锑铜试金-石墨炉原子吸收光谱法测定地球化学样品中痕量钌

钌为工业和科学研究领域有效的贵金属催化剂,其在地球化学样品中的含量测定对于贵金属矿产勘测至关重要。采用氧化锑和硝酸铜共同作为捕集剂,同时加入与熔剂相同配方的混合试剂作为覆盖剂进行熔融;将得到的锑铜扣于镁砂灰皿中灰吹,使锑氧化成氧化锑挥发出去从而除去了大量的锑,而铜作为灰吹保护剂避免钌的挥发损失,从而将钌富集在毫克级的锑铜合粒中;用20%(V/V)王水微波消解锑铜合粒,采用石墨炉原子吸收光谱法测定,建立了锑铜试金-石墨炉原子吸收光谱法测定地球化学样品中痕量钌的方法。选择橄榄岩、辉石橄榄岩标准物质为试验对象,设计了加与不加覆盖剂的对比试验,结果表明,加入覆盖剂后钌的测定结果与认定值吻合性较好,而未加覆盖剂时钌的测定结果与认定值相比偏低,说明覆盖剂的加入显著提高了钌的捕集效率;通过试验对比了锑铜试金、铅试金、镍锍试金这3种试金方法捕集剂中钌的空白值,结果表明,锑铜试金的空白值比其他两种试金方法至少低一个数量级。试验发现,对于较难分解的铬铁矿样品,需预先采用过氧化钠和氧化钙与铬铁矿烧结的方法对铬铁矿进行处理,破碎烧结块,然后再按照锑铜试金法对样品中钌进行分离富集方能得到较为准确的结果。在优化的实验条件下,钌在0.01~50 ng/mL的质量浓度范围内与其对应的吸光度运用二次方程最小二乘法拟合校准曲线,曲线拟合良好,决定系数为0.999 6;特征浓度为2.34 ng/mL。将实验方法应用于多种岩石样品(橄榄岩、铬铁矿)、水系沉积物和土壤等标准物质中痕量钌的测试,测定值与认定值一致。选取3种地球化学样品,按照实验方法对其中痕量钌进行测定并进行加标回收试验,结果的相对标准偏差(RSD,n=5)在4.6%~6.8%之间,加标回收率在95%~105%之间。

Determination of trace ruthenium in geochemical sample by antimony- copper fire assay graphite furnace atomic absorption spectrometry

Ruthenium (Ru) is an effective precious metal catalyst in the fields of industry and scientific research. The determination of Ru content in geochemical samples is essential for the exploration of precious metal minerals. Antimony oxide and copper nitrate were used together as collectors. Meanwhile, the mixed reagent with same composition as the flux was added as the covering agent for melting. The obtained antimony-copper particle was turned over in a magnesia cupel for cupellation. In this process, antimony was oxidized into antimony oxide and volatilized, realizing the removal of much antimony. But copper served as a cupellation protective agent to avoid the volatilization loss of ruthenium, thereby enriching ruthenium in milligram level in antimony-copper particles. The antimony-copper particles were dissolved with 20% (V/V) aqua regia by microwave digestion and then determined by graphite furnace atomic absorption spectrometry. Therefore, the determination method of trace ruthenium in geochemical samples by antimony-copper fire assay graphite furnace atomic absorption spectrometry(GFAAS) was established. The certified reference materials of olivinite and pyroxene peridotite were selected as experiment object. The comparison tests with and without covering agent were designed. The results showed that the measured results of Ru after adding covering agent were in good agreement with the certified values, while the measured results without covering agent were lower compared to the certified values. It indicated that the addition of covering agent significantly improved the collection efficiency of Ru. The blank values of Ru in the collectors of three fire assay methods, i.e., antimony-copper fire assay, lead assay, and nickel sulfide fire assay, were compared. The results showed that the blank values of antimony-copper fire assay were at least one order of magnitude lower than the other two methods. It was found in experiments that the chromite samples, which were hardly decomposed, should be pretreated with sodium peroxide and calcium oxide by sintering. After breaking the agglomerate, the Ru in sample was separated and enriched according to the antimony-copper fire assay method. Using this method, the determination results were relatively accurate. Under the optimal conditions, the mass concentration of Ru in range of 0.01-50 ng/mL and the corresponding absorbance were fitted with least square method of quadratic equation to obtain the calibration curve. The linearity of the calibration curve was good, and the determination coefficient was 0.999 6. The characteristic concentration was 2.34 ng/mL. The proposed method was applied for the determination of trace Ru in certified reference materials of several rock samples (olivinite, chromite), stream sediment and soil. The found results were consistent with the certified values. Three geochemical samples were selected and determined according to the experimental method. Meanwhile, the recovery tests of standard addition were conducted. The relative standard deviation (RSD, n=5) of the results were between 4.6% and 6.8%, and the spiked recoveries were between 95% and 105%.