IMMOBILIZATION OF HEAVY METALS IN PORTLAND CEMENT-MUNICIPAL SOLID WASTE INCINERATION ASH MATRIX

Abstract

A novel composite matrix composed of Portland cement (PC) and municipal solid waste incineration ash (MSWIA) was developed for the simultaneous immobilization of three heavy metals - Ba, Pb and Zn. The main motivation for the research was to exploit and reuse MSWIA to design alternative composite matrix with the ability to immobilize hazardous pollutants, such as heavy metals, which might be used as filler for the cement-based construction materials. In composition of prepared composite matrix, MSWIA was used as addition to PC in the amount of 10 wt%. Silica sand of 0-2 mm fraction was used as aggregate. Water/binder ratio was 0.61. It was adjusted to obtain workable fresh mixture. Soluble heavy metal salts (BaCl2, Pb(NO3)2, ZnCl2) were added to batch water at a rate of 2.5% of the individual heavy metal by weight of the PC. The assessment of developed matrices included basic structural and mechanical properties. To evaluate the immobilization of the studied heavy metals in the prepared composites, the leaching test was performed with a ratio of liquid to solid of 10 l/kg. Atomic absorption spectroscopy (AAS) was used to analyze the concentration of Ba, Pb and Zn in leachates. The presence of heavy metal salts negatively affected the strength of both composite matrices. Nevertheless, the addition of MSWIA improved both flexural and compressive strength in comparison to reference composite matrix. The increase in the flexural strength was 21.4% and 32.4% in the compressive strength. The concentrations of all examined heavy metals studied in the leachates from the developed composite matrices were very low, indicating that they were completely solidified and immobilized in the matrix. Moreover, the application of MSWIA reduced the leaching of Pb and Zn.