Figure 1: Structural representation of the sulphur-modification reaction for TF-VO formation.
AgNO3, a product of Sigma Aldrich, was used to introduce Ag contaminant in water. A stock 600 ppm aqueous solution of AgNO3 was prepared using deionized water. Cation extraction experiments were carried out using 20 mL of the contaminated water for each run. First, the equilibrium liquid-liquid contact time was determined by adding roughly 3.5 g of each of the TF oils to 20 mL of contaminated water in masked conical flask mounted on a stirrer, all within an enclosed dark chamber, due to the light sensitivity of silver salts. In each case, the resulting two-phase mixture was stirred at 200 rpm for up to 10 hours. In the interim of stirring, samples were taken after: 0.5, 1, 2, 4, 6, 8 and 10 hours, and separated. Treated water samples were collected from the clear aqueous layer recovered after centrifugation of the stirred oil-water mixture and Inductively Coupled Plasma Mass Spectrometer (ICPMS-2030 Shimadzu) was used to analyze the water samples, at 328 nm [5], while a commercial standard Ag solution (QMX Laboratories Ltd, UK) was used for calibration.
In order to determine the respective sorption capacities, various amounts of the vegetable oils in the range of 0.1 to 10 g, were respectively added to 20 mL of contaminated water and brought to equilibrium (stirred for the determined equilibrium contact time/period). Separation and analysis of treated water were performed as earlier stated. In this case however, normal oils were also considered.