The production of fine sediments coated with radioisotopes to act as a tracer in studying the movement of dredging spoil involves some physical and chemical treatment of the sediment. The treatment can affect the electrochemical properties of the sediment and hence its behaviour in fresh and saline water. The effect of these changes on the degree of flocculation of the sediment has been studied by measuring the fall velocity distribution in a 4.4m settling column. The results of these tests show that the coating of inactive gold or silver on to natural sediment without any other pretreatment results in a tracer sediment having fall velocities similar to those of natural sediment. Other pretreatments result in variations in the fall velocity distributions owing to different degrees of flocculation induced by the chemical treatments. An artificial sediment consisting of finely ground scandium glass was also tested for comparison.
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