Determination of gold content in rock gold ore samples based on closed water bath aqua regia digestion-polyurethane foam enrichment and using flame atomic absorption spectrometry

At present, due to the uneven distribution and low content of gold (Au) in rock gold ore samples, the separation, enrichment and accurate determination of Au have become daunting tasks in the analysis of rock gold samples. This study established a method for determining the Au content in rock gold ore samples with the advantages of high efficiency, low cost, safety and more environment-friendliness. It was based on closed water bath digestion-polyurethane foam (PUF) enrichment and thiourea release, and then, flame atomic absorption spectrometry was used to determine the Au content. By eliminating interference and optimizing the PUF pretreatment method, aqua regia dosage, water bath dissolution time, oscillation frequency and time, thiourea concentration, release time and temperature and other working conditions, technical problems such as the low adsorption efficiency of the PUF and interference from tungsten, antimony and iron elements were solved. The Au detection limit of this method was 0.03 μg g^-1, the lower limit of determination was 0.1 μg g^-1, and the optimal determination range was 0.1-40 μg g^-1. This method was used to determine 7 national standard materials of gold ores with different high and low contents (GBW07808b, GBW07809b, GBW07297a, GBW07298, GBW07300a, GBW(E)070012a and GBW07807a); the relative error (RE) was ≤3.06% and the relative standard deviation (RSD) was ≤8.35%. This method was performed in 9 laboratories to compare and verify the 7 national standard materials of gold ores with different high and low contents (GBW(E)070067, GBW(E)070262, GBW(E)070138a, GBW07300a, GBW07809b, GBW(E)070141 and GBW07298a); the RE was ≤10.55% and the RSD was ≤3.93%, achieving good results. A total of 85 rock gold ore samples were selected for determination using this method and compared with the results of activated carbon enrichment-flame atomic absorption spectrometry. The qualification rate was 97.65%, and the analysis and testing efficiencies were improved by nearly 10 times.