Sodium Persulfate is a stable, highly soluble, crystalline material, which upon activation generates the sulfate radical, a very strong oxidant, capable of oxidizing a broad range of recalcitrant compounds.
The formation of the sulfate radical is critical for the destruction of volatile organic compounds. One way to activate persulfate to the sulfate radical is by adding a catalyst such as ferrous iron (Fe+2), sodium hydroxide (NaOH), lime or hydrogen peroxide (H2O2).
S2O8-2 + Fe+2 > SO4-· + Fe+3 + SO4-2 Eo = 2.6v
2S2O8-2 + NaOH > H+ + 2SO4-· + 2SO4-2 + ½O2 + Na+
2S2O8-2 + CaO2 + 2H2O® 2SO4-· + 2SO4-2 + O2 + Ca(OH)2+ 2H+
2S2O8-2 + 4H2O2 > 2H2SO4 + 2SO4-· + 2H2O + 3O2
The sulfate radical is a strong oxidizing agent capable of destroying many recalcitrant compounds. For example, the breakdown of common organic solvents in the presence of catalyzed persulfate is as follows:
2Na2S2O8 + 4H2O + C2Cl4 > 4NaHSO4+ 4HCl + 2CO2
3Na2S2O8 + 4H2O + C2HCl3 > 6NaHSO4+ 3HCl + 2CO2
4Na2S2O8 + 4H2O + C2H2Cl2 > 8NaHSO4+ 2HCl + 2CO2
5Na2S2O8 + 4H2O + C2H3Cl > 10NaHSO4+ HCl + 2CO2
15Na2S2O8 + 12H2O + C6H6 > 30NaHSO4 + 6CO2
16Na2S2O8 + 14H2O + C6H5CH3 ® 32NaHSO4 + 7CO2 +2H2
Ethylbenzene and Xylene
19Na2S2O8 + 16H2O + C6H4(CH3)2 > 38NaHSO4 + 8CO2 + 2H2
At some sites, sufficient iron will exist in the soils thus eliminating the need for the iron catalyst. In other cases, soluble forms of ferrous iron need to be added to activate the sulfate radical. Chelated iron (Fe-EDTA) can be added as a soluble iron source. Additional activators that can be utilized are peroxides, alkaline (high pH), and high temperature activation.The byproduct of persulfate reaction with target species is sodium monosulfate that subsequently breaks down into sulfate ions.