Incineration of combustible Mixed Transuranic Waste yields an ash residue that contains oxides of Resource Conservation and Recovery Act (RCRA) and transuranic metals. In order to dispose of this ash safely, it has to be solidified and stabilized to satisfy appropriate requirements for repository disposal. This paper describes a new method for solidification of incinerator ash, using room temperature setting iron phosphate ceramics, and includes fabrication procedures for these waste forms as well as results of the MCC-1 static leach test, XRD analysis, scanning electron microscopy studies and density measurements of the solidified waste form produced

Frank, S.M.

Giglio, J.J.

Hansen, M.

Johnson, S.G.

Macheret, J.

Medvedev, P.G.

Sidwell, R.W.

Wood, E.L.

UNT Digital Library

* t Low Temperature Setting Iron Phosphate Ceramics as a Stabilization and Solidification Agent for Incinerator Ash Contaminated with Transuranic and RCRA Metals ~ ~ F . s ~ o ~ % - z  P.G. Medvedev, M. Hansen, E.L. Wood, S.M. Frank, R. Sidwell, J.J. Giglio, and S.G. Johnson Engineering Division Argonne National Laboratory P. 0. Box 2528 Idaho Falls, Idaho 83403-2528 and J. Macheret Department of Energy, Idaho Office Idaho Falls, Idaho 83415 The submitted manuscript has been authored by a contractor of the U. S. Government under contract No. W-31-1 OSENG-38. Accordingly, the U. S. Government retains a nonexclusrve. royalty-free license to publish or reproduce the published form of thts contribution, or allow others to do 50. for Paper to be submitted for presentation at the The American Ceramic Society 99& Annual Meeting & Exposition Cincinnati, Ohio May 4-7, 1997 Work supported by the U.S. Department of Energy, Reactor Systems, Development and Technology, under Contract W-31-109-Eng-38. OlSTF!lBtmON OF WtS DOCUMENT IS UNLfM DECLAIMER t LOW TEMPERATURE SETTING IRON PHOSPHATE CERAMICS AS A STABEDITION AND SOLIDIFICATION AGENT FOR INCINERATOR ASH C O N T M A T E D  WITH TRANSURAMC AND RCRA METALS. P. G. Medvedev, J. Macheret*, M. Hansen, E. L. Wood, S. M. Frank, R.W. SidweU, J. J. Giglio and S. G. Johnson Argonne National Laboratory-West P.O. Box 2528 Idaho Falls, ID 83403 *Dept. Of Energy, Idaho Office Idaho FalIs, ID 83415 ABSTRACT Incineration of combustibie Mixed Transuranic Waste yields an ash residue that contains oxides of Resource Conservation and Recovery Act (RCRA) and transuranic metals. In order to dispose of this ash safely, it has to be solidified and stabilized to satisfy appropriate requirements for repository disposal. This paper describes a new method for sofidification of incinerator ash, using room temperattm setting iron phosphate ceramics, and includes fabrication procedures for these waste forms as well as results of the MCC-1 static leach test, XRD analysis, scm~ing eIectron microscopy studies and density measurements of the solidified waste form produced. INTRODUCTION The goal of this work is investigation and development of a new method for solidification of incinerator ash, containing oxides of RCRA and transuranic metals using low temperature setting iron phosphate ceramics. More specifically, this work seeks to elucidate the means in which the reaction rate of the settins process can be controlled, easily and economically, while still yielding a waste form with acceptable characteristics and performance. Iron phosphate ceramics represent a large group of acid-base cements, and their properties, as well as, some practical applications are well described in the literature (1-5 ). Iron phosphate ceramics are themselves a sub- DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recorn- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. group of the a larger body of ceramics that include other types, such as magnesia based ceramics, that have been investigated for immobilzation of transuranic wastes (6). Solidification of the ash waste using