Vincent Maio
Advisory Engineer
Idaho National Engineering and Environmental Laboratory
Lockheed Martin Idaho Technologies Company
Idaho Falls, Idaho

Through its annual process of identifying technology deficiencies associated with waste treatment, the Department of Energy's (DOE) Mixed Waste Focus Area (MWFA) determined that the former DOE weapons complex lacks efficient mixed waste stabilization technologies for fly ash and salt containing wastes. The majority of these wastes were generated as secondary effluents from various primary nuclear processes; and well over 10,000 cubic meters exist at 6 complex sites. In addition, future volumes of these problematic wastes will be produced as other mixed waste treatment methods such as incineration and melting are deployed.

The current method used to stabilize these wastes for compliant disposal is grouting with Portland cement. This method is inefficient for both the fine fly ashes containing relatively high heavy metal levels, as well as for the wastes containing highly soluble and reactive salts such as chlorides, nitrates and sulfates. The inefficiency results from having to use low waste loadings to ensure a durable and leach resistant final waste form.

The approach for addressing these deficiencies is based on system engineering principles developed specifically for the MWFA¹. Based on these principles, requirements for resolution were identified and a technology development plan was prepared. The requirements, formulated with technical, regulatory, and stakeholder input, specify the performance levels expected for each fly ash and salt waste stabilization process selected for development. The development plan documents the MWFA strategy for selecting and testing various alternative stabilization technologies. The plan defines the schedule and scope needed to ensure timely and cost effective delivery of adequate solutions to potential end-users. Based on this strategy, three alternative fly ash and five alternative salt waste stabilization technologies were selected for MWFA funding in FY 97 and FY98.

Comparable evaluations are planned for the stabilization development and demonstration efforts. Each technology will stabilize the same types of surrogates or mixed wastes. Final waste form performance data such as compressive strength, waste loading, and leachability can then be equally compared to the requirements originally specified. For fly ash, phosphate bonded ceramics, sintering with a natural clay formation, and sintering after calcination were chosen for testing. For salt waste stabilization, phosphate bonded ceramics, sol-gel, polysiloxane, polyester resin, and enhanced concrete were selected

The performance of each alternative stabilization technology, obtained through development and demonstration testing, will be documented in formal MWFA Technology Performance Reports (TPRs). These reports will provide the end-users in the DOE complex the pertinent information necessary to select, through trade studies, the stabilization technology best suited for their fly ash and/or salt waste applications.

Significant technical deficiencies in the characterization, treatment, and disposal of DOE-complex mixed wastes (i.e., low-level radioactive wastes containing RCRA hazardous materials) were identified and prioritized for development funding during establishment of the Mixed Waste Focus Area (MWFA) Technical Baseline² in FY96 and FY97. These deficiencies, when resolved through technology development and demonstration efforts, will increase the mixed waste treatment capacities and capabilities of the DOE, decrease the amount of waste in inventory, and treat the waste in time to meet established DOE commitments.

In particular, this document presents the MWFA approach for the deficiencies associated with stabilizing fly ash and mixed wastes containing relatively high salt contents (concentrations of greater than 10% by weight). The approach adopted is shown in Figure 1and is based on the system engineering principles³ of problem and requirements definition, selection strategy development, and trade studies. In this paper, fly ash and salt waste deficiencies are described in addition to the stabilization requirements needed for deficiency resolution. The technology selection strategy is also provided along with a brief description of each technology and its respective test program.

Systems engineering requires formulation of a problem statement as the first step in any technical endeavor. This section describes the problem associated with fly ash and salt waste stabilization.

Over the last 50 years of DOE operations, large quantities of mixed low-level wastes (MLLW) were generated from nuclear weapons based industries and more recently from waste treatment processes. Stabilization has been and still is an effective, inexpensive, and simple treatment alternative for many types of these mixed wastes. This alternative is also accepted as safe and environmentally sound by both the regulators and the concerned public. A review of the technical literature and of past DOE experience shows that low temperature hydraulic cement, polymer, bitumen, and ceramic grout based stabilization methods produce waste forms that meet or exceed final disposal requirements^{4, 5, 6.} The success level of the waste form is dependent on the original waste medium and the type and amount of hazardous and/or troublesome components in the untreated waste. Unfortunately, these current stabilization techniques have had limited success in accommodating incinerator fly ash or homogeneous solid and sludge wastes containing relatively high concentrations of salts⁷. These two waste types in and of them selves are not difficult to treat. However the constituents in a major portion of these inventories makes treatment more challenging. For fly ash these constituents include relatively high levels of RCRA hazardous metals, in particular lead, mercury, and cadmium, in the presence of unburned carbon material and salts. For the homogeneous solids and sludges the constituent is again the same RCRA hazardous heavy metals plus nitrate, sulfate, and chloride salts.

