Scaling risk assessment in a closed circuit recycled board mill by speciation methods

Calcium carbonate scaling often is a critical problem for recycled board mills that have closed water circuits. The objective of this study was to determine local scaling risks throughout the production process. To predict scaling potential, we calculated several saturation indexes, based on speciation determined from detailed water analyses. Calculated scaling trends are in accordance with observed dissolution and precipitation of calcium carbonate in the process, when considering local aeration phenomena. The importance of volatile fatty acids (resulting from anaerobic bacterial activity) in calco-carbonic equilibriums is discussed, and taken into account in the speciation calculation. We also demonstrate the need to measure inorganic carbon instead of alkalinity in such conditions. This makes typical scaling indexes, such as the Ryznar Stability Index, irrelevant to predict scaling risk in closed circuit conditions; thus, it is necessary to use general speciation methods, as described in this paper.

Mixing Corrosion of CaCO3in Natural Waters

The methods of aqueous speciation calculation, pH calculation and the solubility (precipitability) calculation of CaCO3were used to study the mixing corrosion of CaCO3in natural waters. Mixing processes were done between two unsaturated (with CaCO3) solutions, two oversaturated solutions and between an unsaturated solution and an oversaturated solution, respectively. Results show that the mixing corrosion can be divided into two different levels: mixing corrosion in strict sense and mixing corrosion in broad sense. When mixing corrosion occurs, the HCO3-concentration in one end member solution is usually higher than that in the other solution, and the Ca2+concentration in the former solution is also usually higher than that in the latter one.

Influence of thermodynamic database on the modelisation of americium(III) speciation in a simulated biological medium

SummaryAn intercomparison exercise was led in order to study the impact of thermodynamic database (TDB) on the speciation of americium(III) in biochemical media.A first exercice was led, considering only the americium(III) species in solution. Even with different data sets, all the exercises are in relatively good agreement, concluding to successive complexation of the radioelement by phosphate (pH range from 0 to 3), citrate (pH range from 3 to 8) and hydroxo-carbonate (pH range from 8 to 14). Nevertheless, the speciation of americium differs for each pH range from one work to an other.These results are still observed when the speciation calculation includes the formation of solids. Nevertheless, some workers did not integrate in their data set the formation constant of Am(POThis work is a representative example of the impact of the thermodynamic data used in speciation exercises. Some exercices, using uncompleted TDB had wrong results and led to the conclusion of the necessity in the use of expertised and extended TDB.

BASSIST: an applied thermodynamic database for radionuclide chemistry

BASSIST (Base Applied to Speciation in Solution, at Interfaces and SolubiliTy) is an applied thermodynamic database (TDB) for chemistry of long-lived radionuclides. This TDB is developed at the French Atomic Energy Commission (CEA) and concerns solution, sorption and dissolution equilibria. The order of the different steps necessary to elaborate this TDB are presented, from a critical review of experimental acquisitions until to a database compilation. Important concepts such as the heterogeneity of data, the coherence of database and the use of chemical analogies between elements are discussed by using an example of application of the TDB in speciation calculation. The TDB BASSIST is built by using "certified" data, such as selected values of the Nuclear Energy Agency (NEA) and some uncertified data from literature. In the last part of this article, the choice of chemical analogies between elements, the impact of different sets of data on uranium(IV) speciation calculations are discussed.