Liisa Carlson

Iron and manganese oxides in Finnish ground water treatment plants

Abstract Large amounts of ochreous precipitates are formed on aeration of Fe containing Finnish ground waters during purification for drinking purposes. Sixty-four precipitates were characterized chemically and mineralogically. X-ray diffraction (XRD) indicated that the Fe-rich precipitates consist mainly of a poorly ordered ferrihydrite (5 Fe 2 O 3 · 9 H 2 O) which only has 2–3 of the 6 XRD lines characteristic of better ordered ferrihydrite. The surface area ranges between 325 and 433 m 2 g −1 corresponding to a particle size of ∼5 nm. The ferrihydrites contain 3–7% Si strongly associated with the ferrihydrite as indicated by an i.r. absorption band at 960–975 cm −1 which is associated to Fe-O-Si bonds. Si-containing ferrihydrite typically forms by rapid oxidation of ground waters with 1–23 mg 1 −1 Fe and 7–12 mg 1 −1 Si at pH 6–7. Very similar products formed in a simulation experiment in which artificial ground water with 20 mg 1 −1 Fe was oxidized in the presence of 12 mg 1 −1 Si. A1 −1 Si lepidocrocite (γ-FeOOH) was formed showing that Si in the system prevents the formation of the more stable and better crystallized FeOOH forms. A transformation of 2-line ferrihydrite to better ordered ferrihydrite or goethite with time is indicated. The Mn-oxide birnessite was identified in black precipitates formed in one plant.

Biogeochemical transformations of Fe and Mn in oxic groundwater and well water environments

Abstract This review presents an overview of the oxidation and precipitation of dissolved Fe(II) and Mn(II) in groundwater when exposed to surface conditions. In water wells, these transformations may eventually result in biofouling problems and deterioration of water quality. Fe(II)‐oxidation products include poorly‐ordered Fe(III)‐oxides such as ferrihydrite which may be converted via solution to Fe(III)‐oxyhydroxides (e.g., goethite) with time. Among Mn‐oxides, a typical oxidation product is birnessite which is structurally analogous to poorly‐ordered ferrihydrite. Bacteria implicated in Fe‐ or Mn‐oxidation in neutral‐pH environments include Gallionella, Sphaerotilus, Leptothrix, Metallogenium, Pedomicrobium spp., and magnetotactic bacteria. Very little information is available on the genera Crenothrix, Clonothrix, Toxothrix, and Siderocapsa. This review focuses on the stalked and sheathed bacteria Gallionella, Leptothrix, and Sphaerotilus.

Jarosite in cultures of iron‐oxidizing thiobacilli

Jarosite [KFe3(SO4)2(OH)6] was precipitated in cultures of Thio‐bacillus ferrooxidans growing on ferrous sulfate. This basic ferric sulfate was characterized by x‐ray diffraction patterns and infrared spectra and was very similar to jarosite produced chemically from acidic ferric sulfate.

Ferrihydrite in water wells and bacterial enrichment cultures

Abstract The chemical and mineralogical composition of Fe(III)-precipitates formed in water wells and laboratory cultures was examined. Ferrihydrite, a poorly ordered Fe(III)-oxide of bulk formula 5Fe 2 O 3 · 9H 2 O, was detected by X-ray diffraction analysis in all samples. The crystallinity varied from one sample to another. Fe was the only major element detected by energy-dispersive X-ray spectrometry; several other elements were present at minor levels reflecting the chemical composition of the medium. The results suggest that the biologically-catalyzed iron encrustation of water wells begins with the initial formation of ferrihydrite.

MINERALOGICAL, GEOCHEMICAL, AND MICROBIOLOGICAL ASPECTS OF IRON DEPOSITION FROM GROUNDWATER

Iron is readily soluble constituent in groundwater and the solubility is further increased by its chelation with organic matter. Iron, and minor elements such as Mn, are undesirable in water supply systems as they cause problems of taste, odour, and discolouration, and clogging and deposition in the screens and pipelines which eventually leads to corrosive conditions. The removal of iron can be accomplished by a sequential treatment involving oxidation, settling, and filtration with various modifications but, as well as the high cost of the treatment, incomplete iron removal and associated problems are frequently encountered.

Surface characteristics of tubercle mass and graphitic residue in cast iron water pipelines

Abstract Graphitic residues from cast iron water mains were characterized by surface area measurements. The surface areas were about 4–5 times higher than those determined for reference graphite Samples. Their capacity to retain water equalled that of activated charcoal. Adsorption properties were examined by using methylene blue and rhodamine B. Under the conditions employed, methylene blue behaved as a cationic species whereas rhodamine B seemed to have little charge effects. Ferric iron was found to adsorb on graphitic residues in a pH-dependent manner. Surface characteristics of tubercle material that overlyes graphitized areas in cast iron pipes were examined by scanning electron microscopy. A high degree of particle aggregation was observed and the size distribution varied with the crystallinity of the tubercle components.