Enhancement of uranium mobility by manure amended in a calcareous soil : A potential use of organic fertilizaer for phytoremediation

Understanding of uranium (U) mobility when a soil amendment is applied for the phytoremediation purposes is important for minimizing U migration in the soil profile. The objective of this study was to evaluate the effect of cattle manure amendment on U solubility and mobility in the soil profile. A 40 cm soil column was filled with calcareous U-contaminated soils to demonstrate uranium behavior under irrigated conditions. Experimental treatments were no amendment (control) and steer manure amendment with 118 ml water irrigated every 48 hours for 200 days. Uranium mobility was enhanced through the columns 23 days after the addition of manure when the U concentration of leachate reached about 200mg l-1. Leachate U concentration of the control increased up to 27.6mg l-1.･The amount of total U leaching relative to the U initially contained in the soil was 1.2% for the control and 6.1% for manure treatment during the study period. Electrical conductivity of leachate was more positively correlated to U concentration for the manure-amended column (r=0.47) than the control (r=0.24), attesting the occurrence of cation exchange processes between the soil solid and solution phases. Because leachate pH was still in a neutral range after the manure addition, U desorption from soil to solution is unlikely to occur, indicating that U mobility could mostly result from U chelation with humic substances contained in the manure