Zinc importance in Portland cement production

Zinc is a well-known retarder of cement setting. In the paper the results of investigation of the influence of zinc content in a kiln feed are presented. The industrial clinker was examined, however, the low zinc content gives no possibility to determine even the solid solution of this metal in clinker phases. Only the balance of the internal recilculating system in industrial kiln was shown that in this system the zinc concentration is six fold higher than introduced to the kiln and in clinker leaving the kiln 96% of zinc is remaining. In this situation the series of clinkers with different zinc content was produced in the semi industrial rotary kiln in the Institute of Ceramic and Building Materials, Krakow Department. The obtained results have shown that the content of up to 1.2% of zinc in clinker is not causing the deterioration of standard cement properties. Higher zinc content is causing unfavourable change of cement properties, by formation of ZnO in clinker which is giving its retarding action. The solid solutions of Zn are the following: in alite – 0.90%, in belite – 0.16%, in C3A – 0.28% and in brown millerite 1.52%. When the Zn content in clinker is higher than 0.61% the own zinc phases: Ca6Zn3Al4O15, Ca6Zn2,8Mg0,2Al4O15 are formed.
Author: P. Zajd, E. Jelito, W. Kurdowski

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