Experiments on the effect of cations on the sediment settling velocity

The Cations such as Na+, Ca2+, Mg2+ and Al3+ in river flows would influence the sediment settling velocity because of the flocculation of fine grains. Based on the experiments of sediments settling with different cation concentration, the relationship between settling velocity and cations concentration has been analyzed. It has been concluded that: (1) In the same condition of temperature, grain sizes and sediment concentration, the settling velocity would increase with increasing cations concentration. There is a critical concentration, if the concentration of cations exceed the critical concentration, little change occurs in spite of the sharp increase of cations concentration. (2) There is significant difference between the critical concentrations of different cations. The ratio for criteria of Na+,Ca2+(orMg(2+)) and Al3+ is 250:100:1. And the cations with high valency have more significant effect on sediment settling velocity.