The precipitation of gypsum, celestine, and barite and coprecipitation of radium during seawater evaporation

Yoav Oved Rosenberg, Ziv Sade, Jiwchar Ganor

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

While the precipitation paths of the major ions (i.e., Ca2+, Na+, K+, Cl and SO4 2−) during seawater evaporation have been extensively studied, the precipitation of minor solutes from evaporated seawater was not thoroughly studied. The present study aims to achieve a quantitative understanding of Sr2+, Ba2+ and Ra2+ removal from evaporated seawater, by exploring in-situ evaporation of seawater in a series of ponds of a salt plant. Seawater samples, at various degrees of evaporation, were collected and analyzed for their solute concentrations. Mass balance and thermodynamic calculations were performed for each sample, revealing that the evaporated seawater remained oversaturated with respect to the three sulphate minerals: gypsum, celestine and barite, for a considerable period before precipitation commenced. In view of this observation, the results are discussed within the framework of the classical nucleation theory. It is hypothesized that the precipitation of these minerals is kinetically hindered by surface area starvation which, in turn, causes the nucleation of these minerals to be the rate determining step. The removal of Ra commences in concordance with the precipitation of Sr and Ba, suggesting that Ra removal is controlled by the formation of a solid solution. Although a ternary solid solution of RaxBaySr1−x−ySO4 actually precipitates, the removal of Ra was modeled by the precipitation of a binary solid solution of RaxBa1−xSO4. Using empirical law from the literature, the removal of Ra could be modeled fairly well. The model suggests that the removal of Ra in evaporated seawater is hindered in comparison to low ionic strength solutions. This inhibition is a result of: 1. The high ionic strength (up to 10.8 mol kg−1); and 2. Precipitation kinetics that may be quantified by the degree of supersaturation with respect to end-member barite in the evaporated seawater (up to 51).

Original languageEnglish
Pages (from-to)50-65
Number of pages16
JournalGeochimica et Cosmochimica Acta
Volume233
DOIs
StatePublished - 15 Jul 2018

Keywords

  • Barite
  • Brine
  • Celestine
  • Co-precipitation
  • Evaporite system
  • Gypsum
  • Ionic strength
  • Kinetic effect
  • Radium
  • Seawater

ASJC Scopus subject areas

  • Geochemistry and Petrology

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