Flocculation of diatomite by methylated milk casein in seawater.

A new biodegradable flocculant was prepared from a common and inexpensive protein. Milk casein was methylated in a 0.05 M HCl methyl alcohol solution at room temperature. The methylated milk casein (MeCS), having a methylation degree of 81%, was applied to the separation or flocculation of diatomite in seawater (pH 8.1+/-0.1) at room temperature (18-23 degrees C). The flocculating ability of MeCS was evaluated by a sedimentation balance method (cumulative measurement method). The diatomite suspension was effectively flocculated by the addition of a small amount of MeCS (0.25 wt% of the diatomite weight). The results of sedimentation analysis showed that the size-frequency curve had a very sharp and high peak; thus the diatomite floc formed by MeCS had a rather uniform size. The settling velocity of diatomite floc at the appropriate MeCS dosages (0.25-2 wt% of diatomite) was about 3 x 10(-3) ms(-1).