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Modified ferron assay for speciation characterization of hydrolyzed Al(III): a precise k value based judgment
Ye Changqing1, Wang Dongsheng, Wu Xiaohong
1Yantai Institute of Coastal Zone Research for Sustainable Development, Chinese Academy of Sciences, Yantai 264003, China. cqye@yic.ac.cn
Summary
This study refines the ferron assay for precise aluminum speciation, specifically determining aluminum-13 (Al(13)) polycation. The enhanced method clarifies the relationship between Al(b) and Al(13) in aluminum-hydroxide complexes.
Area of Science:
- Analytical Chemistry
- Environmental Chemistry
- Inorganic Chemistry
Background:
- Traditional ferron assays allow aluminum-hydroxide (Al-OH) complex speciation (Al(a), Al(b), Al(c)).
- Al(b) is often equated with the Al(13) polycation, but their precise correlation is unclear.
- Understanding Al-OH speciation is crucial for water treatment processes using aluminum-based coagulants.
Purpose of the Study:
- To develop a modified ferron assay for accurate Al(13) determination.
- To elucidate the correlation between Al(b) and Al(13) in aluminum solutions.
- To provide a method for tracing in-situ Al(13) formation in dilute systems.
Main Methods:
- Utilized a modified ferron assay with nonlinear least squares analysis for Al(13) quantification.
- Simulated complex reactions using two parallel pseudo-first-order kinetic models.
- Investigated aluminum solutions with varying OH/Al ratios (b values) from 0 to 2.5.
- Validated Al(13) identification using (27)Al NMR spectroscopy.
Main Results:
- The modified assay precisely determined Al(13) and clarified its relationship with Al(b).
- Four distinct kinetic constants (k values) for Al-OH complexes were identified.
- A kinetic constant around 0.001 s(-1) correlated with the Al(13) polycation, confirmed by NMR.
- Kinetics were well-regulated across a range of OH/Al ratios.
Conclusions:
- The modified ferron assay offers precise Al(13) determination and clarifies Al(b)-Al(13) correlations.
- This method can track the formation of Al(13) in dilute solutions, relevant to coagulation.
- Provides a valuable tool for optimizing aluminum-based water treatment processes.
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