Bonotto, Daniel Marcos [UNESP]Andrews, J. N.2014-05-272014-05-271993-01-05Chemical Geology, v. 103, n. 1-4, p. 193-206, 1993.0009-2541http://hdl.handle.net/11449/132314Experimental etch/leach of Carboniferous Limestone gravels on a laboratory time-scale has demonstrated that 234U 238U activity ratios (AR's) greater than the radiochemical equilibrium value may be generated on short time-scales. The molar U/Ca and Mg/Ca ratios show that both U and Mg are leached preferentially relative to Ca whereas the molar U/Mg ratio is only slightly greater than that of the rock matrix. The generation of enhanced AR's is attributed to a two-stage process in which the limestone surface is dissolved by zero-order etch and silicate minerals so released are subjected to first-order chemical leach of U and Mg. The implications of these results for the production of enhanced AR's in Carboniferous Limestone groundwater are discussed. It is suggested that chemical leaching or exchange of U between groundwater and its particulate load or at the aquifer fluid-solid interface is an important mechanism controlling AR changes as groundwater migrates beyond a redox boundary. AR's for dissolved U in groundwater are more probably related to chemical equilibria than to groundwater age. © 1993.193-206engActivity ratioChemical leachingEtchingGroundwaterGroundwater chemistryIsotope activity ratioKarstLeachingLimestoneLimestone aquiferUranium- 234/uranium-238Uranium-234Uranium-238Artigo10.1016/0009-2541(93)90301-XWOS:A1993KG43500015Acesso restrito2-s2.0-00274495067430102726026121