this process results not only in micro- and macro- encapsulation of contaminants, but also in chemical binding of TRU and RCRA metals in the form of phosphates. Phosphates are known as host miner& for some actinides and heavy metals (7,8). This process has several distinct advantages over other methods: 1) it is very simpre mechanically requiring minimal equipment, 2) the process does not produce secondary waste streams such as fiee standing liquids or off-gases, 3) the process proceeds at mom temperature which eliminates the need for off-gas treatment and 4) the treatment is cost-effective &om a processing standpoint. Components Class F fly ash EXPERIMENTAL Waste stream Solidification experiments were conducted using simuIated incinerator ash. It was prepared and supplied by Dr. Wagh of Argonne National Laboratory East, Energy Technology Division, Ceramic Section. Composition of the waste stream is given in Table 1. Concentration ( g k g )  387.96 Vermiculite 1 93.98 crzo, NO 14.18 6.16 CdO CSCI Ce,O, 5.54 6.15 5.70 As is indicated in Table 1, oxides and chlorides of various metals were added to the ash to simulate actual waste ash. CrL03, PbO, HgCl, and CdO represented compounds of RCRA metals. Ce,O, was used to simulate plutonium oxide. Natural CsCl was used to simulate fission product cesium. Solidification Experiments according to the flow sheet shown on Figure 1. Solidification experiments were conducted in 50 ml plastic beakers Fe304 powder Ash waste powder Figure 1. Flow chart for the process of ash waste solidification .I Homogeneous mixture The ratios of the constituents and the acid concentration were determined by an iterative method based on the composition diagram shown in Fig. 2. The key parameter used to nmow the area of interest in Fig. 2.  was a visibie inspection of the structural integrity of the waste form produced. X large number of cracks or a “crumbly” waste form was regarded as a non-attractive composition. The shaded area on the composition diagram (Fig. 2 )  corresponds to the waste form compositions for which solidification occurs. Investigations presented in this paper were focused on the compositions with a waste loading of 30 and 40%. The waste loadings sired in this paper are cdculared so rhat the weight percent given, i.e., 30 or 40 wt%, is the fraction of the total mass. including waste, binder and phosphoric acid. multiplied by 100%. 50% orthophosphoric acid 0 20 40 60 ao IO0 Ash waste (wt.%) Figure 2. Composition Diagram for the Solidification Process. Leach Tests The leaching properties of the fabricated waste forms were investigated by conducting the iMCC- 1 static leach test (ASTiM C 1220-92). The procedure described in the MCC-1 method was modified in regard to the sample preparation steps. The monolith utilized was obtained via core drilling and the surface finish was 600 grit. The (surface aredvolume) ratio was 10 m-'. The Ieach tests were run for 7 days at 90 "C. The normalized release rate (NRR) was evaluated using the equation: . NRR(i) = C,V/f,Ad where C, is the concentration of the element i in the leachate in glml, V is the volume of leachate in ml. f, is the fraction of the element i in the solid initially. -4 is the macroscopic area of the solid in m'. and d is the duration of the test in days. The surface area was calculated from the linear dimensions of the cylindrical samples. The monolithic specimens, obtained as a result of solidification, were cured for 2 1 days at room temperature, before they were submitted for the leach test. 5 I .  Density measurements Density of the samples was measured using Ultrapycnometer- 1000 (UPY-2, Quantachrome Inc, Boyton Beach, FL). 2. Microscopy studies and EDS analysis An IS1 SS440 scanning electron microscope supplied by Topcon Technologies (Paramus, New Jersey) with a Kevex 7070 EDS system (Kevex Fisons Instruments, San Carlos, CA) was used for microscopy studies and EDS analysis. 