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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Bio-reduction of sulfide minerals to recover invisible gold
    Hol, A. - \ 2011
    Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Renata van der Weijden; J.P.A. de Weert. - S.l. : s.n. - ISBN 9789085859222 - 117
    redoxreacties - pyriet - extractie - goud - redox reactions - pyrites - extraction - gold

    Sulfide minerals, like pyrite and arsenopyrite, are of economical interest due to the presence of invisible gold locked inside these minerals. As fine grinding is often not sufficient to liberate the gold from these minerals, additional destruction techniques, based on chemical and biological oxidation processes, are required to access the gold via cyanidation. These techniques have proven to be successful to reach satisfactory gold recoveries, but operation costs are high and challenging waste streams (sulfuric acid) are produced. As an alternative to the oxidation methods in this thesis the bio-reduction of sulfide minerals was proposed and investigated. Bio-reduction, the use of hydrogen to convert mineral-sulfur to hydrogen sulfide, has as major advantage that the hydrogen sulfide can be recovered from the solution (to produce bio-sulfur) leaving a waste stream without diluted sulfuric acid. Furthermore, electrical energy will be saved. Theoretically, this more environmental friendly alternative should work, but no bio-reduction reaction was observed in practice. It appeared that sulfur/sulfate reducing bacteria were not able to use sulfur when fixed in the crystal lattice of pyrite and arsenopyriteat the selected conditions (pH 5, 35ºC). In order to make the mineral-sulfur bio-available for these bacteria the sulfur should first enter the solution. As alternative the combination between partial bio-oxidation and bio-reduction was therefore investigated. Partial bio-oxidation at pH 2 results in the formation of elemental sulfur, which can serve as a substrate at pH 5 for the sulfur/sulfate reducing bacteria. This combined method was found to be successful at 35°C, as the gold leachability of the used concentrate was increased from 6% to 39%. Optimization of this process is needed to reach gold recoveries >90% in 1 or 2 ox/red cycles, but when successful a new method (called the Paroxsul process) with a lower environmental impact, less costs, and application to a large number of minerals, is ready to be introduced to the precious metal industry.

    Pyrietvorming in relatie tot interne eutrofiëring en verzuring
    Delft, S.P.J. van; Kemmers, R.H. ; Jongmans, A.G. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1161) - 88
    vegetatie - bodemchemie - fosfaten - kwel - eutrofiëring - sulfaten - pyriet - natuur - vegetation - soil chemistry - phosphates - seepage - eutrophication - sulfates - pyrites - nature
    In natte natuurgebieden wordt steeds vaker oppervlakkig pyriet aangetroffen in de bodem. Dit wijst op interne eutrofiering, waarbij sulfaat en ijzer worden gereduceerd en stikstof en fosfaat vrijkomen. Doel van het onderzoek was de ernst en omvang van dit probleem te verkennen. Daartoe werd op 32 standplaatsen in 14 natuurgebieden de pyrietvoorraad in de bodem geanalyseerd. De pyrietvoorraad kan zowel verklaard worden uit de aanvoer van sulfaat via atmosferische depositie sinds 1880 als uit toestroming via lokale kwelsystemen sinds de afgelopen halve eeuw. Micromorfologisch onderzoek toonde aan dat pyrietvorming een actueel proces is, maar kon geen uitsluitsel geven over de herkomst. Via regressieanalyse werden de sleutelfactoren voor pyrietvorming en interne eutrofiering bepaald. Onderzocht werd in welke mate het gevormde pyriet de fosfaatbindingscapaciteit en de fosfaatmobilisatie beïnvloed kan hebben. Uit het onderzoek blijkt dat bij vernatting het sulfaateffect dat door de aanwezigheid van pyriet kan worden verklaard een veelvoud kleiner is dan het vernattingseffect op zich zelf. Lokaal kunnen echter ernstige problemen ontstaan
    Evaluatie van de basen- en voedingstoestand tien jaar na herstelmaatregelen in enkele OBN-referentieprojecten van natte schraalgraslanden
    Kemmers, R.H. ; Delft, S.P.J. van - \ 2003
    Wageningen : Alterra (Alterra-rapport 784) - 85
    graslanden - herstel - bodemchemie - fosfaat - redoxpotentiaal - pyriet - ijzeroxiden - basenverzadiging - grasslands - rehabilitation - soil chemistry - phosphate - redox potential - pyrites - iron oxides - base saturation
