Manganese oxides precipitates

Figure 3. XRD patterns of (A) as-prpared Ni(OH)2-manganese oxide precipitate and hydrothermally treated samples for (B) 7h and (C) 4 days at 150 °C.

The crystal structure of the precipitates was studied by means of x-ray diffraction and electron microscopy. All the initial manganese oxide precipitates displayed patterns characteristic of hausmannite, while some of the precipitates also contained SMnOOH or yMnOOH. After intensive acid treatment the precipitates generally were amorphous. 

The various components of the mixed precipitates that result from these interactions may subsequently or concurrently participate in the redox alterations. Often these eflFects raise the oxidation state of the manganese in the precipitate above what would be expected in a pure manganese oxide precipitated in the absence of other metal ions. Chemical thermodynamic calculations can be used to predict or explain these processes. Some effects of lead and cobalt on manganese behavior have been evaluated theoretically and experimentally. 

Divalent lead has a very low solubility in the pH range where manganese oxide precipitates might form. Lead hydroxide or basic carbonate can form rapidly when the pH of a solution of Pb is increased. 

Previous workers have not agreed on the oxidation state of lead present in manganese oxide precipitates. Cronan (23) stated that lead in manganese nodules is in the Pb state. However, Van der Weijden and Kruissink (24) have concluded from laboratory work and theoretical studies that the Pb form is more likely. 

Figure 3. Top Transmission electron micrograph of a thin section of the metal-oxidizing spores of the marine Bacillus sp. strain SG-1. The spores are coated with manganese oxides. Bar = 0.5 xm. Bottom A todorokite-like manganese oxide precipitate produced by SG-1 as observed directly in the transmission electron microscope. The precipitate has been extracted to remove the organic material of the spore. Bar = 0.1 im. (Reproduced with permission from ref. 123, Copyright 1995 Plenum Press.)...

Analysis. Butenes are best characterized by their property of decolorizing both a solution of bromine in carbon tetrachloride and a cold, dilute, neutral permanganate solution (the Baeyer test). A solution of bromine in carbon tetrachloride is red the dihaUde, like the butenes, are colorless. Decoloration of the bromine solution is rapid. In the Baeyer test, a purple color is replaced by brown manganese oxide (a precipitate) and a colorless diol. These tests apply to all alkenes. 

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). 

As presented by this paper, our aim was to describe some preliminary results demonstrating that amorphous manganese-oxide-based materials synthesised by means of precipitation technique from aqueous solutions could serve as effective cathodes in lithium batteries. 

Manganese (IV) oxide enjoys numerous applications in modem technologies. The most widely known areas of its usage are sorption processes one could recall that co-precipitation of contaminating cations with manganese oxide is still employed as part of the in-tank precipitation in processes of treatment of supernatant wastes at high concentration. Furthermore, co-precipitation data are usually used as benchmark results in studies of novel sorbents for strontium [4],... 

Fig. 6. Thin section of Leptothrix sp. which is precipitating manganese oxide on its outermost structure called a sheath (McLean et al. 2002). The arrows point to the manganese mineral phase identified by EDS. Scale bar = 150 nm. 

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... 

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