TREATMENT STANDARDS FOR FOUNDRY SAND

Transcription

1 TREATMENT STANDARDS FOR FOUNDRY SAND NOVEMBER 1989 Prepared by: Nancy S. Ostrom Under the Direction of Jan Radimsky, P.E. Gary Murchison, P.E. DEPARTMENT OF HEALTH SERVICES TOXIC SUBSTANCES CONTROL PROGRAM ALTERNATIVE TECHNOLOGY DIVISION

2 ACKNOWLEDGEMENTS - The Department wishes to acknowledge all the foundries that participated in the foundry survey and provided information and data on foundry operations and waste treatment. The Department also wishes to thank the Califomia Cast Metals Association for their assistance in gathering information for this report DISCLAIMER - Mention of a commercial product or organization does not constitute endorsement or recommendation for use by the Department of Health Services ii

3 EXECUTIVE SUMMARY Pursuant to Senate Bill 1500 (SB 1500, Roberti, 1986), chaptered as the Hazardous Waste Management Act of 1986, Article 7.7, Division 20 of the Health and Safety Code (HSC), the Department of Health Services (the Department) must adopt treatment standards establishing the level of treatment required prior to land disposal of hazardous waste. This report presents staffs findings of treatment technologies available to treat waste foundry sand and the associated treatment levels. Only hazardous wastes destined for land disposal are required to meet the treatment standards. Staff considered the information contained in the Hazardous Waste Information System, Biennial Generator Reports, the literature and a survey of generators to characterize the volumes and chemical composition of waste foundry sand. DHS-funded waste reduction grant projects, the literature and the affected industry provided information on the availability and effectiveness of the applicable treatment technologies. Staff estimates approximately 18,200 tons of hazardous waste foundry sand are generated each year in California. Staff further estimates approximately 81 % of the generators reclaim metal from their waste foundry sand, approximately 88% recycle some portion of the waste and about 30% treat the unrecycled portion of the waste onsite using chemical stabilization. The overlap indicates that many generators both reclaim metal from the sand and recycle some portion of the sand. Foundry sand is generated by foundries that use sand to form casting molds. The sand generated by brass foundries may contain hazardous levels of copper, lead, zinc, cadmium and nickel. The treatment standard proposes that prior to land disposal the five hazardous constituents must meet the following soluble extractable levels: iii

4 copper 200 mgfl lead 30 mgfl Zinc 250 mg/l C a d " 1.0 mg/l nickel 20 mg/l The concentration of soluble metals in waste foundry sand must be determined using the Waste Extraction Test outlined in the California Code of Regulations (CCR) in $ The treatment standard also proposes that hazardous waste foundry sand that contains metals in addition to the five metals listed is subject to the general treatment standard for solids with metals and hazardous waste foundry sand that contains organic compounds is subject to the general treatment standard for solids with organics. Adequate commercial capacity exists to treat the volume of hazardous waste foundry sand generated is available at a single facility only. To provide time for generators to establish contracts with this facility, staff proposes this treatment standard become effective six months from the date the regulation is adopted. iv

5 TABLE OF CONTENTS Executive Summary... Table of Contents... List of Figures... List of Tables IU v vi...vi Introduction... 1 Chapter 1: Waste Definition Waste Generation... 5 Waste Amount and Current Management Methods... 8 Chapter 2: Waste Characterization Chapter 3: Demonstrated Treatment Technologies Recycling and Reclamation Chemical Stabilization Chapter 4: Best Demonstrated Available Technology (BDAT) BDAT Selection Application to Foundry Sand Capacity Chapter 5: Treatment Standard Chapter 6: Compliance with the Treatment Standard Compliance Determination Compliance Schedule Chapter 7: Impacts of the Treatment Standard Fiscal Impacts Impacts on Small Business Environmental Impacts References Appendix... A- 1 V

6 LIST OF FIGURES Figure 1.1. Waste Foundry Sand Generation... 6 LIST OF TABLES Table 1.1. Foundries Responding to Generator Survey Table 1.2. Waste Generated by Reporting Foundries Table 2.1. Total Concentrations for Untreated Hazardous Foundry Sand and the % of Data Points Exceeding the Regulatory Threshold ("LC) Table 2.2. Soluble Concentrations for Untreated Hazardous Foundry Sand and the % of Data Points Exceeding the Regulatory Threshold (STLC) Table 3.1. Thermal Sand Reclamation Results (mg/l) Table 4.1. Percentage Reduction Achieved by Various Stabilization Processes Table 4.2. Average Percentage Reduction Achieved by BDAT and Achievable Concentrations for BDAT Table 5.1. Achievable BDAT Concentrations (mu) Table 5.2. Soluble Concentration Values for Treated Hazardous Foundry Sand (mg/l) and the 95% Confidence Level Table 5.3. STLCs (md) Table 5.4. Treatment Standards for Hazardous Waste Foundry Sand Table 7.1. Assumptions and Notes Concerning the Financial Cost Analysis for Onsite Chemical Stabilization of Hazardous Waste Foundry Sand Table 7.2. Incremental Costs Attributable to the Treatment Standard (1989 dollars) vi