Salts are highly soluble, easily hydrated, and reactive. As a consequence of these characteristics, low temperature stabilized forms of mixed low level wastes (MLLW) containing salts do not adequately cure or are susceptible to deterioration over time due to the expansion from the water-salt reaction. Salts interfere with the basic hydration reactions of cements and easily undergo dehydration/hydration cycles that can cause deteriorating expansions. This deterioration may lower the durability and strength of the stabilized waste form and create pathways for the hazardous and radiological constituents to be released from the immobilized waste.

Leach resistant salt waste forms of sufficient durability are possible with the current stabilization techniques. However, these techniques usually result in forms with excessive increases in waste volume due to low waste loadings. These process inefficiencies result in higher disposal costs. The limitations of these current methods are of immediate concern since more salt wastes are anticipated as other MLLW treatment processes are implemented. Future effluents from MLLW wastewater treatment systems and scrubber blowdown from future and present MLLW thermal systems (e.g., incinerators and melters) will significantly add to the MLLW salt inventory. Therefore, it is essential that alternative cost-effective stabilization methods be developed over the next few years to address both the current inventory and accommodate the effluents from the start up of these new facilities.

Fly ash is and will be produced at DOE MLLW incineration facilities. Similar to the situation with salt-containing mixed wastes, current stabilization techniques exist for fly ash that meet basic disposal requirements, but at the cost of low waste loadings. This limitation occurs because excessive amounts of stabilization agents are used to ensure low leachability of the RCRA hazardous heavy metals in the presence of the salts and unburned materials. In contrast to incinerator bottom ash, the finer particle size of flyash can also result in insufficient mixing and poor homogeneity of the uncured waste form.

Possible future regulatory interpretations of the Universal Treatment Standard (UTS) may make leach resistance requirements more stringent for some of the heavy metals present in the ash. This possible regulatory interpretation and the potential increase in fly ash generation, requires new and innovative stabilization to increase waste loadings and improve durability of the final waste form in comparison to today's standard practices.

The next major step of systems engineering is to specify a set of end product requirements prior to initiating development. The Requirements Document prepared for the salt waste and fly ash stabilization deficiencies defines the basic requirements that the developed stabilization techniques must meet to be advantageous to the end-user. Table I contains a summarized list of the key requirements pertinent to both deficiencies.

Any development effort initiated to resolve specific deficiencies must ensure the collection of test data necessary for determining compliance with the requirements. The investigators for each stabilization development effort were required to submit, for MWFA approval, test plans describing the experimental protocol and data to be collected. In all cases investigators were given enough resources to determine, as a minimum, waste form strength, leachability, and waste loading.

The above requirements mirror many of those specified by the NRC Technical Position Paper for stabilized low-level radioactive waste forms⁸. The NRC requirements pertaining to allowable free liquids, biodegradation, radiation stability, and chemical durability have been omitted from the MWFA effort to minimize the waste performance testing burden imposed on the developers without compromising the amount of information needed to ensure an adequate final waste form.

In addition to the technical criteria listed in Table I, the Requirements Document contains other criteria that are to be used for comparing developing stabilization technologies if the technologies rate equal with regard to the criteria above. These criteria include standards for complexity of operation, robustness of process, equipment availability, secondary waste generation, through-put potential, scale of proven process, ease of permitting, and public acceptance. Because most stabilization processes have traditionally rated well against these criteria, they will not be utilized as primary criteria for assessing the stabilization technologies.

Cost will be indirectly considered as a criterion even though it is difficult to estimate during the development phase and these estimates are highly sensitive to design assumptions. Low temperature stabilization methods have already been proven to be cost effective MLLW treatment alternatives in many cases. Operating experience indicates that for these methods, volume dependent costs such as packaging, shipping, and disposal of the final waste form are far greater than the actual stabilization process. As such, savings tend to result from increasing waste loadings or decreasing the final waste volume. These two key requirements are easily correlated to cost and will be considered as is shown in Table I.

Predefining the boundaries of an activity through strategy development is a systems engineering technique employed to streamline a process and focus on the defined problem. To ensure that MWFA funds are used in a cost-effective manner, the following strategies were established for selecting the development activities and defining their respective test programs.

