Acidification–Neutralization Processes in a Lignite Mine Spoil Amended with Fly Ash or Limestone

Abstract

A laboratory experiment was conducted to investigate the longterm effects of amending sulfide-rich lignite mine spoil with fly ash (originating from a coal-fired power station and largely comprised of aluminosilicates) and/or agricultural limestone. The experiment was carried out with soil moisture maintained at field capacity or alternate cycles of wetting and drying. Results obtained suggest that the principal acidification processes were oxidation of sulfide and formation of hydroxysulfate (FeOHSO4), whereas the main neutralization processes were weathering of aluminosilicates in fly ash-treated samples and dissolution of calcium carbonate in limestone-treated samples. The highest dose of limestone rapidly raised the pH of the spoil, but this increase was not maintained throughout the one-year experiment. In contrast, fly ash-treated samples showed a more sustained increase in pH, attributable to the gradual weathering of aluminosilicates. The best results (i.e., good short- and long-term neutralization) were obtained in samples treated with both fly ash and limestone. The low liming capacity of the fly ash (47.85 cmol kg(-1)) means that it must be used in large quantities, an advantage in achieving the further aim of disposing of the fly ash.

An appraisal of the potential use of fly ash for reclaiming coal mine spoil

“…Although lime and dolomite could be used for reclamation of acidic mine spoils, these materials are expensive, may be scarce in the future (due to limited reserves), and take longer to elicit significant soil improvements (Yunusa et al, 2006). Seoane and Leiró s (2001) found that FA treatment gradually increased the pH of mine spoil over time due to slow weathering of the aluminum silicates. A similar response was not seen when limestone treatment was used.…”

Introductory Chapter: Serious Pollution of Soil and Groundwater and the Necessity of Bioremediation

“…Therefore, remediation by neutralization is necessary before serious damage occurs. The neutralization of acid with calcium carbonate and calcium hydrate powder is a general and inexpensive procedure [12,13]. Several projects to neutralize lake water were conducted by spraying the powder from a small ship or helicopter.…”

Trace Element Immobilization in Soil Using Amendments

“…Ashes that have high alkalinity and acid neutralization capacity are considered suitable for reclamation of mine spoils and re-vegetation of barren sites [102][103][104][105][106]. Application of ash to sandy soils can improve soil texture and water-holding capacity [107,108] and reduce the swelling potential of clays [109].…”

“…Similar to the iron amendments, excess of reactive ash constituents (Ca, Al, Fe) can sorb and precipitate nutrients, causing their imbalance in amended soils [114,115]. As a result of nutrient deficiency, application of ashes (80 Mg ha -1 ) was observed to reduce maize biomass by half compared with a fertilized (using 20N-20P 2 O 5 -20K 2 O kg ha À1 ) control treatment [104]. Co-application of biosolids however has been suggested to counteract nutrient imbalance and maintain biomass production [99,115,116].…”

“…In addition, in situ soil treatment by altering pH might have only a shortterm effect on metal immobilization. The reactions may be reversible, with eventual soil acidification, and annual measures to keep pH and trace elements stable would be required [104].…”