7 INTRODUCTION In California land disposal restrictions provide an incentive for generators of hazardous waste to move away from using land disposal as the primary option for hazardous waste management. A number of factors drive this movement away from land disposal, including uncertainty in the ability of land disposal units to contain certain wastes and declining land disposal capacity. Incidents of migration of hazardous constituents from land disposal facilities have focused attention on both the need to treat hazardous wastes before they are placed in land disposal units and on the need to ensure land disposal units meet minimum engineering standards that will enhance their integrity and ability to contain wastes. In addition, the available capacity for land disposal for hazardous waste is likely to continue to decline if existing land disposal facilities close and siting new facilities becomes increasingly difficult. To facilitate the movement away from land disposal and to spark development of alternative methods for managing hazardous waste, Califomia passed a number of laws and regulations restricting land disposal and emphasizing alternative management methods. California s original restrictions prohibited the land disposal of liquids containing cyanide, certain metals, high levels of acid, PCBs, and liquids and solids containing halogenated organics (California Code of Regulations (CCR) et seq). The regulation specifies the waste concentrations and schedule of restrictions. California s most recent land disposal restrictions, described in the Hazardous Waste Management Act of 1986, expand the original program by prohibiting all land disposal of untreated hazardous waste in California. These restrictions parallel the federal land disposal restrictions applied to wastes classified as hazardous under the federal regulations. The Hazardous Waste Management Act of 1986, initially proposed as SB 1500 (Roberti 1986), is chaptered as Article 7.7 in Division 20 of the California Health and Safety Code (HSC et seq). This law requires the Department of Health Services (the Department) to prohibit the land 1

8 disposal of all untreated hazardous waste on or before May 8, 1990 and to specify the treatment levels, or standards, for treating hazardous waste prior to land disposal. Because the treatment standards are based on the best demonstrated available technology (BDAT) and focus on waste reduction, recycling, and treatment in that order of priority, the law encourages industry to develop alternative waste management options, shifting the burden away from land disposal. In addition, since the Department sets the treatment standards at a level that minimizes the hazardous characteristics of the waste, the waste becomes more suitable for land disposal, reducing the likelihood that hazardous constituents will bioaccumulate or migrate into air, land or water. The Department develops these treatment standards for wastes considered hazardous in California. The U.S. Environmental Protection Agency (EPA) is developing treatment standards for wastes considered hazardous by the federal regulations and California will review and adopt EPA s treatment standards within six months after they are completed (51 FR 19300). If the Department fails to adopt a treatment standard for a waste, all land disposal of that waste wil be prohibited after May 8, With some exceptions, all hazardous waste destined for land disposal must meet the appropriate treatment standard and deadline before it can be placed in a land disposal facility. The Department may grant a renewable one-year variance to a generator demonstrating, among other things, that the waste cannot be recycled or treated to meet the treatment standard. In addition the Department may grant exemptions to a generator with a special waste classification for its waste if the generator demonstrates no economically and technologically feasible alternatives exist to meet the treatment standard. If the Department fails to adopt a treatment standard for a waste, the Department cannot grant variances or exemptions for that waste. To ensure the treatment standards are based on realistic asshnptions and reflect the best demonstrated available technology, the Department works with the affected industries, whenever 2

9 possible, to solicit waste characterization and treatment data. After the treatment standard is developed, the Department issues a draft staff report summarizing the findings and data supporting the treatment standard. The draft report forms the basis for discussion at the subsequent workshop and serves as the foundation for the final technical report supporting the treatment standard regulation. Through the land disposal restrictions and treatment standard regulations, California hopes to ensure that bioaccumulation and migration of hazardous wastes from land disposal facilities wil be reduced, and encourage generators to reduce their dependence on land disposal and aggressively pursue alternative methods of hazardous waste management. FOUNDRY SAND Typically, foundries generate hazardous waste foundry sand when sand, used as a molding material, becomes contaminated at some point in the production of a casting and exhibits hazardous waste characteristics as determined by CCR Title 22, Article 1 1. The sand also may be considered hazardous according to federal criteria if it contains any of the eight metals identified in 40 CFR above the federal thresholds or exhibits any other hazardous characteristics pursuant to 40 CFR Part 261, Subpart C. Wastes classified as hazardous according to the federal criteria are known as RCRA hazardous wastes. Hazardous waste considered hazardous only according to California s criteria are known as non-rcra hazardous waste. The Department is proposing treatment standards for the levels of copper, zinc, lead, cadmium and nickel in non-rcra hazardous waste foundry sand. If the waste exhibits hazardous characteristics according to federal criteria and is a RCRA hazardous waste, then federal treatment standards as adopted by California apply to the waste. If non RCRA hazardous waste foundry sand contains contaminants other than the five metals the proposed treatment standard sets levels for, or exhibits other hazardous characteristics according to the state regulations, the waste will be required to meet the appropriate generic treatment standard for solids with metals, solids with organics, aqueous waste with metals and aqueous waste with organics. 3

