Control Technologies for Remediation of

Journal of the Air & Waste Management Association

ISSN: 1047-3289 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uawm18

Control Technologies for Remediation of Contaminated Soil and Waste Deposits at Superf und Lead Battery Recycling Sites Michael D. Royer , Ari Selvakumar & Roger Gaire To cite this article: Michael D. Royer , Ari Selvakumar & Roger Gaire (1992) Control Technologies for Remediation of Contaminated Soil and Waste Deposits at Superf und Lead Battery Recycling Sites, Journal of the Air & Waste Management Association, 42:7, 970-980, DOI: 10.1080/10473289.1992.10467046 To link to this article: https://doi.org/10.1080/10473289.1992.10467046

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CONTROL TECHNOLOGY Control Technologies for Remediation of Contaminated Soil and Waste Deposits at Superf und Lead Battery Recycling Sites Michael D. Royer U.S. Environmental Protection Agency Superfund Technology Demonstration Division Edison, New Jersey

Ari Selvakumar and Roger Gaire Foster Wheeler Enviresponse, Inc. Edison, New Jersey

This paper primarily addresses remediation of contaminated soils and waste deposits at defunct lead-acid battery recycling sites (LBRS) via immobilization and separation processes. A defunct LBRS is a facility at which battery breaking, secondary lead smelting, or both operations were performed for the primary purpose of reclaiming lead from spent lead-acid batteries. Metallic lead and lead compounds are generally the principal contaminants of concern in soils and waste deposits (i.e., buried, piled, landfilled waste) at these sites. Other metals (e.g., cadmium, copper, arsenic, antimony, and selenium) are often present at LBRS, but usually at much lower concentrations than lead and often present below hazardous concentrations. This article is primarily based on experience gained from: (1) Superfund site investigation, removal, and remedial actions, and (2) development and demonstration of control technologies under the Superfund Innovative Technology Evaluation (SITE) Program. The primary remedial options for lead contaminated soils and waste deposits include: (1) no action, (2) off-site disposal, (3) containment, (4) immobilization, (5) separation with resource recovery, and (6) separation without resource recovery. In spite of the toxicity of lead at low concentrations, the relative immobility of lead and site-specific risk assessments can still result in the selection of no action or containment remedies. Solidification/stabilization of lead-contaminated soils has been implemented at three Superfund sites and is the selected remedy at several others. Separation technologies (e.g., screening, extraction) are attractive because, if successful, they actually remove the contaminant from the environmental media. Separation technologies also offer the possibility that a valuable product (e.g., lead, plastic, energy) can be recovered, but careful consideration of economic and technical factors are required. Compared to the implementation of containment and solidification I stabilization remedies, separation technologies tend to be relatively novel, complex, and costly.

A defunct lead-acid battery recycling site (LBRS) is a facility at which battery breaking, secondary lead smelting, or both operations were performed for the primary purpose of reclaiming lead from spent lead-acid batteries. Twenty-nine defunct LBRS have been or are being addressed under the Superfund Program. Of the 29, 20 are battery breaking sites, where the operations consisted primarily of battery breaking, draining the spent acid, and separating the battery cases from the lead. The other nine LBRS were integrated battery breaking/ smelting sites, where batteries were not only taken apart to remove the lead, but the lead was remelted and subjected to further processing to produce lead alloys for subsequent re-use. This article primarily addresses remediation of contaminated soils and waste deposits at defunct LBRS via immobilization and separation processes. Containment and no action options are also discussed briefly. This article is primarily based on experience gained from: (1) Superfund site investigation, removal, and remedial actions, and (2) development and demonstration of control technologies under the SITE program. As of February 1992, full-scale implementation of remedies at defunct LBRS has occurred three times for immobilization processes and zero times for separation processes. While this represents a limited amount of full-scale implementation experience, an impressive range of options have been investigated at desktop, laboratory, bench, and pilot-scale levels. A number of technologies have

