Preparation of Perlite Reference Material for Compositional Analysis

Perlite is a vitreous rock formed by rapid cooling of volcanic eruptive acidic lava. It is a very important non-metallic mineral, because of its brittleness, light weight, rapid expansion on heating, and other excellent characteristics, and is widely used in construction, water treatment, agriculture and other fields. However, according to the International Database for Certified Reference Materials (COMAR), there is no reference material for perlite composition analysis at home and abroad. So, in order to meet the research needs of perlite, it is necessary to develop one.

To develop a reference material for composition analysis of perlite. The reference material can basically cover the chemical composition needed by the market.

Perlite samples were collected from Shangcheng County, Henan Province. The collected samples were dried and picked out, the bulk ore was crushed and ground in a ball mill for 40h, then the samples were coarse crushed and discharged, and the debris was removed by 1mm sieve. The samples were dried at 105℃ for 24h, dehydrated and inactivated. After drying, the samples were crushed in a grinder containing high-alumina ceramic balls, and the grinding time was determined by the time required to meet the particle size requirements of the first class standard substance. The processed samples were stored temporarily in polyethylene plastic vats under constant temperature and clean conditions, then sub-packed at 70g per bottle for test. Random samples were taken for homogeneity and stability tests. Through nine collaborative laboratories, more targeted valuation methods such as the gravimetric method, volumetric method, inductively coupled plasma-mass spectrometry, and inductively coupled plasma-optical emission spectrometry were used to ensure the accuracy of the perlite valued components.

Fifteen items of 60 components were tested for uniformity and stability, including Ag, As, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Ga, Hf, Hg, In, Li, Mo, Nb, Ni, Pb, Rb, Sb, Sc, Sn, Sr, Ta, Th, U, V, W, Zn, Zr, SiO₂, Al₂O₃, TFe₂O₃, FeO, MgO, CaO, Na₂O, K₂O, MnO, TiO₂, P₂O₅, LOI, TC, and rare earth elements. The RSD of most of the components was less than 3%, and the F value of the variance test was less than the critical value F_0.05(29, 60)=1.65, indicating that the homogeneity of the reference material was good. During the stability inspection period, there was no significant difference in the content of the 60 components, indicating that the reference material was stable. The data were processed in accordance with General and Statistical Principles for Characterization of Reference Materials and outlier tests were performed using the Grubbs and Dixon methods. According to statistics, there were 2500 original data of perlite reference material, and 68 outliers were eliminated, with an elimination rate of 2.7%. The standard value and uncertainty of the certified reference material for perlite composition analysis were determined by statistical processing of the constant value test data. The normal distribution of the mean data set was tested by the method of Shapiro-wilk, and the test results were all normal distribution. The final values were 63 components, covering major, trace, and all rare earth elements. The contents of three major components MgO, CaO and TFe₂O₃ were all less than 1%, which formed a gradient with the existing silicate reference material content.

The certified reference material for perlite composition analysis developed in this paper has met the requirements of Technical Norm of Primary Reference Material (JJF1006—94) by processing, crushing, homogeneity and stability test of the candidate. The test for uniformity and stability adopts the same detection technology as the fixed value method, and the selected fixed value technology is suitable and accurate, which ensures the accuracy of the fixed value data. The development of perlite composition analysis standard material has enriched the series of China geological mineral composition analysis standard material, and its chemical composition is numerous, it provides important technical support for instrument calibration, analysis method verification, quality control and quantity traceability of modern analytical technology.