10 Two workshops for the proposed treatment standard for foundry sand were held on August 15 and 18,1989. The workshop announcement and lists of workshop attendees are included in the Appendix. The comments received in the workshops and additional information gathered form the basis for the revisions in this report. 4

11 WASTE DEFINITION Defining the waste stream for a treatment standard requires identifying the specific waste types included in the waste stream, the industries generating the wastes, the amounts generated and current methods of managing the waste. To gather this information staff consulted a number of sources including literature, manifests, biennial generator reports and trade associations. Due to the limitations discovered in the available data, staff also conducted a survey of generators. WASTE GENERATION Waste foundry sand is generated by foundries that use sand to form molds for casting. Foundries casting copper-based alloys (brass or bronze foundries), in particular, generate hazardous waste sand contaminated with cadmium, lead, copper, nickel and zinc, often in high total and extractable concentrations. The treatment standard for foundry sand focuses on the hazardous waste sand from these brass and bronze foundries, but any foundry generating waste sand that is considered hazardous according to either the state or Federal requirements will be subject to this and/or other treatment standard(s). Most foundries reuse some portion of their foundry sand; in many cases most of the sand is reused. However, some new sand and binder is typically added to the used sand to maintain the molding properties of the sand and enhance casting quality. Although some sand is lost to spills and shakeout, an additional amount of sand must often be removed so the system can accommodate the portion of new sand that must be added. This amount of removed sand, combined with the sand lost to spills, shakeout and sand not reused, becomes the waste sand. Figure 1.1 illustrates the primary sources of waste sand. In brass foundries such waste sand is often hazardous because it contains high levels of copper, lead, zinc and sometimes cadmium and nickel. 5

12 Figure Waste Foundry Sand Generation r Mixing & mulling - mixsandand binder + form sand into molds mipourmaait 4 sandfromthecasting. Some sand still adhm treak up luge chunks + andscpamtemaal 6

13 The proposed treatment standards apply to the levels of copper, lead, zinc, cadmium and nickel in nonrcra hazardous waste foundry sand or waste sand residue generated by foundries using sand as a molding material. As defined earlier, nonrcra hazardous waste are hazardous wastes considered hazardous only according to California's hazardous waste criteria, as determined according to CCR Title 22, Article 11. If the nonrcra hazardous waste foundry sand contains metals other than the five listed, or it contains organic contaminants, this treatment standard for foundry sand specifies that the waste must also meet the treatment standards for solid waste with metals and solid waste with organics. If the hazardous waste foundry sand is a RCRA waste (hazardous according to federal criteria), however, it is subject only to the applicable federal treatment standard. It is not subsequently subject to state treatment standards. However, if the Department adopts a more stringent standard than the federal standard, the state may require that foundries generating RCRA waste meet the state treatment standard instead of the federal treatment standard. The Department anticipates the federal treatment standards will be promulgated by May 8,1990 and will evaluate the relative stringency of the standards at that time. Staff has identified approximately 65 brass foundries (not all cast exclusively in brass) in the 1988 edition of the California Manufacturer's Re~ster (CMR). Since most of the foundries listed in the CMR employ fewer than 50 people and collect less than $1 million per year in gross receipts, most appear to be small businesses. Because not all of the 65 foundries listed in the CMR specified the casting method used, it is not clear how many of those foundries use sand as a molding material. Although other sources have indicated, but not confirmed, that the number of foundries that pour some brass in California is likely to be higher, in the absence of better information, staff will assume for this report that all 65 of the foundries staff identified use the sand casting method and they represent the brass foundries in California. 7

14 WASTE AMOUNT AND CURRENT WASTE MANAGEMENT While it is clear that the waste sand generated by brass foundries casting in sand is likely to be hazardous, it is less obvious how much of this waste is generated and how it is currently managed. Typically, this information is readily available from manifest records and biennial generator reports. However, in the case of brass foundries the usual sources did not yield adequate data. To supplement this reporting information, staff surveyed over 200 foundries (both those casting in brass and those casting in other metals, including iron and aluminum) enlisting the help of the California Cast Metals Association (CCMA) to survey the brass foundries. Unfortunately, despite CCMA s support, few brass foundries participated in the survey. Hence, staffs estimates of waste amounts generated and current waste management practices reflect extrapolations from the available data. Manifest Records With some exceptions, every shipment of hazardous waste transported off the site of generation must be accompanied by a hazardous waste manifest signed by the generator, the transporter and eventually the receiving facility. Under this system both the generator and the receiving facility send copies of the manifest to DHS notifying the Department both when the waste leaves the site of generation and when it arrives at the receiving facility. These manifest records, maintained in the Hazardous Waste Information System (HWIS), enable DHS to track shipments of hazardous waste identifying the type and amount of waste shipped and its destination. Using HWIS information, staff identified, by the Standard Industrial Classification (SIC) code, eight foundries generating California Waste Code (CWC) 181 in These eight foundries shipped a total of 254 tons of CWC 181 offsite in that year. Records from 1988 had not been entered into HWIS at the time of this analysis. However, the information gathered from manifest records is of limited use if the manifest documents are not completed, if they are completed incorrectly, if all waste management takes 8

