Environmental Chemistry Leaching Labs by EIA



                                  ENVIRONMENTAL CHEMISTRY LEACHING LABS
                                  NETL conducts laboratory-scale leaching studies of particulate solids to assist in
                                  determining the compatibility of coal utilization byproducts with various end-use or
                                  disposal environments. In general, leaching techniques focus on the potential release
                                  of heavy metals to the surface and groundwater environments. In these experiments,
                                  batches of a solid phase are extracted with leachants chosen to dissolve or mobilize a
                                  particular phase or to mimic some aspect of a particular environment. Leaching
                                  techniques can be divided into two broad categories based on whether the leachant is
                                  applied batch-wise or continuously.
CONTACTS                          Batch leaching tests are the most common, and many analyses are based on single
 Karl Schroeder
                                  or multiple batch tests. Batch techniques quickly provide information on metals
                                  released at a set pH and liquid-to-solid ratio. Common examples include the TCLP1
 Environmental Science Division
                                  and SPLP2 tests that are used to mimic the environment in municipal solid waste
 National Energy Technology
                                  landfills, and contact with acid rain, respectively. More recently, NETL has developed
                                  a sequential leaching procedure to provide leaching data at several pH values and
 626 Cochrans Mill Road
 P.O. Box 10940
                                  liquid-to-solid ratios.3 Tessier4 has developed a more severe form of batch leaching,
 Pittsburgh, PA 15236-0940        called sequential extraction, which employs both mild and reactive chemicals to
 412-386-5910                     selectively dissolve and mobilize selected trace metals based on their mode of
                                  occurrence or speciation.
                                  Continuous leaching techniques, including both column and stirred tank approaches,
                                  are much less common. Fixed-bed columns are used to simulate the slow percolation
                                  of water through a stationary bed of material such as may occur when surface water
                                  permeates a land-fill area. In these experiments, columns constructed of 1 meter long
                                  sections of clear 2" PVC pipe and containing about 1 kilogram of material are
                                  leached using a peristaltic pump to deliver leachate to the top of the column at a rate
                                  of about 240 ml/day.5 Typical leachants are shown in Table 1. Column techniques
                                  provide leach data over extended periods of time, at progressively increasing liquid-
                                  to-solid ratios, and often over a range of pH values.

                                                             Table 1. Leachants for Column Leaching Tests

                                                     Leachant                           ID                  pH
                                                     Sulfuric Acid                      H2SO4                1.2
                                                     Acetic Acid                        HAc                  2.9
                                                     Synthetic Precipitation            SP                   4.2
                                                     Deionized Water                    H2O                  6.0
                                                     Sodium Carbonate                   Na2CO3              11.1

                                               Deionized water adjusted to pH 4.2 with a 60/40 mixture of H2SO4/HNO3
                                     ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
                                                                                                                                                                                                                   Unfortunately, clogs can form in fixed-bed leaching columns, either because of
                                                                                                                                                                                                                   cementitious properties of the material itself, such as is seen for FBC fly ash, or
                                                                                                                                                                                                                   because of precipitate formation, such as can occur when a high-calcium ash is
ADDRESS                                                                                                                                                                                                            subjected to sulfate-containing leachates. Also, very fine-grained materials, such as
 National Energy                                                                                                                                                                                                   gypsum, do not provide sufficient permeability for study in a fixed-bed column. A
                                                                                                                                                                                                                   continuous, stirred-tank extractor (CSTX) is an alternative technique that is used at
 Technology Laboratory                                                                                                                                                                                             NETL to provide the elution profile of column leaching without the permeability
 1450 Queen Avenue SW                                                                                                                                                                                              problems. The CSTX also allows fundamental
 Albany, OR 97321-2198                                                                                                                                                                                             chemical information to be obtained, including
 541-967-5892                                                                                                                                                                                                      reaction rates, equilibrium constants, effective
                                                                                                                                                                                                                   solubility products, as well as the effect of
 2175 University Avenue South                                                                                                                                                                                      pH changes. Most recently, the CSTX has
 Suite 201                                                                                                                                                                                                         been used to study the release and retention of
 Fairbanks, AK 99709                                                                                                                                                                                               mercury6 and other trace metals.7
                                                                                                                                                                                                                   Leachates from all of the leaching techniques
                                                                                                                                                                                                                   are analyzed for major and trace elements.
 3610 Collins Ferry Road
                                                                                                                                                                                                                   Mercury analyses are performed using a
 P.O. Box 880                                                                                                                                                                                                      CETAC Quick Trace M8000 CVAFS that
 Morgantown, WV 26507-0880                                                                                                                                                                                         provides quantitation at the sub-parts-per-
 304-285-4764                                                                                                                                                                                                      trillion level. Other metals are quantified using
                                                                                                                                                                                                                   either a Perkin Elmer Optima 3000 ICP-OES
 626 Cochrans Mill Road                                                                                                                                                                                            or a newly acquired Perkin-Elmer ELAN II
 P.O. Box 10940                                                                                                                                                                                                    ICP-MS. The Perkin-Elmer ELAN II instrument
 Pittsburgh, PA 15236-0940                                                                                                                                                                                         provides element detection limits in the sub-
 412-386-4687                                                                                                                                                                                                      parts per trillion range needed for the most
                                                                                                                                                                                                                   exacting environmental work. In addition, plans include interfacing the ELAN II
 One West Third Street, Suite 1400                                                                                                                                                                                 with a High Pressure Liquid Chromatograph (HPLC) which will extend analytical
 Tulsa, OK 74103-3519                                                                                                                                                                                              capabilities into the arena of metal speciation via HPLC-ICP-MS.

WEBSITE                                                                                                                                                                                                            1EPA Method 1311. Toxicity Characteristic Leaching Procedure 1992,
                                                                                                                                                                                                                   Available at http://www.epa.gov/epaoswer/hazwaste/test/pdfs/1311.pdf
                                                                                                                                                                                                                   2 EPA Method 1312. Synthetic Precipitation Leaching Procedure 1994,

                                                                                                                                                                                                                   Available at http://www.epa.gov/epaoswer/hazwaste/test/pdfs/1312.pdf
                                                                                                                                                                                                                   3 Hesbach, P.; Abel, A.S.P.; Kim, A.G.; Lamey, S.C. Rapid Batch Characterization of Coal
                                                                                                                                                                                                                   Utilization By-Products, 2005 Conference Proceedings - World of Coal Ash,
                                                                                                                                                                                                                   4Tessier, A.; Campbell, P. G. C.; Bisson, M. Sequential Extraction Procedure for the
                                                                                                                                                                                                                   Speciation of Particulate Trace-Metals. Analytical Chemistry 1979, 51, 844-851.
                                                                                                                                                                                                                   5Kim, A. G.; Kazonich, G.; Dahlberg, M. Relative Solubility of Cations in Class F Fly Ash.
                                                                                                                                                                                                                   Environ. Sci. Technol. 2003, 37, 4507-4511.
                                                                                                                                                                                                                   6Schroeder, K.; Kairies, C. Distribution of Mercury in FGD Byproducts
                                                                                                                                                                                                                   2005 Conference Proceedings - World of Coal Ash, http://www.flyash.info/2005/100sch.pdf
                                                                                                                                                                                                                   7Kairies, C.; Cardone, C.; Schroeder, K. Leaching of CUB Using a CSTX
                                                                                                                                                                                                                   2005 Conference Proceedings - World of Coal Ash, http://www.flyash.info/2005/99kai.pdf


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