Stabilization and solidification of metal-laden wastes by compaction and magnesium phosphate-based binder

Bench-scale and full-scale investigations of waste stabilization and volume reduction were conducted using spiked soil and ash wastes containing heavy metals such as Cd, Cr, Pb, Ni, and Hg. The waste streams were stabilized a nd solidified using chemically bonded phosphate ceramic (CBPC) binder, and then compacted by either uniaxial or harmonic press for volume reduction. T he physical properties of the final waste forms were determined by measurin g volume reduction, density, porosity, and compressive strength. The leacha bility of heavy metals in the final waste forms was determined by a toxicit y characteristic leaching procedure (TCLP) test and a 90-day immersion test (ANS 16.1). The structural composition and nature of waste forms were dete rmined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), r espectively. CBPC binder and compaction can achieve 80-wt % waste loading and 39-47% red uction in waste volume. Compressive strength of final waste forms ranged fr om 1500 to 2000 psi. TCLP testing of waste forms showed that all heavy meta ls except Hg passed the TCLP limits using the phosphate-based binder. When Na2S was added to the binder, the waste forms also passed TCLP limits for H g. Long-term leachability resistance of the final waste forms was achieved for all metals in both soil and ash wastes, and the leachability index was similar to 14. XRD patterns of waste forms indicated vermiculite in the ash waste was chemically incorporated into the CBPC matrix. SEM showed that wa ste forms are layered when compacted by uniaxial press and are homogeneous when compacted by harmonic press.