Determination of Exchangeable Cations of Ca, Mg, K and Na in Bentonite by Inductively Coupled Plasma-Atomic Emission Spectrometry
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摘要: 对膨润土交换性阳离子和阳离子交换容量的测试是评价膨润土矿的主要指标之一，传统的测定膨润土交换性阳离子通常采用原子吸收光谱法或容量法，操作手续复杂繁琐。本文用氯化铵-乙醇交换液交换出试样中的可交换性阳离子钙、镁、钾、钠，分取蒸至湿盐状，制备成盐酸介质的溶液，电感耦合等离子体发射光谱法测定。通过正交试验确定了最佳实验条件为交换1次，加入25 mL交换液，搅拌30 min，沉淀洗涤2次。分别选择315.887 nm、279.079 nm、766.490 nm、589.592 nm作为钙、镁、钾、钠的分析谱线，绘制的标准曲线中钾、钠的浓度在0~0.6 mmol/L，钙、镁的浓度在0~3.0 mmol/L呈良好的线性关系。方法检出限为0.012~0.048 mmol/100 g。经国家标准物质验证，测定值与标准值吻合，精密度为0.5%～2.5%(RSD，n=11)，准确度为-6.1％~10%，加标回收率为97.0%~100.0%。本方法样品处理方法程序简单快速，分析重现性好，克服了传统分析方法测定手续繁琐、时间冗长且成本高等缺点，适用于批量样品的分析。Abstract: Bentonite exchangeable cations and cation exchange capacity is one of the main indicators of the evaluation of bentonite mineral. The traditional measurement method of bentonite exchangeable cations was made by using either atomic absorption spectrometry or the volumetric method and involved complicated operating procedures and took a long time. In this paper, a description of how the exchangeable cations of Ca, Mg, K and Na were extracted by NH4Cl-ethanol exchange liquid is given. The obtained solution was evaporated to wet salt and dissolved by 5% (by volume) of HCl acid solution, which was ready to be determined by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) for exchangeable cations of Ca, Mg, K and Na. The optimal conditions for the exchange were achieved by adding 25 mL exchange liquid, stirring for 30 min and washing the precipitate twice, then studied by orthogonal experiment. The analysis spectral lines of 315.887 nm, 279.079 nm, 766.490 nm and 589.592 nm were selected for Ca, Mg, K and Na, respectively. Based on the working curves, K and Na have a good linear relationship from 0 to 0.6 mmol/L, Ca and Mg from 0 to 3.0 mmol/L. The method detection limit was 0.012-0.048 mmol/100 g. Verified with national standard materials, the measured values and the certified values were in good agreement. Precision (RSD, n=11) ranged from 0.5% to 2.5%, and accuracies (RE) ranged from -6.1% to 10%. The recoveries with spike were from 97.0% to 100.0%. The proposed method overcame the disadvantages of the traditional analysis, as mentioned above. This simple and fast sample handling method before measurement with good reproducibility is applicable to the analysis of bulk samples.
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Key words:
- bentonite /
- exchangeablecation /
- calcium /
- magnesium /
- potassium /
- sodium /
- InductivelyCoupledPlasma-AtomicEmissionSpectrometry
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表 1 ICP-AES工作参数
Table 1. perating conditions of ICP-AES
工作参数 技术参数 分析元素 分析波长
λ/nm背景校正 射频功率 1150 W Ca 315.887 左，右，自动 雾化气流量 0.7 L/min Mg 279.079 左，右，自动 辅助气流量 0.5 L/min K 766.490 左，右，自动 观测方向和高度 垂直，12 mm Na 589.592 左，右，自动 蠕动泵泵速 50 r/min 
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表 2 膨润土中交换性阳离子正交实验
Table 2. rthogonal experiment of exchangeable cation in bentonite
