Application Of Energy Dispersive X-ray Fluorescence Spectrometry Combined With Sample Chemical Pretreatment In Ores And Water

Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) is a popular on-site analytical technique in mineral prospecting, mine environment monitoring. Lack of sufficient matrix matching calibration samples has been a major problem affecting the accuracy and reliability of on-site EDXRF analysis for highly mineralized samples and metal ores including sulfides. Moreover, the relatively low sensitivity of portable or transportable EDXRF spectrometers prohibit their direct use in on-site monitoring of heavy metals in surface and underground water samples in which the concentrations of heavy metals are far below the detection limits of the technique. Meanwhile, laboratory wet chemical analysis techniques and many preconcentration methods have made substantial developments, which offer opportunity for EDXRF to rely on chemical pretreatment process to overcome the above problems. In this work, two sets of experiments were carried out to establish on-site EDXRF methods for:1) accurate ore forming element analysis of multi-metallic ore after acid digestion of samples;2) heavy metal analysis in water samples after enrichment with ion exchange resin loaded filter paper specially made for the work. Experimental procedures and results are as follows:(1) Sealed digestion of samples by nitric acid and hydrofluoric acid, and EDXRF calibrations were done by utilizing standard solutions. Copper, lead and zinc in sulfide samples were quantified. The established method was verified with seven certified reference materials of multi-metallic ores GBW07162-GBW07168. Results show that almost all the precisions for copper, lead, zinc are better than5%(RSD, n=6),when their concentrations are greater than1%, and the results are in good consistency with the standard values.(2)Combined with the PE-EDXRF, two different procedures of ore sample digestion were tested on-site on multi-metallic ores for Cu, Pb Zn analysis:1)digestion in glass tubes in water bath with aqua regia,2) digestion in glass beakers on a hot plate with sequential adding of hydrochloric acid and nitric acid. These methods were calibrated by standard solutions and Compton scattering intensities of Mo Ka from the secondary target used as internal standard to compensate for the matrix effect. Two kinds of double cabin sample cups with acid absorbent and double supporting films were developed to prevent the spectrometer from damage by the possible leakage and evaporation in Qimantage area, Qinghai province(More than4000meters). When samples were pretreated using procedure2, the relative standard deviations (RSD, n=10) were less than2%for2quality control samples and relative errors were less than5.0%(element concentration were higher than0.5%) for4ones. PE-EDXRF results were compared with Atomic Absorption Spectroscopy(AAS) ones, the obtained mean relative deviation for Cu Pb and Zn were2.87%、2.82%、6.84%for the13local mine unknown samples. We conclude that the vehicle-loaded PE-EDXRF coupled with the double cabin sample cups and sample digestion procedures can solve the problem of matrix matching and offer a satisfactory solution for high precision on-site poly-metallic ore sample analysis. The work expand the capability of PE-EDXRF on-site analysis and improve the already established powder sample preparation method.(3) Ion exchange resin loaded filter papers were made, which were cut to fit the sample cups in the instrument before enrichment procedures. An ion exchange device was specially designed to allow repeated dynamic ion exchange without solution blending between repetitions. Primary ion exchange test and EDXRF measurement showed that the detection limits were as low as several ng/mL for Cu, Zn and Ni and about20ng/mL for Pb. Though the work is on its way yet, it has opened a door for the on-site EDXRF application in water quality monitoring.The above work has paved the way for the extended on-site application of portable and transportable EDXRF for mineral source exploration and water quality survey. The results has been summarized into two academic papers which have been accepted by the journal <Rock and mineral Analysis>, and three patents which are in the course of publicity.