WASTE MANAGEMENT, Vol. I0, pp. 117-124, 1990 0956-053X/90 $3.1)0 + .00 Printed in the USA. All rights reserved. Copyright © 1990 Pergamon Press plc MIGRATION OF LIQUID WASTE 137Cs AND °Co IN CALCAREOUS SOILS A. A. Fahad,* I. B. Razaq, R. M. Shihab, A. W. Ali, H. A. and J. Sh. Mahmood Nuclear Research Centre, P O. Box 765, Baghdad, lraq Tawfeek, ABSTRACT. Two experiments were carried out to determine the leaching characteristics and distribution ofiliquid waste ~Cs and ~eCo in three calcareous soils varied in clay contents. The liquid waste as raw (RLW), diluted (DLW), and diluted then pH adjusted (ADLW) was applied to either large undisturbed soil columns (in 200 mL) and[ leached for 180 d with deionized water and groundwater or to small packed soil columns (in several pore volumes). DiStribution of 137Csand *~o in the large columns was determined nondestructively (with the aid of correction curve) byI scanning of gamma radiation along the soil columns. However, their distribution in the small columns were determined by sectioning and measuring their content. Most of the radionuclides were retained by the upper 10 cm of the large soil columns of which approximately 70% of I~'Cs and 55% of e°Co were held by the surface 1 cm of the columns, suggesting the irreversible sorption of both radionuclides. Differences in leachability of t3'Cs and ~ o were attributed to the differences in sorption mechanisms associated with the varied experimental conditions. The dilution and/or pH adjusting of the liquid waste greatly reduced the mobility of both radionuclide ~ applied in several pore volumes. For instance, the amount of ~37Cs retained by the upper 1 cm of river sediment was al~ ~roximately 10 and 20 folds greater with ADLW and DLW, respectively than RLW. Greater mobility of 6°Co than t37Cs, ts observed in the form RLW. INTRODUCTION Radionuclide contamination from low-level waste disposal area is of considerable interest in many en- vironmental studies. Movement of the disposed waste may occur in soluble forms and the transport vectors include diffusion and/or mass transport as- sociated with water flux (1). The potential for radio- nuclide migration from a nuclear waste repository will depend on the physical and chemical properties of the soil, the chemistry of the soil, the character- istics of the radionuclide, and the chemical nature of the waste itself (2). Understanding of the migration and interaction of waste radionuclides in waste-soil system is a task of major importance in assessing the potential for con- tamination. It is also important to provide a basic RECEIVED 28 Auous'r 1989; ACCePtED 15 Ik~kRCH 1990. *To whom correspondence may be addressed. Acknowledgements -- The authors wish to express theirthanks for the in-part financial support provided by the Intemalional Atomic Energy Agency in connection with the Research Coor- dinated Program on "Migration and BiologicalTransfer of Radio- nuclides From Shallow Land Burial." information for the responsible handling and safe disposing of such radioactive materials. In this re- spect, numerous studies have been cond¢cted on the leaching of waste radionuclides and their!interaction with soil or with host materials. For instaace, Fowler et al. (3) studied three fractions of waste[ (filterable, soluble-sorbable, and soluble-nonsorbal~le) in terms of radionuclides charge, mobility, and !heir distri- bution among the various fractions of waste. Essing- ton et al. (4) and Polzer et al. (5) ~tudied the distribution of liquid waste radionuclides ~mong four soils and in soil from horizons of two soil series. Their results indicate that between 95 to 100% of 137Cswas sorbed by the soils. On the other hand, Mahara and Kudo (6) found that more than 98% and 70% of 6°Co was fixed on coast sediment under aerobic and una- erobic conditions, respectively. This paper presents results related to the leaching characteristics of liquid waste ~37Csand ~°Co in three soils of varied clay content. It is part of or~going work dealing with the migration and interaction of waste radionuclides in major soils of Iraq. Also, the infor- mation presented here will aid in underStanding of the radionuclides dynamics in the event o~ accidental or inadvertent release into the surrounding soils. 117