The effect of TiO2 concentration (1, 2, and 5 mass %) on the reduction of B2O3 content has been studied during isothermal and activated sintering of seawater-derived magnesium oxide at 1550, 1650 and 1750 degrees C for 1, 3 and 5 h. Magnesium oxide is obtained from seawater by precipitation with 80% and 120% of the stoichiometric quantity of the dolomite lime as the precipitation agent. The results indicate that the addition of TiO2 has a, significant effect and it also greatly affects the evaporation of B2O3. The thermodynamic analysis of experimental results, based on Onsager phenomenological postulates, has established the relations of mutual influence of simultaneous irreversible processes, i.e. reactions of the formation of Ca2B2O5 and CaTiO3, during isothermal and activated sintering of seawater-derived magnesium oxide.