EDTA络合滴定法连续测定铁矿石中钙和镁

摘要

利用铁矿石的系统分析中重量法测定二氧化硅的滤液作为分析试液,EDTA络合滴定法测定其中钙和镁量,然后通过计算得到铁矿石中氧化钙和氧化镁含量.铁矿石中铁、铝、钛、铜、镍、锰等干扰元素不需要分离,可在酸性溶液中用酒石酸钾钠、盐酸羟胺、三乙醇胺和在氨性溶液中用铜试剂进行掩蔽消除干扰.在氨性溶液中,以酸性铬蓝K-萘酚绿B作指示剂,用EDTA标准溶液滴定钙镁合量.然后在滴定钙镁合量后的同一溶液中,加入KOH溶液,以钙试剂作指示剂,用钙标准溶液滴定EDTA-Mg络合物中释放出的EDTA,同时做EDTA/Ca的比对试验,求得比对系数.根据比对系数、滴定释放出EDTA时消耗钙标准溶液体积和样品量计算出氧化镁的含量,再用差减法计算氧化钙的含量.使用本方法对铁矿标准样品中氧化钙、氧化镁进行了多次平行测定,测定值与认定值相符,测定结果的相对标准偏差(RSD)在1.1％～4.0％(n=6)之间,回收率在98％～104％范围.%The content of calcium and magnesium in the filtrate which was obtained in the determination of silicon dioxide by gravimetric method during the system analysis of iron ore was determined by EDTA complexometric titration. The content of calcium oxide and magnesium oxide in iron ore was thus calculated out. The method did not require separation of interference elements such as iron, aluminium, titanium, copper, nickel and manganese in iron ore. The interference could be eliminated through adding sodium potassium tartrate tetrahydrate, hydroxylamine hydrochloride or triethano-lamine in acid solution, or adding cupferron in ammonia solution. In ammonia solution, the acid chromium blue K - naphthol green B was used as indicator to determine the total amount of calcium and magnesium by EDTA standard solution titration. Then, KOH solution was added in the same solution to determine the released EDTA from EDTA-Mg complex with calcium standard solution using calcon as indicator. Meanwhile, the EDTA/Ca comparison test was conducted to obtain the comparison coefficient. The content of magnesium oxide was calculated according to the comparison coefficient, consumed volume of calcium standard solution during the titration of released EDTA and the amount of sample. Then, the content of calcium oxide could be calculated by subtraction. The proposed method was applied to the parallel determination of calcium oxide and magnesium oxide in iron ore standard sample. The results were consistent with the certified values. The relative standard deviations (RSD, w=6) of determination results were 1.1 %- 4. 0 %. The recoveries were 98 % -104 %.