The authors investigated in detail the reducing reaction processes of gypsum in the nitrogenous atmosphere without oxygen. Then we clarified the effect of oxygen by introducing air on the samples in order to study the reaction in the industrial process, and tried some experiments to get some suggestions on the conditions favourable to the industrial process.
(1) The reactions are as follows;
CaSO
4+2C→CaS+2CO
2…(1)
3CaSO
4+CaS→4CaO+4SO
2…(2)
2CaSO
4+C→2CaO+CO
2+2SO
2…(A)
There are two steps in the reducing processes of gypsum. The first reduction step (1) begins near 750°C, proceeds quickly between 800° and 900°C and completes almost at 1000°C. The second step begins near 900°C, proceeds quickly between 1000° and 1200°C and completes almost at 1250°C.
Sulphur is formed by the reaction (3) which occurs simultaneously with the reaction (2), but the reaction (3) is not so active as the reaction (2).
CaSO
4+3CaS→4CaO+2S
2…(3)
The following reactions did not occur in this experiments.
CaSO
4+4C→CaS+4CO…(4)
CaSO
4+CO→CaO+CO
2+SO
2…(5)
(2) The amount of CaS formed in the first reduction step is proportional to the amount of the reducing agent. We discussed the appropriate amount of the agent in order to promote the reaction rate effectively and to make the reaction (2) complete.
(3) Pressing of raw mixtures decreases the loss of the reducing agent due to the combustion and promotes the reactions.
(4) It is observed that burning of sulphur with the introduction of air reduces sulphur trouble in the process and promotes the reaction (2) with the production of sulphur dioxide.
(5) Anthracite and coke were used as the reducing agent in this experiments. Anthracite showed a better results rather than coke.
(6) In the first reduction step, when CaSO
4 was used CaS is formed much more than CaSO
4⋅2H
2O was used. But in the second decomposition step there is no obvious difference in the two cases.
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