The direct precipitation of rhabdophane (REEPO4·nH2O) nano-rods from acidic aqueous solutions at 5–100 °C

Determination of the Solubility of Rhabdophanes LnPO4·0.667H2O (Ln = La to Dy)

“…The authors observed the rapid equilibration of rhabdophane supersaturated solutions followed by progressive crystal growth. The equilibration time for Nd at room temperature observed by Roncal‐Herrero et al is very short (less than 1 d) compared with that of 100 d in our experiments. Again, the effect of the crystallization state can explain the discrepancies observed between the values of the steady‐state IAP determined by Roncal‐Herrero et al and the solubility products determined in this work.…”

“…The equilibration time for Nd at room temperature observed by Roncal‐Herrero et al is very short (less than 1 d) compared with that of 100 d in our experiments. Again, the effect of the crystallization state can explain the discrepancies observed between the values of the steady‐state IAP determined by Roncal‐Herrero et al and the solubility products determined in this work. Stumm et al established a relationship between the grain size and the solubility; small crystals are thermodynamically less stable and have a greater solubility than larger ones.…”

“…The values reported by Byrne and Kim[22a] and Roncal‐Herrero et al (Figure ) correspond to the only data approaching the thermodynamic equilibria for supersaturation experiments. Unfortunately, these values probably remain too high as the thermodynamic equilibria were not established in the solubility experiments.…”

“…For instance, five log K° s,0 (294–298 K) values have been reported from –26.2 ± 0.02[22e] to –24.65 ± 0.23 for NdPO 4 · 0.667H 2 O. [22f] Roncal‐Herrero et al also reported a steady‐state ionic activity product (IAP) value close to the equilibrium value for the overall Nd‐rhabdophane crystallization reaction, which reached log IAP = –21.49 ± 0.39. These discrepancies could result partly from some differences in the crystallization state (which could be impacted by ageing, as specified by Cetiner et al) [15] and hydration rate of the samples, which was not systematically specified.…”

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

“…Under typical environmental conditions, the hydrated RE phosphates observed in the present study are expected to initially form at nanoscale sizes. As natural water is not supersaturated with regard to RE phosphates [65] when compared with the composition of solutions used in this study, actual RE phosphates may slowly precipitate as larger crystals locally near apatite grains in natural aquifers than those observed in the present study.…”