15 place onsite, or if the waste type cannot be clearly distinguished from other waste types due to the waste codes used on the manifests. For example, the 254 tons of waste attributed to foundries in the 1987 manifest records may not represent only waste sand; other inorganic solid waste may be included in these amounts. Since California does not have a waste code designated specifically for waste foundry sand, these wastes fall under the waste code 181, other inorganic solid waste. Clearly, this is a broad category and not all generators of California Waste Code (CWC) 181 are foundries. In addition not all foundries may classify their sand as CWC 181. If the foundry mixes its waste sand with other waste such as machining waste or baghouse waste, it may choose another waste code, such as CWC 172, metal dust or machining waste, or CWC 591, baghouse waste, for the waste sand mixture. Finally, of those foundries using CWC 181, the entire volume of that waste may not be waste sand. All or a portion of the waste classified as CWC 181 may actually be some other inorganic solid hazardous waste generated by the foundry. Without a method for confirming that the waste identified as CWC 181 is indeed waste sand and not another waste stream, and that CWC 181 is the only waste code used for waste sand, the uncertainty inherent in the exising system of waste codes will persist. Perhaps more significant, however, is the error introduced because manifests are not used. The eight foundries identified by HWIS are not all brass foundries nor do they all use sand castings or generate waste sand. Staff postulates that few of the 65 brass foundries identified in California used manifests in 1987 either because they managed hazardous waste sand onsite, they managed the foundry sand as nonhazardous or they were unaware that a manifest was required. Many foundries were beginning to learn around 1986 and 1987 that the sand from brass foundries may be considered hazardous and may not have known at that time that manifests were required for that waste stream. 9

16 Biennial Generator Reports Because hazardous waste manifest records only track wastes shipped offsite, biennial generator reports are important information sources for all activities including onsite waste management and waste reduction. All hazardous waste generators are required to submit reports every other year describing hazardous waste generation and management methods for the previous year. In addition, all facilities with treatment, storage or disposal permits are required to submit a report every year describing the permitted activities. The most recent information available at the time of this analysis were reports submitted in 1987 summarizing 1986 activities. In 1987 the Department received reports from only six generators identifying themselves as foundries. Of these, three were brass foundries but none reported generating hazardous waste foundry sand. The three brass foundries generated 71.5 tons of baghouse waste primarily containing zinc oxide. Again, the low reporting rates may be due to foundries not realizing in 1986 that the waste sand may be hazardous and that the biennial generator report is required of hazardous waste generators. Foundry Survey Because very little information on waste foundry sand and its generators is available from the manifest system and the biennial reports, staff elected to conduct a survey of foundries in the state to better characterize the foundry industry in California. Staff administered a written survey to over 200 foundries, enlisting CCMA s aid to send surveys to all the brass foundries on CCMA s list (the Appendix contains a copy of the survey). Of the 48 foundries responding to the survey, 18 were brass foundries (see Table 1.1). Of the 18 brass foundries responding, 16 reported generating approximately 4,500 tons of waste foundry sand in 1988, each foundry averaging around 280 tons/year (see Table 1.2). Of the brass foundries responding to the survey, 81% reclaim metal from the sand, 88% reuse or recycle some portion of the sand and 31% treat the waste sand onsite (see Appendix for raw survey data). Clearly, many foundries both reclaim metal and reuse some portion of their sand. 10

17 ~ Table Foundries Responding to Generator Survey I Brass Foundries 18 Others Iron Foundries 8 Aluminum Foundries 14 S tee1 Foundries 2 Nickel Foundries 1 Unknown Foundries 1 - Facilities not Foundries 4 Total 30 Total Surveys Received: 48 Table Waste Generated by Reporting Brass Foundries ton s/year total= range= average= ,506 tons/year 1.5 to 970 tons/year 282 tons/year 11

18 Assuming each of the 65 foundries identified in California generates an average of 280 tons/year of hazardous waste foundry sand, staff estimates around 18,200 tons of hazardous waste foundry sand are generated each year in California. This figure is higher than an estimate of 12,000 tons/year provided by a CCMA consultant (DHS 1989). Assuming the waste management practices can also be extrapolated over the foundry population, staff estimates that of the 65 foundries assumed to operate in California, 53 currently reclaim metal from the sand, 57 currently recover some portion of the sand and 20 foundries now treat the hazardous waste sand onsite. 12

