Immobilization of simulated evaporator concentrate waste in low density polyethylene

Simulated evaporator concentrate was prepared by pre-treating sodium borate with calcium hydroxide to produce an insoluble, ulexite-like borate salt. The resultant solid waste was blended by extrusion with virgin and recycled low density polyethylene (LDPE) at 30 and 50 wt% load. Samples were evaluate to homogeneity by density determinations (ASTM D792-91), compressive strength (ASTM D695-91) and leaching behavior by accelerated leaching tests (ASTM C1308-95). Coefficient of variation of density was lower than 5% for all evaluated waste forms, indicating a satisfactory homogeneity. Compressive strengths have complied to U.S.NRC standard and were above CNEN standard limit for cement waste products if 5% strain could be considered a reasonable limit to assure the structural integrity of the material. Cumulated fraction leached after 11 days of accelerated leach test was found to be lower than 10%, and diffusion coefficients of boron have varied between 3.86 × 10−10 and 9.06 × 10−10 cm2/s. Boron concentrations for all materials have shown a tendency to reach an asymptotic value at the end of the test (around 0.25 and 0.7 mg/L for 30 and 50% waste load, respectively). Measured cumulated fraction leached (CFL) data with time have shown a tendency of becoming asymptotic sooner than it was predicted by the diffusion model.