Measurement of Sequestration Capacity of Complexing Agents for Calcium and Magnesium in Aqueous Solution

Abstract

In relation to softening of city water, inhibition of boiler scale, retarding action on setting of gypsum hemihydrate and Portland cement, several complexing agents such as sodium citrate, sucrose, α-D-glucose, diglycolic acid were chosen and the sequestration capacity of these agents and the composition of complex ions were studied by means of turbidometric titration, chelatometric titration, potentiometry using ion-selective electrode, electric conductivity for the purpose of forming the complex ions with calcium and magnesium ions in aqueous solution. The sequestration capacities of sodium citrate and saccharides differed considerably by the method of measurement. The reason was considered. The calcium ion was seauestrated very well by sodium citrate, the sequestration capacity toward calcium and magnesium ions being about 26. 8 g and 17. 0 g at pH 8. 5, respectively. Most of the complex ions studied in the present work have the bonding ratio of 1/1 in terms of agent/calcium or magnesium, but the bonding ratio was 2/1 for diglycolic acid/calcium. A more stable complex ions appeared in the range of pH 8. 0 to 9. 5. © 1986, The Chemical Society of Japan. All rights reserved.