Characteristics of simplified ferron colorimetric solution and its application in hydroxy-aluminum speciation

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2006-09, Vol.287 (1), p.203-211
• Main Authors: Feng, Chenghong, Shi, Baoyou, Wang, Dongsheng, Li, Guohong, Tang, Hongxiao
• Format: Article
• Language: English
• Subjects: 27Al NMR spectroscopy; Al 13; Chemistry; Exact sciences and technology; Ferron colorimetric solution; General and physical chemistry; Hydroxy-Al solution; Speciation
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2006.03.053

Despite the wide application of ferron assay in hydroxy-Al speciation, the complexation mechanism in function remains unclear and there is no generally accepted quantification stipulation. In this study, a simplified ferron colorimetric solution was suggested and characterized in its application to the speciation of different hydroxy-Al samples with the aid of 27Al NMR spectroscopy. Results show that with no addition of hydroxylamine and orthophenanthroline, the simplified ferron colorimetric solution can become more stable and is applicable in speciation for Al solutions with no or low content of iron ions (i.e., [Fe]/[Al] ≤ 0.05). Polymeric aluminum species, especially Al 13 ([AlO 4Al 12 (OH) 24(H 2O) 12] 7+) may not react with ferron directly but via the process of Al decomposition. Al species of the similar form may have the same level of reaction rate with ferron. The Al a-ferron interaction time adopted to quantify Al a can greatly affect the speciation of hydroxy-Al solutions. The longer the time adopted, the higher the content of oligomer Al species included in Al a (mononuclear and oligomer Al species). However, the adoption of the duration of ferron interaction with Al a + Al b has little effect on the speciation of Al b (soluble polymeric Al species) only if the time is long enough to ensure no further detectable absorbance increase. At least five kinds of Al species, such as mononuclear Al (Al mon), Al 2, Al 6 polymers, Al 13 and colloidal Al (Al c) exist in hydroxy-Al solutions. Generally, Al a includes Al mon, Al 2 and possibly part of Al 6 polymers. In most cases, Al b is mainly composed of Al 13 and other species like Al 6 polymers can also contribute. Only under certain conditions ( B value ranges), Al b can be equivalent to Al 13.