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DatoValore
TitleThe reduction of selenium (IV) by hydrogen sulfide in aqueous solutions
AbstractThe rates for the reduction of Se(IV) by sulfides were measured in NaCl solutions as a function of pH (2-10), temperature (10-40 °C) and ionic strength (I = 0.01-1 M). The pseudo first-order rate constant (log k1) showed a complex dependence on pH with values decreasing from pH 2 to a minimum at pH 4.5, then increasing from pH 5.5 to a maximum near pH 8 and decreasing again at pH higher than 8. The values of the overall kinetic constant (k) calculated from the values of k1/[H2S]T can be determined from equations: logk=-0.15pH-1355.5/T+0.44I0.5+7.74logk=-0.15pH-1355.5/T+0.44I0.5+7.74 for the pH range 2-4.5 (? = ±0.16), logk=0.28pH-1090.9/T+0.60I0.5+4.68logk=0.28pH-1090.9/T+0.60I0.5+4.68 for the pH range 5.5-7.6 (? = ±0.10) and logk=-0.50pH-1572.1/T+0.45I0.5+12.67logk=-0.50pH-1572.1/T+0.45I0.5+12.67 for the pH range 7.7-10 (? = ±0.05), from 10 to 40 °C and from 0.01 to 1 M ionic strength. The effect of pH and ionic strength on the reaction suggests that the reactions in natural waters are due to the following interactions: H2SeO3+H2S<->products HSeO3-+H2S<->products HSeO3-+HS-<->products while under strong alkaline conditions (pH > 9) a fourth contribution by SeO32-+HS-<->products is also possible. The overall rate expression over the entire pH range investigated can be determined from (H2A = H2SeO3; HA = HSeO3-; A = SeO32-) k=(kH2S-H2A[H+]3+kH2S-HAKHA[H+]2+kHS-HAKHAK1s[H+]+kHS-AKHAKAK1s)/{([H+]2+KHA[H+]+KAKHA)([H+]+K1s)}k=(kH2S-H2A[H+]3+kH2S-HAKHA[H+]2+kHS-HAKHAK1s[H+]+kHS-AKHAKAK1s)/{([H+]2+KHA[H+]+KAKHA)([H+]+K1s)} where kH2S-H2A=2409±566M-1min-1, kH2S-HA=464±233M-1min-1, kHS-HA = 4190 ± 573 M-1 min-1 and kHS-A = 650 ± 382 M-1 min-1 and KHA, KA and K1s are the dissociation constants of selenous acid and hydrogen sulfide. Kinetic runs in natural freshwater samples and natural seawater have confirmed results obtained in simple NaCl solutions suggesting that this reaction may play an important role under anoxic and hypoxic conditions. Sulfide concentrations under these conditions may range from micromolar to millimolar level and Se(IV) half times are in the order of a few hours to minutes, respectively.
SourceGeochimica et cosmochimica acta 83, pp. 37–47
Keywordsseleniumsulfideredoxkinetic
JournalGeochimica et cosmochimica acta
EditorPergamon Press., New York [etc.], Stati Uniti d'America
Year2012
TypeArticolo in rivista
DOI10.1016/j.gca.2011.12.024
AuthorsPettine M., Gennari F., Campanella L., Casentini B., Marani
Text192712 2012 10.1016/j.gca.2011.12.024 selenium sulfide redox kinetic The reduction of selenium IV by hydrogen sulfide in aqueous solutions Pettine M., Gennari F., Campanella L., Casentini B., Marani a Water Research Institute Consiglio Nazionale delle Ricerche, Via Salaria km 29300, C.P. 10, 00015 Monterotondo RM , Italy b Department of Chemistry, La Sapienza University, P.le Aldo Moro, Rome 00198, Italy The rates for the reduction of Se IV by sulfides were measured in NaCl solutions as a function of pH 2 10 , temperature 10 40 °C and ionic strength I = 0.01 1 M . The pseudo first order rate constant log k1 showed a complex dependence on pH with values decreasing from pH 2 to a minimum at pH 4.5, then increasing from pH 5.5 to a maximum near pH 8 and decreasing again at pH higher than 8. The values of the overall kinetic constant k calculated from the values of k1/ H2S T can be determined from equations logk= 0.15pH 1355.5/T 0.44I0.5 7.74logk= 0.15pH 1355.5/T 0.44I0.5 7.74 for the pH range 2 4.5 = ±0.16 , logk=0.28pH 1090.9/T 0.60I0.5 4.68logk=0.28pH 1090.9/T 0.60I0.5 4.68 for the pH range 5.5 7.6 = ±0.10 and logk= 0.50pH 1572.1/T 0.45I0.5 12.67logk= 0.50pH 1572.1/T 0.45I0.5 12.67 for the pH range 7.7 10 = ±0.05 , from 10 to 40 °C and from 0.01 to 1 M ionic strength. The effect of pH and ionic strength on the reaction suggests that the reactions in natural waters are due to the following interactions H2SeO3 H2S< >products HSeO3 H2S< >products HSeO3 HS < >products while under strong alkaline conditions pH > 9 a fourth contribution by SeO32 HS < >products is also possible. The overall rate expression over the entire pH range investigated can be determined from H2A = H2SeO3; HA = HSeO3 ; A = SeO32 k= kH2S H2A H 3 kH2S HAKHA H 2 kHS HAKHAK1s H kHS AKHAKAK1s / H 2 KHA H KAKHA H K1s k= kH2S H2A H 3 kH2S HAKHA H 2 kHS HAKHAK1s H kHS AKHAKAK1s / H 2 KHA H KAKHA H K1s where kH2S H2A=2409±566M 1min 1, kH2S HA=464±233M 1min 1, kHS HA = 4190 ± 573 M 1 min 1 and kHS A = 650 ± 382 M 1 min 1 and KHA, KA and K1s are the dissociation constants of selenous acid and hydrogen sulfide. Kinetic runs in natural freshwater samples and natural seawater have confirmed results obtained in simple NaCl solutions suggesting that this reaction may play an important role under anoxic and hypoxic conditions. Sulfide concentrations under these conditions may range from micromolar to millimolar level and Se IV half times are in the order of a few hours to minutes, respectively. 83 Published version The reduction of selenium IV by hydrogen sulfide in aqueous solutions Gennari_GCA_2012.pdf Articolo in rivista Pergamon Press. 0016 7037 Geochimica et cosmochimica acta Geochimica et cosmochimica acta Geochim. cosmochim. acta Geochimica et cosmochimica acta. barbara.casentini CASENTINI BARBARA dario.marani MARANI DARIO maurizio.pettine PETTINE MAURIZIO TA.P04.021.007 Diffusione, ripartizione, bioaccumulo e trasformazione di inquinanti in ecosistemi acquatici