Experimental Investigation and Geochemical Modelling for Industrial Hazardous Waste Material

Abstract

Till the recent past the cities were small and sparsely populated and the amount of industrial solid waste generated is very less which was stored in the industrial backyards. Due to the rapid increase in population, urbanization and industries, it resulted in the generation of huge quantity of industrial solid waste with wide range of characteristics which when directly disposed on the dumpsite would directly or indirectly affect the surrounding environment and human health. The objectives set include understanding the leaching mechanisms (dissolution and sorption) from the industrial waste such as Ferrochrome Ash (FCA) and Biomedical Waste Bottom Ash (BMWBA), geochemical modelling of leached heavy metals were carried to identify the major oxidation states of leached mineral/metals from FCA and BMWBA and immobilization heavy metals present in the BMWBA using the Ground Granular Blast Furnace Slag (GGBFS). For FCA and BMWBA leaching experiments have been carried out to analyse the leaching concentration of metals such as Hg, Se, Co, Ni, Fe, As, Cd, Zn, Pb, Ca, Cu and Cr by adopting standard procedures viz. ASTM D3987-12, TCLP 1311 and USEPA 1313 (Under various pH conditions 3, 5, 7, 9 and 11) to assess the interactions. Geochemical modelling carried out using Visual MINTEQA 3.1 to recognize the dominant chemical species of redox sensitive metals in leachates. In this investigation, 0, 10, 20 and 30% of GGBFS was added to BMWBA to carried out the immobilization of heavy metals with the help of alkaline solutions (sodium silicate solution and sodium hydroxide solution). From the results of all the three leaching test methods for FCA found that Cr, As, Hg, and Se and BMWBA Hg, Pb, Se and As elements were leaching in very high concentrations. Geochemical modelling for leached concentrations of Ca, Cd, As, Cu, Cr, Fe, Ni, Se and Zn in the FCA and BMWBA were summarized based on their dominant oxide, hydroxide and carbonate minerals and leaching controlling solids for each element of interest. From the solidification/stabilization results shows that the compressive strength of overall mixture of BMWBA and GGBFS solidified matrices were between 0.75 to 10.52 MPa. The process of immobilizing heavy metals a physically encapsulated process, diffusion may cause cation should be substituted by another cation. The leaching test results of the solidified matrices show that the GGBFS addition was able to immobilize the toxic metals found in BMWBA.