Ion-pair formation in aqueous strontium chloride and strontium hydroxide solutions under hydrothermal conditions by AC conductivity measurements

2014 ◽  
Vol 16 (33) ◽  
pp. 17688-17704 ◽  
Author(s):  
H. Arcis ◽  
G. H. Zimmerman ◽  
P. R. Tremaine
Keyword(s):  
Ac Conductivity ◽  
Formation Constants ◽  
Ion Pair ◽  
Pair Formation ◽  
Strontium Chloride ◽  
Conductivity Measurements ◽  
Hydrothermal Conditions ◽  
Ion Pair Formation ◽  
Strontium Hydroxide ◽  
Ac Conductivity Measurements

Stepwise ion pair formation constants for aqueous strontium chloride and strontium hydroxide have been determined fromT= 295 K toT= 625 K atp= 20 MPa, using a high-precision flow AC conductivity instrument.

The limiting conductivity of the borate ion and its ion-pair formation constants with sodium and potassium under hydrothermal conditions

2016 ◽  
Vol 18 (34) ◽  
pp. 24081-24094 ◽  
Author(s):  
H. Arcis ◽  
J. P. Ferguson ◽  
G. H. Zimmerman ◽  
P. R. Tremaine
Keyword(s):  
High Precision ◽  
Ac Conductivity ◽  
Formation Constants ◽  
Ion Pair ◽  
Pair Formation ◽  
Association Constants ◽  
Potassium Ions ◽  
Hydrothermal Conditions ◽  
Sodium And Potassium ◽  
Limiting Conductivity

The limiting conductivity of borate and its association constants with sodium and potassium ions have been determined from T = 298 K to T = 623 K at p = 20 MPa, using a high-precision flow AC conductivity instrument.

scholarly journals Pb Mineral Precipitation in Solutions of Sulfate, Carbonate and Phosphate: Measured and Modeled Pb Solubility and Pb2+ Activity

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 620
Author(s):  
Xinxin Li ◽  
Behrooz Azimzadeh ◽  
Carmen Enid Martinez ◽  
Murray B. McBride
Keyword(s):  
Contaminated Soils ◽  
Formation Constants ◽  
Ion Pair ◽  
Pair Formation ◽  
X Ray Diffraction ◽  
Ion Pair Formation ◽  
Thermodynamic Constants ◽  
Ion Activity ◽  
Ion Activities ◽  
Ph Range

Lead (Pb) solubility is commonly limited by dissolution–precipitation reactions of secondary mineral phases in contaminated soils and water. In the research described here, Pb solubility and free Pb2+ ion activities were measured following the precipitation of Pb minerals from aqueous solutions containing sulfate or carbonate in a 1:5 mole ratio in the absence and presence of phosphate over the pH range 4.0–9.0. Using X-ray diffraction and Fourier-transform infrared spectroscopic analysis, we identified anglesite formed in sulfate-containing solutions at low pH. At higher pH, Pb carbonate and carbonate-sulfate minerals, hydrocerussite and leadhillite, were formed in preference to anglesite. Precipitates formed in the Pb-carbonate systems over the pH range of 6 to 9 were composed of cerussite and hydrocerussite, with the latter favored only at the highest pH investigated. The addition of phosphate into the Pb-sulfate and Pb-carbonate systems resulted in the precipitation of Pb3(PO4)2 and structurally related pyromorphite minerals and prevented Pb sulfate and carbonate mineral formation. Phosphate increased the efficiency of Pb removal from solution and decreased free Pb2+ ion activity, causing over 99.9% of Pb to be precipitated. Free Pb2+ ion activities measured using the ion-selective electrode revealed lower values than predicted from thermodynamic constants, indicating that the precipitated minerals may have lower KSP values than generally reported in thermodynamic databases. Conversely, dissolved Pb was frequently greater than predicted based on a speciation model using accepted thermodynamic constants for Pb ion-pair formation in solution. The tendency of the thermodynamic models to underestimate Pb solubility while overestimating free Pb2+ activity in these systems, at least in the higher pH range, indicates that soluble Pb ion-pair formation constants and KSP values need correction in the models.

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