Preparation of hydroxyapatite via microemulsion route.

Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1).

The kinetics of dissolution of the carbonate minerals of phosphate ores using dilute acetic acid solutions: the case of pH range from 3.96 to 6.40.

In this manuscript we present, in detail, the mechanism of the selective dissolution of calcite from low-grade phosphate ores (Epirus area, Greece) by dilute acetic acid. It was found that mass transfer makes a significant contribution to the rate-determining step of the overall reaction of four separate pH regions discriminated within the pH range from 3.96 to 6.40. Moreover, two different reaction mechanisms were proposed and two different model equations best fitted the corresponding experimental data. By applying a particular treatment to the developed differential equations proposed by us earlier (see Ref. (2)), we estimated the rate constants of specific slow reactions referred to pH regions 3.96-4.95 and 4.95-5.50. However, for pH region 5.50-6.40, we cannot reach a similar conclusion so far.

Dissolution of the carbonate minerals of phosphate ores: catalysis by carbonic anhydrase II, from bovine erythrocytes, in acid solutions.

In this manuscript we report detailed experimental and theoretical evidence of the effect of carbonic anhydrase II, from bovine erythrocytes, on the dissolution process of carbonate minerals of phosphate ores (Epirus area, Greece) in dilute acetic acid, by recording the pH value of the acid solution as a function of time in the pH range from 2.37 to 6.40. We found that mass transfer makes a significant contribution to the determining step of the overall enzymatic reaction, while we distinguished five separate pH regions within the pH range from 2.37 to 6.40. Two different reaction systems and two model equations fitted perfectly the corresponding experimental data, and were used to evaluate all rate constants and parameters. Subsequently, we proposed the possible mechanisms of action for this enzyme from pH 2.37 to 6.40, within which carbonic anhydrase II was found active.