Chemical composition of scales generated from oil industry and correlation to radionuclide contents and gamma-ray measurements of (210)Pb.

Scale generated from the maintenance of equipment contaminated by naturally occurring radioactive materials may contain also chemical components that cause hazardous pollution to human health and the environment. This study spotlights the characterisation of chemical pollutants in scales in relation to home-made comparison samples as no reference material for such waste exists. Analysis by energy dispersive x-ray fluorescence, with accuracy and precision better than 90%, revealed that barium was the most abundant element in scale samples, ranging from 1.4 to 38.2%. The concentrations of the toxic elements such as lead and chromium were as high as 2.5 and 1.2% respectively. Statistically, high correlation was observed between the concentration of Ba and Sr, sample density, radionuclide contents ((210)Pb and (226)Ra) and self-attenuation factor used for the radio-measurements. However, iron showed a reverse correlation. Interpretation of data with regards to the mineralogical components indicated that (226)Ra and (210)Pb co-precipitated with the insoluble salt Ba0.75Sr0.25SO4. Since both Ba and Sr have high Z, samples of high density (ρ) were accompanied with high values of self-attenuation correction factors (Cf) for the emitted radiation; correlation matrix of Pearson reached 0.935 between ρ and Cf. An attempt to eliminate the effect of the elemental composition and improve gamma measurements of (210)Pb activity concentration in scale samples was made, which showed no correction for self-attenuation was needed when sample densities were in the range 1.0-1.4 g cm(-3). For denser samples, a mathematical model was developed. Accurate determinations of radionuclide and chemical contents of scale would facilitate future Environmental Impact Assessment for the petroleum industry.

Recovery of NORM from scales generated by oil extraction.

Scales, containing naturally occurring radioactive materials (NORM), are a major problem in oil production that lead to costly remediation and disposal programmes. In view of environmental protection, radio and chemical characterisation is an essential step prior to waste treatment. This study focuses on developing of a protocol to recover (226)Ra and (210)Pb from scales produced by petroleum industry. X-ray diffractograms of the scales indicated the presence of barite-strontium (Ba0.75Sr0.25SO4) and hokutolite (Ba0.69Pb0.31SO4) as main minerals. Quartz, galena and Ca2Al2SiO6(OH)2 or sphalerite and iron oxide were found in minor quantities. Incineration to 600 °C followed by enclosed-digestion and acid-treatment gave complete digestion. Using (133)Ba and (210)Pb tracers as internal standards gave recovery ranged 87-91% for (226)Ra and ca. 100% for (210)Pb. Radium was finally dissolved in concentrated sulphuric acid, while (210)Pb dissolved in the former solution as well as in 8 M nitric acid. Dissolving the scales would provide better estimation of their radionuclides contents, facilitate the determination of their chemical composition, and make it possible to recycle NORM wastes in terms of radionuclides production.

Sorption of (226)Ra from oil effluents onto synthetic cation exchangers.

Increasing environmental awareness is being urged for the safe disposal of (226)Ra-contaminated production water generated in the oil industry. Birnessite, antimony silicate and their cationic derivatives were studied for the take-up of (226)Ra using the batch-type method under experimentally determined parameters, viz. contact time, solution-solid ratio and (226)Ra concentration. Data was expressed in terms of distribution coefficients. Sorption experiments were performed in different concentrations of nitric acid in order to speculate the mechanism of (226)Ra uptake. Variation in the magnitude of sorption efficiency of the materials in the presence of the major components of waste streams, i.e. Na(+), K(+) and Ca(2+), revealed that K(+) was the greatest competitor and Na(+) the least. The application of the materials to sorb (226)Ra from actual oil co-production water samples, collected from Der Ezzor and Al Fourat petroleum companies (DEZPC and AFPC), was interpreted in terms of the exchange properties of the materials and water characterisation. Of the parameters studied, the selectivity of materials was shown to be greatly dependent on the pH of wastewater to be treated.