混合碱熔融-离子选择性电极法测定矿石中氟

Determination of fluorine in ore by mixed alkali fusion-ion selective electrode method

采用1g过氧化钠-2g氢氧化钠混合熔剂熔融样品,加入热水浸取熔融物,此时铁、钙、钛、铅、铜、锆、稀土等以氢氧化物沉淀的形式被除去,加入少量乙醇煮沸来消除锰颜色的干扰,调节溶液pH值在5.5--6.5之间,在总离子强度调节剂二水柠檬酸钠-硝酸钾存在的情况下,以溴甲酚绿为指示剂,建立了氟离子选择性电极法测定矿石中氟的方法。实验表明：氟离子质量浓度的负对数与其对应的电位（E）存在良好线性关系,相关系数r为0.999,线性范围为0.2--20.0μg/mL,方法检出限为0.019μg/mL。进一步的干扰试验表明,样品中硅、铝、镁、钙、锌、磷和氯均不干扰测定。方法应用于10种矿石标准物质（锂矿石、钽矿石、钼矿石、钨矿石、锡矿石、磷矿石、锌矿石、锑矿石、铅矿石和铜矿石）中氟的测定,测定值与认定值一致,相对标准偏差（n=6或n=12）为0.30%～5.0%。

The sample was fused with mixed flux, i. e. , 1 g of sodium peroxide and 2 g of sodium hydroxide. The melt was leached with hot water. At this time, the elements including iron, calcium, titanium, lead, copper, zircon and rare earths were removed in the forms of hydroxide precipitates. The color inter ference of manganese was eliminated by adding little ethanol followed by boiling. With the pH of solution adjusted to 5.5-6.5 and in presence of total ionic strength adjustment buffer solution of trisodium citrate dihydrate-potassium nitrate, a method was established for determination of fluorine in ore by ion selective electrode method using bromocresol green as indicator. The experimental results showed that the negative logarithm of mass concentration of fluorine ion was linear to the corresponding potential （E）. The correlation coefficient was r=0. 999. The linear range was 0.2-20.0 μg/mL. The detection limit of method was 0. 019μg/mL. The further interference tests indicated that the elements in sample including silicon, alumi- num, magnesium, calcium, zinc, phosphorus and chlorine did not interfere with the determination. The proposed method was applied to the determination of fluorine in ten types of ore certified reference materi- als（lithium ore, tantalum ore, molybdenum ore, tungsten ore, tin ore, phosphorus ore, zinc ore, tanta lum ore, antimony ore, lead ore and copper ore）. The results were consistent with the certified values. The relative standard deviations （RSD, n=6 or n=12） were between 0.30% and 5.0%.