Combined use of Pd and HF as chemical modifiers for the determination of total chromium in produced waters from petroleum exploration by ET AAS

Bench X-ray microtomography of water-salt solution/oil injected into samples of the Botucatu formation

This paper provides a report on the utilization of the X-ray microtomography to obtain images of the internal microstructure of natural sandstone samples from the Botucatu Formation. Its primary objective was to identify the different phases of fluids when injected into the samples to evaluate the various phases through grayscale histograms obtained from 2-D images, quantification of fluid phases, and generation of 3-D images of them. The fluids used in the experiments comprised one type of commercial oil, one type of industrial oil, and an water-salt solution. Quantitative results from 2-D and 3-D analyzes are presented and compared to the volume of injected solution and the measured volume. The phase size distributions indicated which pore radii had a more relevant participation in the percolation of fluids through the samples. Projections in conjunction with 2-D images and profiles of average percentages of air-filled pores indicated the occurrence of preferential percolation flow paths.  The 2-D images allowed the measurement of the contact angle between the phases present in the sample containing industrial oil. Different measurements taken from the sample containing commercial oil showed capillary effects indicated by the average percentage profiles of air-filled pores in the 2-D images.

Thulium hydroxide: a new coprecipitant for speciation of chromium in natural water samples

A coprecipitation procedure has been established for chromium speciation in natural water samples. The procedure is based on the coprecipitation of Cr(III) on thulium hydroxide precipitate. After reduction of Cr(VI) to Cr(III) by using potassium iodide, the presented method was applied to the determination of the total chromium. The level of Cr(VI) is calculated by difference of total chromium and Cr(III) levels. The procedure was optimized for some analytical parameters including pH, sample volume, matrix effects, etc. The detection limits based on 3sigma criterion were 0.87 microg L(-1) for Cr(III) and 1.18 microg L(-1) for Cr(VI). The procedure presented was validated by the analysis of BCR-144R Sewage Sludge (domestic origin). The presented method was applied for the speciation of chromium in environmental sample with satisfactory results (recoveries>95%, R.S.D.s<10%).