Environmental Engineering Reference
In-Depth Information
A
BSTRACT
Jarosite waste arising worldwide from the zinc industry is hazardous
in nature due to the presence of toxic elements such as lead
(1.9±0.023%), zinc (8.24 ±0.075%), sulphur (12.23±0.2%), cadmium
(317±23.8ppm), chromium (178±24.7 ppm) and copper (1043±25.7 ppm)
and thus becomes a major environmental concern. Attempts were made to
recycle the hazardous jarosite waste using coal combustion residues
(CCRs) as an additive. Optimization of solidified sintered jarosite waste
composite characteristics was performed to illustrate the potentials of
hazardous jarosite waste as a raw material in making building
construction elements like bricks/blocks. The Response Surface
Methodology (RSM) model was employed to optimize the process for
maximizing product quality using classic mixture approach, analysis of
variance (ANOVA) and least squares techniques. Further, validation and
interpretation of the results was done graphically using contour plots,
trace plots and 3D graphs followed by numerical optimization using
desirability functions. The results revealed from the statistical analysis of
the resulting compressive strength, water absorption, shrinkage, density,
leachate concentration of Pb, Cd and other toxic elements in the jarosite
waste composite bricks were found to have laudable agreement with
actual performance. Moreover, the concentrations of toxic elements were
below the prescribed limits of United States Environmental Protection
Agency (USEPA) Toxicity Characteristics Leachate Procedure (TCLP)
standard and also the engineering properties of the composite products
met the quality standards required for use in construction applications.
Keywords:
Solid and hazardous waste; Jarosite waste; waste generation;
Characteristics; Waste disposal and recycling; CCRs; Composite brick;
Response Surface Methodology; Toxic substance; Optimization; Classic
mixture approach; Desirability functions
1.
I
NTRODUCTION
The statistical method namely Response Surface Methodology (RSM) can
be used for optimizing the experimental data to achieve the most desired
results (Myers and Montgomery, 1995). Mix design and optimization of
solidified /stabilized sintered jarosite waste composite product's characteristics
was performed to illustrate the potentials of jarosite waste as a raw material in
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