Sorption of Zn(II) to hematite nanoparticles (HN) (av diam = 10.5 nm) and microparticles (HM) (av diam = 550 nm) was studied in the presence of oxalate anions (Ox((aq))(2-)) in acqueous solutions as a function of total Zn(II)((aq)) to total Ox((aq))(2-) concentration ratio (R = [Zn(II)((aq))](tot)/[Ox((aq))(2-))](tot)) at pH 5.5. Zn(II) uptake is similar in extent for both the Zn(II)/Ox/HN and Zn(II)/Ox/HM ternary systems and the Zn(II)/HN binary system at [Zn(II)((aq))](tot) < 4 mM, whereas it is 50-100% higher for the Zn(II)/Ox/HN system than for the Zn(II)/Ox/HM ternary and the Zn(II)/HN and Zn(II)/HM binary systems at [Zn(II)((aq))](tot) > 4 mM. In contrast, Zn(II) uptake for the Zn(II)/HM binary system is a factor of 2 greater than that for the Zn(II)/Ox/HM and Zn(II)/Ox/HN ternary systems and the Zn(II)/HN binary system at [Zn(II)((aq))](tot) < 4 mM. In the Zn(II)/Ox/HM ternary system at both R values examined (0.16 and 0.68), attenuated total reflectance Fourier transform infrared (ATR-FTIR) results are consistent with the presence of inner-sphere oxalate complexes and outer-sphere ZnOx((aq)) complexes, and/or type A ternary complexes. In addition, extended X-ray absorption Fine structure (EXAFS) spectroscopic results suggest that type A ternary surface complexes (i.e., > O-2-Zn-Ox) are present. In the Zn(II)/Ox/HN ternary system at R = 0.15, ATR-FTIR results indicate the presence of inner-sphere oxalate and outer-sphere ZnOx((aq)) complexes; the EXAFS results provide no evidence for inner-sphere Zn(II) complexes or type A ternary complexes. In contrast, ATR-FTIR results for the Zn/Ox/HN sample with R = 0.68 are consistent with a ZnOx((s))-like surface precipitate and possibly type B ternary surface complexes (i.e., > O-2-Ox-Zn). EXAFS results are also consistent with the presence of ZnOx((s))-like precipitates. We ascribe the observed increase of ZnII(aq) uptake in the Zn(II)/Ox/HN ternary system at [Zn(II)((aq))](tot) >= 4 mM relative to the Zn(II)/Ox/HM ternary system to formation of a ZnOx((s))-like precipitate at the hematite nanoparticle/water interface.