Multi-stage clay calcination method for controlling product color

A method for thermal treatment of clays, the method comprising:

• preheating clay, in a heat exchanger, the clay suspended in a carrier gas,
• thermally treating the clay in a first calcination stage conducted under chemically oxidizing conditions, followed by
• thermally treating the clay in a second calcination stage conducted under chemically reducing conditions, wherein the second calcination stage is carried out in a dedicated reactor vessel that is separate from the first calcination stage and is configured for active fuel injection to generate reducing conditions within a high-temperature reaction zone at temperatures above 600° C.
• cooling the clay in a first cooling stage conducted under chemically reducing conditions, and,
• cooling the clay in a second cooling stage conducted under chemically oxidizing conditions, such that a sequence of the method comprises an alternating redox profile of oxidizing, reducing, reducing, and oxidizing conditions.