EFFECT OF PH VARIATIONS ON SORPTION OF 226RA AND OTHER TRACE ELEMENTS IN RUSH CREEK, PERRY COUNTY, OHIO

The discharge of effluent from abandoned open-pit coal mines near the town of New Lexington causes the pH of water in Rush Creek to decrease from 6.1 to 2.5 in less than one kilometer.  Coincident with the entry of acid mine water, the concentrations of major as well as trace elements initially rise and subsequently decrease as the pH gradually rises to 7.4 at the mouth of Rush Creek 50 km downstream.  The pH increase causes first Fe and later Al as well as Mn to precipitate as oxyhydroxides.  These and other suspended solids sorb ²²⁶Ra, REEs, as well as Zn, Cu, Ni, Co, Pb, and others, thereby removing them from solution.  The decay rates of ²²⁶Ra in the ferric oxyhydroxide precipitates range from 400 to 1815 dpm/kg equivalent to concentrations between 183 x 10^-12 g/kg and 826 x 10^-12 g/kg of ²²⁶Ra.  Experimental neutralization of contaminated water indicates that close to 100% of ²²⁶Ra is sorbed at pH>8.0, whereas less than 10% is sorbed at pH<6.0.  The precipitates also contain up to 460 ppm Zn, 14.7 ppm Cu, 12.3 ppm Ni, 10.8 ppm Co, 7.47 ppm Pb presumably derived from the Middle Pennsylvanian Kittanning coal and associated carbonaceous shale.