AcknowledgementsThis project would like to thank the Energy Production and Infrastructure Center (EPIC) at University of North Carolina at Charlotte for providing funding for equipment, materials and the research assistantship position.

Conclusions

Practical Leaching Procedure Recommendations for Coal Ash Treatment Evaluation

IntroductionThe US EPA Method 1311 (TCLP) was established in a revision ofResource and Conservation Recovery Act (RCRA) as the leachingprocedure used to determine toxicity of a material for placement ina landfill. Although the US EPA has established many additionalsubstances as being toxic and having limits, if a constituent ofconcern has a “Regulatory Level” the Toxicity CharacteristicLeaching Procedure (TCLP), Method 1311 is often used as “proof”that a proposed treatment “works” when in truth, TCLP providesfalse positive or negative reductions when used for treatmentcomparison. Changing the pH alone will increase or decrease theconcentration of the particular elements as in “Illustration of LSPCurve Pattern” (adapted from Kosson et al. 2002). TCLP results in asingle value for a pH roughly between 4 and 5 regardless of thestarting pH of the treated or untreated material.

I would also like to acknowledge Dr. John Daniels and the Infrastructure and Environmental Systems (INES) Ph.D. Program

Methodology

Method 1313 demonstrates the effect of pH on the leaching of various elements and why a material’s natural pH under leaching conditions is vital for treatment comparison. The TCLP provides only a concentration at a single pH ≈4 that is unrelated to the materials own pH. Making coal fly ash water resistant (hydrophobic) reduced metals leaching of some elements and increased it for others. Why didn’t the organosilane work as expected? Once the entry pressure has been exceeded, water is in contact with the ash. Then, pH is the strongest influence on the leaching behavior for most elements when the liquid to solid ratio is held constant. This was also true for the chemical fixation product. The newer EPA leaching tests provide more information about the leaching behavior of elements in ash compared to the TCLP but the concentration results are not appropriately compared to the RCRA specified TCLP concentration limits which are more dilute (L/S of 20:1 rather than 10:1 for the newer tests. Converting the TCLP limits and newer tests to a mass of constituent per kg of ash provides a more appropriate comparison. All laboratory based leaching procedures share the same limitations, they are only truly applicable for similar field conditions to the test conditions. Liquid to solid leaching ratio and pH are only two of the factors affecting leaching . Other US EPA and ASTM procedures provide alternative test parameters to address other leaching factors. Although no lab procedure can account for all field relevant parameters, the TCLP is not a good leaching procedure to compare treatment effectiveness for many metals.

MaterialsAbstract

Results

Concern that trace elements may leach from coal fly ash stored inponds and landfills has increased regulation and hindered fly ashrecycling. The pH is an important factor in the leaching response.The limitations of single pH leaching procedures and theimportance of material characterization under field relevantconditions are well known in the published literature. Yet manyremediation projects, legislative initiatives and product evaluationsstill rely on EPA Method 1311, Toxicity Characteristic LeachingProcedure (TCLP). Comparing the results of TCLP, with the results ofEPA Method 1313, the pH dependent leaching procedure, usingfour chemical treatments highlights the tendency of TCLP to underreport leaching concentrations for such elements as arsenic,selenium, and molybdenum when the material has a high pH.Conversely, TCLP over estimates leaching compared to EPA Method1313 for materials with near neutral pH for these same elements.This study recommends that the natural pH of the material and alimited range of pH bracketed on the field relevant pH, be used toprovide more appropriate coal ash treatment evaluation and sourceterm definition than TCLP.

Jenet T. Hattaway, P.E.PhD. Student

Infrastructure and Environmental Systems (INES)

• Method 1311 – Toxicity Characteristic Leaching Procedure (TCLP)• From the USEPA SW-846 Test Methods for Evaluating Solid Waste,

Physical/Chemical Methods.• L/S of 20:1 (2L extracting fluid /100g-dry solid sample)• Single end point pH value. Batch Extraction Procedure.

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TCLP & pH dependent concentration of Arsenic

CFA WK02 ZY TG

DW Limit Minimum Detection Limit TCLP ZY Natural pH

TCLP WK02 TCLP TG TCLP CFA TCLP Limit

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TCLP & pH dependent concentration of Chromium

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TCLP ZY TCLP WK02 TCLP CFA TCLP TG

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TCLP & pH dependent concentration of Selenium

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TCLP Limit Natural pH TCLP ZY TCLP WK02 TCLP CFA TCLP TG

Method 1313 - Liquid-Solid Partitioning as a Function of Extract pH using a Parallel Batch Extraction Procedure • From the USEPA SW-846 Test Methods for Evaluating Solid

Waste, Physical/Chemical Methods. • L/S of 10:1 (200 mL extracting fluid /20 g-dry solid sample)• Nine specified target pH values and material’s own or natural pH.

13, 12,10.5, 9, 8, 7, 5.5, 4, 2 and natural.

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TCLP & pH dependent concentration of Magnesium

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Untreated coal fly ash (CFA) was treated with one of three different products: Two organosilane products, ZY and WK02 which impart hydrophobicity (water repellency) and one chemical fixation product TG which purports to chemically bond constituents of concern in the solid matrix of the fly ash without creating hydrophobicity.

Scanning Electron Microscope (SEM) image of fly ash.

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TCLP & pH dependent concentration of Manganese

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Compare TCLP results for a high and low “own or natural pH.”

It is important to note that unless specifically required in a regulation the EPA SW-846 methods, including Method 1311 (TCLP) are provided as guidance to be used by the regulated community in making judgments to meet the environmental objectives. Using best available information for decisions about treatment options is critical to meeting environmental compliance.

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TCLP & pH dependent concentration of Molybdenum

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Natural pH TCLP ZY TCLP WK02 TCLP CFA TCLP TG

Both Methods: The material and extracting fluid (deionized water and acid or base) were tumbled for 24 hours at 30 ± 2 rpm in a rotary agitator. The leachate was vacuum filtered through 0.45µm pore size polypropylene membrane and acidified for analytical analysis by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

2015 World of Coal Ash (WOCA) Conference in Nashville, TN - May 5-7, 2015 http://www.flyash.info