http://netedu.xauat.edu.cn/jpkc/netedu/jpkc2009/szylyybh/content/wlzy/1/Review%20of%20Arsenic%20in%20natural%20water%20-%20Smedly.pdf

A review of the source, behaviour and distribution of arsenic in natural waters

Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter. The material is stable in air once it has dried and contains 22.6% iron by weight. The supported zero-valent iron nanoparticles (“Ferragels”) rapidly separate and immobilize Cr(VI) and Pb(II) from aqueous solution, reducing the chromium to Cr(III) and the Pb to Pb(0) while oxidizing the Fe to goethite (α-FeOOH). The kinetics of the reduction reactions are complex and include an adsorption phase. About 10% of the iron in the material appears to be located at active surface sites. Once these sites have been saturated, the reduction process continues but at a much lower rate, which is likely limited by mass transfer. Rates of remediation of Cr(VI) and Pb(II) are up to 30 times higher for Ferragels than for iron filings or iron powder on a (Fe) molar basis. Over 2 months, reduction of Cr(VI) was 4.8 times greater for Ferragels than for an equal weigh...

Remediation of Cr(VI) and Pb(II) aqueous solutions using supported, nanoscale zero-valent iron

Schwertmannite and the chemical modeling of iron in acid sulfate waters.

Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6(3)mc; a = approximately 5.95 angstroms, c = approximately 9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis delta-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs.

https://science.sciencemag.org/content/sci/316/5832/1726.full.pdf

The Structure of Ferrihydrite, a Nanocrystalline Material

The limitations of applying zero-valent iron technology in contaminants sequestration and the corresponding countermeasures: the development in zero-valent iron technology in the last two decades (1994-2014).

VII. Synthesis 2569 VIII. Adsorption and Solid Solution 2570 A. General Observations 2570 B. Adsorption of Specific Species 2571 1. Various Cations 2571 2. Various Anions 2572 3. Organic Species 2573 C. Environmental Implications 2573 IX. Transformation of Ferrihydrite 2574 A. Dry Thermal Transformation 2574 B. Aqueous Transformation 2575 C. Effects of Various Ions on the Aqueous Transformation of Ferrihydrite 2576

Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide

Permeable-reactive redox walls, placed below the ground surface in the path of flowing groundwater, provide an alternative remediation approach for removing electroactive chemicals from contaminated groundwater Four types of Fe-bearing solids, siderite [FeCO3], pyrite [FeS2], coarse-grained elemental iron [Fe0], and fine-grained Fe0, were assessed for their ability to remove dissolved Cr(VI) from solution at flow rates typical of those encountered at sites of remediation Batch studies show that the rate of Cr(VI) removal by fine-grained Fe0 is greater than that for pyrite and coarse-grained Fe0 Results from column studies suggest that partial removal of Cr(VI) by pyrite and coarse-grained Fe0 and quantitative removal of Cr(VI) by fine-grained Fe0 occur at rapid groundwater flow velocities The removal mechanism for Cr(VI) by fine-grained Fe0 and coarse-grained Fe0 is through the reduction of Cr(VI) to Cr(III), coupled with the oxidation of Fe0 to Fe(II) and Fe(III), and the subsequent precipitation of 

In-Situ Remediation of Cr(VI)-Contaminated Groundwater Using Permeable Reactive Walls: Laboratory Studies

Mining and mineral processing generates large volumes of waste, including waste rock, mill tailings, and mineral refinery wastes. The oxidation of sulfide minerals in the materials can result in the release of acidic water containing high concentrations of dissolved metals. Recent studies have determined the mechanisms of abiotic sulfide-mineral oxidation. Within mine wastes, the oxidation of sulfide minerals is catalyzed by microorganisms. Molecular tools have been developed and applied to determine the activity and role of these organisms in sulfide-mineral-bearing systems. Novel tools have been developed for assessing the toxicity of mine-waste effluent. Dissolved constituents released by sulfide oxidation may be attenuated through the precipitation of secondary minerals, including metal sulfate, oxyhydroxide, and basic sulfate minerals. Geochemical models have been developed to provide improved predictions of the magnitude and duration of environmental concerns. Novel techniques have been developed to prevent and remediate environmental problems associated with these materials.

