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用煤粉和石灰制作的碳化煤球是小化肥厂的主要制气原料。排除物理因素的影响,其强度决定于煤球中的总钙及有效钙的含量。对于总钙的测定,目前生产上均采用 EDTA 滴定法,试样用 HCl 处理后,需过滤除去其中的煤粉,手续繁琐,分析时间需要一个小时左右。而且当煤球中 Fe~(3+)、Al~(3+)含量稍高时,通常用量的三乙醇胺不足掩蔽,常使指示剂发生封闭现象,终点难观察;当 Mg~(2+)含量较高时,又因 Mg(OH)_2的沉淀吸附 Ca~(2+)而使终点反复,结果偏低。以钙离子选择电极为指示电极,以 EGTA 滴定 Ca~(2+)已有不少报
Carbonized briquettes made from pulverized coal and lime are the main feedstocks for gasification in small-scale fertilizer plants. Excluding the influence of physical factors, the intensity depends on the total and effective calcium content in briquettes. For the determination of total calcium, EDTA titration is currently used in the production. After the sample is treated with HCl, it needs to be filtered to remove the pulverized coal. The procedures are complicated and the analysis time needs about one hour. When the content of Fe ~ (3 +) and Al ~ (3+) in briquettes is slightly higher, triethanolamine is usually not enough to be masked and the indicator is often blocked. The end point is hard to observe. When Mg 2+ content Higher, but also due to the precipitation of Mg (OH) _2 Ca ~ (2+) and the end of the iteration, the result is low. With calcium ion selective electrode as the indicator electrode, there are many reports of Ca ~ (2+) titration with EGTA