How well suited are current thermodynamic models to predict or interpret the composition of (Ba,Sr)SO₄ solid-solutions in geothermal scalings?

Heberling, Frank; Schild, Dieter; Degering, Detlev; Schäfer, Thorsten

Abstract:
In this study, we report results of the analysis of a particularly interesting scaling sample
from the geothermal plant in Neustadt-Glewe in northern Germany, which contained
19% Galena (PbS) and 81% of a heterogeneous assemblage of (Ba,Sr)SO₄ crystals with
varying compositions, 0.15 < X$_{Ba}$ < 0.53. A main fraction of the sample (~56%) has a
barite content of X$_{Ba}$ ≈ 0.32. We try to relate the solid composition of the (Ba,Sr)SO₄
solid-solution to the conditions at the geothermal plant concerning temperature,
pressure, and solution composition, and discuss it with respect to the challenges in
modelling the composition of (Ba,Sr)SO₄ solid-solutions on the basis of thermodynamic
mixing models. We note that considerable uncertainties are related to the description
of (Ba,Sr)SO₄ formation by means of thermodynamic models. The scaling composition
observed in this study would be in line with endmember solubilities as predicted by
the PhreeqC-Pitzer database for 70 °C and an interaction parameter, a0 = 1.6. According
to such a model, the scaling heterogeneity would reflect bimodal precipitation
behaviour due to various degrees of depletion of the brine with respect to X(Ba)($_{aq}$).
Minor fluctuations in X(Ba)($_{aq}$): 0.0017 < X(Ba)($_{aq}$) < 0.0042 explain the full range of
observed solid compositions. ... mehr

 Zugehörige Institution(en) am KIT Institut für Nukleare Entsorgung (INE) Publikationstyp Zeitschriftenaufsatz Jahr 2017 Sprache Englisch Identifikator ISSN: 2195-9706 urn:nbn:de:swb:90-712641 KITopen-ID: 1000071264 HGF-Programm 35.14.01 (POF III, LK 01) Erschienen in Geothermal Energy Band 5 Heft 9 Seiten Art. Nr. 9 Nachgewiesen in Web of ScienceScopus
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