条件 交换次数 搅拌时间
t/min交换液加入量
V/mL沉淀洗涤次数 1 2 30 10 1 2 2 50 10 2 3 2 30 25 3 4 2 50 25 4 5 1 50 25 1 6 1 30 25 2 7 1 50 10 3 8 1 30 10 4
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表 3 交换性阳离子测定条件实验
Table 3. Optimization experiment of exchangeable cations
条
件E/(mol·100 g-1) 
Ca2+
Mg2+Na+ K+ 测定
均值RSD/% 测定
均值RSD/% 测定
均值RSD/% 测定
均值RSD/% 1 2.48 5.3 3.07 4.3 7.24 4.2 0.93 3.4 2 2.50 4.2 2.58 6.4 6.46 4.8 1.18 3.6 3 3.34 6.5 3.70 5.5 7.89 3.8 1.57 2.6 4 3.53 2.2 3.95 1.2 8.57 1.0 1.63 2.2 5 3.35 2.3 4.29 0.9 9.30 0.8 1.71 2.4 6 3.77 1.8 4.37 0.6 9.38 0.4 1.71 0.8 7 2.27 4.5 3.46 3.2 2.16 2.4 1.11 3.0 8 2.63 7.1 2.83 4.1 6.47 3.0 1.11 3.8
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表 4 酸度对测定结果的影响
Table 4. ffect of acidity on determination
酸度/% E/(mmol·L-1)
Ca2+
Mg2+Na+ K+ HCl HNO3 HCl HNO3 HCl HNO3 HCl HNO3 0 0.342 0.345 0.338 0.345 0.055 0.059 0.078 0.081 0.5 0.364 0.368 0.357 0.349 0.061 0.065 0.076 0.074 1 0.367 0.371 0.384 0.394 0.064 0.061 0.085 0.081 2 0.397 0.401 0.405 0.408 0.079 0.084 0.084 0.080 5 0.403 0.405 0.408 0.397 0.078 0.076 0.082 0.084 10 0.391 0.394 0.389 0.401 0.080 0.078 0.080 0.084 15 0.397 0.389 0.402 0.406 0.082 0.080 0.084 0.079 20 0.396 0.399 0.405 0.402 0.078 0.080 0.076 0.078
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表 5 线性范围、相关系数和检出限
Table 5. Linear range,correlative coefficients and detection limits
离子 线性范围
cB/(mmol·L-1)相关系数 检出限/
(mmol·100 g-1)Ca2+0.0～3.0 0.99998 0.036 Mg2+0.0～3.0 0.99997 0.048 K+ 0.0～0.6 0.99991 0.012 Na+ 0.0～0.6 0.99986 0.024
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表 6 方法精密度和准确度
Table 6. recision and accuracy tests of the method
样品 测定元素 E/(mmol·100 g-1) RSD/% RE/% 本法
测定值标准值或
AAS测定值GBW(E)
070049Ca 1.76 1.80 2.3 -2.2 Mg 0.43 0.40 1.5 7.5 Na 0.11 0.10 0.6 10.0 K 0.11 0.10 0.9 10.0 GBW(E)
070050Ca 46.9 47.1 2.2 -0.4 Mg 7.28 7.34 1.3 -0.8 Na 0.79 0.80 1.0 -1.3 K 0.42 0.40 0.8 5.0 GBW(E)
070052Ca 24.0 24.4 2.5 -1.7 Mg 0.83 0.79 1.2 5.1 Na 48.5 48.5 2.0 0 K 1.15 1.12 1.8 2.7 样品1 Ca 3.70 3.94* 1.8 -6.1 Mg 4.40 4.50* 1.2 -2.2 Na 9.40 9.65* 1.0 -2.6 K 1.90 1.90* 1.6 0 样品2 Ca 1.76 1.80* 1.4 -2.2 Mg 0.45 0.47* 0.8 -4.2 Na 0.12 0.12* 0.5 0 K 0.11 0.11* 0.7 0 注：带*的数据为原子吸收光谱的测定值。
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表 7 加标回收试验
Table 7. Recovery tests of the method
样品 测定元素 n/mmol 回收率/% 加标前
测定值加标量 加标后
测定值GBW(E)
070049Ca 0.0035 0.02 0.0232 98.5 Mg 0.0009 0.02 0.0206 98.5 Na 0.0002 0.001 0.0012 100.0 K 0.0002 0.001 0.0012 100.0 GBW(E)
070050Ca 0.0938 0.02 0.1133 97.5 Mg 0.0146 0.02 0.0342 98.0 Na 0.0016 0.001 0.0026 100.0 K 0.0008 0.001 0.0018 100.0 GBW(E)
070052Ca 0.048 0.02 0.0677 98.5 Mg 0.0017 0.02 0.0211 97.0 Na 0.097 0.001 0.098 100.0 K 0.0023 0.001 0.0033 100.0 样品1 Ca 0.0024 0.02 0.0222 99.0 Mg 0.0088 0.02 0.0284 98.0 Na 0.0188 0.001 0.0198 100.0 K 0.038 0.001 0.039 100.0 样品2 Ca 0.0036 0.02 0.0235 99.5 Mg 0.0009 0.02 0.0203 97.0 Na 0.0002 0.001 0.0012 100.0 K 0.0002 0.001 0.0012 100.0
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