Lignite-derived humic substances for treatment of acid mine drainage

William E. Olds, Chiu Wa Tsang, Paul A. Weber

Research output: Journal article publicationJournal articleAcademic researchpeer-review

1 Citation (Scopus)

Abstract

Acid mine drainage (AMD) generated by some coal mines in New Zealand is currently neutralized by the addition of alkaline reagents, triggering the precipitation of dissolved metals as insoluble hydroxides. This study investigated the addition of lignite-derived humic substances (HSs) before, during, and after neutralization of AMD based on two Stockton Mine treatment scenarios: the Blackwater Treatment Plant (BTP) and the Mangatini Stream-Sump (MSS). Supernatant samples collected during the sedimentation period were analyzed for basic water quality parameters: turbidity and suspended solids (SSs). The BTP scenario used calcium hydroxide [Ca(OH)2] neutralization, resulting in low supernatant turbidity (<2 NTU, nephelometric turbidity units) and SSs (<5 mg/L) regardless of the HS addition sequence. The MSS scenario used calcium carbonate (CaCO3) neutralization, and showed HS dosing enhanced flocculation and sedimentation of residual CaCO3SSs when added after neutralization, resulting in up to 75% reduction in SSs compared to CaCO3neutralization alone. When added after neutralization (pH 7), HSs remained dissolved and were incorporated into settling metal precipitates as an organic coating, promoting the coagulation of undissolved CaCO3by charge neutralization. Improvement in water quality was optimized at shorter residence times (0.5-6 h) and smaller HS doses (5-20 mg/L). Addition of HSs before (pH 2.6) and during (pH 4.5) neutralization resulted in the formation of HS precipitates, which probably acted as nucleation sites for adsorption and coprecipitation of metal hydroxides, resulting in good incorporation of HSs into floc, but rendering HSs unavailable for coagulation of residual CaCO3at pH 7. This article shows that incorporation of HSs into AMD treatment is more advantageous for CaCO3than Ca(OH)2neutralization with respect to water quality, and presents a novel method for improving the water quality of CaCO3-neutralized AMD.
Original languageEnglish
Pages (from-to)638-645
Number of pages8
JournalEnvironmental Engineering Science
Volume30
Issue number10
DOIs
Publication statusPublished - 1 Oct 2013

Keywords

  • acid mine drainage
  • flocculation
  • humic substances
  • lignite
  • water quality

ASJC Scopus subject areas

  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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