The effect of mannitol and pH of the solution on the properties of sintered magnesium oxide obtained from sea water

In order to reduce the B₂O₃ content in sintered magnesium oxide as much as possible, in precipitation with 80% of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)₄. Experiments have shown that the B₂O₃ content in the sintered magnesium oxide samples is satisfactorily low. The lowest B₂O₃ content is obtained when mannitol is added; no B₂O₃ was found in these samples after sintering. Magnesium oxide samples were sintered at 1500°C; duration of isothemal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO₂ indicates that forsterite (Mg₂SiO₄), monticellite (CaMgSiO₄) and mervinite (Ca₃MgSi₂O₈) are formed during sintering of the samples.