a large number of samples. In this analysis, the time from sample-to-sample was 28 seconds, which includes sample uptake, sample washout, and in-line dilution.

With this methodology, many more samples were analyzed within a specified time period in comparison to traditional sample uptake while utilizing an autosampler.

Figure 2. Stability plot for copper in SU-1b measured 45 consecutive times, with in-line dilution.

Figure 2 depicts a stability plot of 45 consecutive measurement of SU-1b where the recovery of each sample is normalized to the initial sample. The stability of the system is obvious with deviations of 10% or less from the original reading, except for the second reading that recovered at 113%.  In all the samples, the recoveries were found to be within 10% of the certified value.

Conclusion

This article has shown how the AAnalyst 400 flame atomic absorption spectrometer together with the FAST Flame 2 sample automation accessory enables fast and precise measurement of copper in ore samples.

When using an autosampler, the FAST Flame 2 accessory improves sample throughput by allowing fast sample uptake and washout and performing in-line dilutions, thus removing the necessity to manually dilute samples before analysis.

However, this high sample throughput does not affect stability or accuracy. Thus, the FAST Flame 2 combined with the AAnalyst 400 system proves quite useful for the mining industry.

This information has been sourced, reviewed and adapted from materials provided by PerkinElmer.

For more information on this source, please visit PerkinElmer.

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