tailieunhanh - Heavy Metals Release in Soils - Chapter 8

Sự hiểu biết cơ chế hấp phụ Sulfate sắt (III) oxit và hydroxit: Kết quả từ máy bay ATR-FTIR Quang phổ 2 - Sulfate (SO4 aq) là một Tập đoàn oxyanion VI yếu cơ bản với một trung tâm kim loại có điện tích của 6. Trong dung dịch nước nó tồn tại như một trong hai hoàn toàn-deprotonated - hình thức, hoặc là bisulfate proton đơn lẻ (HSO4 aq) ion (Stumm và Morgan, 1991). PKa cho phản ứng proton là ~ 1,9, làm cho các hình thức đầy đủ deprotonated ion chi phối theo điều kiện đất đai bình thường | CHAPTER 8 Understanding Sulfate Adsorption Mechanisms on Iron III Oxides and Hydroxides Results from ATR-FTIR Spectroscopy Derek Peak Evert J. Elzinga and Donald L. Sparks INTRODUCTION Sulfate SG4-q is a weakly basic Group VI oxyanion with a metal center that has a charge of 6. In aqueous solution it exists as either the fully-deprotonated form or as the singly protonated bisulfate HSG-aq ion Stumm and Morgan 1991 . The pKa for the protonation reaction is making the fully deprotonated form the dominant ion under normal soil conditions. Sulfate ions have a hydrated radius of about 4 Ả. At the present time the chemistry of sulfate in the soil environment is still poorly understood. In fact the mechanisms of sulfate sorption have often been the subject of debate both historically and in the current scientific literature. Sulfate is of interest to soil chemists for environmental and agronomic reasons. It is an essential micronutrient for plant growth. Neither deficiency nor toxicity symptoms are commonly seen in cultivated soils but sulfate can occur in extremely high levels near sites of mine waste deposition as a result of hydrogen sulfide oxidation Persson and Lovgren 1996 . Sulfate is a product in the geochemical cycling of pyrite and therefore plays an important role in marine sediment chemistry. Macroscopic studies of sulfate sorption have suggested that sulfate adsorbs via an outer-sphere electrostatic adsorption mechanism on both soils and reference minerals Charlet et al. 1993 . This conclusion is supported primarily by two observations 1 ionic strength has a great effect on the amount of sulfate that is adsorbed with increasing adsorption as ionic strength decreases and 2 no adsorption of sulfate is usually seen above the point of zero charge of the mineral. This fact potentially makes iron and aluminum oxides important sites for sulfate adsorption 167 2001 by CRC Press LLC 168 HEAVY METALS RELEASE IN SOILS in soils since these components have high points

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