Determination of Ra leachability from filter materials originating from water treatment plant

Abstract

NORM (Naturally Occurring Radioactive Material) waste management is a relatively new issue in Estonia. At the present moment, the largest volumes come from water treatment plants, where the Ra isotopes Ra-226 and Ra-228 accumulate in the filter material in the process of water purification. In the absence of prior experience and legislation, the best solution is considered to be the deposition of such material in landfill (Kiisk, 2016). In order to evaluate the possible leaching of Ra into the groundwater, experimental determination of Ra leachability from filter material is conducted within this study. The activity concentrations of the filter materials used in this study ranged from approximately 4700 to 22100 Bq/kg. The study is based on two standard methods, the batch test and percolation test, and has created environments which, in addition to imitation of natural rainwater (0.001M CaCl₂), could also describe landfill conditions due to their high leachate concentrations. The results obtained suggest that Ra concentrations remains equally low for all solutions, ranging from 0.2 to 4 Bq/kg. Partition coefficient K_d, the parameter describing leaching, ranges mainly from 10000 to 33000 L/kg in the case of dilute solutions (0.001M CaCl₂ solution, TDS of 111 mg/L and dilute artificial leachate with TDS of 809 mg/L) and stays around 3000 L/kg in the case of more concentrated solutions (artificial leachates with TDS of 5467 mg/L and 12160 mg/L).

Keywords: Leaching test; NORM waste; Partition coefficient; Radium mobility.