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MECHANISMS OF HEAVY METAL REMOVAL FROM ACID MINE DRAINAGE USING CHITIN
Citation:
AL-ABED, S. R., D. J. REISMAN, N. DESHPANDE, AND G. JEGADEESAN. MECHANISMS OF HEAVY METAL REMOVAL FROM ACID MINE DRAINAGE USING CHITIN. Presented at 134 American Chemical Society National Meeting, Boston, MA, August 19 - 23, 2007.
Impact/Purpose:
to present information
Description:
Acid Mine Drainage (AMD) emanating from inactive or active mine sites contains elevated levels of toxic heavy metals, which can have an adverse impact to the surrounding environment. The major pathway involved in generation of AMD is weathering of pyritic mineral ores, where in sulfur is oxidized to sulfate followed by the release of metal ions. Due to the low pH of the AMD, the metals are present in dissolved phase and are therefore highly active and more mobile. Increased awareness of heavy metal toxicity and extent of contamination throughout the country have stimulated the regulators to investigate treatment processes which can remove heavy metals present in the surface water including mine drainage. Among the various remediation technologies in practice today, active treatment of the acidic effluent using chemical neutralizing agents is most widespread. The obvious disadvantages of the active treatment process are the requirement of continuous inputs of resources to sustain the process and large amounts of residues generated. In lieu of this, passive treatments (biological treatment or anoxic limestone drains) are preferred due to their low cost, low required maintenance, and because they produce minimal hazardous waste requiring disposal. In passive systems using sulfate reducing bioreactors (SRBRs), the main mechanism is the reduction of sulfate species to sulf!des using carbon sources as the electron donor. Upon sulfate reduction, metal precipitation via the formation of metal sulfides, hydroxides, and carbonates occurs. Additionally, coprecipitation with these (oxy) hydroxides and sorption onto the compost surface is also known to occur3. While the passive treatment technology is well developed, the intrinsic problem is the availability a carbon source, which has spurred interest in the use of a novel organic substrate, called chitin. Chitin is obtained from exoskeletons of crabs and other arthropods are regarded as cellulose with an N-acetyl group shellfish. Chitin contains about 6-7% of nitrogen making it a nearly ideal carbon-nitrogen ratio for bacterial growth. Studies on chitin have confirmed the viability of chitin as a substrate for sulfate reducing bacteria. Chitin is also an excellent physical sorbent, especially at low pH. Chitin retains its permeability during degradation, making it an excellent candidate for use in AMO remediation. Thus, it is essential to evaluate the effectiveness of chitin as a sorbent for heavy metal removal from AMO, prior to evaluating its effectiveness for use in passive remediation systems. In this study, we focus on evaluating chitin as an adsorbent to remove heavy metals from AMO and determine the effect of variables such as pH, adsorbent loading, and redox potential on heavy metal removal. Additionally, since chitin is used as an additive to sand, manure or creek sediment (which serves the purpose of being the filler medium or the inoculum source) in most bioremediation studies, the effect of the addition of sand, manure, and creek sediment individually to chitin on metal removal is also evaluated.