Development of amendments for rehabilitation of soils, contaminated by radionuclides, and assessment of their application efficacy Konoplev A.V. 1 , Popov V.E. 1 and Maskalchuk L.N. 2 1 SI “RPA Association "Typhoon", 82 Lenin av., Obninsk, 249038 Russia; 2 SSO Joint Institute for Power and Nuclear Research - “Sosny”, National Academy of Sciences of Belarus, 99 Ac. Krasin st., Minsk, 220109 Belarus INTRODUCTION Application of selective to radionuclides amendments based on organic and mineral raw materials, including clay minerals, zeolites, sapropels, turf etc is very perspective agrochemical measure. Such countermeasures will result in increase of soil sorption ability to radionuclides and, therefore, decrease their availability to plant (Cremers et al., 1998). The objective of the work was to develop efficacious and ecologically safe amendments based on natural raw materials and industrial waste and to develop methods and models for forecasting effectiveness of countermeasures as part of remediation of soils contaminated by radionuclides. Bottom sediments of freshwater lakes or sapropels surpassing by content of nutrients and microelements are of special interest among such amendments. Hydrolyzed lignin (HL), the multi tonnage trade waste, is the material like sapropel considerably increasing soil sorption ability to 90 Sr. Clay salt slimes (CSS) have considerable stocks in Belarus and Russia and they are promising as a possible additive to amendments. The clay salt slimes are the material characterized by high dispersion and specific surface area, and considerable amount of crystalline structure defects, which increase their sorption ability in relation to 137 Cs. Phosphogypsum (PG), which is a waste of phosphoric fertilizer production, could be another possible mineral addition to amendments and organomineral mixtures (Konoplev and Maskalchuk, 2007). It is well proven now that retention of radiocaesium in soil is determined by two different processes: fixation and reversible selective sorption (Cremers et al., 1988; Konoplev et al., 1992; Konoplev & Konopleva, 1999). Fixation describes the permanent replacement of interlattice K- by Cs-ions. The ability of a solid to sorb radiocaesium selectively is characterised by the capacity of selective sorption sites (frayed edge sites - FES), located at the edges of micaceous clay minerals (Cremers et al., 1988), or by the so called radiocaesium interception potential (RIP), which is the product of FES capacity [FES] and selectivity coefficient of radiocaesium in relation to the correspondent competitive ion K c (Cs/K). RIP(K) can be also represented as a product of radiocaesium distribution coefficient K d and potassium concentration in solution [K + ](Sweeck et al., 1990). Two kinds of RIP(K) can be distinguished: the total radiocaesium interception potential RIP(K) and the exchangeable radiocaesium interception potential RIP ex (K). The first one relates the total value of tot d K 137 Cs in the soil with K + concentration in solution. The second one relates exchangeable value of ex d K 137 Cs in the soil (Konoplev & Konopleva, 1999). The total RIP(K) is a valuable parameter for comparison of different materials ability for specific retention of 137 Cs. Over time, considerable fraction of 137 Cs becomes unavailable for direct ion-exchange due to slow fixation process, thus causing an increase in the total K d value. Being more constant with time the RIP ex (K) can be used to predict the K d value for