Determination of Rare Earth Elements in Barite-associated Rare Earth Ores by Alkaline Precipitation Separation-Inductively Coupled Plasma-Mass Spectrometry
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摘要: 采用电感耦合等离子体质谱法（ICP-MS）测定伴生重晶石轻稀土矿中的稀土元素时，Ba以及轻稀土元素La、Ce、Pr、Nd、Sm等对中重稀土造成严重的质谱重叠干扰，因此在保证矿石完全消解的同时，若能选择合适的前处理方法实现目标元素与基体的有效分离，将有利于减少质谱干扰。本文采用过氧化钠-碳酸钠熔融分解伴生重晶石的稀土矿样品，熔融物用三乙醇胺溶液提取，将沉淀过滤去除硅、铁、锰、铝等大量基体元素，而稀土元素与钡、锶、钙等留存于沉淀中，沉淀经盐酸溶解后再用氨水进行二次沉淀，将稀土元素与伴生的高含量钡、锶、钙等元素分离，分离率超过96%，从而极大地降低了由钡的氧化物和氢氧化物对153Eu等元素质量数的质谱干扰。轻稀土元素对中重稀土元素的干扰则通过测定高浓度的单元素标准溶液在m/z 138~175处的表观浓度来计算干扰校正系数，对干扰量进行扣除校正。该方法通过稀土矿石标准物质GBW07187、GBW07188验证，测定值与认定值的相对误差 < 10%；应用于伴生重晶石稀土矿石实际样品分析，相对标准偏差（RSD，n=12）为0.5%~4.6%，证明了本方法可用于分析高钡矿石中的稀土元素。
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关键词:
- 重晶石 /
- 稀土元素 /
- 过氧化钠-碳酸钠熔融 /
- 沉淀分离 /
- 钡 /
- 电感耦合等离子体质谱法
Abstract:BACKGROUNDWhen inductively coupled plasma-mass spectrometry (ICP-MS) is used to determine the rare earth elements (REE) in the barite-associated light rare earth ores, Ba and light rare earth elements La, Ce, Pr, Nd, Sm, cause severe mass spectral overlap interference to the medium and heavy rare earths. Therefore, under the condition that complete digestion of oress, if the appropriate pretreatment method can be selected to achieve effective separation of the target elements from the matrix, it will be beneficial to reduce mass spectrum interferences. OBJECTIVESTo reduce the mass spectrum interferences by establishing a simple and effective pretreatment method for separation of rare earth elements from barium and other coexisting elements in barite-associated rare earth ores. METHODSThe barite-associated rare earth ores samples were fused with sodium peroxide and sodium carbonate. After dissolution of the fusion cake, the target REE and the undesired barium were precipitated in triethanolamine solution, but some matrix elements like Si, Fe, Mg, and Al in samples, and most fusion agents, were separated by filtration. The target REE were secondly precipitated in ammonium hydroxide after dissolution of the precipitates by acid, so that Ba, Sr and Ca could be separated from REE. The separation exceeds 96%, so the mass spectrum interferences caused by barium polyatomic ions were effectively reduced. In addition, the interference correction coefficients by measuring the interference concentration at m/z 138-175 of the high concentration lighter rare earths standard single element solution were adopted to account for the oxide and hydroxide overlap problem for the determination of middle and heavier rare earth elements. RESULTSThe validity of the method was evaluated by analyses of rare earth ores certified reference materials and the results were in good agreement with certified values (|RE| < 10%). For the actual sample analysis of the barite-associated rare earth ores, the relative standard deviations (n=12) were from 0.5% to 4.6%, which proved that the method can be used to analyze rare earth elements in high-Ba ores. CONCLUSIONSThe results demonstrate that this method is both practical and effective for rare earth elements analysis in barite-associated rare earth ores. -
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表 1 各稀土元素的标准系列浓度
Table 1. Concentrations of REE in calibration standard solutions
稀土元素 标准系列1浓度
(ng/mL)标准系列2浓度
(ng/mL)标准系列3浓度
(ng/mL)标准系列4浓度
