Determination of solid surface alkalinity of steel slags by thermogravimetric acid desorption

Steel slags are waste products of the steel making industry constituted of different kind of materials, depending on the metallurgic process wich generated them. In general, calcium, iron, manganese and other metal oxide could be present [1] together with hydrated phases like calcium silicates hydrate or calcium hydroxides [2]. For this reason, they generally exhibit a certain degree of alkalinity [3], indeed exploited in heterogeneously catalysed organic reactions, such as the transeterification of oil for the synthesis of biodiesel [4]. Since the superficial alkalinity of the solid material is an important feature in these kind of reactions, its quantification could be very useful. Although several kinds of well-known methods have been esteblished to assess the acidity or basicity of a solution, a smaller number of precedures are known to determine the surface acidity or basicity of a solid. Moreover, these reported methods usually focus their attention on the determination of the superficial acidity of a solid and not ita alkalinity [5]. Among all reported methods, the most accurate one is based on the recording of the amount of desorbed acid (ar alkaline) gas from the solid. In fact, the temperature programmed desorption is used to calculare both the strenght and the density of the basic (or acid) sites [6]. However, this analysis require specific instrumentation and the use of CO2 as desorbing gas for the determination of superficial alkalinity [7]. Thus, developing an easy and useful method to quantify the solid surficial alkalinity i still a challenging goal. This presentation deals with the designing of an innovative procedure based on thermogravimetric analysis for assessing the alkalinity features of solid materials, such as steel slags.