Zr, Hf and REE distribution in river water under different ionic strength conditions

Paolo Censi, Inguaggiato, Sposito, Marco Venturi, Inguaggiato, Zuddas

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Abstract

The Platani River flowing in south-central Sicily, interacting with evaporite rocks, generates awide range of ionicstrength in the water catchment from0.1 to 5.0mol kg−1.We sampled 38 river sites and analysed the compositionfor the dissolved fraction filtered through 0.45 μm, the truly dissolved fraction obtained through ultrafiltration(10 kDa) and the relative included colloidal fraction.This study was focused on the recognition of Zr, Hf and REE behaviour under changing ionic strength conditions,since this is one of parameters responsible for colloid stability in natural waters. In turn, this phenomenon leadsto REE release from the colloidal fraction and their scavenging onto surfaces of suspended particles or sediment,or their complexation with dissolved ligands.Our results indicated that in both dissolved and ultra-filtrated fractions REE increases either in themiddle (Sm –Dy) or in the heavier (Ho – Lu) part of the PAAS-normalised distribution, while the Zr/Hf ratio value ranges fromsub-chondritic to super-chondritic.Scanning Electron Microscopic and Energy Dispersive X-ray Spectrometric (SEM-EDS) analyses and dissolvedMg, Al and Fe concentrations suggested that the studied colloids consist of aggregations of Al-oxyhydroxides, carbonatenanoparticles and clayswhere organic traceswere not found. The studied colloids showed greater affinity with dissolved Zr than Hf determining Zr/Hf values larger than the chondritic values. The largest Zr/Hf valueswere found in colloidal fractions from waters with ionic strength larger than 0.6 mol kg−1. These Zr/Hf valuesup to 280 (w/w) are provided by the faster removal of Hf relative to Zr from coagulating colloids and its preferentialscavenging onto authigenic Fe-oxyhydroxides in bottom sediment. Further studies are needed to clarify isthis suggested process can represent a suitable starting point for the Zr-Hf decoupling observed in seawater.
Lingua originaleEnglish
Numero di pagine17
RivistaScience of the Total Environment
Volume645
Stato di pubblicazionePublished - 2018

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All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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