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The use of tyre derived fuel and of lead-zinc slag (alternative iron source), allows interesting cost cutting for the cement industry. It also presents unexpected input of heavy metals, zinc amongst them. This work aims to clarify the role zinc plays in cement production and hydration. Because it is a heavy metal, zinc provoke health and environmental concerns. The first step was to understand its impact on humans and the environment. The paradox of essentiality and toxicity coexist in the case of zinc, with a narrow margin between required and toxic levels. The major risk associated with zinc pollution is not due to the exposure of human beings to this metal in food or physical environment but through the decrease of available living resources because of the susceptibility of aquatic species to tolerate zinc. Relationships between ZnO and the main cement oxides have been studied and the ternary systems CaO-ZnO-Al<SUB>2</SUB>O<SUB>3</SUB> and CaO-ZnO-Fe<SUB>2</SUB>O<SUB>3</SUB> studied thoroughly. Three new phases were found and their crystallographic data determined. Subsolidus relationships were established, solid solution extension calculated, coexistence lines, melting and solidus temperatures determined. In the system C-Z-F one new phase was found, C<SUB>3</SUB>ZF<SUB>7</SUB>. It is hexagonal, with a=5.9925 A and c=31.5885 A. It melts congruently at 1245 ± 5<SUP>o</SUP>C. Solid solution formation of ZF, C<SUB>2</SUB>F and CF was confirmed in this system, and their extensions estimated. In the case of the system C-Z-A I found two new phases, C<SUB>3</SUB>ZA<SUB>2</SUB> isostructural to the magnesium analogue C<SUB>3</SUB>MA<SUB>2</SUB>; and C<SUB>6</SUB>Z<SUB>3</SUB>A<SUB>2</SUB>. C<SUB>3</SUB>AZ<SUB>2</SUB> is orthorhombic, with a=16.7228 A, b=10.7069 A and c=5.1355 A. Its density is 3.385 gr/cm<SUP>3</SUP> and melts congruently at 1340 ± 5<SUP>o</SUP>C. C<SUB>6</SUB>Z<SUB>3</SUB>A<SUB>2</SUB> is cubic, face centred, with a=14.9058 A. Its density is 3.729 gr/cm<SUP>3</SUP> and melts congruently at 1273 ± 5<SUP>o</SUP>C. Composition of both phases was confirmed by electron probe microanalyses. The calcium-rich portion of the CaO-ZnO-Al<SUB>2</SUB>O<SUB>3</SUB>-Fe<SUB>2</SUB>O<SUB>3</SUB> system was studied, and phase coexistence confirmed. No new ternary or quaternary phase was present in this portion of the system. CaO;C<SUB>6</SUB>Z<SUB>3</SUB>A<SUB>2</SUB>, C<SUB>3</SUB>A and C<SUB>4</SUB>AF coexist in equilibrium. Behaviour of zinc oxide in an industrial system was studied and its low volatile nature confirmed. A kiln fed 200 Kg/hr of zinc emitted 0.003 Kg/hr through bag house clean gases. It was confirmed that zinc leaves the system with the clinker.

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