THERMODYNAMIC STUDY ON THE SILICATE TREATMENT IN OILFIELD WASTEWATER

摘要

Removing the pollutants from oilfield wastewater and reinjecting the wastewater to the formation are conducive to the protection of the local environment. Silicate is a kind of common pollutant of oilfield wastewater. And the accurate prediction of its solubility is beneficial to the formulation of wastewater treatment schemes. To predict the silicic acid solubility in varying temperature, multi-component aqueous solutions, a prediction model applicable to such solution is proposed in this paper based on Pitzer electrolyte solution theory and in consideration of the long-range and short-range Coulomb electrostatic interaction and dispersion interaction between cations and anions. For Na~+-K~+-Ca~(2+)-Mg~(2+)-Cl~--SO_4~(2-)-HCO_3~--F~--SiO_3~(2-) solution, the prediction model is used to calculate the silicic acid solubility at different temperature and ion concentration, then the range analysis is used to analyze the factors affecting the solubility of silicic acid. The result indicate that temperature, Ca~(2+) and SO_4~(2-) are the main factors, with the range R of 11.1, 7.8 and 6.9, respectively. The effects of these factors on the enthalpy change, potential energy and single point energy in silicate reaction have been studied by using quantum chemistry method. The research results agree with the range analysis results, which further checks the correctness of the prediction model. Therefore, this prediction model can be used to predict the silicate solubility in the temperature-varying multi-component silicate solution.