ISSN:
1573-5117
Keywords:
phosphate
;
ironhydroxide
;
sulphide
;
apatite
;
sediments
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The accumulation of inorganic phosphate in lake sediments and a possible following release is due to the adsorption of phosphate onto Fe(OOH) and, especially in hard waters, to the precipitation of apatite. Attempts are made to quantify both processes. For the quantification of the P adsorbed, Pads, onto Fe(OOH) the Freundlich adsorption isotherm, Pads=A(o-P)B, gave good results. The constants A and B could be quantified. Constant A appeared to depend on the pH and the Ca2+ and Mg2+ concentrations in the water. Constant B appeared to approach 0.333. The full equation becomes then: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiaadcfadaWgaa% WcbaGaamyyaiaadsgacaWGZbaabeaakiabg2da9iaaikdacaaIZaGa% aGOnaiaaicdacaaIWaGaaiOlaiaacIcacaaIXaGaaGimamaaCaaale% qabaGaaGimaiaac6cacaaI0aacbiGaa8hCaiaa-HeaaaGccaGGPaGa% aiikaiaaikdacaGGUaGaaG4naiaaiEdacqGHsislcaaIXaGaaiOlai% aaiEdacaaI3aGaai4oaiaadwgadaahaaWcbeqaaiabgkHiTiaa-nea% caWFHbaaaOGaaiykamaakeaabaGaam4BaiabgkHiTiaadcfaaSqaai% aaiodaaaaaaa!57AF!\[P_{ads} = 23600.(10^{0.4pH} )(2.77 - 1.77;e^{ - Ca} )\sqrt[3]{{o - P}}\]. with the Ca concentration in mmol l−1 and the o-P and Pads concentrations in mg l−1. For the quantification of the solubility of calcium-bound phosphate the solubility product of apatite being 10−50, as found in the two hard water rivers Rhine and Rhone, was used. With this solubility product the solubility of o-P can be calculated as function of the Ca2+ concentration and the pH. The two equations, for adsorption and precipitation, are put together in a so-called solubility diagramme, which describes the o-P concentration as function of the Fe(OOH) concentration in the sediments, and the pH and the Ca2+ concentration in the overlying water. The release of phosphate from the Fe(OOH)≈P complex under anoxic conditions after adding H2S in inorganic suspensions was shown to be limited. Only when a large excess of H2S was added there was some release, but if less than 75% of the Fe(OOH) was converted into FeS, there was no release. The possibility of organic phosphate as the source of phosphate release under anoxic conditions is discussed. For a full understanding of this possibility, fractionation of sediment bound phosphate must be carried out in such a way, that these organic phosphates are not hydrolysed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00033500
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