Structure and activity of the anticaking agent iron(III) meso-tartrate

PbO2 reductive dissolution by dissolved Mn(III) in the presence of low molecular weight organic acids and humic acid

Although Mn(III) complexes with organic ligands have been previously identified, the information about their stability and reactivity is scarce. In the present study, we analyzed the formation and stability of three different complexes: Mn(III)-citrate, Mn(III)-tartrate, and Mn(III)-humic acid (HA), as well as their reactivity toward an element of high environmental concern, lead (Pb).Our results indicate that the stability of studied complexes is highly dependent on pH. The Mn(III) complexes with citrate and tartrate degrade below pH 8, due to the electron transfer reaction between Mn(III) and the ligand, while the Mn(III)-HA complex's degradation is slower and less sensitive to pH. At pH 4, less than 40% of the initial Mn(III)-HA was found to be stable.The reactivity of the complexes was different depending on the ligand and its concentration. The Mn(III)-citrate and Mn(III)-tartrate complexes effectively reduced PbO2 and releases aqueous Pb2+, although significant differences were found with increasing ligand concentration. There was no evidence of the reduction of PbO2 by Mn(III) when it forms a complex with HA. This is likely due to the large size of HA moieties that prevent the Mn(III) component of the complex from getting close enough to the PbO2 surface to initiate electron transfer and lead to the reduction of Pb(IV) by HA itself.

Multiscale Study on the Mechanism of a Bio-Based Anticaking Agent for NaCl Crystals

Caking constitutes a major problem for the flowability, transport, packaging, and consumption of hygroscopic granular crystalline materials such as salt. Sodium chloride is the most abundant salt on the earth and known to form strong lumps, mainly due to cycles of water uptake and water evaporation. We report on a multiscale study of the anticaking effect of the bio-based additive Fe-mTA, a metal-organic complex of iron (III) and meso-tartrate. Drying-deliquescence cycling experiments are performed to reproduce the situation in which the salt undergoes repeated humidity fluctuations. Our results show that Fe-mTA acts as a nucleation promoter and growth inhibitor by inducing roughness on the surface of crystals. To directly study the effect of Fe-mTA down to the micrometer scale, we study liquid capillary bridges between two macroscopic salt crystals by applying droplets of salt solution with various levels of additives. Scanning electron microscopy and three-dimensional (3D) laser scanning confocal profilometry results show that Fe-mTA produces a surface roughness at the micron scale. This roughness decreases the effective contact area between crystals and promotes the spreading of the liquid bridge; consequently, the formation of a solid bridge between grains with water evaporation is avoided, thus preventing the caking phenomenon and, in addition, preventing adhesion of the crystals to solid substrates.

Additive Enhanced Creeping of Sodium Chloride Crystals

This article investigates the mechanism behind the creeping of sodium chloride induced by additives. Here, an experimental approach is complemented with theoretical considerations to describe how creeping patterns of brine evolve and how the introduction of additives into the solution affects the morphology of the resultant crystals. We have found that these additives cause kinetic roughening and morphological instability mainly due to the reduction of surface free energy. There was also a marked increase in three-dimensional nucleation of the NaCl crystals and thus branching.