Interface precipitation affects the resistance to transport in layered jarosite fly ash

We have studied the effect of interface precipitation on the transport properties under fluid flow condition in a layered jarosite/fly ash system as part of an ongoing case study in geochemical engineering dealing with isolation and immobilization of chemically contrasting wastes. The experiment was carried out to determine the development of hydraulic conductivity in such system. However rather than hydraulic conductivity, we used resistance as the characteristic parameter. Our experimental results show that the overall resistance to transport increases by about two orders of magnitude due to the formation of a self-forming layer at the interface between jarosite and fly ash. Our modelling results suggest that this increase in resistance causes a delay in breakthrough of an inert constituent by more than sixty times. We explore also the advantage of using the theory of electrical conductivity to describe fluid transport in a layered porous medium. Additionally, our results enable a proper assessment of the efficiency of self-sealing/healing isolation. (C) 1998 Elsevier Science B.V. All rights reserved.