19 WASTE CHARACTERIZATION From the literature and analyses of hazardous waste foundry sand obtained from the two DHSfunded waste reduction grant projects, DHS sampling and the foundry survey, staff determined that untreated hazardous waste foundry sand may contain a number of hazardous constituents. For example, when analyzed for totaz concentrations of inorganic Persistent and Bioaccumulative Toxic Substances, as described in CCR Title 22, Article 11, waste foundry sand from brass foundries may exhibit levels copper, lead, zinc and nickel that exceed the regulatory thresholds for each substance. These regulatory thresholds are known as the Total Threshold Limit Concentrations WCs) and are found in CCR 66699(b). Similarly, when analyzed for soluble (or extractable) concentrations using the Califomia Waste Extraction Test (WET) procedure (CCR 66700), the soluble levels of copper, lead, zinc and cadmium typically exceed the regulatory thresholds, known as the Soluble Threshold Limit Concentration (STLC) also found in CCR 66699(b). When the constituents of a waste exceed either of these thresholds or the waste exhibits other hazardous characteristics included in Article 11, the waste is considered hazardous in California. In addition to classification as a hazardous waste in California, the literature demonstrates that waste foundry sand from brass foundries has also been classified as a RCRA hazardous waste, or hazardous according to federal criteria. The concentration of lead in waste brass foundry sand is typically greater than 5.0 mga, using EPA s Extraction Procedure (EP) toxicity test, classifying it as DO08 waste or EP toxic for lead (Zirschky 1988). Although EPA has not yet developed treatment standards for RCRA characteristic wastes, such as DO08 waste, standards are scheduled to be promulgated by May 8,1990. All foundry sand exhibiting hazardous waste characteristics under the federal regulations (40 CFR Part 261, Subpart C) will be subject to the federal treatment standards for characteristic wastes. 13

20 After compiling the data from the waste reduction grant projects (see Appendix for raw data), DHS sampling and the foundry survey, staff estimated the number and percentage of the data points that exceed the total and soluble regulatory thresholds for copper, lead, zinc, cadmium and nickel. Table 2.1 contains total concentration values taken from DHS sampling of untreated brass foundry sand and values reported by foundries in the foundry survey. This table shows 63% of the data points exceed the 'ITLC for copper, lead and zinc. Twenty percent of the data points exceed the threshold for nickel and none of the values exceed the threshold for cadmium.. Copper Lead Zinc Cadmium Nickel n-lc (mgflrg): 2,500 1,OOo 5, ,000 Data Points (mag): 1,180 2, ,500 29,500 5,380 53,540 35, ,310 4,100 1,980 6,030 6,100 2, , , , ,700 7, , ,500 I 96 of Data Points 63% 63% 63% 0 20% 2 TIZC 14

21 Table Soluble Concentrations for Untreated Hazardous Foundry Sand and the % of Data Points Exceeding the Regulatory Threshold (STLC) Copper Lead Zinc Cadmium Nickel ;TLC (md) o 20 lata Points (md): OO OO , , , , , , , , , ,500 1,600 1, ,122 1,208 1, ,600 3, Ib of Data Points 77% 97% 82% 42% 0 E STLC 15

22 Table 2.2 contains values of the soluble or extractable concentrations, as determined using the Waste Extraction Test procedure specified in CCR The raw data for this table include data from the DHS grant-funded waste reduction demonstration project, data from DHS sampling and data reported by foundries in the foundry survey (see Appendix for raw data). In instances where the data reported in the survey were the same as those reported in the demonstration project, the data were used only once. As depicted in Table 2.1,77% of the data points exceed the STLC for copper, 97% of the data points exceed the STLC for lead, 82% exceed the STLC for zinc, 42% exceed the STLC for cadmium and none of the data points exceed the STLC for nickel. As shown in Tables 2.1 and 2.2, most of the data points of untreated brass foundry sand exceed the STLC, and many exceed the TI'LC, for copper, lead and zinc. Some of the data points also exceed the STLC for cadmium and the TLZC for nickel. Hence, assuming the data reported in Tables 2.1 and 2.2 are typical, staff concludes that 97% of the time waste foundry sand will be hazardous because its WE)-soluble lead concentration exceeds the STLC for lead, and much of the time that waste wil also be hazardous because it exceeds the STLC for copper, zinc and cadmium and the ltlc for nickel. Special Waste Under $66740 in Title 22, CCR, foundry sand may qualify as a special waste if it is not considered a RCRA waste under the federal regulations. California's special waste classification, obtained through written approval from the Waste Evaluation Unit of the Department, does not relieve the generator or transporter of any of the generator or transporter requirements. Although special wastes remain hazardous wastes, they may be disposed to a land disposal facility that is not permitted as a hazardous waste disposal facility if the Regional Water Quality Control Board issues waste discharge requirements to the nonhazardous disposal facility allowing disposal of the special 16

23 waste, and the facility has a variance issued by the Department allowing disposal of the special waste. In addition generators of special wastes may petition for an exemption to the treatment standard if the generator can demonstrate that no economically or technologically feasible alternatives exist to meet the treatment standard. This five year exemption is renewable. 17