Copyright 1992—Air & Waste Management Association

970

J. Air Waste Manage. Assoc.

also been tested, but not fully implemented, at full-scale. This article is organized as follows: (1) LBRS are described with particular attention to the types of contaminants and contaminant-media matrices that are encountered; (2) immobilization and separation technologies for lead contaminated soils are addressed; and, (3) immobilization and separation technologies for waste deposits are described and discussed. The immobilization technologies addressed are solidification/stabilization with various agents and vitrification. The separation technologies addressed are various physical sizing and classification processes, soil and debris washing, chemical treatment followed by acid leaching, and lead recovery by thermal and electrochemical methods. The potential for separating and reusing rubber and plastic casing scrap is also discussed. The scope of this article is limited to Superfund sites. Specifically, it does not address sites that may have been or are currently slated for corrective action under the Resource Conservation and Recovery Act. This article also makes no attempt to survey or describe non-Superfund cleanups that may have been done by states or the private sector. This article does not address the remediation of all contaminated media at lead battery recycling sites. Specifically, contaminated water, wastewater, industrial buildings and equipment, and residential buildings are not discussed. Background Information on Lead-Acid Batteries, Battery Breaking, and Secondary Lead Smelting Operations

Metallic lead and lead compounds are generally the principal contaminants of concern in soils and waste deposits during LBRS remediation. Other metals (e.g., cadmium, copper, arsenic, antimony, and selenium) are often present at LBRS, but usually at much lower concentrations than lead and often below hazardous concentrations. Lead, lead compounds, polypropylene battery case scrap, and hard rubber-like battery case scrap are potentially recyclable, so at least a preliminary evaluation of the feasibility of separation and recovery of those materials is often desirable. LBRS characterization and remediation are complicated by the fact that the lead and its compounds appear in a variety of physical forms (e.g., dusts, pastes, chips, chunks), chemical forms (e.g., elemental, oxides, carbonates, hydroxides, sulfates, etc.), and matrices (e.g., soil of various types; slag from reverberatory, blast and rotary kilns; on casing surfaces and in casing cracks; July 1992

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in piles of single or mixed materials, etc.). Below are brief descriptions of lead-acid storage batteries, battery breaking, and secondary lead smelting that explain the origin of the various lead compounds and matrices that one typically finds at a defunct LBRS. Lead-Acid Storage Battery

While all lead-acid storage batteries are not alike, a description is provided below of a typical lead-acid storage battery (i.e., a car battery) that is likely to have been processed at a defunct LBRS that is now on the Superfund cleanup list. A typical automotive battery weighs 17.2 Kg, and contains 8.6-9.1 Kg of lead (equally divided between anode and cathode), 1.4 Kg of polypropylene plastic (the mass of the hard rubber-like casings would be somewhat higher given its greater density and thickness) and approximately 2 liters of 15-20 percent sulfuric acid. This typical battery consists of two electrodes dipped into partly dilute sulfuric acid. The electrodes consist of metallic lead grids containing either lead dioxide paste (cathode) or spongy lead (anode). The grids may contain various additives including antimony, arsenic, cadmium, copper, and tin. A standard automotive battery consists of six cells connected in series with lead lugs. Each cell delivers 2 volts and contains 13 to 15 electrode plates. Anodes and cathodes are isolated by envelope separators. Pplyvinyl chloride (PVC) and fibrous paper are the two most common separator materials. The overall electrochemical reaction that occurs in the battery is as follows: Pb(s) + PbO'2(8) T 4H ( + aq) + 2 S O 4 ( a q ) - 2PbSO4(s) + 2H2O(L) Reversal of this reaction results in recharging the battery. The internal battery components and sulfuric acid solution are contained inside a battery case. Although most battery cases now are constructed of recyclable polypropylene, they were previously composed primarily of a composite hard rubber-like material. When the transition occurred from the rubber-like casings to polypropylene casings was not determined. These hard rubber-like casings were not recycled back into battery casings and gen-

erally appear to comprise the majority of battery casing scrap material at defunct LBRS. Asphaltic materials were used to bind and seal the upper and lower portions of the hard rubberlike casings. As shown in Table I, the hard rubberlike material is actually a composite material consisting of: a carbonaceous filler material such as anthracite coal or carbon black; a binder made from synthetic rubber cross-linked with sulfur; a small quantity of oil added to break down the synthetic rubber; and a small quantity of lime or zinc oxide. These materials are molded into a battery casing under pressure at 385°F. It is important to note that the hard rubber-like battery casing material is frequently called "ebonite." In fact, only a small amount of ebonite, if any, is contained in the hard rubber-like casings. Pure ebonite is a hard rubber that contains at least 15 percent sulfur, while the battery casing materials have sulfur contents in the range of 2 to 5 percent. The U.S. Bureau of Mines performed microscopic evaluations of the hard rubber-like battery scrap from several LBRS, and determined that these casings tend to develop microcracks in which lead sulfate becomes lodged, making it difficult to remove the lead by surface cleaning or abrasion alone. Battery Breaking and Secondary Lead Smelting Description

