Background

Runoff from mine sites, landfills and other metal-bearing sites can have dramatic impacts on aquatic environments. Acidic drainage in particular can dissolve large amounts of metals and it is convenient to know whether seeps, leachates or streams are heavily contaminated. Additionally, there is an increasing call for partial extraction techniques which can produce extracts rich in metals. XRF is an ideal way for an initial appraisal of contaminated mine-site waters, or measurement of the greater concentrations of metal ions found in partial extracts from contaminated soils.

Instrumentation

A PANalytical MiniPal 2 equipped with a 30 kV Rhodium anode tube, 5 different filters and a high-resolution solid state detector was used.

A standard helium purge facility for an improved detection of lighter elements was used for all calibrations and measurements.

Procedure

Synthetic standard solutions were mixed in various ratios and pipetted into P1 'de Kat' cells and loaded into the spectrometer. Two excitation conditions were used to acquire the spectra (Table 1). Matrix correction was made by ratioing to a background channel, Bg, with a Region Of Interest (ROI) of 16.800 to 17.100 keV and Bg2 with an ROI of 4.600 to 4.900 keV.

Table 1. Excitation conditions. All elements were measured using their Kα line except Ag, Cd, Sn and U which were measured using their Lα1 lines and Pb where the Lβ1 line was used.

Element	kV	µA	Filter	Medium	Counting Time (sec)
As,Bg1,Cu,Pb,U,Zn	30	100	Mo	Helium	300
Ag,Al,Bg2,Cd,Cr,Fe,Ni,Sn	15	30	Al_thin	Helium	300

Results

Figure 1 and Table 2 show the calibration results for Cr, Fe, Cu and Zn. There is a good correlation between the supplied concentration values and the measured intensities.

Table 2. Calibration information. Regressions were fitted to 11 Certified Reference Materials analysed as liquids pipetted into P1 cells

Analyte	Concentration Range (mg/l)	RMS (mg/l)	Correlation
Cr	10 – 201	4.46	0.9963
Fe	88 – 491	8.14	0.9981
Cu	8 – 160	1.96	0.9988
Zn	3 – 48	3.40	0.9729

Figure 1. Calibration graphs for Cr, Fe, Cu and Zn in synthetic standards.

Repeat analyses of a single sample show excellent repeatability.

Figure 2. 10 analyses of a contaminated water sample, analysing for chromium, iron, copper and zinc.