Generalized method for determining fluoroacidity by electrochemical diffusion coefficient measurement (application to HfF4)

A universal method for fluoroacidity evaluation was developed and based on a mass transport approach: it simply consists in measuring the diffusion coefficient of an electroactive species in various molten media. The reduction behaviour of Hf(IV) ions was investigated in molten fluorides and diffusion coefficients of Hf(IV) ions were measured. Results showed that diffusion coefficients decrease with fluoroacidity, due to the effect of solvent viscosity (which is linked to bridged fluorines). A global approach of mass transport in solution was then proposed, taking into account both solute and solvent. The Schmidt number (Sc) defined as the ratio between solvent viscosity and solute diffusivity was calculated in order to take into account these two parameters. Results showed that Sc increases with fluoroacidity, in a much more sensitive way than D. This universal method can extended to all electroactive species and to all bath fluoroacidity

Investigating the Drivers of Total Suspended Sediment Regime in the Senegal River Basin Using Landsat 8 Satellite Images

Because total suspended sediments (TSS) influence the penetration of light into the water column and are likely to carry pollutants and nutrients, their study is essential for understanding the functioning of African river ecosystems. If the estimation of solid transport is important in the context of hydro-agricultural developments, its quantification often poses a problem. In addition, in situ data for these areas are rare and, as a result, the environmental factors responsible for the variability of TSS can hardly be understood. This work aims to evaluate the spatiotemporal variability of TSS in the surface waters of the Senegal River using satellite data over the 2014-2018 period. The spatio-temporal dynamics of TSS is reconstructed using a relationship established on several West African sites between in situ data from TSS and satellite reflectances from Landsat 8. These data allow analyzing the relationship between TSS and factors such as rainfall and discharge. We found that the TSS peaks in Bakel coincide with the arrival of the first rains and are followed by peaks in discharge with a lag of 2 months. A time lag between TSS and discharge peaks is also observed on its tributaries like the River Falémé. Concerning the spatial variability, TSS generally increase from the river upstream to the downstream and decrease in the Senegal delta after the Diama dam. The analysis of the TSS upstream and downstream of the Manantali dam, in the upstream area, confirms the relatively low sediment deposits in the dam lake

Investigation on fluoroacidity of molten fluorides solutions in relation with mass transport

Equilibria between species in solution and its corresponding gaseous species were investigated in various molten fluorides mixtures. From the measurements of boron and silicon kinetic constant of gas release, a relative fluoroacidity scale of solvents was proposed. Due to very high kinetic rates of SiF4(g) and BF3(g) release for the most acidic melts, another approach to evaluate fluoroacidity based on mass transport was considered. Relationships between bridging fluorine atoms, viscosity and fluoroacidity was demonstrated. Diffusion coefficients of Si(IV) and B(III) ions were measured and correlated to the viscosity through the Schmidt number (Sc) defined as the ratio between solvent viscosity and solute diffusivity. These results confirmed the fluoroacidity scale previously obtained, validating the original approach developed on mass transport