    In natte schraalgraslanden is onderzocht aan welke abiotische processen het botanisch herstel na effectgericht maatregelen kan worden toegeschreven. Daartoe zijn bodemmonsters verzameld en geanalyseerd op basen-, voedings- en redoxtoestand. De gegevens werden gebruikt als invoer voor een chemisch evenwichtsmodel, waarmee het effect van vernatting op de basentoestand en de fosfaatmobilisatie werden berekend. Er werden twee hypothesen geformuleerd die op houdbaarheid werden getoetst met de modelresultaten. Beide hypothesen moeten worden aangepast. Tegen de verwachting in blijft in een aantal gevallen herstel van de basentoestand uit ondanks voldoende redoxcapaciteit. Niet alleen op plaatsen met veel maar ook op plaatsen met weinig geadsorbeerd anorganisch fosfaat kan een relatief sterke fosfaatmobilisatie optreden bij vernatting. Geconcludeerd wordt dat herstel van de basenverzadiging en fosfaatmobilisatie van een veelheid van factoren afhankelijk is. Vuistregels om kansrijke situaties voor botanisch herstel aan te geven, zijn vooralsnog niet te formuleren.
    Bodemkundige aspecten van bevloeiing als herstelmaatregel voor verzuurde beekdalgraslanden in de Plateaux en Zijdebrug
    Kemmers, R.H. ; Delft, S.P.J. van - \ 2003
    Wageningen : Alterra (Alterra-rapport 585) - 61
    oppervlakte-irrigatie - bodemeigenschappen - graslanden - verzuring - bodemchemie - beekdalen - ijzer - pyriet - fosfaat - ecologisch herstel - zuid-holland - kempen - surface irrigation - soil properties - grasslands - acidification - soil chemistry - brook valleys - iron - pyrites - phosphate - ecological restoration - zuid-holland - kempen
    In de natuurgebieden Zijdebrug (Zuid-Holland) en de Plateaux (Noord-Brabant) zijn vloeivelden al langere tijd operationeel ter bestrijding van verzuring van schraalgraslanden. De bodemkundige toestand van bevloeide en onbevloeide percelen is vergeleken door beschrijvingen van het humusprofiel en chemische analyses van de vaste en vloeibare fase van de bodem. Met het chemische evenwichtsmodel ECOSAT konden geen effecten van bevloeiing op de basen- en fosfaattoestand worden vastgesteld. In bevloeide enonbevloeide percelen bevatten gronden voldoende ijzeroxiden om onder natte omstandigheden via reductie een hoge calciumverzadiging te realiseren. In vrijwel alle gevallen wordt ook pyriet aangetroffen in de bodem, waardoor extra alkaliniteit aanwezig is.Bevloeide en onbevloeide percelen vertonen geen verschil in de fosfaatbeschikbaarheid in de bodem. Bij overmaat van ijzer ten opzichte van sulfaat is de kans op eutrofiëring door bevloeiing gering.
    Effecten van bevloeiing op de basentoestand en nutriëntenbeschikbaarheid van natte schraalgraslanden op klei-, zand-, en veengronden; veldwaarnemingen en laboratoriumexperimenten
    Kemmers, R.H. ; Sival, F.P. ; Jansen, P.C. - \ 2003
    Wageningen : Alterra (Alterra-rapport 534) - 65
    inundatie - oppervlakte-irrigatie - graslanden - kationenwisseling - basenverzadiging - ijzeroxiden - fosfaat - pyriet - zware kleigronden - zandgronden - veengronden - natuur - flooding - surface irrigation - grasslands - cation exchange - base saturation - iron oxides - phosphate - pyrites - clay soils - sandy soils - peat soils - nature
    Er is onderzocht of bevloeiing kan leiden tot een verhoging van de basenverzadiging zonder tevens te leiden tot indirecte eutrofiëring. Daartoe werd in het veld een monitoringprogramma en in het laboratorium een inundatie-experiment uitgevoerd met uiteenlopend bodemmateriaal. Er zijn belangrijke aanwijzingen dat langjarige bevloeiing tot een hogere basenverzadiging van de bodem leidt. Korte perioden van bevloeiing zijn gunstiger dan lange perioden. Uit het experiment blijkt dat in de bodem vergelijkbare effecten optreden ongeacht het gebruikte watertype. Dit is te verklaren uit de aanwezigheid van pyriet in de bodemmonsters. De aanwezigheid van pyriet is volledig bepalend voor het procesverloop na inundatie en overschaduwt het effect van het watertype. Fosfaatmobilisatie vindt bij alle gebruikte bodem- en watertypen plaats. Middellange vernatting leidt aanvankelijk altijd tot fosfaatmobilisatie. Bij veel sulfaat en weinig ijzer is deze mobilisatie blijvend en bij weinig sulfaat en veel ijzer tijdelijk doordat vivianiet gevormd kan worden. Bij inundatie treedt een duidelijk tijdseffect op in het procesverloop.
