The maximum of phosphate adsorption at pH 4.0: why it appears on aluminum oxides but not on iron oxides.
The maximum of phosphate adsorption at pH 4.0: why it appears on aluminum oxides but not on iron oxides.
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DOI：
10.1021/la803302m
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发表时间：
2009-03
期刊：
影响因子：
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通讯作者：
Xiao Huang;Gregory Foster;R. V. Honeychuck;J. Schreifels
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文献类型：
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作者：
Xiao Huang;Gregory Foster;R. V. Honeychuck;J. Schreifels
在一定的初始磷浓度和pH值范围内，我们对氧化铝和赤铁矿进行了一系列的磷吸附实验。结果表明，在较低的初始磷浓度(氧化铝为-323微摩尔/L，赤铁矿为-194微摩尔/L)下，磷的吸附在pH 2.5-6.5之间呈现一个平台，然后在pH 6.5-7.0之间急剧下降。然而，随着初始磷浓度的增加，氧化铝对磷的吸附在pH=4.0时急剧增加，而赤铁矿对磷的吸附随着pH的降低而急剧增加，但即使在pH=3.0时似乎也没有达到最大值。用表面络合理论证明，在pH为4.0时，氧化铝的最大吸附是由于(1)在低pH和高表面磷覆盖率时，磷酸盐优先以质子化络合物的形式被吸附；(2)由于氧化铝的转化表面没有质子反应性但磷酸盐-非反应性的三配位羟基，导致表面电势趋于平台期。水合氧化物表面没有三配位表面羟基，这似乎是吸附极大值出现在Al氧化物上而不是Fe氧化物上的原因。
We conducted a series of phosphate adsorption experiments with alumina and hematite at a range of initial P concentrations and pH values. We found that at low initial P concentration of <323 micromol/L for alumina and <194 micromol/L for hematite, phosphate adsorption showed a plateau from pH 2.5 to pH 6.5, followed by an abrupt decrease at pH 6.5-7.0. However, as initial P concentration increased, adsorption on alumina displayed a sharp maximum at pH 4.0, while adsorption on hematite exhibited a steep increase with decreased pH but did not seem to reach a maximum even at pH<3.0. Using surface complexation theory, this study proves that the adsorption maximum at pH 4.0 for alumina results from (1) phosphate being adsorbed preferentially as protonated complexes at low pH and high surface P coverage and (2) surface electric potential approaching a plateau with decreased pH due to the absence of proton-reactive but phosphate-nonreactive triply coordinated hydroxyls at transformed surfaces of Al oxides. The absence of triply coordinated surface hydroxyls at the hydrated oxide surface seems to be the reason why the adsorption maximum appears on Al oxides but not on Fe oxides.