Figure 6 shows a block flowsheet for the clay-hydrochloric acid process. A double precipitation with HC1 gas has been found necessary in order to obtain an alumina product meeting the specifications for P2O5 and MgO. A two-step thermal decomposition is planned in order to minimize materials of construction problems, simplify HO recovery, and to enable the maximum use of coal as the source of the energy needed for the decomposition.
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