This work focuses on the hydrometallurgical processing of EAF steelmaking dust in laboratory conditions. The behavior of calcium under the influence of sulphuric acid as the leaching agent is discussed. Due to calcium presence the acid is continuously consumed, gradually leaching the calcium phase from EAF dust as well as other zinc- and iron-containing phases. A thorough composition analysis of the input sample of EAF dust was performed. A kinetic study of calcium showed that its leaching is a very fast process, but most of the calcium reacting with sulphuric acid is precipitated from the solution in the form of CaSO4∙2H2O. This causes greater sulphuric acid consumption, and therefore it is necessary to study the calcium behavior during processing of EAF dust. This work is narrowed with calcium behavior during leaching of EAF dust in sulphuric acid and effect of calcium to extraction other metals into solution.