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The challenges and limitations of vivianite quantification with 2,2′-bipyridine extraction

Year: 2025

Type: article

Abstract: Vivianite presents a significant phosphorus pool in iron-rich, reducing environments, necessitating the development of an affordable and routine quantification method. A novel extraction protocol using 2,2′-bipyridine (Bipy) was proposed as a promising approach. However, the efficacy of this protocol in achieving complete vivianite extraction remains uncertain and lacks robust analytical validation. This study systematically assessed the Bipy extraction protocol on known amount of synthetic and two magnetically recovered environmental vivianite samples, with varying oxidation levels, impurity content, and particle size. Extraction efficiencies of iron and phosphorus were 13–44 % and 13–55 %, respectively, indicating incomplete extraction under the original protocol conditions (0.2 % Bipy, 24 h). An initially rapid release of iron and phosphorus slowed down across all samples, indicating non-constant reaction rates, and suggesting that the extraction is governed by mechanisms beyond kinetic control. Extending the extraction time to 48 h and increasing the Bipy concentration to 1 % yielded marginal improvements, with efficiency gains of 14 % or less. Grinding, which reduced particle size, nearly doubled extraction efficiency. Conversely, the sample with the highest Fe 2+ content showed the overall lowest overall extraction efficiencies. Similarly, recovered vivianite samples containing impurities, namely magnesium and calcium, were extracted less efficiently than synthetic vivianite. Additionally, the extracted iron-to‑phosphorus ratio exceeded the theoretical value of 0.67, indicating non-stoichiometric extraction. To establish Bipy extraction as a reliable analytical method, it is crucial to address incomplete extraction and determine whether vivianite can be fully extracted or only to a certain extent. A potential strategy involves reducing extraction time and repeating the extraction step. • 2,2′-bipyridine extraction was tested on recovered environmental vivianite. • Extraction of all vivianite samples was incomplete. • Smaller vivianite particles were extracted more efficiently. • Vivianite extraction is influenced by factors other than just kinetic mechanisms. • The extracted iron-to‑phosphorus ratio over 0.67 shows non-stoichiometric release.

Source: The Science of The Total Environment

DOI: 10.1016/j.scitotenv.2025.179112

Authors: Sabina Bec, Thomas Prot, Iulian A. Dugulan, Leon Korving, Mika Mänttäri

Institutions: Lappeenranta-Lahti University of Technology, Wetsus, European Centre of Excellence for Sustainable Water Technology, Delft University of Technology

Language: English

Topic: Phosphorus and nutrient management

Subfield: Waste Management and Disposal

Field: Environmental Science

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,250

Funders: Ministerie van Infrastructuur en Milieu, Ympäristöministeriö, European Regional Development Fund