Metal Ion Sorption and Desorption on Zeolitized Tuffs from the Nevada Test Site

Abstract

Because of the hundreds of nuclear weapon tests conducted on the Nevada Test Site (NTS) during the Cold War, the migration of radionuclides and contaminants is a potential concern. The mobility of these compounds and our ability to remediate contaminated sites are controlled by sorption and desorption processes, which depend frequently on the nature of the contaminant, the mineralogy of the site, and the geochemical conditions. The sorption and desorption behavior of strontium (Sr) and lead (Pb), two metal cations with different chemistries, commonly found on nuclear test sites were studied. Strontium showed pH-independent and ionic-strength-dependent sorption, consistent with ion exchange processes at permanent charge sorption sites. The sorption uptake of Sr increased with decreasing ionic strength of background solution. Strontium desorption from the adsorbents was enhanced by increased background electrolyte concentration and was a function of background electrolyte composition. The fractional uptake of Pb was higher, compared to that of Sr, and was only pH dependent at the highest ionic strength used (1.0 M). This pH-dependent sorption behavior, consistent with formation of surface complexes at amphoteric surface hydroxyl sites or formation of surface precipitates, could explain the decreased Pb desorption, compared to that of Sr, especially at increased background electrolyte concentrations. Under conditions typical for the groundwater at the NTS (I = 0.003 M, pH = 8.0), both Pb and Sr are expected to bind strongly on tuffs with composition similar to the zeolitized tuffs used in this study. Any increase in the dissolved ion concentration of the groundwater, however, may result in, at least partial, release of Sr and enhanced Sr mobility.

Kinetic and thermodynamic investigations of strontium ions retention by natural kaolinite and clinoptilolite minerals

“…The values are much below those corresponding to inner sphere complex formation (chemical complexation). This is in line with the [11].…”

“…The sorption uptake of Sr was observed to increase with decreasing ionic strength of background solution and desorption of this ion from a sample of zeolitic tuffs, containing clinoptilolite, was reported to be enhanced by increased background electrolyte concentration [11]. The same study reported that the fixation of Sr 2+ by clinoptilolite occurs via ion-exchange in addition to outer sphere complex formation, with the latter being pH dependent.…”

“…Strong sorption abilities of clinoptilolite fractions toward Sr 2+ were documented in a number of studies [11][12][13]. The sorption uptake of Sr was observed to increase with decreasing ionic strength of background solution and desorption of this ion from a sample of zeolitic tuffs, containing clinoptilolite, was reported to be enhanced by increased background electrolyte concentration [11].…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15]. Although these studies have provided valuable information about various macroscopic and microscopic aspects of the fixation behavior of this ion, only a limited area was devoted to reveal the kinetic and thermodynamic characteristics of the sorption process.…”

Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media

“…Um and Papelis [160] studied column experiments to investigate the effect of natural colloids on the transport of a strongly sorbing metal, lead (Pb 2+ ) under different geochemical conditions. Here, natural colloids were generated from zeolitized tuffs from the Nevada Test site (NTS).…”