Scaling Potential Index (SPI) for CaCO_3 Based on Gibbs Free Energies

摘要

A new index (SPI) incorporating the theoretical thermodynamic relationships relating the equilibrium and solubility constants to the Gibbs free energy of reactions is obtained for assessing the scaling potential of carbonate system.Also inclusion of activity and specific ion interactive forces extends the applicability of the SPI over a wide salinity ranges and in presence of other cations and onions that is usually encountered in brackish water and sea water reverse osmosis desalination units,in concentrate management,and in differentiating between reverse osmosis and nanofiltration modules that have different passages for mono-valent and di-valent ions.Some of the industrially used empirical indices for prediction CaCO3 scaling potential are reviewed and their shortcomings are discussed.The theoretically calculated results for SPI have been compared and validated with experimental values and with other commonly and industrially used indices.The results show that SPI is a better predictive approach.This method could be easily extended to take into account the pressure effects in membrane units.Furthermore,the same principle could be applied and the procedure could easily be extended to other salts.This index is a measure of the scaling potential and provides a conservative measure.Use of Gibbs free energy not only provides a theoretical means for assessing the scaling potential but also will enable future incorporation of the interactive and solvent effects in determining the solubility constants which could become readily possible with the advances in computational chemistry and incorporation of the kinetic and hydrody-namic effects in the future studies from the first principles.