Sediments manganese

The process of enrichment of trace metals in these non-biologically produced sediments is probably adsorption to the surface of iron and manganese oxides that form on virtually all particle surfaces in the ocean. This is also the process that forms manganese nodules in vast areas of deep-ocean sediments. Manganese nodules actually accrete on the sea floor at a rate of approximately 1 mm per million years, primarily in areas where there is little accumulation of CaCOs and opal-rich sediments, e.g. the vast red clay provinces of the North Pacific Ocean. Manganese nodules are enriched in the same metals that are found authigenically in the sediments (Table 12.4) to such an extreme... 

Overnell, J., Harvey, S.M. and Parkes, R.J., 1996. A biogeochemical comparison of sea loch sediments Manganese and iron contents, sulphate reduction rates and oxygen uptake rates. Oceanologica Acta, 19 41-55. 

Lynn, D. C. and Bonatti, E. (1965). Mobility of manganese in diagenesis of deep-sea sediments. Marine Geol. 3,457-474. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

Takamatsu, T., Kawashima, M. and Koyama, M. (1985). The role of Mn-rich hydrous manganese oxide in the accumulation of arsenic in lake sediments. Water Res. 19,1029-1032. 

Krishnaswami S, Lai D, Somayajulu BLK (1976) Large-volume in-situ filtration of deep Pacific waters Mineralogical and radioisotope studies. Earth Planet Sci Lett 32 420-429 Krishnaswami S, Mangini A, Thomas JH, Sharma P, Cochran JK, Turekian KK, Parker PD (1982) °Be and Th isotopes in manganese nodules and adjacent sediments nodule growth histories and nuclide behavior. Earth Planet Sci Lett 59 217-234... 

Syn-sedimentary chemical deposits form by chemical and biochemical precipitation of valuable metal components carried in solution, concomitant with the formation of the enclosing sedimentary rock. The manner of such deposition depends on the concentration of the metal in the solvent, the solubility of the precipitating product, the solution chemistry, and the deposition environment. Iron, manganese, phosphorus, lead, zinc, sulfur and uranium are some of the elements that have formed economically valuable deposits by chemical precipitation during sedimentation. 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Malcolm SJ, Kershaw PJ, Cromar NJ, et al. 1990a. Iron and manganese geochemistry and the distribution of 239,240Pu and 241 Am in the sediments of the north east Irish Sea. Sci Total Environ 95 69-87. 

Vertisols formed from amphibolite in the Central African Republic contain 300-1000 mg/kg Cr, 11-200 mg/kg Cu, trace amounts to 6 mg/kg Mo and 60-300 mg/kg Ni (Aubert and Pinta, 1977). In chernozem soils of the flood plains of the Amur region, the average Cr is 400 mg/kg. High Co concentrations (100-300 mg/kg) have been found in soils. Manganese concentrations in lithomorphic vertisols are in the range of 3000-5000 mg/kg. Soils on clayey sediments, solonetses and saline alkali soils contain 50-75, 40-100 and 10-50 mg/kg Ni, respectively. 

Chao T. T. Selective dissolution of manganese oxides from soils and sediments with acidified hydroxylamine hydrochloride. Soil Sci Soc Am Proc 1972 36 704-768. 

Mahan K.I., Foderaro T.A., Garza T.L., Martinez R.M., Maroney G.A., Trivisonne M.R., Willging E.M. Microwave digestion techniques in the sequential extraction of cadmium, iron, chromium, manganese, lead and zinc in sediments. Anal Chem 1987 59 938-945. 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

Key et al. [27] have described improved methods for the measurement of radon and radium in seawater and marine sediments using manganese dioxide impregnated fibres. The basic method that these workers used was that of Broecker [28]. Seawater samples were taken in 30 litre Niskin bottles. 

Copper in livers and muscles of Weddell seals was positively correlated with manganese (Szefer et al. 1994). In general, manganese and copper are positively correlated in tissues of marine vertebrates (Eisler 1984). Uptake of copper from copper-contaminated freshwater sediments by annelid worms is related to the amount of reducible manganese oxide in the sediments (Diks and Allen 1983). 

In Limnodrilus sp., an oligochaete worm, copper bioavailability from surhcial freshwater sediments is associated with the amount of copper present in the manganese oxide fraction of the sediment. The redox potential and pH in the gut of Limnodrilus allows the dissolution of the manganese oxide coating, making copper and other metals available for uptake (Diks and Allen 1983). 

Zinc ligands are soluble in neutral and acidic solutions, so that zinc is readily transported in most natural waters (USEPA 1980, 1987), but zinc oxide, the compound most commonly used in industry, has a low solubility in most solvents (Elinder 1986). Zinc mobility in aquatic ecosystems is a function of the composition of suspended and bed sediments, dissolved and particulate iron and manganese concentrations, pH, salinity, concentrations of complexing ligands, and the concentration of zinc (USEPA 1980). In freshwater, zinc is most soluble at low pH and low alkalinity 10 mg Zn/L of solution at pH 6 that declines to 6.5 at pH 7, 0.65 at pH 8, and 0.01 mg/L at pH 9 (Spear 1981). Dissolved zinc rarely exceeds 40 pg/L in Canadian rivers and lakes higher concentrations are usually associated with zinc-enriched ore deposits and anthropogenic activities. Marine... 

Most of the zinc introduced into aquatic environments is sorbed onto hydrous iron and manganese oxides, clay minerals, and organic materials, and eventually is partitioned into the sediments (USEPA 1987). Zinc is present in sediments as precipitated zinc hydroxide, ferric and manganic... 

Extractable concentrations of sediment-bound zinc were positively correlated with zinc concentrations in deposit feeding clams (Luoma and Bryan 1979). Availability of sediment zinc to bivalve molluscs was higher at increased sediment concentrations of amorphous inorganic oxides or humic substances, and lower at increased concentrations of organic carbon and ammonium acetate-soluble manganese. Zinc uptake by euryhaline organisms was enhanced at low water salinity (Luoma and Bryan 1979). 

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