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25 DEMONSTRATED TREATMENT TECHNOLOGIES Hazardous waste foundry sand can be managed in a number of different ways. Because a large pomon of foundry sand is reused in the molding process and the metals that can be recovered from the sand contain a high percentage of valuable copper, the opportunities for recycling and reclamation are extensive. A chemical treatment process to extract metals from the sand is undergoing study, but is not currently available on a commercial basis (Warren 1988). For the portion of the waste stream that cannot be recycled, chemical stabilization has been demonstrated to be an effective technology for reducing the degree of hazard associated with these wastes. Most chemical stabilization used for treating hazardous waste employs cement or pozzolanic materials as stabilizing agents. These methods, described in detail in this chapter, have been widely used. Some related technologies, encapsulation and thermoplastic binding, are not as widely used and we have no data demonstrating these methods on hazardous waste foundry sand. Vitrification, or glassification, has been demonstrated on sludges containing metals (FOO6 waste). In this process the waste is incorporated into molten glass and cooled. Thermoplastic binders are organic polymers that are fluid at high temperatures but behave as solids at ordinary temperatures. When used for stabilization, thermoplastics bind waste components into a solidified, impermeable matrix. RECYCLING AND RECLAMATION The foundry industry recycles much of its waste sand, reusing the molding sand and remelting or recycling metal. The type of treatment foundries may apply to the sand and metal before reuse varies from complex approaches, such as thermal reclamation, to simple steps, such as screen separation. 18

26 Thermal reclamation Thermal reclamation was initially developed as a method to regenerate molding sand by stripping the used sand of its binder in a rotary kiln or fluidized bed application and restoring the sand to a virgin condition. This approach was first used in large foundries, typically outside of Califomia, to save costs on purchasing new sand. Eventually, the thermal reclamation equipment was adapted to operate at higher temperatures and convey hazardous metal constituents from the waste sand to the same baghouse system that collects the dead clay and silica fines or another baghouse. Organic binders are incinerated in the thermal process, metals captured by the baghouse may be reclaimed, and the treated sand substituted for new sand. According to the survey of foundries in Califomia, brass foundries in the state are not currently using this process. Although several foundries in Califomia are considering installing thermal reclamation units or are in the process of such installations, no data on the performance of this method in the state were available at the time of this report. Some information from tests perfmed outside of California are available and the results are presented in Table 3.1. Table Thermal Sand Reclamation Results (md) Copper Lead Before After Before After Before Zinc After , , , Source: DHS 1989a. Thermal reclamation units typically require a relatively large capital expenditure. However, since the waste sand is regenerated and reused repeatedly, the initial costs are likely to be offset both by 19

27 the cost savings of not having to treat the sand and dispose of the treated sand in a hazardous or nonhazardous waste landfill, and by the cost savings of not having to purchase new raw sand. Based on these cost savings, the payback time for a thermal reclamation system can be relatively short. A drawback of this option is the stringent air pollution controls that will be imposed. In some areas of the state, air pollution control permits to operate thermal reclamation units may be difficult to obtain. Screening and separation Most brass foundries currently screen used sand before reusing the sand, some employing several different screen types and vibrating mechanisms to break down large masses of sand mixed with metal chips. Coarse screens are used to remove large chunks of metal and core butts. The larger metal pieces collected in the screens are usually remelted in the furnace. Increasingly finer screens remove additional metal particles and help to classify the sand before it is molded. Some foundries remelt these smaller metal particles, other foundries sell this portion to metal reclaimers. The metal recovered during the screening process is often mixed with coarser sand components or has sand adhering to it, so remelting these pieces in the furnace generates large amounts of slag, especially when the smaller particles are remelted. After separating the reusable metal from the sand, the used sand is often mixed with a portion of new sand to produce adequate molding properties and new binder material is often added to preserve appropriate binding characteristics. To accommodate this new sand volume, some of the used sand must be removed. When tested, this waste sand often contains high levels of copper, lead and zinc, classifying it as hazardous waste. In some foundries when the new sand is added, it is screened with the used sand to help blend and classify the entire sand volume and simultaneously remove metals and other large sand pieces. 20

28 Some primary smelters will accept waste foundry sand as an adjunct to the ore normally processed. One smelter uses the sand as a flux replacement in the smelting process; others accept the sand to reclaim the copper. In addition some foundries have explored using foundry sand in road beds, asphalt and cement manufacture, making certain that these options are not considered use in a manner constituting disposal. CHEMICAL STABILIZATION For the waste foundry sand that cannot be reclaimed in the sand system, chemical stabilization has been demonstrated as a treatment option for metal-containing solid wastes in general and for foundry sand in particular. Chemical stabilization, often referred to as solidification or fixation, encompasses treatment processes that chemically reduce the mobility of metal constituents in a waste thereby minimizing the tendency for metals to leach from the treated sand. This technology is applicable to wastes containing heavy metals with a high level of suspended solids, low total organic content and low oil and grease content. Stabilizing agents, generally lime- or cement- based, form a lattice structure and/or chemical bonds that bind the metal constituents to the solid matrix. This process reduces the leachability of the metals when the treated sand comes in contact with water or a mildly acidic solution, such as that likely to be found in a land disposal facility. The stabilization process may also employ additives, such as soluble silicates, that accelerate the curing rates or enhance the stabilizing properties of the treated sand. A number of physical and chemical characteristics can affect the performance of chemical stabilization. For example, the particle size of the waste will have an impact on the amount of free water available for the stabilization reaction. The viscosity of the mixture of waste, water and binder, also affected by particle size and shape, can be used as an indicator of free water and the likely effectiveness of the reaction. Particle size also determines the amount of surface area available for the stabilization reaction. Large particles will not have enough surface area available 21

