Effect of silicic acid on aggregation of hydrous ferric oxide

Nguyen Ngoc Minh*, Flynn Picardal
Author affiliations


  • Nguyen Ngoc Minh* 1-School of Public and Environmental Affairs, Indiana University, MSBII, Walnut Grove Ave, Bloomington, USA 2- Faculty of Environmental Science, VNU University of Science, Vietnam National University
  • Flynn Picardal School of Public and Environmental Affairs, Indiana University, MSBII, Walnut Grove Ave, Bloomington, USA




Silicic acid, hydrous ferric oxide, surface charge, aggregation


Colloidal properties of hydrous ferric oxide (HFO) have received much attention due to their environmental relevance. In this study, aggregation of HFO was determined by time-resolved dynamic light scattering and test tube experiments, evaluating surface charge via zeta potential (ζ) measurements. The silicic acid charge varies with protonation and deprotonation at different pH levels. As an adsorbing species, silicic acid could modify surface charge and affect the colloidal stability of HFO. Electrophoretic experiments revealed that silicic acid lowered particle ζ, decreased the isoelectric point (iep), and allowed HFO to aggregate at a lower pH. Reversal of charge was observed at pH 7.5, 7.0, 6.4, and 6.2 for silicic acid concentrations of 0, 0.5, 1.0 and 1.5 mM, respectively. By demonstrating that silicic acid shifts the iep of HFO to lower pH values, results indicate that silicic acid can change the aggregation properties of HFO. Both light scattering and test tube experiments revealed a “peak aggregation” at pH 5.5-7.5 in the presence of silicic acid. As this pH range is typical for many aqueous systems and soils, we conclude that silicic acid likely plays an important role in HFO transport in water and accumulation of particulate HFO in soil horizons.


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How to Cite

Minh*, N. N., & Picardal, F. (2016). Effect of silicic acid on aggregation of hydrous ferric oxide. Vietnam Journal of Earth Sciences, 38(4), 345–355. https://doi.org/10.15625/0866-7187/38/4/8797