Evaluation Of Atomic Absorption Spectrophotometric Determination Methods Of Gold In Its Ores After Aqua Regia Digestion, Cyanide Leach (NaCN) or Fire Assay Method Fusion

Abstract

In the persent research study three analytical methods used in Sudan based on the atomic absorption determination of goldafter aqua regia digestion (AR), cyanide leach(NaCN) or fire assay method fusion(FA)were evaluated. The efficiency of the sample pre-treatment procedures (crushing, splitting and grinding) and size of the subsamplewas also evaluated using both the AR leach and the cyanide leach methods. Twoore samples [1]and [2] from Abouhmd area(north of Sudan ) and four ore samples [3],[4],[5]and [6] from Umtrambesh area(north of Sudan ) were collected,analysed and their results were compared with those ofReference Samples Material (RSM). After crushing, the samples were ground to two grades of fineness (<0.03 and<0.06 mm) and were analysed for gold using the three analytical methods. Each determination was performed five times. According to t-tests on the FA results of the two splits, crushing and splitting produced samples containing equal gold content. Grinding to a finer grain size did not give a significant difference in Au results except for the ore sample [5]. Greater than 95% recoveries were obtained for all samples except sample [1](87% recovery) by the AR leach method assuming that the FA results represent 100% recovery of gold . Recoveries of over 95% by the NaCN leach method for samples [3],[4], and [5] were obtained, whereas recoveries for the other three samples varied between 73% and92%. The AR leach also was performed on 1-g samples; the NaCN leach was performed on 250-g samples. For three of the ores samples, decreasing sample size from 20 g to 1 g did not causeasignificant difference in the variance of the Au results. Increasing the sample size from 20 g to 250 g significantly improved the representatively of only the sample [5]. For the [4], [5] and[6] ores, a sample larger than 250 g was needed to obtain a precision equivalent to that for reference samples.