Effect of soil covers on coal waste dumps in KwaZulu-Natal on abiotic factors and bacteria causing acid mine drainage

[摘要] ENGLISH ABSTRACT:The activity of iron-oxidizing bacteria, for example, Thiobacillut. ferrooxidans, in the outer layers ofcoal waste dumps results in the oxidation of pyrite with the formation of large volumes of acid minedrainage. The process requires atmospheric oxygen and moisture. Acid mine drainage may possiblybe controlled by creating unfavourable environmental conditions in dumps for the iron-oxidizingbacteria. The present research investigated the possibility of inhibiting these bacteria andconsequently acid formation in coal waste dumps by means of different dump constructiontechniques.Physical and chemical conditions, acid formation and populations of four groups of bacteria whichmight produce acid were studied in the outer layers of ten differently constructed pilot scale coalwaste dumps at the Kilbarchan Mine near Newcastle, Kwazulu-Natal, from September 1993 to July1995. Dump covers consisting of a 30-cm or 70-cm layer of Estcourt soil of low permeabilitycovered with 70 cm or 30 cm, respectively, of more permeable Avalon soil produced anaerobicconditions in the dumps throughout most of the 22 months of the test period, as did a cover of 70 cmcompacted 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. Uncovereddumps 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 soillayer from the time of construction and progressively increasing acidity in the uncovered dumps andthe 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 dumpsshowing acidification than in the non-acidified dumps covered with 1 m of Avalon soil or Avalon andEstcourt soil. Associated populations of iron-oxidizing bacteria of the Metallogenium type,acidophilic and non-acidophilic thiosulphate-oxidizing bacteria were generally low in the coal wasteof 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 orless, proved effective for almost 2 years in inhibiting the diffusion of oxygen to the underlying coalwaste 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 coalwaste dumps in South Africa should be covered with soil layers of 0.5-1.0 m thick to prevent thegeneration of acid mine drainage.

[发布机构] Stellenbosch University