Ferric sulfate oxidations

Elemental Sulfur. In 1942, Chatterjee (44) reported the presence of elemental sulfur in weathered Indian coal but not in fresh samples. He suggested that, during weathering, pyrite is first oxidized to ferrous and ferric sulfates, and that then ferric sulfate oxidizes pyrite to elemental sulfur. The presence of elemental sulfur in U.S. coals was confirmed recently by Richard et al. (45) and White and Lee (46). Duran et al. (47) used extraction and gas chromatographic analysis to determine elemental sulfur in a suite of U.S. coals. They found that elemental sulfur (0.03-0.17%) is present in coal that has been exposed to the atmosphere, but is absent in pristine samples that have been processed and sealed under a nitrogen atmosphere. These data support Chatteijee s discovery that elemental sulfur in coal is a weathering product. 

METHOD 1 [112l-5g phenol in dH20 is stirred 5 hours at 20 C with some ferric sulfate (Fe2(S04)3, an additional 7mLs dH20, 13mLs 6% H2O2 and a pinch of aluminum oxide (AI2O3). Yield of catechol is 2.5g (50%). 

Oxidi ng Solutions. In many leaching processes the mineral must be oxidized, as for instance, in the leaching of copper sulfides by ferric sulfate or ferric chloride solutions. 

The foHowing factors are important in dump leaching (/) the role of bacteria (2) the appHcation of acid to prevent or delay precipitation of hydrated ferric sulfate (J) oxidation to remove excess iron from mine water in settling pools, as shown in equations 38 and 39 (4) optimization of dump configuration for good solution distribution and (5) avaHabHity of oxygen. 

A more recent process, the P2 etch [60], which uses ferric sulfate as an oxidizer in place of sodium dichromate avoids the use of toxic chromates, but still provides a similar oxide surface morphology (Fig. 15) allowing a mechanically interlocked interface and strong bonding [9]. The P2 treatment has wide process parameter windows over a broad range of time-temperature-solution concentration conditions and mechanical testing confirms that P2-prepared surfaces are, at a minimum, equivalent to FPL-prepared specimens and only slightly inferior to PAA-prepared surfaces [61]. 

The abiotic rate of the first oxidation reaction is slow the rate of the second reaction increases with increasing pH. The second iron oxidation reaction produces Fe(OH)3(s), ferric hydroxide. "Yellow boy," a limonitic precipitate, is produced when the ferric hydroxide mixes with ferric sulfates when formed, "Yellow boy" gives receiving waters an unappealing yellow tint. 

The soluble ferrous ions produced are further oxidized rapidly by the bacteria to ferric sulfate ... 

Sulfide minerals can also be oxidized by the acidic ferric sulfate solutions produced (as shown in the last two equations), with the formation of elemental sulfur ... 

Chalcocite and covellite are also oxidized by ferric sulfate, with the resulting ferrous sulfate reoxidized back to the ferric form. This mechanism is termed indirect bacterial oxidation. Ferric oxidation of chalcocite can also be seen to proceed through two stages, with very quick conversion to covellite in the first stage, and the completion of the oxidation in the second stage ... 

The bacterial leaching of uranium minerals is complex. This is because of the fact that uranium minerals are not sulfides and are not, therefore, directly attacked by the bacteria. However, the uranium sources usually have a substantial pyrite content which can be bac-terially oxidized to give an acidic ferric sulfate solution which is an effective leaching medium for uranium minerals. The reactions involved in the system can be shown in a simplified form as ... 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

TRW Meyers [Named after the three CalTech professors who founded the company Thompson, Ramo, and Wooldridge] A chemical method for desulfurizing coal. The iron pyrites is leached out with a hot aqueous solution of ferric sulfate, liberating elemental sulfur. The resulting ferrous sulfate solution is re-oxidized with air or oxygen ... 

