Figure 8 shows a block flowsheet for the carbochlorination of clay. It should be noted that this is a completely dry reaction, and that the chlorine, except for losses, is recycled. Bureau of Mines research, coupled with a feasibility study contracted to Kaiser Engineers, led to the conclusion that in the United States, the clay-hydrochloric acid process, using HO gas sparging crystallization to separate aluminum chloride hexahydrate, is the most likely to be commercially competitive with the Bayer- bauxite process. Alkaline sinter processes are more costly both to build and to operate and are energy intensive. Carbochlorination holds promise, but there are a number of important technical problems for which there are insufficient large-scale test results to make good decisions. As far as processing on the Moon is concerned, there are major problems with all three techniques. Presumably, there has not been on the Moon the kind of weathering of aluminum silicate rocks that has occurred on Earth. Thus, acid leaching processes are less favorable than alkaline sinter processes. The Bureau of Mines is working on a fluoride-catalyzed acid leach of clay or anorthosite which is promising, but at present the fluoride consumption is high and there are unsolved problems related to recovering and recycling acid values from alkali and alkaline earth constituents of the raw materials. On the other hand, to use the alkaline sinter process would require a large supply of limestone—twice the weight of the anorthosite processed. The waste product, dicalcium silicate, cannot be recycled, although it is a useful raw material for making Portland cement. In either of the two above cases, large volumes of aqueous solutions are involved, and settling and thickening to separate solids from liquids is practiced. In the low- gravity lunar environment, these operations would be difficult to carry out. As mentioned, carbochlorination is a dry process, but both chlorine (the initial charge plus makeup) and carbon (all consumed) would have to be transported to the Moon. Processing problems still requiring large-scale testing are as follows: • catalysts to speed up the chlorination reactions (NaCl, KA1C14, and BCl:i are mentioned in patents); • modifiers to inhibit chlorination of the silica content of the material being chlorinated (oxyanions of alkali metals, such as Na2CO3 have been patented); • separation of the various chlorinated species (there are large differences in boiling points, but vapor complexes are known); • oxidation of the purified A1C13 to A12O3 (the technology would be similar to that used to make TiO2 pigment, but has not been tested); • materials of construction (possibly not a major problem, but requires investigation);
RkJQdWJsaXNoZXIy MTU5NjU0Mg==