Is Magnesium Oxide used in the soil and groundwater remediation?

Yes, it is.

Magnesium oxide is used extensively in the soil and groundwaterremediation, wastewater treatment, drinking water treatment, air emissionstreatment, and waste treatment industries for its acid buffering capacity andrelated effectiveness in stabilizing dissolved heavy metal species.

Many heavy metals species, such as lead and cadmium are mostsoluble in water at acidic pH (below 6) as well as high pH (above 11).Solubility of metals affects bioavailability of the species and mobility soiland groundwater systems. Most metal species are toxic to humans at certainconcentrations, therefore it is imperative to minimize metal bioavailabilityand mobility.