TY - JOUR
T1 - Sorption of Yttrium and Rare Earth Elements by Amorphous Ferric Hydroxide: Influence of Temperature
AU - Quinn, Kelly A.
AU - Byrne, Robert H.
AU - Schijf, Johan
PY - 2007/1/1
Y1 - 2007/1/1
N2 - The sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide was investigated between 10 and 40 °C over a range of pH (4.7−7.1) in the absence of solution complexation. Distribution coefficients, defined as i K Fe = [MS i ] T /([M] T [Fe 3+ ] S ), where [MS i ] T is the concentration of sorbed YREEs, [M] T is the total dissolved YREE concentration, and [Fe 3+ ] S is the concentration of precipitated iron, increased with increasing temperature over the entire investigated pH range. The observed increase in i K Fe was largest for the heavy REEs, indicating that relative log i K Fe values (i.e., YREE patterns) vary somewhat with temperature. The pH dependence of YREE sorption was described by a surface complexation model of the form i K Fe = ( S β 1 [H + ] -1 + S β 2 [H + ] - 2 )/( S K 1 [H + ] + 1), where S β n are stability constants for sorption of free YREE ions (M 3+ ) and S K 1 is a surface protonation constant for amorphous ferric hydroxide. The influence of temperature on the YREE surface stability constants ( S β 1 and S β 2 ) was characterized by calculating molar enthalpies for M 3+ sorption (Δ H 1 0 and Δ H 2 0 ) using the van 't Hoff equation. The Δ H 1 0 values appropriate to S β 1 range from 11.8 to 13.4 kcal/mol, whereas the Δ H 2 0 values appropriate to S β 2 range between 7.7 and 12.3 kcal/mol. These values are on the same order of magnitude as enthalpies of the first hydrolysis step for a variety of cations.
AB - The sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide was investigated between 10 and 40 °C over a range of pH (4.7−7.1) in the absence of solution complexation. Distribution coefficients, defined as i K Fe = [MS i ] T /([M] T [Fe 3+ ] S ), where [MS i ] T is the concentration of sorbed YREEs, [M] T is the total dissolved YREE concentration, and [Fe 3+ ] S is the concentration of precipitated iron, increased with increasing temperature over the entire investigated pH range. The observed increase in i K Fe was largest for the heavy REEs, indicating that relative log i K Fe values (i.e., YREE patterns) vary somewhat with temperature. The pH dependence of YREE sorption was described by a surface complexation model of the form i K Fe = ( S β 1 [H + ] -1 + S β 2 [H + ] - 2 )/( S K 1 [H + ] + 1), where S β n are stability constants for sorption of free YREE ions (M 3+ ) and S K 1 is a surface protonation constant for amorphous ferric hydroxide. The influence of temperature on the YREE surface stability constants ( S β 1 and S β 2 ) was characterized by calculating molar enthalpies for M 3+ sorption (Δ H 1 0 and Δ H 2 0 ) using the van 't Hoff equation. The Δ H 1 0 values appropriate to S β 1 range from 11.8 to 13.4 kcal/mol, whereas the Δ H 2 0 values appropriate to S β 2 range between 7.7 and 12.3 kcal/mol. These values are on the same order of magnitude as enthalpies of the first hydrolysis step for a variety of cations.
UR - https://digitalcommons.usf.edu/msc_facpub/1637
UR - https://doi.org/https://doi.org/10.1021/es0618191
U2 - 10.1021/es0618191
DO - 10.1021/es0618191
M3 - Article
C2 - 17310719
VL - 41
JO - Environmental Science Technology
JF - Environmental Science Technology
ER -