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Amorphous Aluminum Hydroxide Control on Sulfate and Phosphate in Sediment-Solution Systems |
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| Authors: | Tomas Navratil Jan Rohovec Aria Amirbahman Stephen A Norton Ivan J Fernandez |
| Institution: | 1. Czech Geological Survey, Klárov 3, Prague 1, 118 21, Czech Republic 2. Institute of Geology, Acad. of Sci. v.v.i, Rozvojová 269, Prague 6, 16502, Czech Republic 3. Department of Civil and Environmental Engineering, University of Maine, Orono, ME, 04469-5711, USA 4. Department of Earth Sciences, University of Maine, Orono, ME, 04469-5790, USA 5. Department of Plant, Soil, and Environmental Sciences, University of Maine, Orono, ME, 04469-5722, USA |
| Abstract: | We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)3 for SO4 and PO4. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO4 prior to acidification experiment; this sorbed PO4 was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)3 appears to be an important control on dissolved PO4 concentration in surface waters, unless there is a large excess of PO4. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO4. Maximum SO4 adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO4 + inhibited the increasing SO4 adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)3 substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)3, or in Al(OH)3-rich sediment, PO4 mobility will be severely restricted. Suspended Al(OH)3 in acidified surface waters cannot strongly influence SO4 concentrations because of the considerably higher total SO4 concentrations compared to the available surface area. |
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