Experimental characterization of CVOC removal from fractured clay during boiling

A series of experiments was conducted to evaluate the mass transport of a chlorinated volatile organic compound (CVOC) at boiling temperatures in low permeability clays where 20-100% of the pore water was removed. A kaolin clay matrix saturated with water containing 1,2-dichloroethane (DCA) and bromide (Br-) was packed into two columnar cells, a rigid-wall and a flexible-wall tube, which created different external boundary conditions. Both cells were heated to boiling temperatures and the recovered outflow was condensed and analyzed for DCA and bromide, and the clay remaining in the cell was cooled and analyzed for water and DCA content. Clay in the vertically oriented rigid-wall cell was heated to 130 degrees C with a power density of similar to 80 kW/m(3) and then depressurized at its upper end. DCA was nearly completely removed in approximately 15 min after 0.3 of pore volume water was recovered. The recovered condensate was enriched to more than 10 times the DCA concentration of the pore water. The flexible-wall cells were heated to 110 degrees C with a lower power density of similar to 44 kW/m(3). These tests resulted in slower recovery rates, and condensate concentrations that were approximately twice the pore concentration of DCA. The concentration of DCA in the clay was reduced by two orders of magnitude after approximately 0.5 of the pore volume was removed. Boiling was inferred to occur within the clay matrix because (a) DCA concentrations were enriched; (b) pressure and temperature conditions in the clay intersected the saturated vapor pressure curve; (c) Br- was absent from all but the initial outflow; (d) change in DCA and water content was roughly uniformly distributed over the length of the cell. Fractures appeared to have formed during heating, increasing the permeability, dropping the internal pressure and enabling stripping of DCA during boiling. (C) 2013 Elsevier Ltd. All rights reserved.