Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Manganese occurrence

We may note (a) the common occurrence of oxidation state +2 where the 4s electrons have been formally lost, (b) the increase in the number of oxidation states from scandium to manganese in the latter element, the oxidation state + 7 corresponds to the formal loss of the and 3d electrons, (c) the sharp decrease in the number of oxidation states after manganese—suggesting that removal of the paired id electrons is less easy (d) the oxidation state 0, occurring for many of the later elements in the series. ... [Pg.362]

The De Wolff disorder model has been extended to the cation vacancy model for /-Mn02 and -Mn02 by Ruetschi [42]. In this model the occurrence of manganese cation vacancies and the non stoichiometry of electrochemical Mn02 have been taken into account. Furthermore, the vacancy model deals with the explanation of the different water contents of manganese dioxide. Ruetschi makes some simple assumptions ... [Pg.90]

Note that the occurrence of a maximum oxidation state, corresponding to the removal of all the valence shell electrons and the adoption of a configuration, does not occur after manganese. In Chapter 9 we see how this reflects the contraction of the poorly penetrating 3d orbitals as the nuclear charge increases and it becomes progressively more difficult to remove electrons. [Pg.18]

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. [Pg.49]

Minerals belonging to the category of insoluble oxide and silicate minerals are many in number. Insoluble oxide minerals include those superficially oxidized and those of oxide type. The former category comprises mainly superficially oxidized sulfide minerals, including metals such as aluminum, tin, manganese, and iron which are won from their oxidic sources. As far as silicate minerals are concerned, there can be a ready reference to several metals such as beryllium, lithium, titanium, zirconium, and niobium which are known for their occurrence as (or are associated with) complex silicates in relatively low-grade deposits. [Pg.192]

Occurrence. In order of abundance in the earth s crustal rocks, it is the third within the transition elements (after Fe and Ti) and the 12th in the general order of all the elements. It occurs in several minerals such as primary deposits of silicates and as secondary deposits (commercially more important) of oxides and carbonates as pyrolusite, Mn02, hausmannite, Mn304, rhodochrosite, MnC03, etc. Large amounts of manganese are present in the deep sea nodules located over certain areas of the ocean floor. [Pg.422]

Repeated subcutaneous or intraperitoneal injection of manganese dichloride caused increased incidences of lymphosarcomas in mice. Chronic oral exposure of rats to manganese sulfate led to a slight increase in pancreatic tumors that was not dose responsive." There is no information relating manganese exposure to cancer occurrence in humans." Genotoxic assays have yielded mixed results."... [Pg.434]

Saric M, Lucic-Palaic S Possible synergism of exposure to airborne manganese and smoking habit in occurrence of respiratory symptoms. In Walton WH (ed) Inhaled Particles, rV pp 773-779. New York, Pergamon Press, 1977... [Pg.435]

Boero.V. Schwertmann, U. (1987) Occurrence and transformations of iron and manganese in a colluvial terra rossa toposequence of Northern Italy. Catena 14 519-531 Boesen, C. Postma, D. (1988) Pyrite formation in anoxic environments of the Baltic. [Pg.562]

Hatva, T. (1989) Iron and manganese in ground-water in Finland Occurrence of glacifluvial aquifers and removal by biofiltration. Publ. Water environmental research institute. Nat. Board Waters Envir., Finland, No. 4, 99 p. Haupt, S. Strehlow, H.H. (1987) Corrosion layer formation and oxide reduction of passive iron in alkaline solution A combined electrochemical and surface analytical study. Langmuir 3 837-885... [Pg.588]

Synonyms manganous carbonate manganese spar rhodochrosite Occurrence and Uses... [Pg.543]

Occurrence Manganese(ll) hydroxide occurs naturally as the mineral pyrochroite... [Pg.548]

This circular reviews the occurrence of 34 trace elements in coal and the occurrence and distribution of chlorine, phosphorus, titanium, and manganese, which are not considered rare in coal. Separate chapters are devoted to germanium, gallium, and uranium in coal. [Pg.27]

The occurrence of anoxic conditions causes cycling of iron and manganese at the oxic-anoxic interface (6-10). In lakes with a significant seasonal cycle, iron and manganese oxides are reduced during anoxia, and Fe(II) and Mn(II) are released into solution. The Fe(II) and Mn(II) species are reoxidized, and Fe(III) and Mn(III,IV) precipitate as oxides during lake overturn, when the reduced species come into contact with oxygen. [Pg.470]

The retention of zinc in the lake sediments appears to be efficient under botlToxic and anoxic conditions no indication of a release of zinc from the sediments into the water column was found. In a similar way, the retention of chromium in the sediments appears to be efficient. Under anoxic conditions Cr(III) is formed, which is strongly bound to particles and is thus retained in the sediments.The occurrence of anoxic conditions favors the retention in the sediments of chromium and of zinc, in contrast to the release of manganese and of iron. [Pg.490]


See other pages where Manganese occurrence is mentioned: [Pg.887]    [Pg.85]    [Pg.97]    [Pg.204]    [Pg.383]    [Pg.7]    [Pg.38]    [Pg.518]    [Pg.531]    [Pg.571]    [Pg.118]    [Pg.187]    [Pg.589]    [Pg.238]    [Pg.524]    [Pg.98]    [Pg.852]    [Pg.717]    [Pg.244]    [Pg.290]    [Pg.424]    [Pg.8]    [Pg.214]    [Pg.469]    [Pg.479]    [Pg.484]   
See also in sourсe #XX -- [ Pg.346 ]

See also in sourсe #XX -- [ Pg.8 ]

See also in sourсe #XX -- [ Pg.8 ]

See also in sourсe #XX -- [ Pg.846 ]

See also in sourсe #XX -- [ Pg.625 ]




SEARCH



Manganese history, occurrence, uses

Manganese occurrence, extraction and uses

© 2024 chempedia.info