Determination of Clay Suspension Concentration Profile in a Settling Column Using the Fall-Drop Technique

The determination of clay suspension concentration can be done either by nondestructive or by destructive techniques. Non-destructive techniques such as transmission by radiation and total pressure measurement devices are either expensive or have a limited range of application, whereas destructive tests such as ovendrying require a large amount of sample, whch can limit both the number of sampling ports and the frequency of sampling.

An apparatus has been developed which permits us to draw small-size specimens (less than 0.5 mL volume) from the settling columns, simultaneously from various depths, while at the same time causing minimum disturbance to the sample in the sedimentation column.

The determination of solids concentration in the small size specimen drawn from the sedimentation column is by “fall-drop” technique, whereby a drop of known volume (20 μL) is allowed to fall through a column of immiscible organic liquid. From the velocity of the falling drop the concentration of the suspension can be computed using a calibration curve. Various organic liquids with different densities at room temperature have been tested. The requirements for the selection of these liquids include: reasonable price, low melting point, high boiling point, low vapor pressure, nontoxicity, Newtonian, and immiscible with water, and no chemical reaction with salt solutions. The variations in density and viscosity of these liquids with temperature are presented in this paper. Based on this information, the proper choice of the organic liquid required for measuring the anticipated concentration of the suspension can be made so that the time measured for the fall of a drop between two points (400 mm apart) is sufficiently large (>30 s) and laminar flow prevails for the liquid through which the drop falls.