The lead recovery aspects of leadacid battery recycling operations consist of battery breaking, component separation, lead smelting, and refining, as shown in Figure 1. The flow diagram in Figure 2 depicts the leadacid battery breaking process. A more complete description of these processes can be found in "Selection of Control Technologies for Remediation of Lead Battery Recycling Sites." 2 The discussion below will focus on a few points that are particularly pertinent to remediation of soils and waste deposits. With respect to cleaning up the site, two points relating to the battery breaking operation are of particular importance: 1. What was done with the sulfuric acid? • If it was dumped on the ground it may have degraded and modi-

Table I. Hard rubber compositions.1 Component

Composition 1

Composition 2

Anthracite coal or carbon black Synthetic rubber (styrene-butadiene cross-linked with sulfur) Oil Sulfur (total) Lime

65%

75%

10% 10% 5% 10%

10%-12% 6% 2% 6% 971

CONTROL TECHNOLOGY fied the soil as compared to other soil at the site. Also, the lead solubilized in the acid will have eventually precipitated out in the soil, with the lead precipitate being determined by the soil anions. • If the acid was neutralized and then dumped on the ground or in a lagoon, a precipitated lead compound (depending on the neutralization agent) will be present in soils or sediments. • The soil area where it was dumped will be high in residual sulfates. This may be important, as explained later, if solidification/stabilization is attempted as a remedy. • The acid may have been neutralized and the sludge properly discarded, resulting in no residual soil contamination. 2. How were the solid battery components and casings normally processed? • In one extreme situation both plastic and rubber casing debris will simply have been placed in a waste pile or pit with a variety of other process, construction, and other wastes from the site. Relatively inefficient separation may have left a substantial amount of lead (e.g., 30 percent by weight) attached to the casings. Due to the physical and chemical heterogeneity of a waste mixture of this type, application of an immobilization or separation technology in this case is expected to be difficult and costly. • In the extreme opposite situation, the casings may have been

subjected to a variety of sizing and washing processes in order to maximize lead and plastics recovery. In the ideal situation these processes would produce: • A separate polypropylene stream with minimal amounts of attached metallic lead or surface-adhering lead sulfate, lead oxides, or other materials; • A separate hard rubber-like casing stream; • A lead fines stream (e.g., mixed powdered lead, lead oxides, lead sulfide, and soil); and • A metallic lead stream (e.g., terminals, plates, chips). If this type of process was in place during operation of the facility, then it favors recycling or re-use of the caisings because it minimizes the amount of additional processing that might be required to produce a uniform feed for resource recovery. The actual situation will probably lie somewhere in between the two extremes described above, and therefore control technologies must be determined on a site-by-site basis. Sites where smelting and refining, as well as battery breaking, were performed pose additional challenges for remediation. The discussion here of the smelting process will be limited to citing the likely contributions of smelting operations to soil contamination and waste deposits at an LBRS. The smelting process at Superfund sites typically produced: • Stack emissions (e.g., lead oxides) some of which may have been deposited in the soil, and which can be expected to be more prevalent if the facility operated before pollution controls were required. • Air pollution control residuals (e.g.,

Disposal

Oxide Plant

Market

Market

Figure 1.

972

Generalized secondary lead smelting/refining process. Source: Exide Corporation, 1992.

baghouse dust or wet scrubber sludges) if controls were required during the facility's operation. • Blast furnace slag that typically contains lead in the 1 to 4 percent range, and typically fails Toxicity Characteristic Leaching Procedure (TCLP) testing (i.e., leachate >5 mg/L). • A landfill where both air pollution and water pollution control residuals and slag were discarded. • Fugitive emissions from various thermal and materials handling processes that result in lead contaminated soil. Another important factor affecting both soil and waste deposit composition is previous cleanup efforts at the site. For example, neutralization of soil with lime has been performed at a number of sites, causing an increase in the presence of carbonate-containing lead compounds. Finally, the soil type also has an effect on the lead compounds that are found in the soil. Summary Description of Lead Behavior in Soil and Common Cleanup Goals

