Determination of Gold in Carbonate Geological Samples by Hydroquinone Volumetric Method with Aqua Regia Digestion
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摘要: 应用王水溶样-活性炭富集金-氢醌容量法测定岩石、土壤等一般地质样品中的金时，王水溶样后经布氏漏斗抽滤后剩余的不溶物残渣中金含量小于金总量的4%，通常不计入分析结果。而碳酸盐地质样品经焙烧后在王水溶解过程中因为钙和镁的硅酸盐含量较高，形成了不溶于王水的二氧化硅凝胶及大量钙镁胶状物，包裹和吸附样品溶液中的金，造成分析过程中金的损失。本文将抽滤后的滤液和不溶物残渣分别处理，收集王水分解样品抽滤步骤后的不溶物残渣，用氢氟酸-硫酸除硅，王水溶解测定残渣中的金含量，滤液和残渣两次测试合量为样品中金含量。实验研究了不溶物残渣中的金量、金的来源以及样品中硅钙镁的含量对金测定的影响。结果表明，不溶物残渣吸附和包裹的金量占样品金总量的18%~22%，残渣中金的主要来源是已被王水溶解但被二氧化硅等胶状物包裹吸附而未进入溶液的金，其次是未被王水溶解的单质金。胶状物的形成与样品中钙镁硅含量有直接的关系，当CaCO3、MgCO3含量达到30%以上时，必须考虑残渣中的金，以保证金的测试结果准确。Abstract: When using the traditional aqua regia decomposition aqua regia dissolving digestion-activated carbon enrichment and Hydroquinone Volumetric Method to determine gold in rock and soil geological samples, the gold in the insoluble residue on the Buchner funnel filter is less than 4% of the total gold, which is always dismissed. However, carbonate samples, dissolving by aqua regia, can form a large amount of silica, insoluble calcium and magnesium gels which lead to gold loss from inclusion and adsorption by the gels. In this study, the insoluble residues on the Buchner funnel filter were collected. The silicon in residues was removed using HF-H2SO4, and then dissolved by aqua regia again before measuring the gold in residues. The total gold in the sample is the sum of gold in the filtrate and insoluble residue. The gold contents in residues, source of gold and the effect of silica, calcium and magnesium gels on gold measurement were examined. Experimental results indicate that the content of gold in insoluble residue could account for approximately 18%-22% of the total gold in the carbonate sample. Standard addition recovery experiments also showed that gold in residues was from coated and adopted gold by silica gel and insoluble calcium and magnesium gel. The native gold which cannot be dissolved by aqua regia is minor. The formation of gels was directly related to the contents of Si, Ca and Mg. When the contents of CaCO3 and MgCO3 are more than 30% in the sample, the gold in insoluble residue must be considered in order to obtain an accurate result.
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Key words:
- carbonate geological samples /
- gold /
- aqua regia /
- Hydroquinone Volumetric Method
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表 1 滤液与残渣中金的含量
Table 1. Analytical results of gold in the liquid phase and the remainder phase
样品编号 Au含量(μg/g) 残渣中的金量占样品金总量的比例(%) 标准值 滤液 残渣 总量 碳酸盐样品1 - 2.22 0.52 2.74 18.97 碳酸盐样品2 - 3.28 0.81 4.09 19.80 碳酸盐样品3 - 1.38 0.37 1.75 21.14 GBW 07300 5.72 5.44 0.21 5.65 3.72 GBW 07298 32.3 32.4 1.13 33.5 3.37 
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表 2 方法加标回收实验
Table 2. Recovery tests of the method
样品编号 Au含量
(μg/g)残渣中的金量占样品金总量的比例
(%)加标回收率(%) 加标前总量 加标量 滤液中金的测定值 残渣中金的测定值 加标后测定的金总量 4.09 0.00 3.25 0.84 4.09 20.54 - 4.09 0.50 3.75 0.88 4.63 19.01 107.0 4.09 0.50 3.61 0.95 4.56 20.83 93.0 2号样品 4.09 1.00 4.06 0.98 5.04 19.44 94.5 4.09 1.00 4.00 1.09 5.09 21.41 99.5 4.09 1.50 4.51 1.18 5.69 20.74 106.3 4.09 1.50 4.42 1.20 5.62 21.35 101.7
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表 3 金含量低的碳酸盐样品加标回收实验
Table 3. Recovery test of containing carbonate materials without gold
Au含量(μg/g) 残渣中金量占金总量的比例
(%)回收率
(%)加入金量 滤液中金测定值 残渣中金测定值 总量 3.00 2.44 0.56 3.00 18.7 100.0 3.00 2.42 0.63 3.05 20.7 101.7
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表 4 样品中SiO2、CaCO3、MgCO3含量对残渣中金量的影响
Table 4. Effect of SiO2，CaCO3，MgCO3dosage on gold in the remainder phase
样品编号 Au含量(%) Au含量(%) SiO2 CaCO3 MgCO3 加入金总量 残渣中金量测定平均值 残渣中金量占金总量的比例(%) a 68.1 5.70 5.00 3.00 0.08 2.67 b 63.4 10.1 8.50 3.00 0.04 1.33 c 53.5 16.4 13.9 3.00 0.25 8.33 d 40.7 24.4 20.6 3.00 0.43 14.3 e 28.1 32.2 27.4 3.00 0.56 18.7 f 17.9 39.7 33.0 3.00 0.38 12.7 g 11.2 43.0 36.6 3.00 0.26 8.67
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表 5 方法精密度
Table 5. Precision tests of method
样品编号 Au含量(%) Au测定值
(%)RSD
(%)SiO2 CaCO3 MgCO3 1 22.7 22.2 31.6 4.09 4.0 2 27.7 20.2 28.5 2.71 3.4 3 28.8 21.3 31.5 1.77 3.2 4 29.2 22.4 29.3 1.02 4.4
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