Manganese sulfate, decomposition

Aqueous solution of manganese(ll) sulfate undergoes double decomposition reactions precipitating insoluble manganese(II) salts for example, adding caustic soda solution precipitates manganese(II) hydroxide. 

As shown in these reactions, reduction of iron and manganese results in the consumption of H ions, thus resulting in a decrease in H+ ion activity or an increase in pH. For example, in paddy soils of Philippines (Table 4.4) iron comprises 0.63-4.7% of the total soil mass, and manganese content can be as high as 0.1%. The proton to electron ratio is 3 for Fe(OH)3 reduction, as compared to a ratio of 2 for Mn02 reduction. Thus, iron reduction will have a greater effect on the pH increase in acid soils. Reduction of other electron acceptors such as nitrate and sulfate can also have a similar effect on the soil pH. In acid soils, an initial increase in pH can also occur due to rapid decomposition of soil organic matter and accumulation of carbon dioxide. However, acid soils eventually increase in pH due to reduction of oxides of Fe and Mn. 

Iron and manganese reduction in wetland soils and aqnatic sediments is linked to organic matter decomposition. In the absence of oxygen, microbial commnnities nse a wide range of electron acceptors, inclnding nitrate, Mn(IV), Fe(III), sulfate, carbon dioxide, and several simple organic componnds. 

The first reaction predominates if the product contains a large amount of water (-18%). This reaction is analogous to the disproportionation of aqueous hypochlorite. However, disproportionation is much slower in solid calcium hypochlorite than in solution. Under dry conditions, the second reaction predominates. It is catalyzed by transition metals including iron and manganese. It may occur explosively 150°C. Thus, calcium hypochlorite products usually contain some water or an additive such as magnesium sulfate heptahydrate. The third reaction is the reverse of chlorination. The fourth reaction is due to the adsorption of carbon dioxide from air or the release of carbon dioxide from carbonate salt impurities. It is accelerated by water and temperature. The first reaction accounts for -70%, and the second reaction -30%, of the decomposition of solid calcium hypochlorite made in the United States and stored in sealed containers at 25°C. ... 

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