2007/11/20 by Juan Diego Rodriguez‐Blanco, Amalia Jiménez, Manuel Prieto Rubio · 3 citations
Materials Science · Environmental Science · #Calcium Carbonate Crystallization and Inhibition #Clay minerals and soil interactions #Chemical Synthesis and Characterization
paper · doi:10.1021/cg070222+
openalex publication_date 2007/11/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/15
At neutral pH and 25 °C, the interaction of arsenate-bearing aqueous solutions with gypsum results in surface precipitation of pharmacolite (CaHAsO 4 ·2H 2 O) crystals. The crystals grow oriented onto the gypsum surface, forming an epitaxy. Using an A -centered unit-cell setting for both pharmacolite ( Aa ) and gypsum ( A 2 /a ), the epitaxial relationship is found to be (010) Gy ∥ (010) Ph and [101] Gy ∥ [101] Ph . Pharmacolite forms thick three-dimensional crystals elongated on [101] with 010, 1̅11, and 11̅1̅ as major forms. Both the crystal morphology and the epitaxial orientation are interpreted on the basis of the bond arrangement in the structure of both phases. The reaction can be envisaged as a sort of solvent-mediated replacement of gypsum by pharmacolite. Under these experimental conditions, the process stops at a “pseudo-equilibrium” end point in which the reactive solids become completely isolated from the aqueous solution by the epitaxial coating of pharmacolite crystals. The thermodynamic solubility product of pharmacolite was determined at this stage and found to be p K = 4.68 ± 0.04. The reaction paths actually followed by the system and the “true equilibrium” end point are modeled using the geochemical code PHREEQC.