Table 5. Response surface methodology (RSM) equations for residual chromium concentration, with model fit metrics for different stabilizing reagentsa.
| Stabilization reagent | Equation for residual chromium concentration (mg L−1) | R 2 | R 2 adjusted | p-Value |
|---|---|---|---|---|
| FeSO4 | 1.00000 − 2.01875 × D − 0.02875 × F − 0.01750 × L + 1.53875 × D2 + 0.00375 × F2 + 0.00125 × L2 + 0.01750 × D × F + 0.01500 × D × L | 100% | 100% | <0.0001 |
| Na2S | 13.3500 − 20.9825 × D − 0.3900 × F − 0.3350 × L + 8.2800 × D2 + 0.0300 × F2 + 0.0250 × L2 + 0.1700 × D × F + 0.2150 × D × L − 0.0300 × F × L | 100% | 100% | <0.0001 |
| Na2SO3 | 3.0200 − 7.8788 × D − 0.1488 × F − 0.0875 × L + 5.3388 × D2 + 0.0687 × F2 + 0.0362 × L2 + 0.0725 × D × F + 0.0300 × D × L + 0.0700 × F × L | 100% | 99.99% | <0.0001 |
| Na2S2O5 | 0.3700 − 2.8971 × D − 0.1666 × F − 0.0563 × L + 2.5904 × D2 − 0.0121 × F2 + 0.0221 × L2 + 0.1867 × D × F + 0.0475 × D × L − 0.0050 × F × L | 99.98% | 99.95% | <0.0001 |
| Na2S2O3 | 0.35000 − 0.36250 × D − 0.04750 × F − 0.02750 × L + 0.17375 × D2 + 0.00375 × F2 − 0.00625 × L2 + 0.01250 × D × F + 0.00250 × D × L + 0.00750 × F × L | 99.93% | 99.81% | <0.0001 |
a
D – dosage of reagent; F – fly ash; L – lime.