熔融制样-X射线荧光光谱法测定菱镁矿和白云石中6种组分

菱镁矿、白云石的化学成分是钙镁质耐火材料检测的重要指标,由于菱镁矿、白云石烧失量大,加热易分解,灼烧后的试样放置时间长或放置方式不当,极易吸收空气中的水分和CO₂,导致样品变质结块,影响测定结果的准确性,因此合理地优化测定条件对提高分析方法的准确度非常关键。实验采用熔融制样-X射线荧光光谱法(XRF)测定菱镁矿、白云石中CaO、MgO、SiO₂、Al₂O₃、Fe₂O₃、P₂O₅含量。直接以烧失量测定后的试样质量作为试样量,最大限度地避免了空气中水分和CO₂对称样量的影响,简化操作步骤,缩短检测时限。经试验确定采用Li₂B₄O₇-LiBO₂(m∶m=67∶33)混合熔剂,灼烧后样品与熔剂的稀释比为1∶10,NH₄I溶液为脱模剂,熔融温度1050℃,熔融时间15min制备试样玻璃片。选取12种国家标准样品绘制校准曲线,线性相关系数为0.9997~0.9999。对菱镁矿、白云石标准物质进行精密度试验,各组分测定结果相对标准偏差(RSD,n=10)为0.14%~1.6%;应用实验方法对菱镁矿、白云石标准样品进行测定,结果与认定值基本一致,各组分的相对误差(n=5)为0.15%~5.88%。

Determination of six components in magnesite and dolomite by X-ray fluorescence spectrometry with fusion sample preparation

Chemical composition of magnesite and dolomite is an important index for the detection of calcium-magnesium refractories. Magnesite and dolomite have large loss on ignition and are easily decomposed by heating. If the samples after burning are placed for long time or in improper way, it is very easy for them to absorb moisture and CO₂ in the air, which leads to the deterioration and agglomeration, thus affecting the accuracy of determination results. Therefore, it is crucial to improve the accuracy of analytical methods by optimizing the measuring conditions reasonably.The contents of CaO, MgO, SiO₂, Al₂O₃, Fe₂O₃ and P₂O₅ in magnesite and dolomite were determined by X-ray fluorescence spectrometry (XRF) with fusion sample preparation. The mass of sample after loss-on-ignition measurement was directly used as the amount of sample, which avoided the influence of moisture and CO₂ in the air on sample mass to the maximum extent. Meanwhile, the operation steps were simplified and the detection time was shortened. The following experimental conditions were finally selected for sample preparation: Li₂B₄O₇-LiBO₂ (m∶m=67∶33) mixed flux was used; the dilution ratio between the burned sample to the flux was 1∶10; the ammonium iodide (NH₄I) solution was used as the release agent; the melting temperature was 1050℃; the melting time was 15min. 12 certified reference materials were used to prepare the calibration curve, and the linear correlation coefficient was between 0.9997 and 0.9999. The certified reference materials of magnesite and dolomite were used for precision test. The relative standard deviations (RSD, n=10) of determination results of components were between 0.14% and 1.6%. The proposed method was applied for the determination of certified reference materials of magnesite and dolomite. The measurement results were basically consistent with the certified values. The relative errors (n=5) of components were between 0.15% and 5.88%.