A common and inexpensive protein, egg albumin, was applied to the solid-liquid separation or flocculation of diatomite. Egg albumin was methylated in a 0.05 M HCl methyl alcohol solution at room temperature. About 90% of the carboxylic groups of egg albumin could be methylated within 24 h. The adsorption of egg albumin onto diatomite at pH 6.8 was remarkably enhanced by methylation. The adsorption constant of methylated egg albumin to diatomite at 30 degreesC was about 100-fold larger than that of native egg albumin; however, the adsorption constant of methylated egg albumin decreased to about 1/100 with temperature decreasing from 30 to 6 degreesC. The saturated adsorption amount of egg albumin was also increased by the methylation. The flocculating ability of methylated egg albumin was examined with a diatomite suspension at 6 and 30 degreesC in the pH range from pH 2 to 11. The diatomite suspension was effectively flocculated by the addition of small amounts of methylated egg albumin (only 0.5-1 wt% against diatomite) over a wide pH range from pH 3 to 10. (C) 2003 Elsevier Science (USA). All rights reserved.