Abstract：In order to solve the problem of low whiteness of fly-ash cenospheres, the paper takes calcined fly-ash cenospheres as raw materials, Na OH and MgSO4 as the coating agents, composite powder of fly-ash cenospheres coated with Mg (OH) 2 nano-particles was prepared with heterogeneous nucleation method.The composite powers were characterized by the whiteness analyzer, particle size analyzer, specific surface area analyzer, X-ray diffractometer (XRD) and scanning electron microscope (SEM) . The effect of different factors on the whiteness of the composite powders was studied. The results show that the whiteness increases from 27.1% to 51.2%, the particle size of D98 increases from 60.81 μm to 66.72 μm, the specific surface area increases from 4.512 m2/g to 31.697 m2/g when the coating amount is 50%, the coating agents are dropped at the same time and the reaction temperature is 80 ℃. XRD and SEM show that the surface of fly-ash cenospheres is coated with nano-lamellar Mg (OH) 2. The composite powder is expected to be used in the field of filling plastics and sewage treatment.

Keywords： fly-ash cenospheres; Mg(OH)₂ nano-particle; whiteness; heterogeneous nucleation