Page 221 - Materials Chemistry, Second Edition

204 Practical Design Calculations for Groundwater and Soil Remediation

Example 5.28: Determine the Stoichiometric Amount of Oxidant
The soil at a site is impacted by perchloroethylene (PCE). The soil on top of
the capillary fringe contains 5,000 mg/kg of PCE. In situ chemical oxida-
tion is considered as one of the remedial alternatives. Determine the stoi-
chiometric amount of potassium permanganate that needs to be delivered
to the impacted zone. What would be the amount if sodium persulfate is
used?

Solution:
(a) MW of PCE (C Cl ) = (12)(2) + (35.5)(4) = 166
2
4
MW of potassium permanganate (KMnO ) = (39)(1) + (55)(1) + (16)
4
(4) = 158
Concentration of PCE = 5,000 mg/kg = 5.0 g/kg soil
= (5.0 g ÷ 166 g/mole)/kg soil = 3.01 × 10 mole PCE/kg soil
−2
As shown in Equation (5.42), the stoichiometric requirement to
oxidize PCE is 4/3 mole permanganate per mole of PCE.
Stoichiometric amount of KMnO 4
= (4 moles of KMnO /3 moles of PCE) × (3.01 × 10 mole PCE/
−2
4
kg soil)
= 4.02 × 10 mole KMnO /kg soil
−2
4
= (4.02 × 10 mole × 158 g/mole KMnO )/kg soil
−2
4
= 6.35 g KMnO /kg soil
4
(b) MW of sodium persulfate (Na S O ) = (23)(2) + (32)(2) + (16)(8) = 238
8
2 2
As shown in Table 5.3 and as discussed previously, the stoichio-
metric requirement of sodium persulfate will be 1.5 times
that of potassium permanganate.
Stoichiometric amount of Na S O 8
2 2
= (3 moles of Na S O /2 moles of KMnO ) × (4.02 × 10 mole
−2
2 2
8
4
KMnO /kg soil)
4
= (6.02 ×10 mole Na S O /kg soil)
−2
8
2 2
= (6.02 ×10 mole × 238 g/mole Na S O /kg soil)
−2
2 2
8
= 14.3 g Na S O /kg soil
2 2
8
Example 5.29: Determine the Stoichiometric Amount of Oxidant
The soil at a site is impacted by xylene. The soil on top of the capillary fringe
contains 5,000 mg/kg of xylenes. In situ chemical oxidation is considered
as one of the remedial alternatives. Determine the stoichiometric amount of
oxidant that needs to be delivered to the impacted zone.