Biological sulfate reduction process

For the treatment of battery pastes, which are a mixture of PbS04, Pb02, PbO and metallic lead, a sulfidisation process has been proposed, converting all lead components into PbS, which can then be subjected to ferric fluoborate leaching as above. Sodium sulfide can be used for this step but involves a complex procedure for its recovery. Alternatively, a biological sulfate reduction process developed by PAQUES Biosystems of the Netherlands has been applied (Olper et al, 2000). 

R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

More direct biological channels also seem promising as sources. Land plants release H2S, but the process has not been considered for marine algae ( ). Intermittent deep sulfide maxima could be connected with anoxic microenvironments recently located in marine snow. These organic particulates accumulate in the pycnocline and offer potential sites for contrary redox reactions such as dissimilatory sulfate reduction (34). 

The formation of sulfur intermediates is both chemically and biologically mediated. Oxidation of hydrogen sulfide with oxygen and Fe(Mn) oxyhy-droxides and sulfate reduction are the main processes responsible for sulfur intermediates formation in the euxinic water columns, except for elemental sulfur, which is formed only during hydrogen sulfide oxidation. Chemically mediated reactions of thiosulfate formation are elemental sulfur(polysulfides)... 

This phenomenon forms the basis for the formulations of Urey (1947) and Bigeleisen and Mayer (1947) for the temperature dependence of isotopic exchange between two molecules. With the nearly simultaneous development of the isotope-ratio mass spectrometer by Nier et al. (1947), the potential for application of stable isotopes was created. Other isotopic fractionation processes are observed in kinetics, diffusion, evaporation-condensation, crystallization, and biology (e.g., photosynthesis, respiration, nitrogen fixation, sulfate reduction, and transpiration). The concomitant isotopic fractionations can also be used to provide details of the relevant process. 

The primary process by which sulfur is fractionated in hydrologic environments is via biologically mediated sulfur transformations. The most important of these is the dissimilatory sulfate reduction (DSR) reaction... 

Biological activities, such as photosynthesis and respiration, physical phenomena, such as natural or induced turbulence with concomitant aeration, and above all processes such as the precipitation and dissolution of CaC03 and of other minerals influence pH regulation through their respective abilities to decrease and increase the concentration of dissolved carbon dioxide. Besides photosynthesis and respiration, other biologically mediated reactions affect the H" ion concentrations of natural waters. Oxygenation reactions often lead to a decrease in pH, whereas processes such as denitrification and sulfate reduction tend to increase pH. 

Table 15.4 gives a rough mass balance of riverine inputs and the various outputs by atmospheric cycling, ion exchange processes, deposition in sediments, and hydrothermal activities. One important part of the mass balance is the deposition of CaCOs. Biological processes also cause the removal of S04, which is consumed in biologically mediated sulfate reduction and deposited as pyrite. 

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