Abstract
An experimental study using both laboratory permeability testing apparatus and permeating soft groundwater contaminated by sexivalent chromium (Cr6+groundwater) was carried out to develop a measure on groundwater pollution prevention (caused by Cr6+compound leached from chromium containing wastes such as scoriae dumped out from smelting works in the past), by providing cut-off barriers which were made from a mixture of blast furnace slag cement and a sodium type bentonite (CB) cut-off barrier.
From the laboratory tests, it was necessary to maintain the permeability coefficient of 2×10-9m/s or less, as soon as possible after the barrier provision.
Through Test I, in which MgCl2270 mg/l and some amounts of Ca (OH) 2for pH adjustment were added to the permeating Cr6+groundwater, it was found that adjusting the pH within a range of 9.0 to 9.5 was an appropriate approach. Through Test II, in which MgCl2270 mg/l and some amounts of either Poly-aluminum chloride (PAC) or Al2 (SO4) 3were 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 T-Cr containing leachate. It was confirmed from Test III that the minimum requirement of PAC was 30 mg/l approximately as Al2O3.
No ettringite existed in CB test pieces which had had PAC added, while much ettringite was found in inlet and outlet sides of the test piece which had had Al2 (SO4) 3added. The ettringite generated in the test piece did not exert a favorable influence upon the reduction of permeability coefficient.