A. Scope Strategy The development efforts are to focus only on enhanced or alternative stabilization techniques that meet or exceed basic disposal requirements and lower costs by decreasing volumes, increasing waste loadings, and enhancing operability (refer to Table I). Based on their probable higher cost, longer development time, lower stakeholder acceptance, greater generation of secondary wastes, and the amount of additives necessary, vitrification of salt waste or salt separation technologies have been eliminated from consideration. The existence of developmental and operational data from past ash vitrification programs also precludes any more investigations in this area. The development efforts must also build on past successful achievements and operating experiences with currently available stabilization techniques (i.e. hydraulic cement). As applied to MLLW sludges, solids and soils not containing fly ash or salt constituents, these techniques already have a proven track record in meeting basic disposal requirements, being cost effective and simple, and achieving stakeholder acceptance. Development efforts that enhance these current techniques for ash and salt wastes by accommodating higher waste loadings with lower net volume increases are low risk approaches that have a high probability of resolving these deficiencies.

B. Schedule Strategy Individual development elements are to be structured to maximize the probability of successfully resolving the deficiencies within two to three years. This time limitation was imposed to ensure that stabilization alternatives are available concurrent with the earliest start-up dates of the new MLLW treatment facilities that will produce ash and salt containing wastes. This limitation is based on actual waste treatment deadlines and start-up dates for planned DOE treatment facilities as documented in published Site Treatment Plans (STPs). These STPs result in legally binding agreements established between the DOE and an environmental regulatory agency, and provide the strongest driver for resolving the deficiencies in a given amount of time. The two to three year time frames are to be considered a maximum target date, and every effort shall be made to accelerate each development activity to support up-coming privatization efforts.

C. Test Program Strategy The development efforts must test all stabilization technologies with the same actual or surrogate MLLW . These actual or surrogate wastes must represent the majority of the current and predicted future fly ash and salt containing MLLW inventories. For salt, this waste is wet and dry homogeneous solids and sludges containing primarily nitrate, chloride and sulfate salts. The nitrate and chloride salts of sodium and potassium are of key concern due to their abundance, high solubility and high reactivity. The volumes of MLLW that contain other salts such as carbonates and/or fluorides are not significant enough to warrant specific development funding at this time. Likewise, fly ash (as opposed to bottom ash) is of primary concern due to the relatively high concentrations of soluble RCRA hazardous metal oxides.

To facilitate trade studies by potential end-users, systems engineering requires the development of alternatives. As indicated by figure 2, the MWFA initiated parallel programs that will develop alternative stabilization technologies for both fly ash and salt waste.

In particular, the fly ash demonstration is to involve three promising stabilization technologies and provide data on their performance after stabilizing actual mixed waste ash. Due to its abundance and challenging composition, fly ash from INEEL's Waste Experimental Reduction Facility (WERF) incinerator was chosen for the demonstrations.

The demonstrations will consist of two phases. The first phase requires that each of the investigators formulate and produce waste forms using their technology and relatively small quantities of WERF fly ash from the same drum as the other two investigators. The purpose of this treatability study is to optimize the investigator's process for the selected ash population, identify the parameters to accomplish this optimum waste form, and ensure future disposal of larger volumes of the waste form produced in Phase II. Phase II is the actual treatment of up to 1000 kgs (eight drums) of the WERF fly ash. As such, this series of demonstrations could deplete the current WERF inventory of fly ash by as much as 24 drums.

On an annual basis, the MWFA made a call-for-proposals to treat small quantities of actual waste streams through the use of innovative technologies. Known as "quick wins" this call was expanded (based on responses) to initiate the fly ash comparable demonstrations. Selected processes for the demonstration include the following stabilization technologies:

