Huang Xiao
Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095, China.
J Colloid Interface Sci. 2004 Mar 15;271(2):296-307. doi: 10.1016/j.jcis.2003.12.007.
Adsorption isotherms for phosphate on hematite were prepared at pH 3.39, 4.16, 5.10, 5.63, and 6.71 in this study. It was found that the adsorption isotherms at pH 5.63 and 6.71 intersected those at pH 4.16 and 5.10. Using surface complexation theory, this study demonstrates that the intersection of adsorption isotherms results from (1) phosphate being adsorbed mainly as protonated complexes at pH 4.16 and 5.10 but as nonprotonated complexes at pH 5.63 and 6.71; (2) the electric potential (psi) at the surface of hematite changing with pH at a rate less than 29.5 mV per pH unit (-d psi /dpH approximately equal 8.9 mV/pH). Fundamentally, however, it seems that the dominance of an imperfect (001) crystal face in the hematite sample is responsible for a low value of -d psi/dpH and the intersection of adsorption isotherms. The adsorption behavior may be regarded as characteristic behavior of protonation of adsorbed phosphate on an oxide with a small value of -d psi / dpH.
本研究制备了在pH值为3.39、4.16、5.10、5.63和6.71条件下，磷酸根在赤铁矿上的吸附等温线。研究发现，pH值为5.63和6.71时的吸附等温线与pH值为4.16和5.10时的吸附等温线相交。利用表面络合理论，本研究表明吸附等温线的相交是由于：（1）在pH值为4.16和5.10时，磷酸根主要以质子化络合物形式被吸附，而在pH值为5.63和6.71时以非质子化络合物形式被吸附；（2）赤铁矿表面的电势（ψ）随pH值变化的速率小于每pH单位29.5 mV（-dψ/dpH约等于8.9 mV/pH）。然而，从根本上来说，似乎是赤铁矿样品中不完美的（001）晶面占主导地位，导致了-dψ/dpH值较低以及吸附等温线的相交。这种吸附行为可被视为在-dψ/dpH值较小的氧化物上，吸附磷酸根质子化的特征行为。
