Laboratory study on dispersion prevention of dissolved sexivalent chromium in groundwater by cement-bentonite cut-off barriers

Abstract

Laboratory permeability tests with soft groundwater contaminated by Cr6+ were carried out to develop measures to prevent dispersion of Cr6+ concentrate into a large amount of groundwater by providing cut-off barriers made from a mixture of blast furnace slag cement and sodium type bentonite. From these tests, it was necessary to maintain the permeability coefficient of 3×10−9 m/sec. or lower as soon as possible after the barrier provision. Through a test in which MgCl2 of 270 mg/L and some amounts of Ca(OH)2 for pH adjustment were added to the permeating Cr6+ groundwater, it was found that for the pH to be adjusted within a range of 9.0 to 9.5 was an appropriate approach. Through the other test in which MgCl2 of 270 mg/L and some amounts of either poly-aluminium chloride(PAC) or Al2(SO4)3 were added to the permeating Cr6+ groundwater, it was also found that the addition of PAC brings a good result due to the reduction of permeability and no breakthrough of Cr6+ containing leachate. It was confirmed that the minimum requirement of pAC was 30 mg/L as Al2O3.