The geochemistry of acid mine drainage

The alunite supergroup consists of more than 40 minerals with the general formula DG 3( T O4)2(OH,H2O)6, wherein D represents cations with a coordination number greater or equal to 9, and G and T represent sites with octahedral and tetrahedral coordination, respectively (Smith et al. 1998). The supergroup is commonly subdivided into various groups, but the simplest primary subdivision is on the basis of the G cations. For all of the minerals in the supergroup, the dominant G cation is trivalent; most of the minerals have G represented by Fe3+ or Al3+, but exceptions are the rare minerals gallobeudantite, in which G is Ga3+, and springcreekite, in which G is V3+ (Table 1⇓). Thus, the primary grouping adopted here is on whether formula Fe3+ exceeds or is subordinate to Al3+. The hierarchical sequence in mineralogy seems to be variable, but here the decreasing sequence is given as supergroup, family, group, and subgroup. Minerals with Fe3+ > Al3+ are referred to as belonging to the jarosite family, and those with A13+ > Fe3+ are allocated to the alunite family.

View this table:

 Table 1. 
Minerals of the alunite supergroup.



Subdivision of the alunite and jarosite families has also been variable; Scott (1987), for example, used seven groups, Novak et al. (1994) used six, Gaines et al. (1997) used four, and Mandarino (1999) used three. The arbitrary decision here is to use three groups, which differ from those of Mandarino (1999) but which, in general, indicate whether sulfate, phosphate, or arsenate predominates in the T O4 tetrahedra. The three groups are the alunite group, in which T O4 is dominated by SO4, the crandallite group, in which (PO4) is …

Jarosites and Their Application in Hydrometallurgy

“It is plain that almost all kinds of atramentum are made of Earth and Water At first they were liquid and afterwards solid, and still they can be redissolved, by heat and moisture” Albertus Magnus (1205–1280) Book of Minerals (transl D Wyckoff, 1967) 

The observation of “efflorescences,” or the flowering of salts, associated with periods of dryness in soils, in closed-basin lakes, in rock outcrops, and in mines and mine wastes has been noted since early antiquity The formation of metal-sulfate salts, in connection with the mining of metals, was a phenomenon well known to the early Greek and Roman civilizations Alum, most commonly potash alum KAl(SO4)2 · 12H2O, which is from the Latin alumen , was extensively mined and used by goldsmiths, dyers, paper manufacturers, and physicians in ancient civilizations It forms from the oxidation of pyrite in shales and slates and from oxidation of sulfurous gases in geothermal areas The Greeks and the Romans described stalactites of atramentum (soluble metal-sulfate salts) that formed within mines and along rock faces (Agricola 1546, 1556) Furthermore, the toxic effects of these salts on animals were also noted For example, in De Natura Fossilium , Agricola (1546) stated “…I mention the congealed acid juice which usually produces cadmia  It is white, hard, and so acrid that it can eat away walls, grills and even destroy all living matter” Cadmia is thought to be derived from the oxidation of zinc, cobalt, and arsenic sulfides, such as cobaltite He goes on to say that “Pyrite, unless it contains sulphates, is either a golden or silver color, rarely any other, while cadmia is black, yellow brown, or gray The former will cure gatherings while the latter is a deadly poison and will destroy any living substance It is used …

John L. Jambor

Papers

Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide

In-Situ Remediation of Cr(VI)-Contaminated Groundwater Using Permeable Reactive Walls: Laboratory Studies

The geochemistry of acid mine drainage

Jarosites and Their Application in Hydrometallurgy

Metal-sulfate Salts from Sulfide Mineral Oxidation