1. Chemically Bonded Phosphate Ceramics (CBPC): A ceramic based low- temperature stabilization process developed by Argonne National Laboratory-East, (ANL-E). The process has been successfully demonstrated with surrogates and actual mixed waste soils, bottom ash and wastewater at the bench, pilot, 5-gallon, and 55-gallon scale. Current demonstrations are also planned for small debris and Pu-contaminated ash. The process involves the acid-base reaction of phosphoric acid or monopotassium phosphate with magnesium oxide. This process creates insoluble phosphates of the RCRA hazardous metals and radiological components and creates a physical ceramic barrier to leaching. The process is simple, has shown good final waste form durability, nonleachability, and sufficient compression strength, generates little heat, and uses off-the shelf equipment. All of the treatability study/demonstration work will be completed at the INEEL. To accommodate this work at the INEEL, a full-scale mixer system will be designed, purchased, and installed at or near the WERF incinerator. INEEL scientists and engineers under the direction of ANL-E scientists will then complete the demonstration.
2. Clemson University Sintered Ceramic Stabilization, CSC, Process: This proprietary process involves the preparation of a naturally occurring Red Roan Clay Formation, (RRF) that is blended with the waste to be stabilized. The waste loading is variable depending on the specific waste, but 50% loading by volume is possible. The blend of waste and RRF material is physically mixed together along with a liquid and formed into a shape by pressing or extrusion. Formed parts are then fired in a kiln at temperatures ranging from 1050 ⁰C to 1150 ⁰C depending on the waste stream and waste loading. Firing times also vary depending on the materials involved, size of the parts, and kiln loading. Like CBPC, CSC is low cost and simple to scale up using available industry processing equipment. Both the Phase I treatability and 1000 kg demonstration tests will be performed at the Clemson Environmental Technical Laboratory in Anderson, South Carolina.
3. "Roc-Tec" Process: This stabilization process combines the waste and low cost additives to form a high density ceramic material that past testing has shown to be resistant to leaching at percent levels of RCRA metal oxides. Waste loadings for past applications have generally exceeded 90%. In the "Roc-Tec" process, the waste to be stabilized is first calcined at approximately 500 ⁰C to eliminate excess carbon and drive off any chemically bound water, and then ground and mixed with the additives. This mixture is then pressed into briquettes, air-dried and sintered at approximately 1100 ⁰C. This technology will be demonstrated jointly by a company in Salt Lake City, Utah and the "Roc-Tec" developers in Idaho Falls, Idaho, and South Carolina. Both the Phase I treatability study and the Phase II 1000 kg demonstration on the WERF fly ash will be conducted in Barnwell, SC.

To date all three investigators have received the smaller Phase I ash samples from WERF and have initiated some testing. The composition of the ash has provided a challenge to the developers in a way that may lead to an alteration or addition to their respective formulations. However, Phase I testing for all three stabilization technologies is expected to be complete by March 1998. At this time the developers will document their results to the MWFA and recommend the operating parameters and formulations necessary to ensure the successful and compliant Phase II demonstrations of larger scale. Once WERF operations personnel has had an opportunity to review and approve the Phase I test data, the larger drums of fly ash will be shipped to the three various Phase II demonstration sites. The schedule is to complete the demonstration and their documentation in MWFA Technology Performance Reports (TPRs) by the end of 1998.

Information in the TPR will enable end-users in selecting a technology that best fits their fly ash stabilization needs based on their ash inventory, ash generation rate, ash composition, and local regulatory and stakeholder environment. TPR data will consist of waste performance information such as leachability and compressive strength, as well as waste loading and volume reduction/expansion determinations (refer to Table I). Additional information assessing the technologies' operability at full-scale applications, as well as cost data will be provided to assist end-users in their comparative evaluations, cost-benefit analyses, and trade studies.

Like the fly ash stabilization demonstrations, the salt waste stabilization techniques will also be equitably compared. However these technologies will be compared based on their performance after stabilizing two types of standard waste surrogates. One of the surrogates represents the majority of previously grouted dry solids in the complex and contains a high level of nitrates. The other surrogate waste contains both chlorides and sulfates and represents an unconcentrated blowdown from an incinerator or thermal unit. Both surrogates contain RCRA heavy metals in the 1000 ppm range, thus providing a challenge to the stabilization technique. The inerts of the surrogates are mostly oxides and hydroxides.

Stabilization technologies chosen for development testing on salt wastes are described below. They were selected after a MWFA call for proposals specifically for salt stabilization waste technologies and were chosen based in part on their potential to meet the requirements and criteria presented in this paper.

