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Author |
Evangelou, V.P. |
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Title |
Pyrite microencapsulation technologies: Principles and potential field application |
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Journal Article |
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Year |
2001 |
Publication |
Ecological Engineering |
Abbreviated Journal |
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Volume |
17 |
Issue |
2-3 |
Pages |
165-178 |
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Keywords |
mine water treatment Acid mine drainage Acidity Alkalinity Amelioration Coating Oxidation Surface reactions |
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Abstract |
In nature, pyrite is initially oxidized by atmospheric O2, releasing acidity and Fe2+. At pH below 3.5, Fe2+ is rapidly oxidized by T. ferrooxidans to Fe3+, which oxidizes pyrite at a much faster rate than O2. Commonly, limestone is used to prevent pyrite oxidation. This approach, however, has a short span of effectiveness because after treatment the surfaces of pyrite particles remain exposed to atmospheric O2 and oxidation continuous abiotically. Currently, a proposed mechanism for explaining non-microbial pyrite oxidation in high pH environments is the involvement of OH- in an inner-sphere electron-OH exchange between pyrite/surface-exposed disulfide and pyrite/surface-Fe(III)(OH)n3-n complex and/or formation of a weak electrostatic pyrite/surface-CO3 complex which enhances the chemical oxidation of Fe2+. The above infer that limestone application to pyritic geologic material treats only the symptoms of pyrite oxidation through acid mine drainage neutralization but accelerates non-microbial pyrite oxidation. Therefore, only a pyrite/surface coating capable of inhibiting O2 diffusion is expected to control long-term oxidation and acid drainage production. The objective of this study was to examine the feasibility in controlling pyrite oxidation by creating, on pyrite surfaces, an impermeable phosphate or silica coating that would prevent either O2 or Fe3+ from further oxidizing pyrite. The mechanism underlying this coating approach involves leaching mine waste with a coating solution composed of H2O2 or hypochlorite, KH2PO4 or H4SiO4, and sodium acetate (NaAC) or limestone. During the leaching process, H2O2 or hypochlorite oxidizes pyrite and produces Fe3+ so that iron phosphate or iron silicate precipitates as a coating on pyrite surfaces. The purpose of NaAC or limestone is to eliminate the inhibitory effect of the protons (produced during pyrite oxidation) on the precipitation of iron phosphate or silicate and to generate iron-oxide pyrite coating, which is also expected to inhibit pyrite oxidation. The results showed that iron phosphate or silicate coating could be established on pyrite by leaching it with a solution composed of: (1) H2O2 0.018-0.16 M; (2) phosphate or silicate 10-3 to 10-2 M; (3) coating-solution pH [approximate]5-6; and (4) NaAC as low as 0.01 M. Leachates from column experiments also showed that silicate coatings produced the least amount of sulfate relative to the control, limestone and phosphate treatments. On the other hand, limestone maintained the leachate near neutral pH but produced more sulfate than the control. |
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0925-8574 |
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July 01; Pyrite microencapsulation technologies: Principles and potential field application; file:///C:/Dokumente%20und%20Einstellungen/Stefan/Eigene%20Dateien/Artikel/10063.pdf; Science Direct |
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CBU @ c.wolke @ 10063 |
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37 |
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Author |
Van Hille, R.P.; Boshoff, G.A.; Rose, P.D.; Duncan, J.R. |
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Title |
A continuous process for the biological treatment of heavy metal contaminated acid mine water |
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Journal Article |
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Year |
1999 |
Publication |
Resour. Conserv. Recycl. |
Abbreviated Journal |
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27 |
Issue |
1-2 |
Pages |
157-167 |
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Keywords |
mine water treatment biological treatment heavy metal acid mine water alkaline precipitation green-algae chlorella |
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Abstract |
Alkaline precipitation of heavy metals from acidic water streams is a popular and long standing treatment process. While this process is efficient it requires the continuous addition of an alkaline material, such as lime. In the long term or when treating large volumes of effluent this process becomes expensive, with costs in the mining sector routinely exceeding millions of rands annually. The process described below utilises alkalinity generated by the alga Spirulina sp., in a continuous system to precipitate heavy metals. The design of the system separates the algal component from the metal containing stream to overcome metal toxicity. The primary treatment process consistently removed over 99% of the iron (98.9 mg/l) and between 80 and 95% of the zinc (7.16 mg/l) and lead (2.35 mg/l) over a 14-day period (20 l effluent treated). In addition the pH of the raw effluent was increased from 1.8 to over 7 in the post-treatment stream. Secondary treatment and polishing steps depend on the nature of the effluent treated. In the case of the high sulphate effluent the treated stream was passed into an anaerobic digester at a rate of 4 l/day. The combination of the primary and secondary treatments effected a removal of over 95% of all metals tested for as well as a 90% reduction in the sulphate load. The running cost of such a process would be low as the salinity and nutrient requirements for the algal culture could be provided by using tannery effluent or a combination of saline water and sewage. This would have the additional benefit of treating either a tannery or sewage effluent as part of an integrated process. |
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0921-3449 |
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Jul; A continuous process for the biological treatment of heavy metal contaminated acid mine water; Isi:000081142100017; file:///C:/Dokumente%20und%20Einstellungen/Stefan/Eigene%20Dateien/Artikel/9937.pdf; AMD ISI | Wolkersdorfer |
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CBU @ c.wolke @ 9937 |
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26 |
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Author |
Ueki, K.; Kotaka, K.; Itoh, K.; Ueki, A. |
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Title |
Potential availability of anaerobic treatment with digester slurry of animal waste for the reclamation of acid mine water containing sulfate and heavy metals |
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Journal Article |
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Year |
1988 |
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Journal of Fermentation Technology |
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66 |
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1 |
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mine water treatment |