3. Analysis of leachates Leachates were analyzed using an ICP system that included a plasma unit consisting of a 40 MHZ, 1600 W generator and a torch box (ICP 16L, RFPP, New Jersey, USA). The torch box was fitted with a demountable Fassel type torch. A 1.5 path length monochromator, fitted with a 2400 lines per mm holographic grating (THR 1500, ISA Inc. Metuchen, NJ, USA) was used to detect andyte emissions from ICP. The monochromator stepper motor was controlled via a Spectrolink control unit, (ISA Inc., Metuchen, NJ, USA). 4. X-ray diffraction anuiysis were performed in order to identrfy the crystalIine phase that is present in the ceramics. A Scintag XI Powder X-ray DEactometer (Scintag, Inc., CA) with a Theta-Theta type goniometer, Cu K-alpha x-ray tube with normal focus, and top loading powder sample holder was used for this purpose. RESULTS AND DISCUSSION The methodology pursued for this study revolved around first investigating the appropriate binder compositions to provide the desired setting kinetics, not too slow or too fast. Once the approximate composition was determined the waste loading was optimized and the final fine tuning of the components was attempted. The waste forms produced were characterized by means of SEM, XRD, density and setting times. The durability of the waste forms produced was assessed by the MCC- 1 test. A> Estimation of Reaction Rates and Settinu Times The quick setting behavior of the Fe,O,-H,PO, system is caused by the rapid formation of normal and acidic iron phosphates (2). Since this reaction is exothermic, its rate can be monitored via the temperature rise of the slurry. As can be seen in Fig. 3, the reaction rate is controllable at several waste loadings of interest by the simple addition of a single agent. The reaction retardant is dissolved in phosphoric acid before the acid is reacted with the powder mixture of ash waste and magnetite. Varying concentration of the retardant in the acid from 0.025 g / d  to 0.1 g /d ,  we were able to fabricate waste ceramic waste forms with the setting time fiom 5 minutes to 2 hours. The degree of flexibility that this affords the process in the field can not be over-stated. Parameters B) Densitv Results of density measurements are summarjzed in Table 2. The true density of the fast setting compositions is less than that of the slow setting. A difference between the true and bulk density is explained by the presence of air voids, trapped in the matrix. Bulk density was determined using the macroscopic volume and mass. The higher the density, the lower the porosity and this should be reflected in better normalized release rates from the MCC-1 test. A method of removing this variable fiom the leach test would be to apply the product consistency test (PCT), ASTM 1285-94, which utilizes a crushed sample and not a monolithic one. Providing the compressive strength measurments are acceptable the PCT test may be the method of choice in the immediate future for our research needs. Fast setting compositions Compositions with extended setting time Table 2. Densities and Setting Times of Selected Waste Form Compositions I , 1 Amount of 0 0 0.025 0.05 0.075 0.1 0.025 0.05 0.075 0.1 retardant added, glml H,PO, Setting time, min 5 5 8 30 60 90 8 30 60 90 Density, true 2.68 2.50 2.62 2.78 2.80 2.90 2.63 2.77 2.83 2.67 bulk 1.46 1.57 1.37 1.58 1 1.67 1.63 1.79 1.57 1.67 1.68 g/cm’ ‘ I I Wasteloading, I 30 I 40 1 c/o 30 40 C) Static Leach Results The results of a 7 day MCC-I results are presented in Table 3. These are normalized release rates for the cations of interest including Fe. Concentrations of Ce, Cs and RCRA metals in the leachate solutions were below detection levels. Relatively high weight losses of the samples are explained by leaching of unreacted phosphoric acid from the samples. Parame ters Waste loading, %I Amount of retardant added, g/ml