As described above, lead is the primary contaminant found in soils at LBRS. Concentrations up to 7 percent lead in soil have been noted. Lead (Pb), lead sulfate (PbSO4), lead oxide (PbO), and lead dioxide (PbO2) are the predominant species found at LBRS. Sites with carbonate soils generally contain lead carbonate (PbCOs), hydrocerussite (Pb3(CO3)2(OH)2), or lead hillite (Pb4SO4(CO3)2(OH)2). Other heavy metals, such as antimony, arsenic, cadmium, and copper are sometimes present, but normally at relatively low concentrations. Battery casing scraps may be intermixed with the soil. Lead is generally not very mobile in the environment, and tends to remain relatively close to its point of initial deposition following its escape from the recycling process. Soils strongly retain lead in their upper few centimeters; they are the major sinks for pollutant lead. The capacity of soil to adsorb lead increases with increasing pH, cation exchange capacity, organic carbon content, soil/water Eh (redox potential), and phosphate levels. Lead exhibits a high degree of adsorption on clay-rich soil. Lead compounds can also be adsorbed onto hydrous oxides of iron and manganese and thus be immobilized in salts containing two or more cations. Metallic lead and its insoluble/precipitated compounds are heavier than water and tend to settle out. Some of the lead compounds are slightly soluble in water, while others are insoluble in water. The solubility of lead increases at low and very high pH. Soil cleanup goals vary depending on J. Air Waste Manage. Assoc.

Disposal

Rubber/ebonite Reuse * - Fuel supplement • Fill and paving material - Oil drilling mud additive -Other

Plastic, rubber/ebonite

Plastic

Batteries

Battery breaking (primarily hammer mill or saw-type breaker)

Flotation

• Battery cases -Fuel •Other

Lead plate, posts, sludge

Acid

Secondary lead smelters

Direct discharge to environment ion facility Collection

|

Treatment

|

* Feasibility of reuse/recycling depends upon several factors including: quantity, quality of materials, . economics, technical feasibility, and regulations.

T Acid recycle Figure 2.

Flow diagram of lead-acid battery breaking.

site specific factors, such as exposure routes and location of humans and sensitive environmental receptors. In spite of this variability, two common cleanup goals do tend to recur. One of these common cleanup goals includes reduction of lead concentrations in the soil so the leachate contains less than 5 mg/L of lead when soil is subjected to the TCLP. Soil with a TCLP leachate above 5 mg/L lead is considered to be hazardous waste, which means that it generally cannot be landfilled until it has been treated to yield a leachate less than 5 mg/L lead when subjected to either the TCLP procedure or the Extraction Procedure Toxicity Test.3 A second common cleanup goal is the reduction of the total lead content in residential soil to a level less than 500 to 1000 mg/Kg. In accordance with EPA Office of Solid Waste and Emergency Response (OSWER) Directive 9355.4-02, an interim soil cleanup level of 500 to 1000 mg/kg total lead was adopted for protection from direct contact at residential settings. OSWER is in the process of revising this directive to account for the contributions of various media to total lead exposure and to produce a scientific basis for choosing a soil lead cleanup level for a site. OSWER believes that the best available approach to set soil lead cleanup levels is to use the EPA uptake biokinetic model.4 Control Technologies for Lead-Contaminated Soils at LBRS

The primary remedial options typically selected to date for Superfund remedial and removal actions for lead July 1992

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contaminated soils include: (1) no action, (2) off-site disposal, (3) containment, (4) immobilization, (5) separation with resource recovery, and (6) separation without resource recovery. The first three options do not reduce the toxicity, mobility, or volume of the contaminant through treatment, and are therefore not considered control technologies for the purposes of this article. However, these options may be viable remedies given the specific nature of the site, and the outcome of the risk assessment and feasibility study. The generally immobile behavior of lead in soil and limited solubility in water tend to favor a limited remedy (i.e., no action, containment, off-site disposal) unless there are conditions at the site that tend to promote mobility (e.g., porous soil, acidic conditions, large quantities of contaminants), or if there is a high risk if migration occurs, due to proximity to human and environmental receptors. No action remedies were selected in two out of ten Records of Decisions (RODs) for LBRS. Capping was selected in one ROD, and was also implemented for at least one other site as part of a removal action. Excavation and removal of contaminated soil was a popular remedy in the past for smaller sites, and may still be viable in some instances, but due to current Land Disposal Restrictions, treatment prior to disposal may be required. Immobilization Options for Lead-Contaminated Soil

