A Particle Electrophoresis Study of Barium Sulfate Inhibition
Authors: Coffey M.D. , Lauzon R.V. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
Electrophoretic mobilities of barium sulfate particles were studied varying pH, barium sulfate particles were studied varying pH, barium sulfate inhibitor concentration and ionic strength of the aqueous dispersing medium. A relationship was shown to exist between the electrophoretic mobilities of barium sulfate particles with added inhibitor and the effectiveness of that inhibitor to slow barium sulfate crystallization.

Introduction
In 1939 Hatch and Rice reported that polyphosphates, by way of a surface reaction, polyphosphates, by way of a surface reaction, inactivate calcium carbonate scale forming nuclei on the threshold of precipitation. Thus chemicals which retard scale precipitation at a substoichiometric concentration of scale inhibitor to precipitating ions are widely referred to as "threshold" scale inhibitors. Since 1939, hundreds of chemicals have been used to prevent precipitation and or adherence of undesirable prevent precipitation and or adherence of undesirable inorganic scale. We will address ourselves only to the prevention of crystallization. The ability of scale inhibitors to modify crystal morphology and produce non-adhering crystals will not be discussed in this paper.
The classes of chemicals most commonly used for inorganic scale inhibition are polyphosphates, low molecular weight polymers of the polyphosphates, low molecular weight polymers of the acrylate-acrylamide type, organic phosphates and organic phosphonates. These chemicals are all effective calcium sulfate, calcium carbonate and barium sulfate inhibitors. The efficiency of the various inhibitors vary considerably and cost-performance evaluations are widely used.
Corsaro in 1956 studied the mechanism of polyphosphate threshold action using polyphosphate threshold action using electrophoresis and adsorption tests and showed adsorption of polyphosphates on calcium carbonate nuclei to be the operative mechanism of inhibition. Corsaro stated that inhibition of precipitation is probably caused by the large precipitation is probably caused by the large ratio of double layer to particle size produced by adsorption. He also concluded that the saturation concentration of calcium carbonate is extended. This implies that inhibitors change the thermodynamic equilibrium significantly. Evidence has been published, which indicates the systems actually are kinetically controlled and eventually precipitation will occur.
During this study five chemicals reported to inhibit inorganic scale crystallization were evaluated; these inhibitors are fairly representative of the different chemical classes of scale inhibitors.