An alternative approach for nitrate and arsenic removal from wastewater via a nitrate-dependent ferrous oxidation process

Passive systems that utilize a natural power such as a pond, plant, or microorganisms, is expected to be a cost-effective method for acid mine drainage (AMD) treatment. The Ningyo-toge mine, a non-operational uranium mine located in Okayama Prefecture, Japan, generates AMD containing arsenic and iron. To quantitatively study arsenic and iron ion removal in an artificial wetland and pond, chemical reactions were modeled and incorporated into the GETFLOWS (general-purpose terrestrial fluid-flow simulator) software. The chemical reaction models consisted of arsenite and ferrous oxidation equations and arsenic adsorption on ferrihydrite. The X-ray diffraction analysis of sediment samples showed ferrihydrite patterns. These results were consistent with the model for arsenite/ferrous oxidation and arsenic adsorption on ferrihydrite. Geofluid simulation was conducted to simulate mass transfer with the utilized topographic model, inlet flow rate, precipitation, and evaporation. The measured arsenic and iron ions concentrations in solution samples from the wetland and pond, fitted well with the model. This indicated that the main removal mechanism was the oxidation of arsenite/ferrous ions and that arsenic was removed by adsorption rather than dilution.

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Control of Metal Alloy Oxidation with Electric Fields

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071260 ◽

1973 ◽

Vol 31 ◽

pp. 164-165

Author(s):

R. R. Dils ◽

P. S. Follansbee

Keyword(s):

Electric Fields ◽

Oxidation Process ◽

Base Alloy ◽

Oxide Surface ◽

Platinum Electrodes ◽

Insulating Layer ◽

Iron Base Alloy ◽

Alloy Oxidation ◽

Aluminum Oxide Layer ◽

And Control

Electric fields have been applied across oxides growing on a high temperature alloy and control of the oxidation of the material has been demonstrated. At present, three-fold increases in the oxidation rate have been measured in accelerating fields and the oxidation process has been completely stopped in a retarding field.The experiments have been conducted with an iron-base alloy, Pe 25Cr 5A1 0.1Y, although, in principle, any alloy capable of forming an adherent aluminum oxide layer during oxidation can be used. A specimen is polished and oxidized to produce a thin, uniform insulating layer on one surface. Three platinum electrodes are sputtered on the oxide surface and the specimen is reoxidized.

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Structural Imperfections in thin Oxide Films Formed on Some Fe- and Ni-Base Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069545 ◽

1970 ◽

Vol 28 ◽

pp. 510-511

Author(s):

L. P. Lemaire ◽

D. E. Fornwalt ◽

F. S. Pettit ◽

B. H. Kear

Keyword(s):

Oxide Scale ◽

Oxidation Process ◽

Short Circuit ◽

Protective Oxide ◽

Protective Oxide Scale ◽

Thin Oxide Films ◽

Diffusion Paths ◽

Oxidation Resistant ◽

Structural Imperfections ◽

Short Circuit Diffusion

Oxidation resistant alloys depend on the formation of a continuous layer of protective oxide scale during the oxidation process. The initial stages of oxidation of multi-component alloys can be quite complex, since numerous metal oxides can be formed. For oxidation resistance, the composition is adjusted so that selective oxidation occurs of that element whose oxide affords the most protection. Ideally, the protective oxide scale should be i) structurally perfect, so as to avoid short-circuit diffusion paths, and ii) strongly adherent to the alloy substrate, which minimizes spalling in response to thermal cycling. Small concentrations (∼ 0.1%) of certain reactive elements, such as yttrium, markedly improve the adherence of oxide scales in many alloy systems.

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