In Situ Monitoring of Barium Sulfate Crystallization in a Supersaturated Medium by Electrochemical Impedance Spectroscopy

The synthesis of high-value materials for advanced industrial applications is essential for sustainable resource utilization and circular economy strategies. In this work, barium sulfate (BaSO4) was synthesized via the metathesis reaction between barium chloride dihydrate (BaCl2·2H2O) and anhydrous calcium sulfate (CaSO4) recovered from phosphogypsum after sulfuric acid treatment. The reaction was performed in a highly concentrated medium (50×) to promote rapid precipitation and strong ionic interactions. The synthesis was monitored in situ and in real time for 48 h using electrochemical impedance spectroscopy (EIS). Unlike previous studies focused on BaSO4 scaling or surface deposition, this work applies EIS to directly monitor BaSO4 precipitation in the bulk solution. Nyquist and Bode plots, complex conductivity (σ′ and σ″), DC conductivity (σdc), and relaxation time (τ) were analyzed using an equivalent electrical circuit (R1/(R2 + CPE1)). After approximately 40 h, the EIS response became stable and exhibited a consistent electrochemical behavior, suggesting that the BaSO4 formation process had approached completion. The synthesized BaSO4 was characterized by XRD, SEM, FTIR, BET, PSD, and XRF. Correlating the EIS response with the structural, morphological, textural, and physicochemical properties of the final product demonstrates the potential of EIS as a non-destructive tool for real-time monitoring of precipitation reactions and highlights an effective strategy for phosphogypsum valorization into high-purity BaSO4.