Chemically Bonded Phosphate Ceramics: III, Reduction Mechanism and Its Application to Iron Phosphate Ceramics

In this, the last of a series of three papers, we discuss a method of forming iron phosphate ceramics by a reduction process. We report the formation of iron oxide ceramics by reducing hematite with iron in a phosphoric acid solution. The reaction results in a rapid‐setting ceramic (at room temperature) with a compressive strength of 3700 psi and a density of 1.7 g/cm 3 . Although the exact mineral form of the binder is difficult to determine because it is mostly amorphous and hence is not amenable to X‐ray diffraction analyses, this material is expected to consist of iron hydrophosphates. The reduction process is very useful in recycling several industrial wastes that are rich in hematite, including iron mine tailings, red mud (a caustic waste from the alumina industry), and machining swarfs. Formation of ceramics with red mud and swarfs is also discussed.