A marked increase in Ra adsorption was observed with increasing
Tolvaptan (Fig. 6a). pH-dependent sorption trends followed the sigmoid curve typical of cation sorption (e.g., Dzombak and Morel, 1990). The extent of Ra sorption varied among different substrates (Fig. 6b), as did the sorption edge pH (the pH at which sorption change is greatest; Fig. 6a). Ra distribution coefficients were highest for Mn-oxide fiber (102–103 L kg− 1, for pH range 2–10), and lowest for the clean, silicate Acros sand (10− 2–100 L kg− 1). GP sand had higher Ra sorption when coated with natural Fe-oxides (0.2–9 L kg− 1; Fig. 6; #8, Table 2) than when not visibly coated (0.2–2 L kg− 1; Fig. 6; #3, Table 2). Variation in sorption edge
pH generally matched the differences in measured ZPC. Sorption edges for Mn-fiber, Fe-coated GP sand, GP sand, and Acros sand were at pH 9.8, respectively. The ZPC varied similarly, although not for the Mn-fiber sample: 7.11, 5.71, 7.65, and > 9, respectively.