The immobilization options for leadcontaminated soils are: (1) ex situ solid-

ification/stabilization, (2) in situ solidification/stabilization, (3) ex situ vitrification, and (4) in situ vitrification. Solidification/Stabilization (S/S). To date, five of ten RODs for LBRS have selected ex situ S/S as an integral part of a treatment alternative. Solidification processes, either in situ or ex situ, produce monolithic blocks of waste with high structural integrity. The contaminants do not necessarily interact chemically with the solidification reagents (typically cement/lime) but are primarily mechanically locked within the solidified matrix. Stabilization methods usually involve the addition of materials such as fly ash or blast furnace slag which limit the solubility or mobility of waste constituents—even though the physical handling characteristics of the waste may not be changed or improved.5 Ex situ S/S is widely demonstrated and equipment is readily available. However, long-term reliability of S/S is not yet established. Ex situ S/S involves mixing the excavated contaminated soil with portland cement and/or lime along with other binders such as fly ash or silicate reagents to produce a strong, monolithic mass. Cement is generally suitable for immobilizing metals (such as lead, antimony, and cadmium) which are found at LBRS. Because the pH of the cement mixture is high (approximately 12), most multivalent cations are converted into insoluble hydroxides or carbonates. They are then resistant to leaching. Costs to use S/S technology are expected to be in a range of $30-170 per 973

CONTROL TECHNOLOGY cu yd.6 Data needs to evaluate S/S as a remedial alternative are summarized in Table II. Three full-scale S/S operations have been implemented at LBRS. Approximately 7,300 tons of soil contaminated with lead (EP Tox >400 mg/L) were treated in a mobile plant with portland cement, fly ash, and water at a rate of 300 tons/day at Norco Battery Site in California. EP Toxicity of the treated soil after 28 days was less than 5 mg/L.9 Approximately 11,000 tons of soil (TCLP as high as 422 mg/L) were treated by the proprietary MAECTITE® process developed by Maecorp, Inc. at the Lee's Farm in Wisconsin. TCLP of the treated soil was less than 1 mg/L. About 20,000 cubic yards of lead-contaminated soil were recently solidified at Cedartown Battery, Inc. in Georgia. Analytical data on this site are being processed. Numerous S/S treatability studies have been completed at LBRS. A pilotscale treatability test conducted at the Gould Site in Oregon demonstrated that a mix of approximately 14 percent Portland cement Type I-II, 25 percent cement kiln dust, and 35 percent water successfully stabilized soils and waste products crushed to 1/8-inch size. Bench-scale treatability studies conducted on soils from three LBRS (C&R Battery Site in Virginia, Sapp Battery Site in Florida, Gould Site in Oregon) demonstrated that cementbased (i.e., cement or cement with additives) blends decreased the leachability of lead and met the EP Toxicity criterion of 5 mg/L. In situ S/S of contaminated soils is innovative. The following two processes under the Superfund Innovative Technology Evaluation (SITE) Program hold promise for LBRS. International Waste Technologies (IWT)IGeo-Con, Inc. This in situ S/S process is claimed to be able to immobilize organic and inorganic compounds in wet or dry soils. The process con-

Table II. Data needs for solidification/stabilization of soils. Technology

Data requirement

Solidification/ • Metal concentrastabilization7'8 tions Moisture content Bulk density Grain-size distribution Waste volume Sulfate content Organic content Debris size and type • TCLP

974

sists of the following main components: 1. A proprietary IWT additive is chosen for the specific site. This additive is a silicate-based cementitious material, which also includes organophilic clays. 2. A batch mixing plant prepares a slurry of water and the proprietary additive. 3. A mechanical mixing and injection system delivers the additive-water slurry to the subsurface soil. The system provides mechanical mixing and injection, and consists of one set of cutting blades and two sets of mixing blades attached to a vertical drive auger. The slurry is injected on the downstroke. A demonstration was conducted under the SITE Program at a PCBcontaminated site in Hialeah, Florida in April 1988.10 Two 10-ft x 20-ft sections were treated to depths of 14 and 18 feet. The soils at the site were unconsolidated sand (5 ft); Miami limestone (5 to 10 ft); and, uncemented fine quartz sand. Although there was some lead contamination in the soil, there was not enough to verify its successful solidification. Otherwise, the test was basically successful, except in regard to freeze/thaw testing, where weight losses of 6 percent were observed.11 S.M.W. Seiko, Inc. The Soil-Cement Mixing Wall (S.M.W.) technology involves the in situ stabilization and solidification of contaminated soils. Multi-axis, overlapping, hollow-stem augers are used to inject solidification/ stabilization agents and blend them with contaminated soils in situ. The product is a monolithic block down to the treatment depth. This technology applies to soils contaminated with metals and semi-volatile organic compounds. The search for a demonstration site is underway.12 Vitrification. As with solidification, there are both ex situ and in situ procedures for vitrification. In situ vitrification converts contaminated soils into chemically inert, stable glass and crystalline materials by a thermal treatment process. Large electrodes are inserted into soil containing significant levels of silicates. Because soil typically has low conductivity, flaked graphite and glass frit are placed on the soil surface between the electrodes to provide a starter path for electric current. A high current passes through the electrodes and graphite. The heat melts contaminants, gradually working downward through the soil. Volatile compounds are collected at the surface for treatment. After the process ends and the soil has cooled, the waste material remains fused in a chemically inert and crystalline form

