The wet ball-milling tests were conducted at different rotating speeds (20, 25, 35, and 45 rpm) using the 20-mm balls. Figure 7a shows the wet ball-milling separation results in n-butyl acetate. Complete separations are achieved within 90, 70, 60, and 50 min of wet ball milling at rotating speeds of 20, 25, 35, and 45 rpm, respectively.