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Abstract |
The use of an anaerobic digester slurry of cattle waste for the reclamation of acid mine water was examined. When the digester slurry was mixed with acid mine water, anaerobic digestion, including sulfate reduction and methanogenesis, was enhanced. In the mixture of acid mine water and the digester slurry, sulfate reduction proceeded without diminishing methanogenesis. The digester slurry and its supernatant (SDF-sup) showed a significant capacity to act as a strong alkaline reagent, and the pH of the acid mine water was markedly elevated by the addition of the digester slurry of SDF-sup even at the low ratio of 1% (v/v). Precipitation of heavy metals in the acid mine water occurred as the pH was elevated by the addition of SDF-sup. When the digester slurry was added at the ratio of 5% (v/v) to acid mine water which had been pretreated with SDF-sup, the rate of sulfate reduction increased with increasing the concentration of sulfate in the mixture up to about 1,400 mg·l-1. In acid mine water pretreated with SDF-sup and supplemented with the digester slurry at the ratio of 5% (v/v), the maximum amount of sulfate reduced within 20 d of incubation was about 1,000 mg·l-1, and the maximum rate of sulfate reduction was about 120 mg SO42-·l-1·d-1. |
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0385-6380 |
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Potential availability of anaerobic treatment with digester slurry of animal waste for the reclamation of acid mine water containing sulfate and heavy metals; Amsterdam [u.a.] : Elsevier; file:///C:/Dokumente%20und%20Einstellungen/Stefan/Eigene%20Dateien/Artikel/7036.pdf; Opac |
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CBU @ c.wolke @ 7036 |
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75 |
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Author |
Juby, G.J.G.; Schutte, C.F. |
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Title |
Membrane Life in a Seeded-slurry Reverse Osmosis System |
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Journal Article |
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Year |
2000 |
Publication |
Water Sa |
Abbreviated Journal |
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Volume |
26 |
Issue |
2 |
Pages |
239-248 |
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Keywords |
mine water treatment desalination |
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Abstract |
Membrane replacement can be a major operating cost of a membrane plant. During the development of a novel desalination technique (the SPARRO process) for treating calcium sulphate scaling mine waters the expected life of tubular cellulose acetate membranes operating in the seeded-slurry mode was investigated.During four operating phases of the plant over a five-year period more than 9 000 h of operating data were obtained. Performance data showed that each operating phase was dominated by either membrane fouling or membrane hydrolysis. Membrane fouling was observed to begin near the front-end of the membrane stack and proceed towards the back. Hydrolysis, on the other hand, occurred first in the tail end of the stack and moved backwards towards the Front end modules. Although two detailed membrane autopsies were carried out no definitive statement can be made in respect of the causes of either membrane hydrolysis or membrane fouling. However, suggestions are presented to explain the observed fouling phenomenon in relation to the turbidity of the pretreated feed water and the presence of chlorine. It is proposed that the presence of radioactive isotopes in the mine water which become concentrated in the process contributes to the observed membrane hydrolysis. A membrane life of up to two years is projected for an improved pretreatment arrangement. |
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0378-4738 |
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Membrane Life in a Seeded-slurry Reverse Osmosis System; Isi:000087101400013; file:///C:/Dokumente%20und%20Einstellungen/Stefan/Eigene%20Dateien/Artikel/9715.pdf; AMD ISI | Wolkersdorfer |
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CBU @ c.wolke @ 9715 |
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8 |
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Author |
Burt, R.A.; Caruccio, F.T. |
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Title |
The effect of limestone treatments on the rate of acid generation from pyritic mine gangue |
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Journal Article |
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Year |
1986 |
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Environmental geochemistry and health |
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8 |
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8 |
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mine water treatment |
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Surface water enters the Haile Gold Mine, Lancaster County, South Carolina by means of a small stream and is ponded behind a dam and in an abandoned pit. This water is affected by acidic drainage. In spite of the large exposures of potentially acid producing pyritic rock, the flux of acid to the water is relatively low. Nevertheless, the resulting pH values of the mine water are low (around 3.5) due to negligible buffering capacity. In view of the observed low release of acidity, the potential for acid drainage abatement by limestone ameliorants appears feasible. This study investigated the effects of limestone treatment on acid generation rates of the Haile mine pyritic rocks through a series of leaching experiments. Below a critical alkalinity threshold value, solutions of dissolved limestone were found consistently to accelerate the rate of pyrite oxidation by varying degrees. The oxidation rates were further accelerated by admixing solid limestone with the pyritic rock. However, after a period of about a month, the pyrite oxidation rate of the admixed samples declined to a level lower than that of untreated pyrite. Leachates produced by the pyrite and limestone mixtures contained little if any iron. Further, in the mixtures, an alteration of the pyrite surface was apparent. The observed behaviour of the treated pyrite appears to be related to the immersion of the pyrite grains within a high alkalinity/high pH environment. The high pH increases the rate of oxidation of ferrous iron which results in a higher concentration of ferric iron at the pyrite surface. This, in turn, increases the rate of pyrite oxidation. Above a threshold alkalinity value, the precipitation of hydrous iron oxides at the pyrite surface eventually outpaces acid generation and coats the pyrite surface, retarding the rate of pyrite oxidation. |
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0269-4042 |
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Sept; The effect of limestone treatments on the rate of acid generation from pyritic mine gangue; London: Chapman & Hall; file:///C:/Dokumente%20und%20Einstellungen/Stefan/Eigene%20Dateien/Artikel/7021.pdf; Opac |
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no |
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CBU @ c.wolke @ 7021 |
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14 |
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