• Materials for Ceramics

Laterite Red Clay

Alternate Names: IMCO Laterite

Notes

Laterites are products of intense and prolonged chemical weathering, most commonly associated with tropical and subtropical environments. During the process, soluble and mobile components such as Na, K, Ca and Mg are strongly depleted and silica can also be progressively removed. Iron and aluminum become residually concentrated. Thus laterites are not defined by a specific chemistry or mineralogy; their composition depends on the parent rock, climate, drainage and degree of weathering.

Typical laterite mineral assemblages contain varying proportions of kaolinite, goethite, hematite, gibbsite and residual quartz. Some can contain extraordinary amounts of iron, while strongly aluminous ones grade toward bauxitic materials. This mineralogical variation means that chemical analyses alone do not reveal how the Al₂O₃ and Fe₂O₃ are actually hosted.

Laterites are often refractory because the weathering process that forms them removes many of the alkali and alkaline-earth oxides that normally act as ceramic fluxes. Thus an iron-rich laterite can be much more refractory than an ordinary red-burning sedimentary clay having a similar Fe₂O₃ content. This material, for example, has a reported pyrometric cone equivalent of 19 despite its very high iron content.

Plasticity is variable. Strongly laterized, oxide-rich or concretionary materials can have little plasticity, whereas kaolinite-rich lateritic clays can be plastic. In ceramics these materials can be useful as unusual sources of iron and alumina in red- and dark-burning bodies and as additions where their combination of high iron content and refractoriness is desirable.

The published analysis for this example IMCO material requires interpretation: the listed SiO₂, Al₂O₃, Fe₂O₃ and TiO2 already total 100%, before the reported 11% LOI is added. The oxide values may therefore have been reported on a calcined basis rather than as a conventional analysis including LOI.

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