Preparationof Lamellar Mg(OH)2with CausticCalcined Magnesia through Apparent Hydration of MgO.

A processusing plentiful and inexpensive caustic calcined magnesia(CCM; main component is MgO) to prepare lamellar MH of high purityis described. The process begins with the reaction of MgO in CCM withNH4NO3at ∼100 °C to produce ammoniagas and Mg(NO3)2solution and the subsequentfiltration of Mg(NO3)2solution to remove impurities(e.g., SiO2). Then, the obtained ammonia is introducedinto the Mg(NO3)2solution to produce MH precipitateand NH4NO3. After the MH precipitate is separatedby filtration, the filtrate containing NH4NO3is returned to the initial step. The overall reaction of this processis the hydration of MgO to MH. Therefore, this process is called theapparent-hydration method. This apparent-hydration method overcomesthe disadvantages of the true hydration method, such as the inabilityto remove impurities. A crucial finding is that, because of the presenceof trace SO42–in the obtained Mg(NO3)2solution, a MH product with a narrow particlesize distribution cannot be produced. After removal of the SO42–with Ba(NO3)2,lamellar MH with a narrow particle size distribution can be synthesizedat 120 °C in one step. This work provides a promising route tothe use of CCM to prepare MH. [ABSTRACT FROM AUTHOR]