There was no particle larger than 500 mm after two times of fine grinding. For both HRS and HRW, the particles which
passed through 500 mm sieve but retained on the top of 300 mm sieve had the largest proportion in the 1st grinding group, as for the 4th grinding group, the largest portion was the particles that passed through 212 mm sieve but retained on the top of 150 mm sieve.