During ironmaking processes, iron is not the only element to be charged in the reactor. Unwanted and harmful elements like alkali metals are also present during iron ore reduction and smelting. For instance, a higher load of sodium (Na) and potassium (K) leads to an increase in emissions (dust, cyanides, etc.) and causes malfunctions in the process performance. So, it is in the interest of operators to gather knowledge about the interaction of K and Na during iron ore reduction—specifically their effect on reactivity and mechanical properties, softening and melting behaviour, and circulation within the reactor. This thesis sought to determine two important aspects of alkalis during ironmaking: the macroscopic behaviour of enrichment and circulation, and the microscopic effects on ferrous burden materials during reduction. An alkali model for ironmaking reactors was developed to demonstrate the behaviour and distribution of alkali compounds in the blast furnace and during smelting reduction processes. Based on empirical models and thermochemical calculations, it is possible to define the amount and the composition of alkali compounds for different reactor areas. The results were compared with industrial data and they show certain analogies. By modifying the process parameters (temperature profile, gas volumes, etc.), the effect on the distribution, flow, and load of alkalis is determinable. To investigate the key aspects of alkalis microscopically, experimental simulations derived from industrial-scale ironmaking processes were performed. After an aqueous K/Na treatment of ferrous burden materials, the assimilation behaviour of different morphological phases was evaluated. Thereafter, reduction and tumbling tests were carried out to define the reactivity and mechanical properties of the iron carriers. To complete the interaction of iron carriers and alkali metals, softening and melting tests were performed. It was shown that the morphological structure is a main factor in the resistance against alkali influence. Lumpy iron ores were less affected than artificial materials like pellets and sinter. Pellets, in particular, showed a lower mechanical stability and an increase in reactivity during reduction. With regard to their melting behaviour, both pellets and sinter demonstrated significantly lower temperatures during phase transformations on the addition of alkali metals.