    Acid sulfate soils
    Ritsema, C.J. ; Mensvoort, M.E.F. van; Dent, D.L. ; Tan, Y. ; Bosch, H. van den; Wijk, A.L.M. van - \ 2000
    In: Handbook of soil science / Sumner, M.E., - p. G121 - G154.
    kattekleigronden - pyriet - bodemchemie - bodembeheer - modellen - acid sulfate soils - pyrites - soil chemistry - soil management - models
    Pyriet in afzettingen bij het Pompstation Vierlingsbeek : een micromorfologisch en geochemisch onderzoek
    Bisdom, E.B.A. ; Breeuwsma, A. - \ 1990
    Wageningen : Staring Centrum (Rapport / Staring Centrum 56) - 53
    grondwaterwinning - horizontale bronnen - hydraulica - hydrodynamica - pyriet - monolietpreparatie - sediment - suspensies - slijpplaatje preparatie - nederland - noord-brabant - groundwater extraction - horizontal wells - hydraulics - hydrodynamics - pyrites - monolith preparation - sediment - suspensions - thin section preparation - netherlands - noord-brabant
    Pyrite accumulation in salt marshes in the Eastern Scheldt, southwest Netherlands
    Oenema, O. - \ 1990
    Biogeochemistry 9 (1990)1. - ISSN 0168-2563 - p. 75 - 98.
    water - eigenschappen - estuaria - delta's - kattekleigronden - zoutmoerassen - vegetatie - wetlands - polders - pyriet - zeeland - schelde - water - properties - estuaries - deltas - acid sulfate soils - salt marshes - vegetation - wetlands - polders - pyrites - zeeland - river scheldt
    Pore water composition, pyrite distribution and pyrite crystal morphology of sediments from salt marshes in the Eastern Scheldt, southwestern Netherlands, were examined from July 1984 to October 1986. Hydrology and marsh vegetation were the chief determinants of pyrite accumulation. In the bare sediments of pans in the low marsh, highly reducing conditions prevailed just below the surface. At these sites, practically all the incoming detrital pyrite (0.5–1% FeS2) was preserved. The in-situ formation of pyrites was negligible in these anoxic sediments. All incoming detrital pyrite was oxidized in the surface layers (0–10 cm) of the medium-high marsh overgrown withSpartina anglica. Pyrite was formed at a rate of 2.6–3.8 mol S-FeS2m–2yr–1 in a narrow range of depths (15–20cm), at the interface of the oxidizing and underlying reducing sediment. At this interface the concentration profiles of Fe2 and dissolved S intersected. The role of the rhizosphere is discussed in connection with pyrite formation. No further pyrite formation occurred deeper in the sediment. This resulted in the build up of high concentrations of dissolved S and acid volatile sulfides (AVS). The decrease with depth in oxalate-extractable Fe indicated that most of the iron oxyhydroxides (70–80%) had been transformed to pyrite. Another 10–20% of oxalate-extractable Fe was present as AVS. The abundance of framboidal pyrite particles and the high concentrations of AVS and dissolved S indicated that the formation of pyrite occurred via iron monosulfide intermediates There was a linear relationship between the organic carbon and the S-FeS2 content in theSpartina overgrown reducing sediment. The mean C/S ratio was 4.2.
