HCIO4

N aO H and HCIO4 w ere u sed to ad ju s t pH va lues o f sam p le so lu tio n s , and N aC 1 0 4 w as u sed to ad ju s t the ion ic s tren g th o f sam p les and s tan d a rd so lu tio n s. I n s t r u m e n t s a n d M e a s u r e m e n ts

T h e ac tiv ity o f free u n c o m p le x e d C d 2+ ion w as m easu red u s in g an O rion C d 2+ ion se lec tiv e e lec tro d e . T h is e lec tro d e w as ca lib ra ted u s in g 1 O'2-10 "6 M C d (C 1 0 4)2 so lu tio n s in 0 .0 0 5 M N aC 1 0 4. A n O rion p H m e te r e q u ip p e d w ith a g lass e lec tro d e w as u sed to m easu re pH values. T he co n cen tra tio n o f P A A in sam p les w as d e te rm in ed by m easu rin g the to ta l carb o n (T C ) o f each sam p le u sin g a S h im ad zu T O C -5 0 0 0 an a ly z e r and w as e x p re ssed in m g C /L . T h e to tal C d (II) co n c e n tra tio n s in so lu tio n w ere m easu red u sin g a P erk in E lm e r M odel 5 1 0 0 Z L flam e a to m ic ab so rp tio n sp ec tro p h o to m e te r (A A S ). A d so rb ed C d w as ca lc u la ted as th e to ta l C d (II) co n cen tra tio n m in u s the to tal C d rem ain in g in so lu tio n a fte r eq u ilib ra tio n w ith A I2O 3. T h e P A A -C d co m p lex w as c a lc u la ted as th e d iffe ren ce b e tw een th e to ta l C d an a ly z ed w ith , th e A A S m in u s the free cad m iu m (C d 2+-e lec tro d e an a ly zed ). E x p e r im e n ta l m e th o d s

A d so rp tio n e x p e rim en ts w ere run fo r b in a ry sy s tem s C d (II)-A İ203 an d P A A - A I2O 3, an d fo r th e te rn a ry sy s tem C d (II)-A l20 3 -P A A . T e rn a ry sy s tem s in v o lv in g all th ree c o m p o n en ts w ere s tu d ied u sin g seria l c o m p o n e n t ad d itio n seq u en ce to fac ilita te co m p ariso n b e tw een m etal a d so rp tio n an d fo rm a tio n o f th e C d -P A A co m p lex . T w o ty p es o f ad so rp tio n w ere p e rfo rm e d in the a d so rp tio n e x p e rim e n ts fo r th e te rn a ry sy s tem s; one seq u en tia l ad so rp tio n (P A A firs t ad so rb ed on A I2O 3) an d one s im u ltan eo u s ad so rp tio n (C d (II) an d P A A ad so rb ed to g e th e r on A I2O 3). A d so rp tio n ex p e rim en ts w ere p e rfo rm e d in 14 m L p o ly s ty re n e tu b es . In th e b in a ry sy s tem s sam p les c o n ta in in g 10 '5 M C d(II) an d 2 g /L A I2O 3 (in sy s tem C d ^ I j -A h C b ) and , re sp ec tiv e ly , 60 m g C /L and 2 g /L A I2O 3 (in sy s tem P A A -A I2O 3) w ere eq u ilib ra ted o v e rn ig h t b e in g shaken on a h o rizo n ta l ro tam ete r. A fte r eq u ilib ra tio n tim e w as reach ed , sam p les w ere c e n tr ifu g e d a t 1800 rp m fo r 25 m in u tes w ith a B eck m an G P R C en trifu g e . 5 m L o f each sam p le w as filte red u s in g a 60 m L m ed ica l sy rin g e , a 0 .2 μηη m em b ran e filte r, an d a 25 m m easy p re ssu re sy rin g e filte r h o ld e r fro m G elm an S c ien ce s , in w h ich th e firs t 1 m L o f the filtra te w as d isca rd ed as w aste . T h e filte red su p e rn a tan t w as an a ly z ed fo r C d (II) u s in g A A S and fo r P A A u sin g T O C an a ly zer. In th e seq u en tia l a d so rp tio n , sam p les c o n ta in in g 60 m g C /L P A A and 5 x 1 0 '3 M N a C 1 0 4 a t a sp ec ific pH v a lu e w ere e q u ilib ra ted w ith 2 g /L A I2O 3 p rio r th e a d d itio n o f 10' M C d(II). B e fo re C d (II) w as sp ik ed in to th e P A A - A I2O 3, 5 m L w ere rem o v ed fo r T O C an a ly s is to e s tab lish th e a m o u n t o f P A A rem a in in g in so lu tio n in the b in a ry sy s tem . A fte r tha t, th e sam p les w ere e q u ilib ra te d ag a in o v ern ig h t, fo llo w ed by c en tr ifu g a tio n fo r so lid /liq u id sep ara tio n . T h e frac tio n o f ad so rb a te C d (II) an d P A A rem a in in g in so lu tio n w as d e te rm in ed as ab o v e , by a n a ly z in g an a liq u o t o f th e filte red su p e rn a ta n t u sin g A A S an d T O C an a ly s is .