熔融制样-X射线荧光光谱法测定轻稀土矿石中8种主量稀土氧化物

稀土矿种类繁多,矿物组成复杂,常富含Ca、P、Fe、Ba、Si、S、Mn、Pb等元素,而采用熔融法制样时,富含Fe、Mn、Pb等单质元素的稀土矿样会腐蚀Pt-Au坩埚。试验将稀土矿石与混合熔剂m(Li₂B₄O₇)∶m(LiBO₂)=33∶67]以质量比1∶14(稀释比)混合,再加入1mL 500g/L NH₄NO₃溶液为氧化剂、0.2mL 100g/L LiBr溶液为脱模剂,在1050℃下熔融制成均匀玻璃片,使用波长色散X射线荧光光谱法(WDXRF)测定轻稀土矿石中La₂O₃、CeO₂、Pr₆O₁₁、Nd₂O₃、Sm₂O₃、Eu₂O₃、Gd₂O₃、Y₂O₃等8种主量稀土氧化物。方法中稀土氧化物的检出限为5~159μg/g。实验方法用于测定两个稀土矿石标准物质GSB04-3549-2019(稀土总量为4.44%)和GSB04-3309-2016(稀土总量为29.09%)中8种稀土氧化物,低品位稀土矿石标准物质(GSB04-3549-2019)中稀土氧化物测定结果的相对标准偏差(RSD,n=7)小于13%,高品位稀土矿石标准物质(GSB04-3309-2016)中稀土氧化物测定结果的相对标准偏差(RSD,n=7)小于2%。选取2个轻稀土矿石样品(稀土总量分别为2.55%和24.64%),按照实验方法进行稀土总量的加标回收试验,回收率为96%~100%。选取2个稀土矿石标准物质GSB04-3550-2019和GSB04-3311-2016以及2个轻稀土矿石样品,按照实验方法测定La₂O₃、CeO₂、Pr₆O₁₁、Nd₂O₃、Sm₂O₃、Eu₂O₃、Gd₂O₃、Y₂O₃,测定值与标准值或电感耦合等离子体原子发射光谱法(ICP-AES)测定值相吻合。实验方法具有较广的适应性,能满足复杂矿物组成轻稀土矿石中主量稀土氧化物的检测。

Determination of eight major rare earth oxides in light rare earth ore by X-ray fluorescence spectrometry with fusion sample preparation

The rare earth ore has a wide range of variety with complex composition and is usually rich in Ca, P, Fe, Ba, Si, S, Mn and Pb. During sample preparation by fusion sample preparation method, the rare earth ores containing simple substances of Fe, Mn and Pb will corrode the Pt-Au crucible.The rare earth ore sample was mixed with mixture flux m(Li₂B₄O₇)∶m(LiBO₂)=33∶67] with mass ratio of 1∶14 (dilution ratio). Then 1mL of 500g/L NH₄NO₃ solution was added as oxidizer and 0.2mL of 100g/L LiBr solution was added as release reagent. The uniform glass tablet was prepared by fusion at 1050℃. Eight major rare earth oxides in light rare earth ore (including La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃ and Y₂O₃) were determined by wavelength dispersive X-ray fluorescence spectrometry (WDXRF). The detection limits of rare earth oxides ranged from 5μg/g to 159μg/g. The proposed method was applied for the determination of eight rare earth oxides in two certified reference materials of rare earth ore, GSB04-3549-2019 (total rare earth content was 4.44%) and GSB04-3309-2016 (total rare earth content was 29.09%). The relative standard deviations (RSD, n=7) of determination results for rare earth oxides in low-grade rare earth ore (GSB04-3549-2019) were less than 13%, while the RSD (n=7) for high-grade rare earth ore (GSB04-3309-2016) were less than 2%. Two light rare earth ore samples (total rare earth content was 2.55% and 24.64%, respectively) were selected. The recovery test of total rare earth content was conducted according to the experimental method. The found recoveries were between 96% and 100%. The contents of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃ and Y₂O₃ in two certified reference materials of rare earth ore (GSB04-3550-2019 and GSB04-3311-2016) and two actual samples were determined according to the experimental method, and the found results were consistent with the certified values or those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES). The proposed method had relatively wide adaptability and it could meet the detection requirements of major rare earth oxides in light rare earth ores with complex composition.