On the Effect of Opal Exerting upon Sulphur Refining

Abstract

Opal, as well-known, is a amorphous mineral that contains from 3 to 10 per cent combined water, and its molecular formula is given by SiO₂⋅nH₂O.
The writer, to ascertain the effect of opal on sulphur refining, made differential thermal analysis of opaline clay collected from the Matsuo Sulphur mine with an electric furnace that was adjusted to rise 10°C per minute.
The results of the differential thermal analysis indicate that discharge of adsorbed water from the opaline clay is completed at 150°C. And endothermic peak between 400°C and 530°C, is caused by decomposition of marcasite and pyrite which accompany the clay.
If the temperature of the retort is raised higher than 530°C, sulphur is naturally separated from both marcasite and pyrite. But the recovery percentage of sulphur in, the refinery may be less than 100 per cent, because massive ore is used instead of powdered ore as in the laboratory.
On the other hand, it is impossible to dry ore completely that contains more or less opal, by heating higher than 110°C before refining, because it always contains considerable amounts of native sulphur. The ore, therefore, that is sent to the refinery still contains some adsorbed and almost all combined water of opal. This water combines with sulphur to form H₂S and SO₂, if the temperature of the retort rises higher than 400°C.
3S+2H₂O 2H₂S+SO₂
Theoretical and practical volume ratios of H₂S and SO₂ are 100:50 and 100:75, respectively, because oxygen in the air, which flows into the retort during the refining process, combines with sulphur to form SO₂. The amount of sulphur which is collected from the above-mentioned H₂S and SO₂ in the reaction tower is restricted by the volume percentage of H₂S:SO₂=100:50.
So, nowadays, in the case of the Matsuo mine, excess S0₂ gas is wasted.