Ustulation

various tests were performed in the differential thermo-gravimetric analyser (TG-DTA) with the intention of observing the behaviour of the material duirng the heating. The rate of heating used was of 10 K/Min, reaching to 850°C for limit of the apparatus. The patron substance of comparison was alumina (A12O3), with weight which is equal to that of the material being studied (30mg). The graphs obtained and the diagrams of equilibrium Fe-S-O allowed to choose the temperature of practice (680°C).

The reactor of the rotational oven, used in the ustullation was of quartz, with useful capacity maximum of 250 grs, for the material in question (1 = 4.27 g/cm). above this value, problems of homogenousness of the final product occurred. The speed of turning of the reactor was of 3.7 rpm. Tests of two hours were performed in dead atmosphere (N2), oxidant (air), and in two stages (1 hour with N2 and 2.5 hours with air). The evacuations were controlled by firmed rotometer in 1.5 1 min. The speed of injection of the gasses, through a lance did not allow the obstruction of the tube, caused by the enormous amount of condensed matter in the extremity of the outlet of the oven. This matter, of variable color between the colors yellow and red, was identified (defraction of x-rays) as being a mix of elemental arsenic and of its sulphates and oxydes.

Once the test was finished, and after the cooling of the tube, the condensed material in the extremities (of vitreous aspect) was removed with a spatula, with the intent of not contaminating the ustullated product, which was then unloaded and weighed to control the loss of weight (generally of 25%, with 3% of humidity).