Toward a better understanding of molybdenum fixation in sediments
- 出版日期：2002.
- 页数：154 p. :
- 第一责任说明：Trenton Phillip Vorlicek.
- 分类号：a421.5 ; a371
- ISBN：0493903240(ebk.) :
MARC全文
02h0025417 20110921153200.0 cr un||||||||| 110921s2002 xx ||||f|||d||||||||eng | AAI3070553 0493903240(ebk.) : CNY371.35 NGL NGL NGL a421.5 ; a371 Vorlicek, Trenton Phillip. Toward a better understanding of molybdenum fixation in sediments [electronic resource] : the roles of mineral catalysis, zero-valent sulfur, and metal sulfides / Trenton Phillip Vorlicek. 2002. 154 p. : digital, PDF file. Source: Dissertation Abstracts International, Volume: 63-11, Section: B, page: 5121. ; Director: George R. Helz. Thesis (Ph.D.)--University of Maryland College Park, 2002. Field studies indicate that Mo capture in temporally anoxic basins often occurs within sediments but not in overlying waters, suggesting that mineral surfaces accelerate thiomolybdate (MoOxS4-x 2-) interconversions. To test this, the rate of MoS4 2- hydrolysis was investigated in the presence and absence of natural kaolinite and synthetic Al2O3 and SiO2 phases. Comparison of rates achieved with these phases suggests the Al oxyhydroxide component in kaolinite furnishes the catalytic activity. The pH dependence suggests that weak acid sites (pKa-9) on kaolinite promote hydrolysis. A mechanism is postulated involving expansion of the coordination number of Mo from 4 to 6 under influence of the surface.;The presence of adventitious S0 in kaolin slurries alters the expected reaction pathway in the sulfidation direction. A portion of MoOS 32- is transformed to one or more Mo-polysulfido complexes possibly related to known complexes like [(S4)2 Mo(IV)S]2- and [(Mo(V)) 2(S)n(S2)6-n]2- ; n = 0, 2–6. Experiments in the absence of a solid phase show that both MoOS32- and MoS4 2- react with dissolved S0 to form Mo-polysulfido complexes. Second order kinetics are observed for MoOS3 2- loss in polysulfide solutions, implying formation of a Mo (V) dimer. MoS42- is rapidly released from Mo-polysulfido complexes upon removal of S0 from solution. Dissolved S0 accelerates rates of sulfidation. A reaction scheme consistent with the experimental data is presented. S0 may facilitate Mo uptake by causing a reduction in the oxidation state of Mo via formation of Mo-polysulfido complexes prior to deposition as an Mo-Fe-S cubane.;Scavenging of MoO42- or MoS4 2- by metal sulfide precipitates (Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Hg, Pb) shows that MoS42- is scavenged to a greater extent than MoO42-. Scavenging experiments involving pyrite additions to thiomolybdate solutions demonstrate that dissolved S0 facilitates uptake of Mo. A thiomolybdate solution containing negligible S0 showed negligible ΣMo loss to pyrite regardless of Mo speciation. A thiomolybdate solution saturated with S0 showed substantial (up to -25%) ΣMo loss to pyrite; the loss of ΣMo appears to correlate with MoS4 2- in solution, with MoOS32- negligibly removed. Formation of Mo-Fe-S complexes occurs upon addition of thiomolybdates to pyrite despite the extreme insolubility of this mineral. The optical properties of Mo-Fe-S complexes are studied via competitive ligand studies using EDTA or 2-ME and MoS42-. Molybdenum ores. ; Sediments (Geology) Electronic books. aeBook. aCN bNGL http://proquest.calis.edu.cn/umi/detail_usmark.jsp?searchword=pub_number%3DAAI3070553&singlesearch=no&channelid=%CF%B8%C0%C0&record=1 NGL Bs949 rCNY371.35 ; h1 bs1107