    Contribution of microorganisms to the oxidation of pyrite
    Arkesteyn, G.J.M.W. - \ 1980
    Landbouwhogeschool Wageningen. Promotor(en): E.G. Mulder. - Wageningen : Arkesteyn - 80
    kattekleigronden - bodem - pyriet - zware kleigronden - acid sulfate soils - soil - pyrites - clay soils
    Optimum conditions for the accumulation of substantial amounts of pyrite (FeS 2 ) in the sediment are found in estuarine areas, especially in the tropics. In such areas anaerobic conditions prevail owing to continuous saturation with water. There is an abundant supply of organic matter, in the tropics mainly derived from extensive mangrove forests. Continuous supply of sulphate takes place from the see by the tidal movement. The complex organic material is decomposed by anaerobic bacteria into low-molecular compounds which in turn can be utilized as energy and/or carbon source by sulphate-reducing bacteria. Sulphate is utilized as electron-acceptor by these bacteria and reduced to hydrogen sulphide. Part of the latter compound is fixed as iron sulphide from which pyrite can be formed. Iron is mostly present in such amounts that accumulation up to 10% pyrite is possible. As a result of the strong tidal movement, partial oxidation of sulphide to elemental sulphur (S 0 ) is possible and there is a constant removal of alkaline compounds like HCO 3- which is formed during sulphate reduction. S 0 is a necessary intermediate in the formation of pyrite, whilst the continuous removal of the bicarbonate results in a decreased pH which is kinetically favourable for the formation of pyrite.
    Drainage of the sediment leads to cracking of the unripened clay through which air can penetrate into the soil. Pyrite is then oxidized partly to sulphuric acid that causes a pH drop of the soil near neutral to 4 or even lower. Such soil is useless for agricultural purposes as a result of the low pH. Besides sulphuric acid, the straw-yellow mineral jarosite, KFe 3 (SO 4 ) 2 (OH) 6 , is formed from which the name "cat clay" originates.
    The oxidation of pyrite at a pH below 4, is mainly a microbial process. When starting the experiment it was unknown in what way the initial acidification of the sediment from near neutral to pH 4 proceeds.
    Chapter 2 contains the results of a study of microbial processes involved in the formation of acid sulphate soils. Special attention was given to the initial drop of pH from 7 to 4. It appeared that the initial acidification is a non-biologically catalysed process.
    Thiobacillus thioparus, Thiobacillus thiooxidans and heterotrophic thiosulphate-oxidizing bacteria were isolated from acidifying potentially acid sulphate soil. However, these bacteria were not able to oxidize pyrite. The oxidation of the mineral in synthetic media inoculated with Thiobacillus thioparus, Thiobacillus thiooxidans, Thiobacillus intermedius or Thiobacillus perometabolis did not proceed faster than that in sterile media. Nevertheless, the numbers of cells in the inoculated media increased by a factor of 10-100 to a maximum of 10 5 cells/ml medium (2. Fig. 3). The thiobacilli probably oxidize a small amount of the reduced sulphur compounds which are formed during the non-biological oxidation of pyrite. Experiments with sterilized potentially acid sulphate soil to which pure cultures of different thiobacilli or a suspension of unsterilized potentially acid sulphate soil were added aseptically corroborated the above-mentioned findings (2. Table 2). The initial acidification of sterile potentially acid sulphate soils was comparable with that of the inoculated soils. Only after the pH had decreased to values below 4.0 the oxidation of pyrite in the sterile soil was significantly slower than that in the soils inoculated with cultures of Thiobacillus ferrooxidans.
    Although the addition of lime prevented acidification, the non- biological oxidation of pyrite was not abolished during the 68 days the process was followed (2. Table 2b).
    Attempts to isolate. other microorganisms that might be involved in the oxidation of pyrite such as Leptospirillum ferrooxidans or members of the genus Metallogenium were not successful. The only organism which is responsible for the oxidation of pyrite is Thiobacillus ferrooxidans.
    Two mechanisms of the oxidation of pyrite by Thiobacillus ferrooxidans are known viz.: "the indirect contact mechanism" and the "direct contact mechanism" According to the former mechanism, the sulphur moiety of pyrite is oxidized to sulphate by ferric ions which in turn are reduced to ferrous iron. Thiobacillus ferrooxidans oxidizes the ferrous iron to ferric iron to complete a cyclic process. According to the second mechanism the bacterium is in direct contact with the mineral and it oxidizes the iron as well as the sulphur moiety of pyrite. When starting the experiments it was evident that pyrite can be oxidized by Thiobacillus ferrooxidans according to the indirect contact mechanism but there were some indications that the direct contact mechanism can also occur.
