© 2006 by Taylor & Francis Group, LLC

More documents

Recommendations

Info

90 Corrosion Control Through Organic Coatings 5.3 METHODS FOR STABILIZING LEAD Stabilizing lead means treating the paint debris so that the amount of lead leaching out is lowered, at least temporarily. There are concerns about both the permanence and effectiveness of these treatments. The major stabilization methods are explained in this section. 5.3.1 STABILIZATION WITH IRON Iron (or steel) can stabilize lead in paint debris so that the rate at which it leaches out into water is greatly reduced. Generally, 5% to 10% (by weight) of iron or steel abrasive added to a nonferrous abrasive is believed to be sufficient to stabilize most pulverized lead paints [1]. The exact mechanism is unknown, but one reasonable theory holds that the lead dissolves into the leachate water but then immediately plates out onto the steel or iron. The lead ions are reduced to lead metal by reaction with the metallic iron [5], as shown here: Pb 2+ + Fe 0 → Pb 0 + Fe 2+ (ion) (metal) (ion) (metal) The lead metal is not soluble in the acetic acid used for extracting metals in the TCLP test (see Section 5.1.2); therefore, the measured soluble lead is reduced. Bernecki et al. [10] make the important point that iron stabilizes only the lead at the exposed surface of the paint chips; the lead inside the paint chip, which comprises most of it, does not have a chance to react with the iron. Therefore, the polymer surrounding the lead pigment may break down over time in the landfill, allowing the bulk lead to leach out. The size of the pulverized paint particles is thus critical in determining how much of the lead is stabilized; small particles mean that a higher percentage of lead will be exposed to the iron. The permanency of the stabilization is an area of concern when using this technique. Smith [11] has investigated how long the iron stabilizes the lead. The TCLP extraction test was performed repeatedly using paint chips, coal slag abrasive, and 6% steel grit. Initially, the amount of lead leached was 2 mg/L; by the eighth extraction, however, the lead leaching out had increased to above the permitted 5 mg/L. In another series of tests, a debris of spent abrasive and paint particles (with no iron or steel stabilization) had an initial leaching level of 70 mg/L. After steel grit was added, the leachable lead dropped to below 5 mg/L. The debris was stored for six months, with fresh leaching solution periodically added (to simulate landfill conditions). After six months, the amount of lead leached had returned to 70 mg/L. These tests suggest that stabilization of lead with steel or iron is not a long-term solution. The U.S. EPA has decided that this is not a practical treatment for lead. In an article in the March 1995 issue of the Federal Register [12], ‘‘The Addition of Iron Dust to Stabilize Characteristic Hazardous Wastes: Potential Classification as Impermissible Dilution,” the issue is addressed by the EPA as follows: © 2006 by Taylor & Francis Group, LLC
Abrasive Blasting and Heavy-Metal Contamination 91 While it is arguable that iron could form temporary, weak, ionic complexes…so that when analyzed by the TCLP test the lead appears to have been stabilized, the Agency believes that this ‘‘stabilization” is temporary, based upon the nature of the complexing. In fact, a report prepared by the EPA on Iron Chemistry in Lead-Contaminated Materials (Feb. 22 1994), which specifically addressed this issue, found that iron-lead bonds are weak, adsorptive surface bonds, and therefore not likely to be permanent. Furthermore, as this iron-rich mixture is exposed to moisture and oxidative conditions over time, interstitial water would likely acidify, which could potentially reverse any temporary stabilization, as well as increase the leachability of the lead…. Therefore, the addition of iron dust or filings to…waste…does not appear to provide long-term treatment. 5.3.2 STABILIZATION OF LEAD THROUGH PH ADJUSTMENT The solubility of many forms of lead depends on the pH of the water or leaching liquid. Hock and colleagues [13] have measured how much lead from white pigment can leach at various pH values using the TCLP test. The results are shown in Figure 5.1. It is possible to add chemicals, for example calcium carbonate, to the blasting medium prior to blasting or to the debris afterward, so that the pH of the test solution in the TCLP is altered. At the right pH, circa 9 in the figure above, lead is not soluble in the test solution and thus is not measured. The debris ‘‘passes” the test for lead. However, this is not an acceptable technique because the lead itself is not permanently Leachable lead, ppm 30.0 25.0 20.0 15.0 10.0 5.0 0.0 Leachable lead (ppm) 5.0 6.0 7.0 7.4 8.1 8.7 9.1 9.6 9.9 10.9 12.0 12.9 pH FIGURE 5.1 White lead leachability as a function of pH. Source: Hock, V. et al., Demonstration of lead-based paint removal and chemical stabilization using blastox, Technical Report 96/20, U.S. Army Construction Engineering Research Laboratory, Champaign, IL, 1996. © 2006 by Taylor & Francis Group, LLC
Page 1 and 2:
© 2006 by Taylor & Francis Group,
Page 3 and 4:
Corrosion of Ceramic and Composite
Page 5 and 6:
Published in 2006 by CRC Press Tayl
Page 7 and 8:
Preface This book has been written
Page 9 and 10:
Author Amy Forsgren received her ch
Page 11 and 12:
Contents Chapter 1 Introduction ...
Page 13 and 14:
2.4.2 Reactive Reagents ...........
Page 15 and 16:
6.2.4.1 Alkaline Blistering........
Page 17 and 18:
1 Introduction This book is not abo
Page 19 and 20:
Introduction 3 • A dissolution pr
Page 21 and 22:
Introduction 5 1.2.2 ELECTROLYTIC R
Page 23 and 24:
Introduction 7 to the metal is a ne
Page 25 and 26:
Introduction 9 9. Thomas. N.L., Pro
Page 27 and 28:
12 Corrosion Control Through Organi
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54: 38 Corrosion Control Through Organi
Page 81 and 82: 4 Blast Cleaning and Other Heavy Su
Page 83 and 84: Blast Cleaning and Other Heavy Surf
Page 99 and 100: 5 Abrasive Blasting and Heavy-Metal
Page 101 and 102: Abrasive Blasting and Heavy-Metal C
Page 103: Abrasive Blasting and Heavy-Metal C
Page 113 and 114: 6 Weathering and Aging of Paint Thi
Page 115 and 116: Weathering and Aging of Paint 101 c
Page 117 and 118: Weathering and Aging of Paint 103 I
Page 119 and 120: Weathering and Aging of Paint 105 c
Page 121 and 122: Weathering and Aging of Paint 107 S
Page 123 and 124: Weathering and Aging of Paint 109 e
Page 125 and 126: Weathering and Aging of Paint 111 I
Page 127 and 128: 7 Corrosion Testing — Background
Page 129 and 130: Corrosion Testing — Background an
Page 143 and 144: 130 Corrosion Control Through Organ
Page 155 and 156:
142 Corrosion Control Through Organ
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167:
show all

© 2006 by Taylor & Francis Group, LLC

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?