Constant Composition Study of Crystal Growth of Mixed Calcium-Ferrous Carbonate salt

The formation of iron carbonate films, or by converting carbonate to magnetite at higher temperatures, are important means used to control the rate of corrosion in the oil and gas industry.  The FeCO₃ film can slow the corrosion process by covering up the steel surface and preventing the diffusion of corrosive species to the pipe surface. On the other hand, the excessive build up of iron carbonate salt in the oilfield production line can be a major issue, particularly, in the absence of effective inhibitors.  The growth and thickness of the film depend upon the kinetics of precipitation and crystal growth of iron carbonate. The kinetics of pure salts is also expected to be effected by the impurities. Work has been done to study the kinetic of precipitation of different types of slightly soluble salts formed in oilfield brines. Only few studies of iron carbonate precipitation kinetics have been completed. Previous studies of iron carbonate precipitation kinetics were typically based upon the spontaneous precipitation, where in several factors such as initial concentration, pH and ionic strength change simultaneously during the experiment. In such kinetic studies, it is important to keep these parameters constant.  This work was intended to study the kinetics of crystal growth of mixed calcium-ferrous carbonate salts at constant experimental conditions. In this study all the parameters are well controlled. A special experimental design is used to keep the initial concentrations, pH (7.1) and ionic strength (0.5 M) constant during the course of the experiment. The composition of calcium-ferrous carbonate salt that formed was determined. The mass flux of crystal growth was also investigated and found to be constant.