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Suggested Citation:"Solid Wastes." National Research Council. 1993. Alternative Technologies for the Destruction of Chemical Agents and Munitions. Washington, DC: The National Academies Press. doi: 10.17226/2218.
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Page 98
Suggested Citation:"Solid Wastes." National Research Council. 1993. Alternative Technologies for the Destruction of Chemical Agents and Munitions. Washington, DC: The National Academies Press. doi: 10.17226/2218.
×
Page 99
Suggested Citation:"Solid Wastes." National Research Council. 1993. Alternative Technologies for the Destruction of Chemical Agents and Munitions. Washington, DC: The National Academies Press. doi: 10.17226/2218.
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Page 100

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THERMAL TREATMENT AND PREPROCESSING AND POSTPROCESSING OPERATIONS 98 A subsequent oxidation process could probably be easily incorporated into a combined thermal decomposition and oxidation system, because decomposition products of concern are likely to be gases under 5X treatment conditions. Such a system would have the advantage over an incinerator of a substantially lower rate of gas production. Equipment required for temporary gas storage and certification would be correspondingly smaller. POSTPROCESSING OPERATIONS Because any process can only transform agents from one chemical form to another, all processes have waste streams. These waste streams must be suitable for disposal to the environment or for reuse. Although many conventional processes are available for use in waste treatment, the nature of chemical agents invokes some special considerations and requires the use of protective measures that go beyond those of normal industrial practice. Chapter 4 addressed the need for effluent retention systems for dynamic processing units to certify the suitability of all effluents for disposal. Other postprocessing operations that could be used in a system for chemical demilitarization are described below. Solid Wastes The two major solid waste streams in chemical demilitarization axe decontaminated metal and salts formed from neutralization of the acidic products of oxidation (HF, HCl, H2PO4, H2SO4, and CO2). There are proposals to solidify organic wastes from chemical processes for subsequent disposal, thus avoiding the necessity for complete oxidation (Kalyon, 1992). Metal wastes. Chapter 4 discussed the need to use high temperatures to achieve full decontamination of metals (i.e., to the 5X level). The baseline process is designed to meet the 5X requirement of treatment at 1000°F for 15 minutes. The ability of alternative technologies to carry out this step is discussed in Chapters 7 and 8. Chemical decontamination to the 3X level would allow transportation and storage, but it is not currently believed capable of reaching the 5X level required for release of materials to the general public. If materials decontaminated to the 3X level can be disposed of in central hazardous waste facilities, the high-temperature 5X treating requirements could be modified, making construction and operation of the baseline traveling-grate metal deactivation furnace for large metal parts or any similar alternative unnecessary. Small metal parts would still require, along with energetics, a

THERMAL TREATMENT AND PREPROCESSING AND POSTPROCESSING OPERATIONS 99 high temperature for destruction and deactivation to meet the 5X criterion as currently carried out in the rotary kiln in the baseline technology. Salt wastes. The quantities of waste salts produced will vary with the agent feed rate and the processes used. As a theoretical minimum, if all carbon atoms are converted to CO2, the only salts produced would be those resulting from oxidation of fluorine, phosphorus, sulfur, chlorine, and nitrogen to acids, which could be neutralized by NaOH or Ca(OH)2. Table 5-1 presents the weight of salts formed from Ca(OH)2 neutralization of GB. If CO2 is discarded as a gas, the minimum produced would be 2.3 pounds of salts per pound of GB, with calcium phosphate representing the largest component (65 percent). For most systems, some CO2 will also be captured. If all the CO2 generated by agent oxidation was captured, calcium carbonate would be the major component; the total salt weight would approximately double to 5.1 pounds of salts per pound of GB. A process to capture all the CO2 would probably require excess base, and any CO2 from fuel combustion would also increase the total amount of salts. Decontamination fluid, when oxidized, would also add to total salt loading, as would the use of organic solvents such as alcohol or organic reagents such as ethanolamine. Total dry waste salts for GB, then, would probably be from 5.1 to perhaps 20 pounds per pound of agent. The character of the waste salts will influence their ultimate disposition. Notably, their solubility will be a major determinant of their acceptability for land disposal. If NaOH is used as the reactant to destroy agent, then the fully oxidized reaction products would be sodium carbonate, sodium fluoride, sodium phosphate, sodium sulfate, sodium chloride, and sodium nitrate. Although most of these sodium salts are relatively innocuous, all are quite soluble, requiring that land disposal methods take into account potential groundwater contamination. (There would be a greater potential for contamination by the more soluble chlorides if a destructive reagent containing chlorine atoms was used.) Sodium fluoride is considered a toxic waste and might present a special problem. Calcium fluoride, which has low solubility, would probably be a more acceptable waste product. Metals used as catalysts or in small metal parts, which might be mixed with the salts, could also require special handling. An alternative approach would be to produce the generally less soluble calcium salts, by substituting Ca(OH) 2 for NaOH as the reagent when possible. The same result could be achieved by a later reaction step in which calcium ions would be substituted for the sodium ions in the waste salts. Such a method would convert the salts to generally less soluble forms and also regenerate the sodium ions for reuse in agent destruction. However, it would not solve the problem of generating soluble calcium chloride when mustard is destroyed.

THERMAL TREATMENT AND PREPROCESSING AND POSTPROCESSING OPERATIONS 100 TABLE 5-1 Salt Formation from GB Oxidation Products Management of CO2 Salt lb/lb GB CO2 release as gas CaF2 0.8 Ca3 (PO4)2 1.5 Total 2.3 All CO2 captured CaF2 0.8 Ca3 (PO4)2 1.5 CaCO3 2.8 Total 5.1 Drying of solids. Most chemical processes, such as the various forms of hydrolysis, will produce a wet, dilute slurry of salt that can then be converted to a wet cake by appropriate precipitation and/or filtering. The storage volume required to retain these more concentrated salts for certification for release is not usually excessive, but the residual moisture content is often sufficiently high so that it is economical to dry the material further before shipping it to its disposal destination. Standard commercial drying equipment (e.g., spray dryers) can be used but usually depend on mechanical techniques to bring the wet waste into contact with warm, dry, fresh air that is then released to the atmosphere. However, such a release is also an effluent stream, and if the material being dried has only been treated to the 3X level, the moist air discharge must also be treated as potentially contaminated. Thus, for present purposes, such systems might have to be modified to recycle the air through indirect heat exchangers, which would cool the air, condense the bulk of the water, and recycle the dried air stream to the dryer or send it to an afterburner. The condensed water stream would then also have to be treated as potentially contaminated and be recycled, preferably as part of the feed stream. The equipment and technology to perform these additional functions is readily available, but they would involve added complications to integrated system operations as well as added costs. Methods of shipping of by-product 3X salts. The standard method of shipping contaminated wastes involves packaging them in barrels or in larger

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The U.S. Army Chemical Stockpile Disposal Program was established with the goal of destroying the nation's stockpile of lethal unitary chemical weapons. Since 1990 the U.S. Army has been testing a baseline incineration technology on Johnston Island in the southern Pacific Ocean. Under the planned disposal program, this baseline technology will be imported in the mid to late 1990s to continental United States disposal facilities; construction will include eight stockpile storage sites.

In early 1992 the Committee on Alternative Chemical Demilitarization Technologies was formed by the National Research Council to investigate potential alternatives to the baseline technology. This book, the result of its investigation, addresses the use of alternative destruction technologies to replace, partly or wholly, or to be used in addition to the baseline technology. The book considers principal technologies that might be applied to the disposal program, strategies that might be used to manage the stockpile, and combinations of technologies that might be employed.

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