29 to bind well and must be ground into smaller particles before being treated by chemical Stabilization. The presence of organic compounds and certain inorganic compounds, namely sulfate and chloride, in the waste interferes with the chemical stabilization reactions and bond formation. These compounds inhibit curing of the stabilized material. In particular, sulfate and chloride may reduce the dimensional stability of the cured matrix resulting in reduced resistance to leaching and weakened structural strength. Also, high oil and grease content, over 3% by weight, will coat the waste particles and inhibit the bond between the stabilizing agent and the waste particles. This weakened bond may decrease the treated waste's resistance to leaching and weaken its structural strength. Although there are many variations, two basic forms of stabilization, cement-based and limebased, are most often used. The cement-based stabilization process combines portland cement and water to form calcium hydroxide and a calcium silicate hydrate called tobermorite gel, the main cementing component of concrete. For most effective stabilization the waste must be completely covered by this gel filling any void spaces in the cemendwaste mixture. As the mixture sets and cures, the compounds in the portland cement complete the hydration reactions and the waste constituents are incorporated into the interstices of the cement matrix. The high ph of the cement mixture helps to keep metals in the form of insoluble hydroxides and carbonate salts. The limebased process uses pozzolan, a finely divided, noncrystalline siiica, such as fly ash or cement kiln dust. When combined with lime and water, the pozzolan becomes cementitious and incorporates the waste into the stabilized structure. This process also results in a highly alkaline mixture. In most stabilization applications the process consists of first mixing the waste, stabilizing agent and additives, and then curing the mixture for seven to 28 days. Frequently, commercial concrete mixing and handling equipment, including weighing conveyors, metering cement hoppers and 22

30 cement mixers, can be applied to stabilization. In addition most stabilizing agents are readily available commercially either in a generic form or in spcially blended formulations. The selection of stabilizing agents and additives and their amounts depends upon the chemical and physical characteristics of the waste. To select the best stabilizing procedure for a particular waste stream, the waste should be tested with a variety of materials to determine the best combination of agents and additives. The mixing and curing conditions should also be carefully controlled to ensure optimum stabilization. For example, to determine the appropriate weight ratios of waste to stabilizing agent, water and other additives, different mix ratios should be tested for strength and leaching characteristics of the stabilized material. If too little water is added, mixing will be difficult and the hydration reactions needed to bind the waste to the stabilizing mamx may not be completed. Too much water will result in low compressive strength of the stabilized material. The structural strength of the material is an important measurement because it can be used as an indicator of chemical stabilization. Unconfined compressive strength (UCS) above 50 pounds per square inch (psia) is characteristic of chemically stabilized waste (40 CFR ). The mixing and curing parameters are also important to developing an effective stabilizing procedure. If the waste and stabilizing agent are not mixed well, some waste particles will not chemically bond to the stabilizing agent and will not be held within the stabilized lattice structure. However, overmixing may inhibit gel formation. Testing the results of different mixing procedures will reveal the optimum conditions for a particular waste stream. Similarly, testing various curing times and temperature and humidity conditions will help determine the appropriate curing methods for the waste stream and stabilizing agent. High temperature and low humidity generally increase the curing rate by increasing the rate of water evaporation. However, if the temperature is too high, the rate of evaporation will be too rapid and inadequate water will be available to complete the hydration reaction. 23

31 Staff has collected some data on chemical stabilization of hazardous waste foundry sand. This data is presented and discussed in the fifth chapter entitled Treatment Standard. 24

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33 BEST DEMONSTRATED AVAILABLE TECHNOLOGY (BDAT) In selecting the best, demonstrated, available technology (BDAT) for a treatment standard, staff considers a number of factors including the effectiveness, applicability and availability of different treatment technologies. The best technology treats the waste most effectively. Demonstrated technologies have been employed in full-scale operations. Available technologies are ones in which the equipment to perform the treatment are commercially available and/or commercial treatment capacity is sufficient to treat the expected amount of waste to be generated. When considering treatment technologies, staff must evaluate the applicability of waste reduction first, recycling second and treatment last. BDAT SELECTION Encapsulation and viaification have been demonstrated on some inorganic waste streams, but they have not been demonstrated on hazardous waste foundry sand and they are not yet available. Hence, they are eliminated from consideration as BDAT. Similarly, although thermal treatment has been demonstrated on foundry sand and looks promising as a method to reduce the amount of waste sand generated, its successful demonstration and subsequent available data on hazardous waste foundry sand generated by brass foundries have been limited. Although the equipment is commercially available for onsite treatment, the technology is not yet commercially available for offsite treatment in Califomia so this technology is also eliminated from consideration as BDAT. Finally, because the chemical acid leach method is not commercially available and has not been demonstrated in a full-scale operation, it was also eliminated from BDAT consideration (Warren 1988). The technologies considered for the waste foundry sand treatment standard include methods for recycling and reclamation and chemical stabilization. 25

