Environmental Engineering Reference
In-Depth Information
al., 1995). Also, lead solidified with cement fly ash mixture showed a slightly
less leaching as compared to the cement binder. When CCRs substituted as
portland cement, strength maintained constant and it increased when active
silica is higher than that of cement (Papodakis, 2000). In the present study,
during sintering process, under solid-state reaction, the toxic substance/
elements were expected to be detoxified/ immobilised through complexing in
silicate matrix. Further, jarosite waste pH was just below neutral (pH= 6.78)
and hence the concentration of toxic elements such as Zn, Cd, Pb, Cr etc.,
might probably stabilised with CCRs-jarosite matrix. Constantino et al., (2001)
and Jang & Kin, (2000) reported that CCRs can be used as a fundamental raw
materials and main binder for s/s of electric arc furnace dust and mine wastes
containing hazardous metals such as Pb, Cd, Cr, Zn and Cu.
The toxicity leachate characteristics of sintered jarosite waste clay
composite products revealed that the concentration of almost all the toxic
elements in the sintered composite bricks developed using jarosite clay ratio of
1:1, 2:1 and 3:1 with 15 -30 % CCRs were found to be within the permissible
limits of the United States Environmental Protection Agency (USEPA)
approved Toxicity characteristics Leachate Procedure (TCLP) norms (Asokan,
2007) for safe utilization. Sintering influenced transformations of texture and
structure resulting significant changes in the mechanical, thermal and chemical
characteristics of the jarosite waste composite bricks. Most of the heavy metal
oxides are part of low-soluble crystalline phases or of the glassy phase yielded
at the higher temperatures and this behavior could contribute to reduce the
toxic elements leaching potentials (Montanaro et al., 2001). The sintering
efficiency is depends on the presence of contaminates such as SiO
2
, PbO, CaO
and alkaline oxides, contributes for the formation of a transitory liquid phase
which help the densification of the main crystalline phases, hematite,
magnetite and zinc ferrite.
3.3. Modeling and Statistical Analysis
Mix design and optimization of s/s sintered jarosite waste composites
bricks characteristics was performed to illustrate the potentials of jarosite
waste as a raw material in making building construction element. The
Response Surface Methodology model was employed to optimize the process
for maximizing products quality using classic mixture approach. To verify, the
model was fit to data using analysis of variance (ANOVA) and least squares
techniques, validated and interpreted graphically using contour plot, trace plots
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