DESIGN AND OPTIMIZATION FOR HAZARDOUS JAROSITE WASTE RECYCLING IN ENVIRONMENTALLY SUITABLE COMPOSITE PRODUCTS USING RESPONSE SURFACE METHODOLOGY - Management of Hazardous Residues Containing Cd - page 92

(i) Compressive strength  35 kg/cm 2
(ii) Water absorption  20%
(iii)Shrinkage  15% and
(iv) Brick density below 1.75 g/cm 3
(v) Leachate concentration of Cd from the TCLP extracts < 1 ppm
(vi) Leachate concentration of Pb from the TCLP extracts < 5 ppm

For compressive strength, a range of 8.15 to 115 kg/cm 2 was specified, but
35 kg/cm 2 was selected as the desirable value (the targeted value). Therefore, a
desirability of 1 is given to the target value of 35, with a linear decrease in
desirability to a value of zero at the lower and upper specification limits.
Similarly, for brick density the desirability can be written as;

d i = 0 if response < low value
d i = 1 as response varies from low to high
d i = 0 if response > high value

The ‗target' desirability function was also used for other responses: brick
shrinkage and water absorption. The optimal mixture is the one with a
maximum value of desirability. Based on the experimental results, the mixture
which maximizes desirability, is Jarosite waste = 362 gms, clay = 405 gms,
PCCRs = 232 gm as shown in Table 32. The overall desirability value for this
mixture is 0.973, and the predicted response values are compressive strength =
40 kg/cm 2 , water absorption = 17.99, shrinkage = 16.42 (%) and density =
1.62 gm/cm 3 . Similarly, for another set of mixture proportion, as shown in
column number 2 of Table 32, the desirability value is 0.887

Table 32. Optimum mix design to maximize the brick properties

No. Jarosite
waste
(gm)

Clay
(gm)

PCCRs
(gm)

Comp
Strength
(kg/cm 2 )

Water
Abs.
(%)

Shrinkage
(%)

Density
(gm/cm 3 )

Desirability

1 362.66 405.23 232.11 39.99 17.99 16.42 1.62 0.973

2 515.33 449.66 35.02 62.92 18.00 14.00 1.70 0.887