Determination of free silica in limestone by inductively coupled plasma atomic emission spectrometry
LI Haijuan1, YANG Lin*1, SUI Dong1, ZOU Guoqing1, FEI Jianliang1, ZHANG Xingrong2
1. CMGB Bu-1 (Hebei) Analysis & Technology Co.,Ltd.,Langfang 065201,China; 2. College of Chemical Engineering,Qingdao University of Science and Technology,Qingdao 266042,China
Abstract：In standard method of GB/T 14840-2010, the silicate minerals in limestone are dissolved with hot phosphoric acid to separate free silica, then the content of free silica is determined by gravimetry. However, the operations are cumbersome and time-consuming. In this paper, free silica in limestone was separated from limestone by means of the property that hot phosphoric acid could dissolve silicate minerals but hardly dissolve free silica. Then, the dissolved silicic acid was depolymerized with fluoroboric acid. After filtration with dense filter paper, free silica could be fully separated from other minerals. Then the precipitates were washed with hot water for three times followed by ashing in silver crucible. After fusion with 1.5 g of sodium hydroxide and leaching with hydrochloric acid, the content of silica in sample solution was determined by inductively coupled plasma atomic emission spectrometry(ICP-AES) with Si 251.611 nm as analytical line. Consequently, a method for determination of free silica in limestone was established. The linear correlation coefficient of silica calibration curve was 0.999 9, and the linear range was 0.024%-10.0%. The limit of detection and the limit of quantification were 0.008% and 0.024%, respectively. The contents of free silica in 4 certified reference materials of limestone were determined according to the proposed method, and the relative errors between the determination results and certified values were in range of -0.18%-0.48%. The relative standard deviations (RSD, n=12) were between 1.2% and 1.9%. The proposed method and the gravimetric method in standard method of GB/T 14840-2010 were applied in determination of 4 limestone samples for method comparison, and the determination results of the two methods were basically consistent.
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