Lessons Learned While Injecting More Than One Hundred Tons of Potassium Persulfate
Persulfate has long been known to present very strong oxidation potential as well as versatility in treating a wide range of contaminants. For soil and groundwater remediation, it has become commercially available only in the last five years as potassium persulfate (KPS), the chemical properties of which require different injection methods compared to its more widely applied sibling, sodium persulfate. Solid KPS, as well as various activators, can be placed in the subsurface to act as a long-term source of oxidant that distributes in situ by both diffusive and advective processes.
Hydraulic fracturing with potassium permanganate (KMnO4), another persistent oxidizer, has been conducted since the mid-1990s, and many of the established paradigms and protocols for its safe and efficient use are employed for KPS. However, the properties of KPS and its activators require important procedural modifications to ensure that handling, mixing, and injection processes are safe for personnel and compatible with equipment.
In aggregate, approximately 118 metric tons of KPS were injected into contaminated formations at four sites. Handling KPS and its activators presents many similar challenges to handling KMnO4. Dust generation needs to be kept to a minimum. The oxidative strength deserves respect, and neutralization should occur in dilute settings. Prudent secondary containment measures are deployed. From the perspective of personnel exposure, light contact with KPS solution does not result in problematic effects, and yet uncontrolled contact can cause irritation and needs to be avoided. With respect to equipment, some formulations of KPS slurry attack carbon steel aggressively. Consequently, injection equipment must be compatible with persulfate or may corrode significantly and require replacement at some point during a project. This presentation summarizes relevant experience accumulated since 2017 injecting KPS via hydraulic fracturing.