Sediment manganese removed from

Oxidation of Mn(II) and Mn(III) up to Mn(IV) accompanied by precipitation of hydrated oxides is an important process in the course of manganese removal from waters. In comparison with Fe(II), Mn(II) is more resistant to oxidation. Oxidation with dissolved oxygen proceeds more markedly only at pH > 9. On the contrary, it is easier to achieve reduction of Mn(III) or Mn(IV) to Mn and thus also dissolution and release of manganese from the sediments into the liquid media under conditions where the reduction of Fe(IIl) to Fe(II) does not yet take place. 

In the case of iron and manganese, most of these metals are removed from the hydrothermal fluids and converted to particulate form close to their point of entry. Some of these removals are in the form of sulfides, which fc>rm as the fluids emerge into the deep sea. The rest occurs as the fluids mix with cold, oxic, alkaline seawater, which promotes the oxidation of reduced metals. Thus, Fe (aq) and Mn (aq) are transformed into insoluble iron and manganese oxides, forming colloids and particles, the latter of which eventually settle onto the sediments. As described in the next chapter, at least some of these oxidation reactions are biologically mediated. Some of... 

Various chemical extraction techniques have been introduced in order to selectively remove metals from the different adsorption or complexation sites of natural sediments (e.g., Tessier et al, 1979 Erel et al, 1990 Leleyter et al., 1999). It is, for example, shown by Leleyter et al. (1999) that between 20% and 60% of REE in various suspended river sediments are removed by successive extractions by water, by Mg(N03)2 (exchangeable fraction), sodium actetate (acid-soluble fraction), NH2OH - - HCl (manganese oxide dissolution) ammonium oxalate (iron oxide dissolution) and a mixture of H2O2 + HNO3 (oxidizable fraction). The complexity of... 

Reduction plays a major role in the behavior of iron and manganese as well as in the behavior of pollutant chemicals in the environment. The solids Fe(OH)3 and Mn02 are strong adsorbents of many chemicals, especially metals. When particles of these oxides form in, or are transported into, surface waters, they can sorb metals the suspended particles may then be removed from the water column by settling, as previously discussed. Such a process may lead to either temporary or long-term deposition of the metals into the sediment. Retention in the sediment is only short term if iron reduction and manganese reduction subsequently lead to dissolution of the oxides and release of the metals back into the water column. 

When the actual concentration at the pipe s exit were less than expected, that element was removed from solution presumably by scavenging or precipitation this was valid for iron (approx, half of the expected concentration) and - to a lesser extent - for manganese. When the exiting solution was greater than the expected concentration in Table 7-3, mobilization from sediments was assumed in this respect, highest rates of release were found for zinc, followed by copper, lead and cadmium. 

Lead enters surface water from atmospheric fallout, run-off, or wastewater. Little lead is transferred from natural minerals or leached from soil. Pb ", the stable ionic species of lead, forms complexes of low solubility with major anions in the natural environment such as the hydroxide, carbonate, sulfide, and sulfate ions, which limit solubility. Organolead complexes are formed with humic materials, which maintain lead in a bound form even at low pH. Lead is effectively removed from the water column to the sediment by adsorption to organic matter and clay minerals, precipitation as insoluble salt (the carbonate, sulfate, or sulfide) and reaction with hydrous iron, aluminum, and manganese oxides. Lead does not appear to bioconcentrate significantly in fish but does in some shellfish such as mussels. When released to the atmosphere, lead will generally occur as particulate matter and will be subject to gravitational settling. Transformation to oxides and carbonates may also occur. 

The technique for the removal of iron and manganese during water treatment employs the oxidation of bivalent well-soluble forms to multivalent low-soluble hydrated oxides, which can be removed from water either by sedimentation or filtration. Oxidizing agents in this case are atmospheric oxygen, chlorine, potassium permanganate, ozone and chlorine dioxide. 

Canney and Nowlan (47) have shown that the amount of dithizone-extractable heavy metals removed from stream sediments with ammonium citrate-hydroxylamine hydrochloride was linearly related to the amount of manganese dissolved. This indicates that the cobalt is present in the manganese oxides. In accordance with this data, it has been found that the slope of plots of the extraction rate vs, time (with dithionite-citrate) for cobalt from < 60 mesh fraction of Whiteoak Creek sediment was closer to that of manganese than that of iron, indicating that more of the... 

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... 

Several reactions between constituents in As-contaminated groundwater and oxic sediments controlled As mobility in the laboratory experiments. Adsorption was the primary mechanism for removing As from solution. The adsorption capacity of the oxic sediments was a function of the concentration and oxidation state of As, and the concentration of other solutes that competed for adsorption sites. Although As(lll) was the dominant oxidation state in contaminated groundwater, data from the laboratory experiments showed that As(lll) was oxidized to As(V) by manganese oxide minerals that are present in the oxic sediment. Phosphate in contaminated groundwater caused a substantial decrease in As(V) adsorption. Silica, bicarbonate and pH caused only a small decrease in As adsorption. 

For the removal of Zn from the water column by sedimentation, both algal material and manganese oxides are likely to be important carrier phases. The Zn sedimentation rates show maxima from June to August, at the time of the maximum sedimentation of P (indicating the sedimentation of algal material), and in December, in line with the sedimentation of manganese oxides (86). 

The Relationship Between Manganese and Iron in Sediment Ponds. To under-stand the behavior in and removal of iron and manganese from water, it is important to know the interactions of these two metals. A common occurrence in sediment ponds is the sudden development of a dissolved manganese problem. The cause may be ferrous iron from the incoming water due to the disturbance of a new site. The ferrous iron can react with insoluble manganese oxide (Mn02) in the sediments at the bottom of the pond according to Equations 12.5 and 12.6 ... 

---