    Chapter 3 gives the results of a study in which it was clearly shown that Thiobacillus ferrooxidans is able to oxidize pyrite according to the direct contact mechanism. Inhibitors of the oxidation of Fe 2+ and S 0 , NaN 3 and N-ethylmaleimide (NEM), respectively, partially abolished the oxidation of pyrite when added separately but when the inhibitors were added together the oxidation of the mineral completely stopped (3.Table 1).
    The electrons released during the oxidation of ferrous iron are transferred to cytochrome c, whilst the electrons derived from the oxidation of elemental sulphur probably reduce acceptors with a lower redox potential. Cytochromes of the b-type were clearly shown to be present in cells grown in media with S 0 or FeS 2 as energy source, but they were not observed in cells grown in media with Fe 2+ as electron donor (3. Fig. 3). The efficiency of the utilization of released electrons at pH 4.0 was highest with S 0 less with FeS 2 and lowest with Fe 2+ as energy source. This was investigated by measuring the incorporation of radio-active carbon dioxide ( 14 CO 2 ) into the bacteria in media with the three different electron donors (3. Table 3).
    Additional evidence for the direct oxidation of the sulphur moiety of pyrite by Thiobacillus ferrooxidans was obtained from the fact that the oxidation of Fe 2+ at pH 5.0 was negligible, whereas the oxidation of S 0 and FeS 2 clearly proceeded at this pH. Separation of bacteria and pyrite by means of a dialysis bag to prevent direct contact resulted in a decrease of the rate of oxidation of the mineral which was comparable with the inhibition of pyrite by NEM (3. Table 2). The oxidation of the sulphur moiety of pyrite by Thiobacillus ferrooxidans was relatively more important with increasing pH.
    During the study of the oxidation of pyrite by Thiobacillus ferrooxidans it appeared that cultures of this bacterium grown in media with Fe 2+ as energy source without exception contained Thiobacillus acidophilus. Nothing was known about factors which can explain the close association between the two organisms.
    Chapter 4 contains a survey of the results of an investigation into factors responsible for the presence of Thiobacillus acidophilus in Thiobacillus ferrooxidans cultures. The most obvious explanation would be that Thiobacillus ferrooxidans is able to utilize Fe 2+ as energy source. But attempts to adapt the mixotroph to the oxidation of Fe 2+ were not successful. Thiobacillus acidophilus grew in modest numbers on organic matter excreted by Thiobacillus ferrooxidans (4. Table 2). Oligocarbophilic growth also was observed (4. Table 6). Possible substrates for such a growth are: methanol and ethanol whilst hydrogen sulphide also can be utilized as energy source by the organism.
    Thiobacillus ferrooxidans may profit from the presence of Thiobacillus acidophilus in mixed cultures containing organic compounds such as alcohols, amino acids or organic acids which are toxic to Thiobacillus ferrooxidans. Such compounds are utilized by the mixotroph after which the autotrophic organism can grow.
    Experiments with fluorescent labelled antibodies against Thiobacillus acidophilus showed that in mixed cultures of both organisms the cell numbers of the mixotroph were comparable with cell numbers of the autotroph (4. Table Also the fact that Thiobacillus ferrooxidans cultures are hard to purify indicates that both organism are present in almost equal numbers in heterogeneous cultures. These observations might be an indication that Thiobacillus ferrooxidans excretes more assimilable organic matter in the presence of Thiobacillus acidophilus than in pure cultures. More research is necessary to prove this assumption.

    Het voorkomen en de vorming van pyriet in diverse mariene afzettingen in Nederland en een verklaring voor het ontstaan van het knipverschijnsel
    Pons, L.J. - \ 1960
    Wageningen : Stichting voor Bodemkartering (Voorlopige wetenschappelijke mededelingen no. 13) - 30
    alkaligronden - nederland - bodemalkaliteit - pyriet - alkaline soils - netherlands - soil alkalinity - pyrites
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