Multiple Extraction Procedure

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The standard extraction tests (TCLP or California STLC) provide a one-time equilibrium solubility value of the heavy metal compounds in the extraction fluid but do not give an indication of the time-dependent stability of the residual matrix. The EPA multiple extraction procedure, designed for evaluating the leachability of materials exposed to so-called acid rain conditions, was used to test the stability of the polysilicate cementitious treatment protocol.

Table 3 Effect of Particle Size on Constituent Downwind Total Metal Concentrations for Metal System 5"

Compound

Mass fraction X l(T3

Conen, 0.8 mm particle (ng/m3)

Conen, 6.4 mm particle (ng/m3 x 10"5)

Arsenic

2.759

3.09

4.36

Copper

1.627

1.82

2.57

Lead

1.55

1.74

2.45

Nickel

0.47

0.526

0.174

Cadmium

0.048

0.054

0.076

Zinc

0.325

0.364

0.51

"Mean wind speed = I0 mph.

"Mean wind speed = I0 mph.

Late Decelerations
Figure 11 Effect of multiple extractions on soluble metal concentrations.

The evaluation consisted of an initial STLC extraction (as described in CCR title 26, Ch22-66261 Appendix 2) followed by 10 consecutive acid rain extractions (using a 60/40 solution of sulfuric/nitric acid with a pH of 3 as described in SW846 Volume C, Ch. 6, Method 1320). The predominant metals in the sample being treated were copper, lead, and zinc with initial STLC concentrations of 22, 110, and 106 ppm, respectively. Thus, in this sample the summed value for the STLC soluble metal concentration would be 238 ppm. Following treatment, the summed STLC concentration value was 11.7 ppm. The results of the subsequent acid rain extractions for both the treated and untreated materials are shown in Figure 11. Basically, the stability of the treated material is illustrated by the fact that the equilibrium leachable value was reached following the second acid rain extraction and remained unchanged. On the other hand, the metallic compounds in the untreated material continued to ionize and leach following each additional extraction step.

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Renewable Energy 101

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