Biogenic Mn oxides

Nelson YM, Lion LW, Ghiorse WC, Shuler ML (1999) Production of biogenic Mn oxides by Leptothrix discophora SS-1 in a chemically defined growth medium and evaluation of their Pb adsorption characteristics. Appl Environ Microbial 65 175-180... 

Trace Metal Adsorption to Mixtures of Biogenic Mn Oxides and Fe Oxides... 

The first measurement of trace metal adsorption to laboratory-prepared biogenic Mn oxides was reported by Nelson et al. (1999b). In these experiments both Mn oxidation and trace metal adsorption were carried out under controlled conditions with L. discophora grown in a defined medium. The use of pH controllers in these... 

FIGURE 7.3 Effect of biogenic Mn oxide deposits on Pb adsorption by L. discophora cells at pH 6.0 and 25°C. Cell concentration = 63 mg/1, Mn loading = 0.8 mmol/g cells. (From Nelson, Y.M. et al., Appl. Environ. Microbiol., 65, 175, 1999b. With permission.)... 

FIGURE 7.6 X-ray diffraction pattern of biogenic Mn oxide produced by L. discophora prepared at pH 7.5. Peaks corresponding to polyhydroxybutyrate are labeled PHB, and the peak corresponding to ramsdellite is labeled accordingly... 

Specific surface area and Pb adsorption capacity of biogenic Mn oxide, fresh abiotic Mn oxide precipitate and pyrolusite minerals. 

As expected, trace metal adsorption to biogenic Mn oxides is dependent on pH. Wilson et al. (2001) measured and modeled the pH dependence of Pb to biogenic Mn oxides and compared it to that of colloidal iron oxides. As seen in Figure 7.7, the adsorption of Pb to Mn oxide exceeds that of Fe oxide (on a per mole of Mn or Fe basis) at pH values below 8.5. The pH dependence of Pb adsorption to Fe was greater than that for Pb adsorption to biogenic Mn oxides and thus, adsorption to Fe oxides is expected to become relatively more important as pH increases. 

TRACE METAL ADSORPTION TO MIXTURES OF BIOGENIC Mn OXIDES AND Fe OXIDES... 

In natural environments, Mn and Fe oxides often coexist as mixtures, making it important to determine if their trace metal adsorption properties are altered by interactions with each other. To test this hypothesis we measured Pb adsorption to mixtures of biogenic Mn oxide and colloidal Fe oxide. The mixtures were prepared in two ways. First, previously prepared biogenic Mn oxide was mixed in suspension with previously precipitated amorphous Fe(III) oxide. Second, Mn(II) was biologically oxidized in the presence of a previously prepared Fe(III) oxide suspension (Nelson et al., 2002). As above, all adsorption measurements were made in a chemically defined medium (Nelson et al., 1999b). In both cases, observed Pb adsorption by the Fe/Mn oxide mixtures was similar to that predicted using Langmuir... 

FIGURE 7.9 Relative contribution to Pb adsorption by biogenic Mn oxide. Fe oxide and natural organic matter in a natural surface coating as a function of pH. Below pH 6.5, biogenic Mn oxide dominates Pb adsortion, while above pH 6.5, Pb adsorption to biogenic Mn oxide is second to that of Fe oxide. (See Wilson, A.R. et al., 2001.)... 

FIGURE 7.10 Relative roles of biogenic Mn oxide, Fe oxide, and organic material in controlling Pb adsorption to biofilms as determined using a novel selective extraction technique. (From Dong, D. et al., Water Res., 34, 427, 2000. With permission.)... 

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