that has very low leachability rates. This process can be used to remove organics and/or immobilize inorganics in contaminated soils or sludges. It has not yet been applied at a Superfund site. However, it has been field demonstrated on radioactive wastes at the DOE's Hanford Nuclear Reservation by the Geosafe Corporation.12 Geosafe has also contracted to conduct two Superfund site cleanups, one in Spokane, Washington, and another in Grand Ledge, Michigan. Large-scale remediation of this process has been suspended temporarily because of the loss of ofFgas confinement and control during the recent large-scale testing of its equipment that resulted in fire. Ex situ vitrification involves heating the excavated soil by a thermal process to form chemically inert materials. Two specific ex situ vitrification techniques under the SITE Program may be applicable to LBRS. Retech, Inc. Plasma Reactor. This thermal treatment technology uses heat from a plasma torch to create a molten bath that detoxifies contaminants in soil. Organic contaminants vaporize and react at very high temperatures to form innocuous products. Solids melt into the molten bath. Metals remain in this phase, which—when cooled— forms a non-leachable matrix. It is most appropriate for soils and sludges contaminated with metals and hard-todestroy organic compounds. This technology was demonstrated in July 1991 at a Department of Energy research facility in Butte, Montana and the final demonstration report will be completed in August 1992.12 Babcock and Wilcox Co. Cyclone Furnace Process. This cyclone furnace technology is designed to decontaminate wastes containing both organic and metal contaminants. The cyclone furnace retains heavy metals in a nonleachable slag and vaporizes organic materials prior to incinerating them. The treated soils resemble natural obsidian (volcanic glass), similar to the final product of vitrification. This technology is applicable to solids and soil contaminated with organic compounds and metals.12 This technology was demonstrated in November 1991 at the Babcock and Wilcox Co. research facility in Alliance, Ohio. Separation Options for Lead-Contaminated Soils

The separation options for leadcontaminated soils are soil washing and acid leaching. Soil Washing and Acid Leaching. Soil washing is a water-based process for mechanically scrubbing soils ex situ to remove undesirable contaminants. The process removes contaminants from soils in one of two ways: by dissolving or suspending them in the wash soluJ. Air Waste Manage. Assoc.

tion or by concentrating them into a smaller volume of soil through simple particle size separation techniques. Acid leaching removes lead from soils by first converting the lead to a soluble salt, leaching the soluble salt with an appropriate acidic solution, and then removing the lead salt from solution via precipitation or electrowinning. One ROD out of ten for LBRS has selected acid leaching as an integral part of the treatment alternative. Implementation of this technology requires excavating the lead-contaminated soil, washing the lead on-site with a solution (such as nitric acid or EDTA), and returning the treated soil to the site for disposal in the excavation area. One of the limitations of soil washing as a viable alternative concerns the physical nature of the soil. Soils which are high in clay, silt, or fines have proven difficult to treat. Table III summarizes the data needs to evaluate soil washing/acid leaching as a remedial alternative. Figure 3 is a processflowdiagram of an Acid Leaching Process developed by U.S. Bureau of Mines. This process converts lead sulfate and lead dioxide to lead carbonate, which is soluble in nitric acid. Lead is recovered from the leaching solution by precipitating with sulfuric acid.15 There is a potential market for lead sulfate. The Bureau of Mines also investigated converting the lead compounds to carbonates followed by leaching with fluosilicic acid. Electrowinning recovers metallic lead from solution while regenerating the acid for recycle. The clean soil can be returned to the site but waste streams from either soil washing process require further treatment before final discharge. Actual field experience of cleaning soil at LBRS is limited. Two sites (Lee's Farm in Woodville, Wisconsin and ILCO site in Leeds, Alabama) have unsuccessfully attempted soil washing of contaminated soil. At the United Scrap Lead Site in Ohio, acid leaching was selected in the ROD as an integral part of the treatment alternative, but full-scale treatment has not occurred. The Bureau of Mines (BOM) conducted bench-scale studies to evaluate the performance of acid leaching solutions on lead in contaminated soil at battery recycling sites. Table IV shows some representative results from the Bureau of Mines tests. The results indicated that nitric and fluosilicic acid solutions can achieve very high removal efficiencies for soil (greater than 99 percent) and an EP Toxicity level less than 1 mg/L. 15 EPA conducted a series of laboratory tests on soil and casing samples from metal recycling sites. The soil samples from these sites were subjected to bench-scale washing cycles July 1992

