Oil Retention (OR) by Sediment
Oil retention is a function of
Droplet size
Oil droplets should be smaller than sediment pores for easy transport
~ 1 µm easily pass through most pores (30 - 100 µm)
‘Capacity' of soil to hold oil droplets
Silts and clays have more charged sites ? hold more oil
Surfactant type
Non-ionics typically have lower sorption
Ionics have higher sorption (lecithin sorption is very high)
Surface charge (zeta potential) of sediments and droplets
Most clays have a net negative charge
Negatively charged droplets will have lower retention
The maximum oil retention by the sediment is one of the most important parameters in your design.
Unfortunately, it is also one of the most poorly understood.
From what we know, oil retention is a function of the droplet characteristics, surfactant type and soil type.
The oil droplets need to be smaller than the sediment pores, or they will be rapidly strained out. For many commercially prepared emulsions, this is not a significant issue since the average droplet size is much smaller than most soil pores.
Silts and clays have more charged sites on their surfaces so they hold more oil droplets.
The type of surfactant used to prepare the emulsion seems to be important since this controls the affinity of the oil droplets for sediment surfaces.
Emulsions prepared with non-ionic surfactants seem to have a lower oil retention.
Emulsions prepared with ionic surfactants generally have a higher retention.