A conventional, molal-based Pitzer model for the (H+ – Nd3+ – NO3−){aq} system valid to stoichiometric ionic strengths near 40 mol·kg−1 at 298 K and 0.1 MPa

Abstract

Existing molal-based Pitzer activity coefficient models for (H + Nd + NO3){aq} mixtures are either inaccurate, ill-formed, or do not span the ionic strength (I) range of the solid solubility data for the (H + Nd + ox + NO3){aq} system. As a precedential step in developing a thermodynamic model for aqueous neodymium-oxalate-bearing systems, a speciated, conventional Pitzer model was fitted to the osmotic coefficient and solid solubility data for the (H + Nd + NO3){aq} system at 298 K and 0.1 MPa. The presented HNO3{aq} model spans the range, 0 < I < 30 mol·kg−1, using fewer parameters than previously published molal-based conventional Pitzer models for the speciated system. The Nd(NO3)3{aq} and novel (H + Nd + NO3){aq} models reproduce the fitted isopiestic and solid solubility data within their accuracy between infinite dilution and stoichiometric ionic strengths up to ∼40 mol·kg−1.