Upcycling of FGD Gypsum into a Product to Reduce Interrill Erosion: A Study Assessing Methods of Soil Surface Application

Soil conditioners have shown benefits in the reduction of soil erosion. A concomitant application of gypsum and polyacrylamide promotes aggregate stability and reduces the amount of runoff discharge and soil losses. Synthetic gypsum produced from flue gas desulfurization (FGD) at coalfired power plants has the potential to serve as a more sustainable source for the agricultural application of this soil conditioner. Upcycling of FGD gypsum into a pellet of a mixture of ground FGD gypsum and polyacrylamide (PAM) was compared to other types of soil surface application methods. Results confirm that surface application of PAM and FGD gypsum reduced soil erosion. Depending on the type of application method, addition of PAM and FGD gypsum presented different effects on the local hydrological processes and microtopography. Though PAM in solution acts as a physical net on the soil surface, the amount of water needed for its application makes it impractical for agricultural fields. Granular application of PAM and FGD gypsum, as well as pellets (upcycled product) has been shown to have a delayed effect in reducing soil erosion, as these methods required PAM particles to be activated. The upcycled product of FGD gypsum and PAM in the form of pellets demonstrates that the sudden expansion of the pellets due to PAM hydration results in the rapid release of the gypsum grains, providing a better treatment on the soil surface. Moreover, the increased surface area of PAM and gypsum due to the grinding is advantageous for a more rapid activation of the soil conditioners. The upcycled product of FGD gypsum and PAM is a practical application method that could be adapted by farmers to be used at field scale.