Stabilisation of heavy metals in polymeric matrices: Studies on leaching behaviour

• Solidification/stabilisation of heavy metal salts in epoxy resin.
• Correlation of water penetration and salt leaching and their quantification.
• Estimation of maximum leachable salt in the stabilised polymeric matrix.
• Correlation of leaching data, for different salts, using a single equation based on dimensionless time.

Heavy metal salts of Cr, Pb, Hg, Ni, Mn and Zn were stabilised in a cycloaliphatic epoxy resin as the immobilising material. The polymeric matrices were subjected to leaching studies as per ANSI/ANS-16.1-1986 leach test. The leachability index was found to be acceptable as per the test standard. The leach test data was used to develop an understanding of the leaching behaviour of the metal salts. The leaching rate was found to be dependent on the water penetration depth, the total leachable salt and leaching depth. Leaching depth was controlled by effective diffusivity and solubility of the salt. Salt leaching depth signifies the dissolution front, which progresses with time. A leach model based on diffusion controlled dissolution kinetics was developed to simulate the tests, which can be used to formulate standards for safe disposal. The leaching data was further correlated using the dimensionless time approach. The critical model parameters included effective unencapsulated salt concentration, salt leaching depth, porosity of matrix and effective diffusivity of salt.