Volume 42, No. 7

using water, EDTA, or a surfactant (Tide detergent), respectively. Soil washing did not remove significant amounts of lead from any of the soil fractions. The lead was not concentrated in any particular soil fraction but rather was distributed among all the fractions. A comparison of lead concentrations in the wash waters indicated that the EDTA wash performed better than the surfactant and water washes.16 While EDTA was reasonably effective in removing lead, Bureau of Mines researchers observed that its effectiveness seemed to vary with the species of lead present. 15 Additional bench-scale studies are required to verify that site-specific cleanup goals can be achieved employing these techniques. EPA researchers are also in the early stages of investigating the use of milder acids (e.g., acetic acid) than those acids used to date (e.g., nitric, fluosilicic) for leaching of lead from soils,17 and hydrochloric acid leaching is being evaluated in the SITE program. European vendors in the soil washing business have been remediating lead-contaminated sites for a number of years. Most of their experience has been with relatively lower lead concentrations (typically less than 500 ppm) from mine tailings and smelter waste materials (baghouse dust and slag). No European firms have been found to date who have direct experience in treating soils from lead battery recycling sites (or equivalent) where the lead contamination typically could be around 7,000 ppm total lead. However, in discussions with certain of these vendors, they are of the opinion that soil washing may have application although bench-scale treatability tests would be needed to verify performance. Control Technologies for Waste Deposits at LBRS

Waste deposits at LBRS may be found in surface piles, burial pits, or landfills. Predominant types of materials found in these waste deposits are: (1) battery casing scrap intermingled with lead and lead compounds (concentrations up to 30 percent by weight have been found); (2) blast furnace slag; (3) air and water pollution control residuals; and, (4) miscellaneous debris (e.g., kiln refractory, construction debris, etc.). The primary potential remedial options for these waste deposits include: (1) no action, (2) off-site disposal, (3) containment, (4) immobilization, (5) separation with resource recovery (e.g., lead, plastic, energy), and (6) separation without resource recovery (e.g., separation of contaminants from media to produce a "clean stream" and

Table III. Data needs for soil washing/acid leaching of soils. Technology

Data requirement

Soil washing/acid leaching13'14

• Soil type and uniformity • Moisture content • Bulk density • Grain-size distribution • Clay content • Metal concentrations/species • pH • Cation exchange capacity • Organic matter content • Waste volume • Mineralogical characteristics • Debris size and type • TCLP

contaminated residuals which are discarded). The first three of these options do not reduce the toxicity, mobility, or volume of the contaminant through treatment and are therefore not considered control technologies for the purposes of this article. However, for reasons similar to those discussed for contaminated soils, these remedies may be applicable and should be considered, although they will not be discussed further in this article. Immobilization Options for Waste Deposits

Immobilization of Battery Casings. With regard to battery casings, vitrification would be unsuitable due to the combustible nature of the casings, leaving solidification as the only potential immobilization remedy. No published data were found that indicate battery casings had been solidified. However, it is known that ex situ S/S of casings and casings mixed with soil is currently being tested in the laboratory for the Calwest Metals site in Lemitar, NM. If the lead content in a battery scrap pile is high (up to 30 percent has been noted), it may be necessary to sort and wash the pile to some extent to ensure adequate mixing and reduce the quantity of S/S agent that is used. Also, it may be necessary to reduce the size of the battery casing scrap pieces in order to promote adequate mixing. If these pretreatment steps are necessary, this will add to the cost of solidification. The presence of sulfates is frequently cited as a potential interference to solidification, so it will be interesting to see whether the lead sulfate in and on the casings has any adverse effects. Whether in situ solidification on buried casings could be performed 975

