MadSci Network: Chemistry

Re: process of flocculation between clay and oil

Date: Mon Sep 15 16:05:37 2003
Posted By: Leslie Allen, Staff, Laboratory Chemist, Valero Refining Company
Area of science: Chemistry
ID: 1058454302.Ch

Pure Appl. Chem., Vol. 71, No. 1, pp. 83–93, 1999.
Printed in Great Britain.1999 IUPAC83
The interaction of fine particles with stranded oil*
Edward H. Owens 
Owens Coastal Consultants Ltd,
 755 Winslow Way East, Bainbridge Island, WA 98110, USA

...The natural cleaning and removal processes of stranded oil from 
shorelines on exposed coasts have been understood for many years; they 
involve a simple relationship between the level of wave energy and the 
location of the oil. On open coasts, oil in the zone of normal wave action 
is rapidly abraded by physical processes and removed into the water 
column. The understanding of how shorelines clean themselves in the 
absence of wave energy and erosion, however, was not understood until a 
study conducted following the Exxon Valdez oil spill in 1989 provided an 
explanation [1]. During laboratory work on oiled sediments collected from 
Prince William Sound, Alaska, Bragg and his co-workers observed a process 
that involved the creation, in seawater, of a stable emulsion of micron-
sized droplets of oil surrounded by micron-sized clays. The process of 
clay-oil flocculation reduced the adhesion of oil to other materials, such 
as sediment or bedrock and, once formed, the clay-oil flocs were easily 
removed by even gentle water motion. From a scientific point of view this 
discovery was not new. Studies on the surface properties of mineral, 
organic, and biologic fines had provided a body of knowledge related to 
the interactions of fine particles with hydrocarbons, and a number of 
investigators had studied these interactions as a mechanism for the 
adsorption and transport of hydrocarbons in seawater (e.g. [2,3]). These 
studies focused primarily on the offshore environment. The new element 
provided by the Bragg study was the recognition that this active, natural 
process was a mechanism that could explain how and why residual oil is 
removed from shorelines in the absence of hydraulic activity (waves and 
currents).The implications of the laboratory studies by Bragg’s team were 
quickly seen to be significant in developing an explanation for the 
documented large-scale removal of oil from sheltered shorelines in Prince 
William Sound that had occurred during the 1989–90 winter months [4]. The 
natural cleaning of exposed shorelines in Prince William Sound could be 
explained easily as a consequence of hydraulic removal by winter wave 
action. The fact that many sections of oiled shoreline were naturally 
cleaned in the absence of wave action, in sheltered areas such as 
Northwest Bay or Herring Bay, could now be explained by the mechanism of 
clay-oil flocculation. Over the two years that followed, the new 
understanding gained from this study was applied to explain the changes 
that had been observed or documented on numerous other spill situations 
.*Pure Appl. Chem. 71(1) (1999). An issue of special reports reviewing oil 
spill countermeasures.

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