Bridging the gap between macroscopic and spectroscopic studies of metal ion sorption at the oxide/water interface: Sr(II), Co(II), and Pb(II) sorption to quartz.

Metal sorption mechanisms were investigated for strontium, cobalt, and lead using sodium chloride, sodium nitrate, and sodium perchlorate as background electrolytes and quartz as the adsorbent. Spectroscopic analyses of concentrated sorption samples were evaluated for their ability to provide insight into the controlling sorption process for more dilute systems. For strontium, outer-sphere complexes identified using X-ray absorption spectroscopy (XAS) of concentrated samples were consistent with macroscopic sorption data collected in more dilute systems. XAS results indicated that cobalt formed a new solid phase upon sorption to silica. Macroscopic studies of cobalt sorption supported the spectroscopic data for total cobalt concentrations of 10(-5) M, regardless of the background electrolyte composition or concentration. At a lower total cobalt concentration (10(-7) M), adsorption appeared to be the prevailing mechanism of cobalt removal. Spectroscopic results suggested that lead adsorbed as an inner-sphere complex on silica. The decrease of lead removal with increasing chloride concentration was attributed to competition with aqueous lead-chloride complexes, based on thermodynamic calculations.