Thesis (MSc)--Stellenbosch University, 1997. / ENGLISH ABSTRACT: The activity of iron-oxidizing bacteria, for example, Thiobacillut. ferrooxidans, in the outer layers of
coal waste dumps results in the oxidation of pyrite with the formation of large volumes of acid mine
drainage. The process requires atmospheric oxygen and moisture. Acid mine drainage may possibly
be controlled by creating unfavourable environmental conditions in dumps for the iron-oxidizing
bacteria. The present research investigated the possibility of inhibiting these bacteria and
consequently acid formation in coal waste dumps by means of different dump construction
techniques.
Physical and chemical conditions, acid formation and populations of four groups of bacteria which
might produce acid were studied in the outer layers of ten differently constructed pilot scale coal
waste dumps at the Kilbarchan Mine near Newcastle, Kwazulu-Natal, from September 1993 to July
1995. Dump covers consisting of a 30-cm or 70-cm layer of Estcourt soil of low permeability
covered with 70 cm or 30 cm, respectively, of more permeable Avalon soil produced anaerobic
conditions in the dumps throughout most of the 22 months of the test period, as did a cover of 70 cm
compacted plus 30 cm uncompacted Avalon soil alone. An uncoMpacted 30-cm or compacted 50-
cm Avalon soil cover proved ineffective in causing prolonged anaerobic conditions. Uncovered
dumps showed only slight reduction of oxygen in the coal waste after heavy rains.
Pockets of acidity were detected on several occasions in the coal waste below the 50-cm Avalon soil
layer from the time of construction and progressively increasing acidity in the uncovered dumps and
the waste below the 30-cm Avalon soil cover. Iron-oxidizing bacterial populations of the T.
ferrooxidans type have tended to be higher in the uncovered dumps and Avalon soil-covered dumps
showing acidification than in the non-acidified dumps covered with 1 m of Avalon soil or Avalon and
Estcourt soil. Associated populations of iron-oxidizing bacteria of the Metallogenium type,
acidophilic and non-acidophilic thiosulphate-oxidizing bacteria were generally low in the coal waste
of the dumps.
Thus, five of the soil covers, all with a thickness of 1 m, but not covers with a thickness of 0.5 m or
less, proved effective for almost 2 years in inhibiting the diffusion of oxygen to the underlying coal
waste in the pilot scale dumps and also appeared to suppress the populations of iron-oxidizing bacteria believed to be implicated in acid formation in the coal waste. These results suggest that coal
waste dumps in South Africa should be covered with soil layers of 0.5-1.0 m thick to prevent the
generation of acid mine drainage. / AFRIKAANSE OPSOMMING: Die aktiwiteit van ysteroksiderende bakteriee soos Thiobacillus ferrooxidans, in die buitenste lae van
steenkoolafvalhope, veroorsaak die oksidasie van piriet met die gevolg dat groot volumes suur
mynafloopwater gevorm word. Hierdie proses benodig suurstof en vog. Suur mynafloopwater kan
moontlik beheer word deur 'n situasie te skep waar die toestande in die hope ongunstig is vir die
ysteroksiderende bakteriee. Die huidige navorsing het die moontlikheid ondersoek om hierdie
bakteriee te inhibeer deur verskillende afvalhoopontwerpe op die proef te stel en sodoende
suurvorming in steenkoolmynhope te beperk.
Die fisiese en chemies kondisies, suurvorming en populasies van vier verskillende bakterie-groepe
wat dalk by suurvorming betrokke is, is vanaf September 1993 tot Julie 1995 bestudeer in die
buitenste lae van tien verskillend gekonstrueerde loodsskaalafvalhope by die Kilbarchan myn naby
Newcastle in KwaZulu-Natal. Afvalhoopbedekkings bestaande uit 'n 30-cm of 70-cm Estcourt
grond met 'n lae permeabiliteit bedek met'n 70-cm of 30-cm laag van meer deurlaatbare Avalon
grond het anaerobe kondisies veroorsaak. Ongekompakteerde 30-cm en gekompakteerde 50-cm
Avalon grondlae het egter nie bestendige anaerobe kondisies in die hope veroorsaak nie. Die
onbedekte hope het aerobics gebly met slegs effense dalings van suurstofkonsentrasies gedurende en
na swaar reens.
Geisoleerde monsters uit die steenkoolafval onder die 50-cm Avalon grondlaag het vanaf die begin
van die toetsperiode tekens van suurvorming getoon. Die onbedekte steenkoolafval en die van die
sel met 'n 30-cm Avalon grondlaag het met verloop van tyd al hoe meer suur geword. Die
ysteroksiderende bakterie-populasies van die T. ferrooxidans tipe het geblyk om in die onbedekte en
Avalon grondbedekte hope wat tekens van suurvorming getoon het hoer te wees as in die hope wat
met 'n 1-m laag Avalon grond of Avalon en Estcourt grond bedek is en geen tekens van
suurvorming getoon het nie. Ysteroksiderende bakteriepopulasies van die Metallogenium tipe, nieasidofiele
en asidofiele tiosulfaatoksiderende populasies was oor die algemeen laag in die
steenkoolafvalhope.
Vyf van die grondlae wat alma! 1 m dik was het dus geblyk om effektief te wees in die bekamping
van die infiltrasie van suurstof na die onderliggende steenkoolafval in die loodskaalhope. Dit lyk asof
daardie lae die ysteroksiderende populasies betrokke by suurvorming onderdruk het. Die 0.5-m grondbedekking het egter nie so 'n sterk onderdrukkende effek op die suurstofinfiltrasie of die
bakteriepopulasie gehad nie. Na aanleiding van hierdie resultate blyk dit dat steenkoolafvalhope in
Suid-Afrika met minstens 0.5 tot 1..0 m grond bedek moet word om effektief die probleem van suur
mynafloopwater te bekamp.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/55521 |
| Date | 03 1900 |
| Creators | Cleghorn, Charles, 1970- |
| Contributors | Loos, M. A., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 131 p. : ill. |
| Rights | Stellenbosch University |
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