CONTROL

TECHNOLOGY

is not known at this time, and until the feasibility of applying S/S chemistry (ex situ) to casings is verified, there does not seem to be much reason to proceed with exploring this option. Immobilization of Slag. The solidification of slag is a bit of a paradox. Slag often appears rock-like and impermeable. However, it may fail the TCLP leaching test (sample is ground up and exposed to a leaching medium). If the slag failed the leaching test, and if immobilization is selected as the remedy, then the waste slag must be ground up and mixed with solidification agents in order to be turned back into a rock-like material, of larger volume, that could, however, pass the TCLP test. This seems, particularly for slags that only marginally fail the TCLP test, to be a lot of effort and expense for little benefit. This problem was noted in the preamble to the Third Third Land Disposal Restriction regulations, and slags may at some point be considered for special treatment. Immobilization of Pollution Control Dusts and Sludges. If these materials are in separate piles, then ex situ solidification may be applicable, although this does not appear to have been done or planned during any LBRS remedial or removal actions. Immobilization ofMixed Debris. Immobilization of mixed debris in any significant quantity is generally not practical, due to physical and chemical heterogeneity and resultant difficulties involved in effective mixing and quality control.

Separation Options for Waste Deposits Separation schemes for LBRS waste piles have been developed that are based on physical differences (e.g., color, appearance, size, hardness, density, magnetic properties), chemical interactions in aqueous solutions (e.g., solubility, reactivity, chelation, pH effects) and high temperature properties in smelting furnaces (e.g., melting, density separation, oxidation, and reduction). Table V summarizes basic data needs for separation technologies for LBRS waste deposits. Separation processes must meet at least the following conditions in order to be acceptable for use on the contents of LBRS waste piles: • The separation process, must extract enough contaminant from the waste matrix so that the waste matrix meets the cleanup goal(s) (e.g., total lead and/or TCLP extractable lead); • The separation process residuals must pose significantly less environmental risk (i.e., less volume, toxicity, mobility) than the original waste matrix; and • The combination of the environmental and health benefits produced by extracting the contaminants, treating the residuals, and removing the contaminants from the site must be perceived as sufficient to warrant costs that will probably exceed those of less permanent remedies such as capping, landfilling, or solidification. Although resource recovery is attractive from an environmental standpoint, it is not expected to typically be

a main consideration in remedy selection. The value of the lead, plastic, and energy that can be recovered from LBRS waste piles will infrequently, if ever, be sufficient to make a profit. The best that can be expected is that the value of the recovered product will reduce the overall cost of the recovery process to a point where it is competitive with other remedies. For example, assume the going price for lead is $600/ton. If the concentration of lead in the waste pile is 10 percent, and all of the lead is recovered, then 10 tons of waste would need to be processed to produce one ton of lead. So, the maximum credit for sale of the lead amounts to $60/ton of waste processed. If the example concentration of lead in the waste pile is reduced to 1 percent, then the maximum credit for sale of lead falls to only $6.00/ton of waste processed. Since there is typically a smelting fee of $200+/ton of waste processed, the net cost just to process the waste through the smelter is $140/ton for the situation with 10 percent lead and $194/ton for the 1 percent lead waste deposits. Data needs for resource recovery for waste deposits are listed in Table VI. An impressive range of options has been attempted by a variety of private and governmental organizations to separate lead and other re-usable materials from waste deposits at LBRS. Some of the more important efforts include: 1. Failed commercial attempt (USL Site, Troy, OH) to recover lead from battery scrap piles and re-sell the lead to a smelter;18 2. An evaluation for the Gould Site, Portland, OR of several commercial battery component separation

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Figure 3.

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Bureau of mines acid leaching process.15

J. Air Waste Manage. Assoc.

devices (including limited fullscale testing) as to their ability to separate and clean battery cases to non-toxic levels, resulted in a determination that commercial equipment was not directly suitable for LBRS scrap piles;19 3. The successful development, field testing, and marketability study (for the Gould Site, Portland, OR) of the Canonie process (discussed below) which specifically separates battery scrap into lead fines, rubber, plastic, and metallic lead streams; 19 ' 20 4. The characterization of battery scrap and the development of the Bureau of Mines process (discussed below) involving granulation, carbonation, and acid leaching for treating battery casings to meet cleanup goals of