Supersaturation-driven seed optimization and nucleation-regime transition in Vivianite crystallization

Area of Science:

• Environmental Chemistry
• Materials Science
• Chemical Engineering

Background:

• Nonclassical nucleation of vivianite often suffers from long induction times and inconsistent phase selectivity.
• Efficient phosphorus recovery from industrial wastewater and sludge sidestreams is crucial for resource management and environmental protection.

Purpose of the Study:

• To establish a supersaturation-driven comparative framework for elucidating seed-dependent nucleation mechanisms of vivianite.
• To enable controllable formation of the vivianite phase for enhanced phosphorus recovery.
• To optimize seeding strategies for improved kinetics, iron utilization, and phase purity.

Main Methods:

• Comparative framework based on supersaturation levels to study nucleation mechanisms.
• Evaluation of different seeding materials (graphite, sponge iron, vivianite) and their optimal conditions (concentration, particle size).
• Characterization using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).

Main Results:

• Vivianite seeds and sponge iron demonstrated superior performance over graphite, achieving >80% phosphate removal with near-stoichiometric iron consumption (Fe/P ≈ 1.5).
• Optimal conditions for vivianite and sponge iron seeding were identified as 4 g L^-1 (200 μm) and 3 g L^-1 (200 μm), respectively.
• Seeding significantly accelerated phosphate removal kinetics, especially at low supersaturation (SI = 2-4), and increased overall removal efficiency.

Conclusions:

• The critical-supersaturation-index (SI)-based seed-selection framework allows for joint regulation of induction time, iron utilization, and vivianite quality.
• The ability of the interface to sustain a growable Fe-P deposit/epitaxial layer is critical under low supersaturation conditions.
• This framework provides reproducible criteria for engineering vivianite recovery processes from wastewater and sludge.