https://zenodo.org/record/1253884/files/article.pdf

Sorption of divalent metals on calcite

Calcite precipitation mechanisms and inhibition by orthophosphate: In situ observations by Scanning Force Microscopy

Precipitation of calcium carbonate

Experimental conditions of Busenberg and Plummer for 1atm p[sub CO[sub 2]] and variable saturation states were reproduced and growth mechanisms were examined in situ at these conditions. Using a pH-stat method, calcite seeds were reacted in solutions of known calcite saturation state at 25 C for 1--2 days before transferring to an SFM fluid cell for continued reaction in the same solutions. The authors observed that when solution saturations with respect to calcite were >1--2, precipitation began with the formation of surface nuclei. These nuclei spread, coalesced, and continued growing. Only after more than 1 hour was there a transition to a mechanism resembling spiral growth. At these long reaction times, migrating steps assumed individual heights of 1--3 monolayers. The influence of phosphate was examined and observations suggested two inhibition mechanisms, depending on surface history. Phosphate (6 [mu]mol PO[sub 4]) introduced during the nucleation stage results in the formation of nuclei with amorphous shapes. Phosphate introduced during layer growth disrupts the relatively straight steps produced during PO[sub 4]-free growth to form jagged steps. A comparison of their observations with kinetic interpretations reported by solution chemistry studies of calcite precipitation suggests that some rate experiments may include the early influence ofmore » a rapid nonlinear growth phase caused by surface nucleation. If true, the analysis of data and interpretations of growth mechanisms may be affected and suggests that rates of stable calcite growth in natural systems may be slower than experimentally determined values would predict. Both of the phosphate-calcite surface interactions are consistent with mechanisms proposed in previous studies.« less

Calcite precipitation mechanisms and inhibition by orthophosphate: In situ observations by scanning force microscopy

Transesterification of palm kernel oil with methanol over mixed oxides of Ca and Zn has been investigated batchwise at 60 °C and 1 atm. CaO·ZnO catalysts were prepared via a conventional co-precipitation of the corresponding mixed metal nitrate solution in the presence of a soluble carbonate salt at near neutral conditions. The catalysts were characterized by using techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). The results indicated that the mixed oxides possess relatively small particle sizes and high surface areas, compared to pure CaO and ZnO. Moreover, the combination of Ca and Zn reduced the calcination temperature required for decomposition of metal carbonate precipitates to active oxides. Influences of Ca/Zn atomic ratio in the mixed oxide catalyst, catalyst amount, methanol/oil molar ratio, reaction time, and water amount on the methyl ester (ME) content were studied. Under the suitable transesterification conditions at 60 °C (catalyst amount = 10 wt.%, methanol/oil molar ratio = 30, reaction time = 1 h), the ME content of >94% can be achieved over CaO·ZnO catalyst with the Ca/Zn ratio of 0.25. The mixed oxide can be also applied to transesterification of palm olein, soybean, and sunflower oils. Furthermore, the effects of different regeneration methods on the reusability of CaO·ZnO catalyst were investigated.

Abraham Glasner

Papers

The thermal decomposition of lanthanum oxalate

The crystallization of NaCl in the presence of [Fe(CN)6]4- ions

The crystallization of KCl from aqueous solutions in the presence of lead ions. I. A calorimetric study

Thermal decomposition of the light rare earth oxalates

Crystal habit modifiers: I. The relationship between the structure of the additive and the crystal lattice