Bulletins of Indian Industrial Research The Preparation of Alumina and Sulphur Dioxide from Bauxite-Gypsum Mixtures

In the present paper it is shown that by mixing bauxite and gypsum and heating the mixture to the required temperature all the oxides of sulphur can be expelled and that the resulting calcium aluminates on hydrolysis will funishpure alumina The proportion of bauxite to gypsum the temperature the time of heating and the extraction of alumina from the heated residue are given in the following [...] From the amount of alumina recovered by the acid treatment of the furnace products in these various experiments it is inferred that 3 4 or 5 parts of gypsum to every two parts of bauxite by weight are the most suitable proportions and for getting the best yield the temperature should be above 1160° C. To get a nearer approach to the optimum conditions the experiments indicated in table 2 were c [...] In each of the groups A B and C the proportion of bauxite to gypsum and the time of heating were kept constant while the teperature was varied from 1080° to 1240° C. In group D the proportions of bauxite and gypsum were varied the temperature and time of heating being kept constant. [...] By extrapolation of the graph of the recovered alumina against time under the same proportion of bauxite to gypsum and the temperature it will be seen that the time required to obtain the complete. yield is probably 6-6i hours. [...] (7) The yield of alumina from the water extraction by hydrolysis is found to depend upon (i) the proportion of bauxite to gypsum (ii) the tempeature and (iii) the duration of heating.