Silica from ionic solutions

Migration and deposition of iron and silica from ionic solutions... 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

Figure 3 Dissolved As(V) concentrations in porewater ( X/L) as a function of the arsenic content of the sediment ( Xg/g) where partitioning between the solid and solution is controlled by sorption onto hydrous ferric oxide (HFO) with 1 or 1.5 mg/g Fe(III) (as HFO) present in the sediments. Modeling was performed using MINEQL (133) which incorporates constants for sorption onto HFO from Dzombak and Morel (134). Constants for sorption of silica from Hansen et al. (114) and of fluoride estimated by Dzombak and Morel (134) were included in the modeling. Calculations were performed at pH 8 with ionic strength fixed at 0.01. Dissolved concentrations of major ions were fixed at the values reported for Figure 2 (i.e., sorption of these ions onto HFO was not allowed to deplete their concentration in the porewater). Contents of As and Fe in the sediments were calculated based on Eq. (1) using D = 2.6 g Ian and ( ) = 0.3.

Ti02 has been prepared by the careftd hydrolysis ofTiCl4 in [BMIM](BF4] [23]. The Ti02 precipitated from the solution and, as with the silica preparation described above, acetonitrile was used to extract any of the ionic liquid contaminating the product (for more details see Section 6.3). 

In cases where these assumptions are not valid, deviations from the expected behavior can be found. In fact, the three latter assumptions are only reasonable at a limited range of low surfactant concentration. For instance, adsorption of SDS does not occur on naked silica until 0.1 M concentration is reached. Therefore, the model should fail with silica as the stationary phase. In fact, it was observed that the change on the silica surface due to SDS adsorption caused a variation in the K s values of several nonionic and ionic solutes, so that the plots of 1/k vs. SDS micellar concentration were no longer linear [10]. 

Ir(IV), Rh(III), Pt(IV), Os(VIII), Pd(II), and Au(III) were sorbed from aqueous solution by silica gel, which was chemically modified with nitrogen-containing organic ligands. This was performed as a function of hydrochloric acid concentration, time of contact, concentration of the element, and the ionic strength. Extraction, followed by determination on the sorbent surface by x-ray fluorescence of Ir(IV), and Rh(III), from 10 to 10 M solutions, were achieved. An atomic emission method was used to determine Au(III) on the surface of the sorbent containing bonded diethy-lenetriamine groups. 

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