H,PO, Weight loss, wt % pH of the leacate solutions - ~ ~ Ct Normaii zed glm2/day release rate, Pb Ce Fe I Fast setting compositions 30 40 30 40 Compositions with extended setting time 0.00 0.00 0.075 0.1 0.05 0.075 0.1 5.95 7.10 2.02 1.95 2.32 2.13 1.48 3.47 3.32 3.36 3.33 3.51 3.55 3.37 ~~~ ~~ ~ ~ ~ ~ ~0.049 c0.037 c0.049 c0.051 4.036 <0.037 c0.036 ~0.294 4.220 <0.294 4.305 4.217 <0.219 4.219 ~0.049 4.037 4.049 4.051 <0.036 4.037 4.036 0.042 0.038 0.018 0.039 4.016 0.036 0.039 CONCLUSIONS The preliminary study presented in this paper using surrogate fly ash has demonstrated the potential of the iron phosphate ceramic system for application to actual TRU containing waste. Furthermore, the results show promise and the need for further work in this area using both surrogates and actual TRU containing fly ash. The following points deserve emphasis as the significant findings of this work 1) High, 40 wt%, waste loadings of surrogate fly ash containing Cs, Ce and RCRA metals have been successfully immobilized using an iron phosphate ceramic waste form 2) The ceramic waste fonn shows preliminary normalized release rates for the RCRA metals that are promising. 3) The setting time of the waste form compositions is easily controUed in a wide range using a retardant. 4) The method outlined in this work is quick, effective, economical and displays a significant waste Ioading. ACKNOWLEDGMENTS Argonne National Laboratory is operated for the U.S. Department of Energy by the University of Chicago. This work was supported by the US. Department of Energy, Reactor Systems, development and Technology, under Contract W-3 1-109-ENG-38. The Plutonium Focus Area, Dept. Of Energy, Idaho Ofice is gratefkllyacknowledged for supporting one of us, P. G. M., for this work. Dr. Arun Wagh is gratefully acknowledged for providing the surrogate ash used for this study and for helpful discussions with P. G. M. REFERENCES 1. L. I. Turkina, L G. Sudakas, V. A. Paramonova, and A.A. Chernikova, “Phase Composition and Strength of Iron Phosphate Binders,” Izvestiya Akademii Nauk SSSR, Neorganicheskie Materialy, Vol.26, No. 9, pp.  1967-1972, September, 1990. 2.  V. V. Gerasirnov and S. P. Sheptinskii, “X-Ray Phase and Electron Microscopic Studies of Pyrite Phosphate Mixtures”, Izvesriya Akodemii Nauk SSSR, Neorganicheskie Mam-iuIy, VoI.22, No. I ,  pp. 3. S. S. Zhukovskii, Yu. M. Yunovich, and O.E. Nevskaya,” Phosphate-Bonded Cold Setting Sands for Steel and Iron Casings Production,” Liteinoe Proizvodstvo, No. 4, pp .  19-20, 1987. 4. L. I. Turkina et. ai., “Principles of Cold-Setting Sand Preparation Using Iron Phosphate Binders,” Liteinoe Proizvodstvo, No. 4, p.5, 1989 5 .  M. M. Sychev and V.G. Komlev “Setting of Iron, Cobalt, and Nickel Phosphate Cements,” Izvestiya Akudemii Nauk SSSR, Neorganicheskie Materialy, Vol. 7, No. 9, pp. 1612-1615, 1971. 6.  Jeong, S. ;  Wagh, A.S.; Singh, D., “Chemically bonded phosphate ceramics for stabiiizing low-level radioactive wastes”, April 1996, NTiS Order Number DE96009457. 7.  “Handbook of Geochemisrq, *’ edired by K.H. Wedepohl, Berlin, Heidelberg, New York, Springer, 120-12.5, J o ~ u u ~ ,  1986 v.2, pp. 82B9-89BI I ,  9204-9205,1969. 0 10 20 30 40 50 60 Time, min -+ 0 qml  retardant -&- 0.075 @nl retardant -x- 0.1 g'ml retardant -e- 0.025 gml  retardant -8- 0.05 g'ml retardant Figure 3. Temperature rise during setting of iron phosphate ceramics Amount of the retardant added is in gams per milliliter of phosphoric acid. i t 

Low temperature setting iron phosphate ceramics as a stabilization and solidification agent for incinerator ash contaminated with transuranic and RCRA metals

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Low temperature setting iron phosphate ceramics as a stabilization and solidification agent for incinerator ash contaminated with transuranic and RCRA metals

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