High chloride, sulphate and fluoride concentrations in clay-rich aquitard porewater, the North China Plain: Evidence of geochemical behavior

Dongmei Han, Guoliang Cao, Andrew J. Love

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Abstract

The focus of this investigation was to constrain the porewater chemistry from tracer and ion profiles in a 128 m thick clay-rich sequence of Quaternary sediments comprising the clay, silt and fine sand formation in the North China Plain. Porewater are much more saline (1.1-71.0 g/L) than the lower confined groundwaters (0.3-1.3g/L). Chloride profiles from aqueous extraction (AE) (ranging from 117 to 3260 mg/L) generally keep good consistent with that obtained from squeezing test (ST). However, the sulphate and fluoride concentrations by AE (ranging from 340 to 48,700 mg/L and from 8.8 to 144 mg/L, respectively) are far greater than that by ST. Dissolution of evaporites may be responsible for the high Cl/Br ratios greater than 1000, probably indicating recharge occurred during much wetter periods. The original stable isotopic and chemical compositions in the aquitard porewater have been modified by transpiration and evaporation processes concentrating Cl and causing isotopic enrichment during their formation periods. Dissolution of fluorite, hieratite, and cryolite caused by weathering behavior and ion-exchange reactions should be responsible for the high fluoride concentrations in the aquitard porewater. High sulphate levels found in aqueous samples may arise from pyrite oxidation during sampling, storage and/or porewater extraction procedure.

Original languageEnglish
Article number01019
Number of pages6
JournalE3S Web of Conferences
Volume98
DOIs
Publication statusPublished - 7 Jun 2019
Event16th International Symposium on Water-Rock Interaction - Tomsk, Russian Federation
Duration: 21 Jul 201926 Jul 2019

Keywords

  • Aquitard porewater
  • North China Plain
  • Geothermal behaviour

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