Odvisnost med toplotno obdelavo serpentina in njegovo aktivnostjo

Abstract

In this research the effect of the thermal treatment of chrysotile serpentine on the increase in the reactivity during the process of its leaching in a diluted hydrochloric acid was investigated. Measurements were made on samples of 5 g taken from the heap by selecting the fractions of 3–5 mm. The calcination in air of individual samples, required for the analysis, was carried out in an electric muffle furnace at temperatures from 500 to 1100 °C at intervals of 50 °C. The specific surface areas of the calcined samples were measured with the multipoint B.E.T. method and the relative density with a mercury high-pressure porosimeter. The results were related with the yield of Mg2+ in an extract of 1 g of a ground serpentine fraction from 0 to 315 μm in 250 cm3 of 0.25 M HCl, taken after 5 min from a reactor stirred at 500 min–1 and at 20 °C. The strong relation between the temperature of the serpentinite calcination and the rate of leaching was confirmed. The specific surface area of the examined serpentine rose from 16.2 m2 g–1 at a calcination temperature of 600 °C to the maximum value of 45.2 m2 g–1 at a calcination temperature of 700 °C. At this temperature, the degree of dehydroxylation was 82 % and, at the same time, the maximum rate of dissolution of Mg2+ was reached. Above this temperature, the specific surface area decreased and, at a temperature of 1100 °C, it fell to a value of 2 m2 g–1, which also resulted in a reduction of the yield of Mg2+.