DESIGN AND OPTIMIZATION FOR HAZARDOUS JAROSITE WASTE RECYCLING IN ENVIRONMENTALLY SUITABLE COMPOSITE PRODUCTS USING RESPONSE SURFACE METHODOLOGY - Management of Hazardous Residues Containing Cd - page 93

Based on the model prediction, the optimum mix design which
maximizes the overall brick properties for use in environmental friendly
application is shown in Table 33. However, the leachate concentration (from
TCLP extract) of lead and cadmium found to be within the USEPA limits
when the mixture proportion of jarosite waste, clay and PCCRs were 362 gms,
405 gms and 232 gms respectively.

Table 33. Optimum mix design to maximize the brick properties
for use in environmental friendly application

Mixture
proportion

Jarosite
waste
(gm)

Clay
(gm)

PCCRs
(gm)

Pb
(ppm)

Cd
(ppm)

1 362.66 405.23 232.11 0.34 0.28

2 515.33 449.66 35.02 7.2 0.31

3.4. Validation of Model Results with Experimental Results

To validate the theoretical (model) results with actual (experimental)
results of jarosite- clay-PCCRs composite products, experiments were carried
out in making s/s sintered composites products with the combination of
jarosite waste, clay and PCCRs concentration optimised by mixture approach
model (Table 34). Further, the quality of the s/s sintered jarosite clay PCCRs
products were evaluated for their engineering properties and toxicity leachate
characteristics. The responses considered for the composite products are
compressive strength, water absorption, shrinkage, density, leaching of
cadmium and lead. Since the leachate concentration for the other response like
Ag, As, Se, Cu, Cr, Co, were very low as well as the concentration were below
the toxic limits recommended by USEPA, these responses were not reported in
this chapter. The experimental results of the jarosite waste composites
products under optimized condition showed the compressive strength, water
absorption, shrinkage and density of 41.6 kg/cm 2 , 17.2%, 15.2% and 1.6
gm/cm 3 respectevelly. Moreover the leachate concentration of cadmium and
lead in the jarosite composite made under actual condition was 0.30 ppm and
0.33 ppm respectively. It reveals from these experimental results that there is
an excellent agreement between predicted and experimental results (Table 34).
Hence, from the RSM model validation, it is evident that the optimized