Discussion on the improvement of determination accuracy of gold content in heavy sand based on screening pretreatment
There is a small amount of large grain gold in the heavy sand,leading to the nonuniformity of gold grade,which increases the difficulty for determination of gold content.In this paper,the conventional sampling mode was improved based on the screening pretreatment method.The uniformity of gold content in sieved sample was greatly improved,thus enhancing the sampling representativeness.Through explo-ring the change rule of grain size and shape of gold particles in the sample grinding process,the grinding conditions were optimized,the screening treatment effect was improved,thereby improving the determina-tion accuracy of heavy sand sample.The experiments showed that the gold content of in sieved sample was determined by multiple fire assay-gravimetric method(hereinafter referred to as fire assay)after screening pretreatment of heavy sand,and the minimum relative standard deviation(RSD)was 1.10％,which was obviously lower than that without screening pretreatment(i.e.,9.66％).2-3 sieved samples and total samples on sieve were used for determination,then the average gold content in sample was calculated.It could effectively improve the determination accuracy of gold content in heavy sand,and also avoid the cost waste caused by multiple determination to obtain the average value.The factors of screening difficulty,sample mass on sieve and the uniformity of sieved sample were considered comprehensively.The optimal sieving parameter was 200 mesh(74 μm).When 500 g of sample was ground for 7 h in rod mill,giant grain gold and coarse grain gold would be ruptured and passed the sieve,deteriorating the uniformity of sieved sample.The grinding extent of sample could not be too high in order to guarantee the uniformity of sieved sample.The loss of sample and gold was little in screening pretreatment process,and it had little influence on the accuracy of determination results.The proposed method was applicable for the fire assay testing laboratories.
heavy sandscreeningsample preparation by grindingfire assayuniformitygranular gold
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