In this paper, the theoretical and industrial definitions of metallic calcium production by the metallothermic process in a vacuum atmosphere were investigated. In the experiments, Al is the only reductant used for metallothermic calcium production. The effects of Al stoichiometry, time variances, and temperature changes were investigated. The experiments were carried out at 1200 degrees C, 1250 degrees C, and 1300 degrees C, and with 100% Al, 125% Al, and 150% Al stoichiometry to produce metallic calcium from the residue of metallic magnesium production. Both the raw materials and the residue phases were characterized by atomic absorption spectrometry (AAS), X-ray diffraction (XRD) spectrometry, and chemical analysis techniques. Experimental results were investigated to determine the highest efficiency of reduction conditions. From the results of the experiments, reaction kinetics and activation energy were calculated. According to the experimental results, the highest recovery rate parameters for the reduction of calcium are 150% stoichiometric Al for 480 min at 1300 degrees C, with 72% recovery.