1. Chemically Bonded Phosphate Ceramics (CBPC): Identical to the method being applied for fly ash, the ANL-E CBPC process utilizes the low temperature stabilization reaction of magnesium oxide and mono potassium phosphate for salt waste. Recently the investigators have fabricated the MWFA standard surrogate and are attempting to identify additives to avoid leachability of the salt anions as well as the RCRA metals.
2. Sol-gel Techniques: Sol-gel is the general scientific term given to processes that start as a mixture of liquid solutions, that subsequently solidify or gel into a 3-D solid form upon reacting at low temperature. Investigators at the University of Arizona, via a contract through Pacific Northwest National Laboratory, are developing various Sol-gel processes that will microencapsulate the salt surrogates after their addition to the base sol-gel solutions. Inorganic (ceramic), organic (polymer), and inorganic-organic combinations (poly-cerams) are being formulated and tested as base Sol-gel systems. Results to date indicate that the poly-cerams are most effective for stabilization of the salt containing mixed waste surrogates.
3. Polysiloxane: The polysiloxane process is a room temperature polymeric process, whereby the waste and the polysiloxane base monomer of silicon dioxide are added together in the presence of a platinum catalyst. A private company developed the method and testing was done in conjunction with scientists at the INEEL. To date testing with the MWFA surrogate waste recipes is complete and results are encouraging.
4. Polyester: This Hanford development effort focuses on the testing of four types of commercially available polyester resins for both wet and dry salt wastes. A statistical test program was established to determine the effects of waste loading and resin type on waste form performance and cure time. Successful testing of the standard MWFA surrogates have been completed and treatability studies on an actual Hanford waste stream is in progress.
5. Enhanced Concrete Grouting: The development of enhanced salt waste stabilization techniques involving Portland cement grouting are advantageous in that DOE end-users are already familiar with the processes, and the enhanced methods will be compatible with existing grout equipment. Through a contract with developers at Oak Ridge National Laboratory, methods are being investigated to increase the salt waste loading in various test matrices of blast furnace slag, Portland cement, clay, and fly ash. The clay is being added in an attempt to suppress the mineral expansion that may result from the salt-water reactions with in the waste form. An array of statistical tests is being completed. In these tests the above stabilizers are added to salt waste surrogates containing varying amounts of nitrates, chlorides, and sulfates. The standard MWFA surrogate composition is included in the array to facilitate equal comparison to the other four processes.

Later this month testing and documentation of waste form performance will be completed for all five technologies on both surrogates. The MWFA will then compare this performance in a manner to assist end-users in choosing a technology based on their specific salt waste composition, volume, generation rate, and available disposal route. Since only surrogate data will be available, it is recommended that specific treatability studies on actual waste be performed with the chosen technology.

Systems engineering principles have proven to be effective in addressing complex technical problems and are applicable for the resolution of mixed waste treatment deficiencies identified in the DOE complex. These systems engineering techniques include: precise problem definition, requirements identification, selection strategy development, and the generation of alternatives data to complete trade studies. In particular use of these principles has led to the establishment of an end-user based development program for resolving the MWFA identified deficiencies associated with stabilizing salt containing mixed waste and fly ash.

Data collected upon completion of the three-way fly ash stabilization demonstration and on the five-way salt waste stabilization development effort will be formally documented in MWFA Technology Development Reports (TPR) by the end of FY98. The TPRs will assess each stabilized waste form's performance against the requirements and provide data for trade studies by potential end-users of the developed methods. End-users in the DOE complex will then have a method to assist them in selecting stabilization technologies to best fit their fly ash and/or salt containing waste treatment needs.

1. Beitel, G. A., Systems Engineering Identification and Control of Mixed Waste Technology Development, Journal of Franklin Institute, Vol. 334A, Issue 2-6, 1997.
2. Mixed Waste Focus Area Integrated Technical Baseline Report, Phase 2, Volumes 1and 2, DOE/ID- 10524, Revision 1, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID, April 1997.
3. Martin, James N., Systems Engineering Guidebook-A Process for Developing Systems and Products, Chapter 2, CRC Press, 1997.
4. Kalb, P. D., Conner, J. R., Mayberry, J. L., Patel, B. R., Perez, J. M., Treat, R. L., Stabilization/Solidification¾ Innovative Site Remediation Technology-Design and Application, WASTECH and The American Academy of Environmental Engineers, 1997.
5. Moghissi, A. A., Godbee, H. W., Hobart, S. A., Radioactive Waste Technology, Chapter 8, The American Society of Mechanical Engineers, 1986.
6. Stabilization/Solidification Processes for Mixed Wastes, United States Environmental Protection Agency, EPA 402-R-96-014, June 1996.
7. Bleier, A. Evaluation of Final Waste Forms and Recommendations for Baseline Alternatives to Grout and Glass, ORNL/TN-13214, DOE-Oak Ridge National Laboratory, September 1997.
8. Stabilization /Solidification of CERCLA and RCRA Wastes-Technical Position on Waste Form, Revision 1, USNRC, January 1991.

BACK