Proposed modifications to the method for the determination of available lime

Abstract

Lime is an important industrial chemical used widely in the steel manufacturing and water treatment industries. One of the major procedures employed to control the quality of lime during its production process is the so-called available lime (Av CaO) method. This method measures the theoretical amount of lime available for neutralisation purposes, and also gives an indication of the degree of conversion from limestone to lime. It entails the dissolution of the material in a sugar solution, followed by subsequent titration of the resultant solution with a standardised acid. The standard SABS procedure requires a shaking time of at least four hours. This is followed by a prolonged period of standing to allow colloidal metal oxides (mostly Fe 2O 3 and MnO 2), as well as grit, to settle from the solution. Usually it is only possible to remove a clear aliquot from the solution for titration purposes after at least six hours of standing. This all result in the method requiring at least 1–2 days to perform before a final value can be obtained. This investigation describes proposed changes to the current method, with the aim to save both time and quantities of reagents used in the process. It entails alternative methods of agitation, variation in the concentration of reagent used and employing microwave extraction of the lime from the sugar solution. It was found that the current method can be streamlined to yield similar results in a much shorter time period and with vastly smaller amounts of reagents consumed. The time and materials savings can be translated into significant financial benefits in everyday plant operations.