(ng/mL)La 200 2000 20000 - Ce 200 2000 20000 - Pr 50 100 1000 2000 Nd 100 1000 2000 5000 Sm 10 50 200 500 Eu 1.0 10 50 100 Gd 1.0 10 50 100 Tb 1.0 5.0 10 50 Dy 5.0 10 50 100 Ho 1.0 5.0 10 100 Er 1.0 5.0 10 50 Tm 0.5 1.0 5.0 50 Yb 1.0 5.0 10 20 Lu 0.1 0.5 1.0 5.0 Y 50 100 200 - 
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表 2 不同溶样方法处理样品MNP-2的稀土元素测定结果
Table 2. Analytical results of REE in MNP-2 with different sample digestion methods
稀土元素 样品MNP-2测定值(μg/g) 四酸敞开酸溶法 五酸敞开酸溶法 氢氟酸-硝酸封闭压力酸溶法 过氧化钠-碳酸钠碱熔法 La 7014 7471 8153 10720 Ce 9668 11760 11287 15020 Pr 822 905 965 1278 Nd 2331 2626 2900 3567 Sm 196 243 233 300 Y 93.8 114 88.6 146
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表 3 残留的共存元素含量(μg/g，结果均按0.25g称样量换算至样品含量)
Table 3. Residual content of coexisting elements (μg/g, results were converted to sample content by 0.25g weighing amount)
共存元素 MNP-1 MNP-2 碱熔-水提取-沉淀过滤
(方法1)碱熔-水提取-沉淀酸溶后氨水二次沉淀
(方法2)碱熔-三乙醇胺提取-沉淀过滤
(方法3)碱熔-三乙醇胺提取-沉淀酸溶后氨水二次沉淀
(方法4)碱熔-水提取-沉淀过滤
(方法1)碱熔-水提取-沉淀酸溶后氨水二次沉淀
(方法2)碱熔-三乙醇胺提取-沉淀过滤
(方法3)碱熔-三乙醇胺提取-沉淀酸溶后氨水二次沉淀
(方法4)Ba 18025 296 17510 232 29310 1136 28555 1112 Al 34770 8282 3106 2793 52526 14204 5027 4486 Ca 14303 428 8026 292 111652 2980 112635 3070 Fe 90997 83757 922 859 31034 27652 442 452 K 464 ND 156 ND 427 ND 191 ND Na 185222 487 79675 433 247129 708 114542 721 Mg 6875 265 6963 124 6890 274 6317 267 Ti 4572 4551 3523 3868 1808 1817 1499 1470 Mn 1205 924 50 51 1452 1351 128 119 Sr 175 ND 183 ND 38330 566 37460 578 Cu 46.8 2.9 4.0 3.9 65.1 2.6 1.7 1.2
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表 4 稀土元素测量质量数及干扰校正系数
Table 4. Measured m/z and the interference correction coefficient for rare earth elements
稀土元素 选择质量数 干扰元素 干扰系数(k) La 139 - - Ce 140 - - Pr 141 - - Nd 146 - - Sm 147 - - Eu 153 Ba 0.0003837 Gd 160 Ce 0.0000332 Pr 0.0000330 Nd 0.0262500 Sm 0.0011850 Dy 0.0939759 Tb 159 Ce 0.0001934 Pr 0.0000568 Nd 0.0027455 Dy 163 Nd 0.0005330 Sm 0.0036453 Ho 165 Nd 0.0000450 Sm 0.0009010 Er 167 Nd 0.0001986 Sm 0.0001243 Eu 0.0023075 Tm 169 Sm 0.0001023 Eu 0.0005733 Yb 172 Ce 0.0000098 Gd 0.0125540 Lu 175 Ce 0.0000363 Gd 0.0003113 Tb 0.0151550
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表 5 标准物质分析结果
Table 5. Analytical results of REE in reference material samples
稀土元素 GBW07187 GBW07188 认定值
(μg/g)测定值
(μg/g)加钡后测定值
(μg/g)认定值
(μg/g)测定值
(μg/g)加钡后测定值
(μg/g)La 2132 2100 2067 1961 1817 1784 Ce 171 165 160 431 391 392 Pr 546 556 548 737 680 681 Nd 2058 1903 1947 3429 3213 3246 Sm 569 526 526 1725 1831 1821 Eu 8.26 8.32 8.23 18.9 20.5 20 Gd 790 796 791 2169 2156 2148 Tb 162 150 154 468 454 450 Dy 1046 969 972 3224 2979 2947 Ho 201 196 199 559 536 536 Er 595 604 601 1749 1769 1756 Tm 72.6 74.3 76.1 271 251 252 Yb 448 427 428 1844 1737 1706 Lu 56.7 59.9 59.2 264 243 249 Y 6300 6464 6491 17009 17130 17400
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表 6 实际样品分析结果
Table 6. Analytical results of rare earth elements in practical samples
稀土元素 MNP-1 MNP-2 测定平均值(μg/g) RSD(%) 测定平均值(μg/g) RSD(%) La 15805 1.0 10780 0.5 Ce 21023 1.4 15108 1.7 Pr 1664 2.2 1272 1.6 Nd 4934 1.4 3545 1.6 Sm 348 1.7 299 1.4 Eu 52.7 1.5 60.4 1.3 Gd 106 4.6 111 1.3 Tb 5.83 4.3 7.04 3.2 Dy 30.6 0.8 30.6 1.7 Ho 4.72 0.8 4.14 2.3 Er 11.8 1.4 8.45 1.3 Tm 1.78 0.5 1.01 1.0 Yb 11.2 1.7 5.82 3.3 Lu 1.77 3.9 0.77 3.7 Y 140 0.6 145 1.5
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