Method of ball milling aluminum metaphosphate

A method of preparing an aluminum metaphosphate particulate product, comprising:

• charging a milling chamber of a ball mill with grinding media;
• loading an aluminum metaphosphate feedstock into the milling chamber;
• milling the aluminum metaphosphate feedstock with the grinding media into aluminum metaphosphate particles at a particle reduction index in a range from 0.25 to 0.5;
• at a plurality of time steps during a period in which the milling is carried out, removing a fine fraction of the aluminum metaphosphate particles from the milling chamber while leaving a coarse fraction of the aluminum metaphosphate particles in the milling chamber for additional milling;
• and
• preparing an aluminum metaphosphate particulate product with a particle size distribution having a median particle size in a range from 100 μm to 700 μm from the aluminum metaphosphate particles removed from the milling chamber.