34 According to the results of the foundry survey, many, if not most, foundries practice some form of sand and metal reclamation as a standard foundry practice, demonstrating that sand and metal recycling options are feasible and appropriate for hazardous waste foundry sand. These practices reduce the hazardous fraction of the sand and may render subsequent treatment of the unrecoverable portion more effective. Staff recognizes that waste reduction options may not apply to the entire hazardous foundry sand waste stream and there may be some pomon of the waste stream that wil require treatment prior to land disposal under the land disposal restrictions. Hence, staff has identified a two phase BDAT in which sand and metal recycling are followed by chemical stabilization for the remaining unrecoverable waste fraction. In some cases particularly aggressive recycling and reclamation efforts, either on the site of generation or by a commercial metal recovery service, may eliminate the unrecoverable fraction and preclude chemical stabilization. APPLICATION TO FOUNDRY SAND The foundries responding to the sulvey indicate that an overwhelming majority already undertake some form of sand reclamation and metal recovery. Some sand systems use binders that make sand reclamation prohibitively difficult, so foundries using these systems may have to rely on metal recycling only to render the waste more amenable to treatment using chemical stabilization. Chemical stabilization is widely recognized as an appropriate technology for solid inorganic waste streams and waste foundry sand is particularly applicable because it typically does not contain large amounts of the constituents, such as chlorides, acids or oil and grease, known to inhibit stabilization. Chemical stabilization, using lime, pozzalime and Portland Cement and other adjuncts such as silicates, has been demonstrated on hazardous waste brass foundry sand in Califomia. In a number of cases the outcome of these demonstrations have been made available to staff for developing the treatment standard for foundry sand. In addition an offsite commercial treatment facility and a transportable treatment unit both perform chemical stabilization and other offsite commercial facilities are planning to add chemical stabilization capacity. Finally, generic 26

35 formulations of the stabilizing agents and simple mixing equipment also contribute to making the stabilization technology widely available. A chemical stabilization process using pozzalime or Portland Cement with potassium silicate, known as the Trezek process, has been demonstrated on a number of solid hazardous wastes containing metals, including brass foundry sand. Trezek has theorized that this process forms relatively insoluble metal metasilicates within the stabilized matrix, among other reactions (Trezek, 1987). The Appendix contains a summary of the results of this process on foundry sand. A stabilization technique using calcium oxide (lime) and sodium silicate, known as the Fumess process, has been demonstrated on hazardous waste foundry sand in two demonstration projects DHS funded for the CCMA. Because the Furness process and the Trezek process both use silicate compounds with various cementing agents, the stabilization reaction is thought to be similar. In the first demonstration project of the Furness process the foundry sand treatment took place on the site of two brass foundries using a transportable treatment unit. Other foundry owners and operators were invited to visit the demonstration foundries and observe the sand treatment. The transportable treatment unit is currently in long tenn use at a foundry in Southem Califomia. In the second demonstration project seven brass foundries volunteered to apply the treatment process on waste foundry sand. The foundries performed the chemical stabilization onsite using small mullers or mixers already onsite and treatment systems that the foundries purchased. The stabilizing agents were specially formulated for the demonstration projects, but generic substitutes are available. A summary of the results from the demonstration projects is included in the Appendix. The ratios of waste to the stabilizing agents and water in the Furness process vary according to the characteristics of the sand to be treated. These ratios are usually derived empirically and may range from 10% to 30%. In a typical procedure 15 lbs of powdered calcium oxide are mixed with 100 lbs of waste sand and 15 lbs of water. When the powdered calcium oxide is dissolved, after about 27

36 2 minutes of mixing, 15 lbs of sodium silicate is added and mixing continues until the mixture begins to thicken in about 45 seconds. The mixture is then poured into ingot molds and allowed to cure 24 to 72 hours. In these projects the treated sand was used as backing in ingot molds. After facing the backing with a thin layer of sand an inch or two thick, the excess metal remaining in the ladles was poured into these molds to make ingots. Reusing the treated sand in this manner in the demonstration project was considered onsite recycling and did not require a treatment permit (CCMA 1989). As depicted in the Appendix, the results of chemical stabilization on waste foundry sand vary widely. In most cases the concentrations of lead, zinc cadmium and nickel are significantly reduced after treatment, but the process effectiveness on the copper contained in the sand is inconclusive. These results for stabilization of copper have been observed in applications of the technology on other waste streams containing copper and is not clearly understood. However, efforts to recover metal from the sand stream by using finer screens in the screening steps seemed to improve the stabilization results. In addition, avoiding mixing the sand with metal dust by improving and changing the foundry ducting and baghouse systems also helped improve the stabilization results for copper (CCMA 1989). Although the Fumess process and Trezek process are similar, staff feels the slight differences in stabilizing agents and procedures may have an impact on the results of the stabilization. In order to evaluate the differences in these processes, staff calculated the percentage reduction achieved with the processes (see the Appendix for these calculations). Results are shown in Table 4.1.