反应条件对SnCl_2-TiCl_3-K_2Cr_2O_7法的影响

Improvement on Method of SnCl_2-TiCl_3-K_2Cr_2O_7

为了从理论上对矿物质中全铁含量的测定进行深入研究，利用SnCl2-TiCl3-K2Cr2O7法对其实验条件进行了较详细的分析和研究。SnCl2-TiCl3-K2Cr2O7法即试样用盐酸加氟化钠加热分解，让有铁的氧化物及硅酸盐都变成氧化铁进入溶液中。先用氯化亚锡将大部分三价铁离子还原成二价铁，以钨酸钠为指示剂，用三氯化钛将剩余的三价铁还原成二价铁至生成“钨蓝”，再用重铬酸钾标准溶液氧化至蓝色消失，加入硫磷混合酸以二苯胺磺酸钠为指示剂，用重铬酸钾标准液滴定。通过调节不同的还原酸度，还原温度，试剂用量和溶样时间，对其最佳实验条件进行了优化。结果表明，当还原酸度为4．0mol·L^-1，还原温度范围在60--70℃，浓HCI选取30mL进行溶解，溶样时间25min时，测定全铁含量的准确性最高。为SnCl2-TiCl3-K2Cr2O7法准确测定矿物质中全铁含量提供了最佳的实验条件。

In order to understand the measurement of iron content in iron ore theoretically, the experimental conditions of SnCl2-TiCl3-K2Cr2O7 were researched and analysized. The method of SnCl2-TiCl3-K2Cr2O7 was that hydrochloric acid plus sodium fluoride under the thermal decomposition, so that iron oxides and silicates have become iron oxide into the solution. First of all, the stannous chloride makes the ferric ions reduced to two-valent iron, other ferric iron reduced to ferrous iron by titanium trichloride to generate ＂tungsten blue＂ with sodium tungstate as the indicator. Next, potassium dichromate standard solution was oxidated until the blue colour was disappeared. Droplets of potassium dichromate standard set by adding parathion mixed acid with diphenylamine sulfonante as indicator. The experimental conditions were optimized through improving the reduction acidity, reduction temperature, time of dissolved sample and reagent dosage. The results show that reduction acidity was 4.0 mol·L^- 1 ; the reduction temperature was between 60 and 70℃ ; the volume of concentrated hydrochloric acid was 30 mL; the time of dissolved sample was 25 min. It supplied an opitimized condition on the method of SnCl2-TiCl3-K2Cr2O7.