The bishydrazones of the 1,2-diketones from inositols have also been converted into triazoles.222,223 The conversion of arylosazones into the corresponding osotriazoles requires the presence of an oxidant, and it is obvious that simple removal of aniline from the osazone, as suggested by the equation, is not involved. In addition to copper(II) sulfate, the reagent most commonly used, other oxidizing heavy-metal salts, such as ferric sulfate and chloride,224 and mercuric acetate,223 have been used, as well as halogens225 and nitro-sulfonates.226 The osazone acetates are converted into osotriazoles by nitrous acid,227 which decomposes the unacetylated osazones to the aldosuloses228 and the osazone formazans are cyclized with warm... 

As a preliminary, ferric sulfate is made by the oxidation of ferrous sulfate. Dissolve 100 g. of ferrous sulfate in 100 cc. of boiling water, to which has been added before heating 10 cc. of sulfuric acid. Add concentrated nitric acid portionwise to the hot solution, until a diluted sample gives a reddish-brown (not black) precipitate with ammonia. This will require about 25 cc. Boil the solution down to a viscous liquid to get rid of excess nitric acid, dilute to about 400 cc., and add the calculated weight of ammonium sulfate. The crystallization is conducted as in the former exercise, preferably under 20°. By the addition of potassium sulfate, the corresponding potassium iron alum may be secured. In this case, it is necessary to concentrate the solution until there is about four parts of water to one of the hydrated alum and cool to about zero to secure crystallization. Both of these alums are amethyst in color, the potassium salt being much less stable and having a rather low transition point. 

POUR PERMANGANATE INTO IRON SALT. GREEN FERROUS SULFATE IS OXIDIZED TO BROWN FERRIC SULFATE (Fe.lSO ),). 

ADD HYDROGEN PEROXIDE SOLUTION. LIGHT-GREEN FERROUS SULFATE SOLUTION TURNS REDDISH-BROWN. H,Oj HAS OXIDIZED FeSO TO FERRIC SULFATE (FeJSO, ,). 

Aldoses can be degraded by the following two reactions. First the aldehyde is oxidized with bromine water to form a carboxylic acid. Next the carboxylic acid is decarboxy-lated with hydrogen peroxide and ferric sulfate leaving an aldehyde. The new aldose is one carbon shorter. When glucose is degraded in this manner, and the product is oxidized by dilute nitric acid, an optically active compound is formed. 

A simple method of regeneration of the sulfided sorbent is by its reaction with oxygen in air. With most metal sulfides this reaction results in sulfates at the temperatures of interest, Ferric sulfate has the lowest limit temperature of stability as shown in Table I (1). Hence, iron oxide is directly formed by regeneration in air, A major obstacle in... 

Can this model published in 2003 (Marion et al. 2003a) explain all the geochemical findings of the 2004 Mars Exploration Rover (MER) missions Not exactly In our model we predicted that ferrous iron would precipitate as siderite (FeCOo) early in the temporal sequence, and siderite would ultimately be oxidized to ferric minerals such as ferrihydrite [Fe(OH)3] and hematite (FeoOo) (Fig. 5.10). There is no place in this conceptual model for the precipitation of ferrous or ferric sulfate minerals as suggested by the MER missions (Squyres et al. 2004 Lane, 2004). This problem could be simply rectified by drawing an arrow from siderite through the surface acidification... 

Beyer et al. (49) found that, during microbial desulfurization, pyritic sulfur decreases and elemental sulfur increases with time, whereas the organic sulfur remains unchanged. They suggested that microbial oxidation of pyrite produces ferric sulfate [Fe2(S04)3] and that the simultaneous inorganic reaction of ferric iron with pyrite produces elemental sulfur and ferrous iron, as follows ... 

Cell-free extracts were preincubated in buffer in the cold or at 30°C for 2 hr to assess the stability of the expandase over time [43]. After 2 hr, the remaining components of the reaction mixture were added and the tubes were incubated under standard conditions for another 3 hr. In all cases, the initial rates were similar to that of the control (no preincubation) and amounts of product obtained were almost equal to the control value. Thus the lack of activity after 2-3 hr could not be attributed to enzyme instability during shaking at 30°C. When Fe3+ (as ferric sulfate) was substituted for Fe2+ in the reaction, activity was unaffected. Therefore, inactivation was apparently not due to oxidation of Fe2+. 

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