Figure 7 shows a block flowsheet for the anorthosite-alkaline sinter process. This process is energy intensive, partly because of the need to grind the anorthosite to a very fine powder before pelletizing and sintering, and partly because of the high temperature (~1603°K, 1330°C) required for sintering. The soaking and “dusting” step avoids the need to grind the sinter product before leaching. By holding the sintered pellets at about 973°K for 1/2 hour, a phase change from /3-dicalcium silicate to y-dicalcium silicate takes place, and the sinter falls to a powder on cooling. Key reactions for the carbochlorination process are as follows:
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