- Email: [email protected]
Adsorption of copper, lead and cobalt by activated carbon
Water Res. Vol. 18. No. 8. pp. 927-933. 1984 Printed in Great Britain. All fights reserved
00-13-135484 S300 + 0.00 Copyright ~') 1984 Pergamon Press Ltd
ADSORPTION OF COPPER, LEAD AND COBALT BY ACTIVATED CARBON A. NETZERt and D. E. HUGHES" tEnvironmental Sciences,The University of Texas at Dallas, Richardson, TX 75080 and '- Western Electric Company, Mesquite, TX 75149, U.S.A. (Received March 1982)
Abstract--The phenomena of lead, copper and cobalt adsorption by activated carbon from aqueous solution was studied in detail. Laboratory studies were conducted to evaluate and optimize the various process variables (i.e. carbon type, solution pH, equilibrium time and carbon dose). A quantitative determination of the adsorptive capacity of activated carbon to remove these metals was also determined. Significant differences were found in the ability of different types of activated carbons to adsorb lead, copper and cobalt from aqueous solution. Solution pH was found to be the most important parameter affecting the adsorption. It was found that there was practically no adsorption of lead, copper and cobalt by activated carbon below a well defined solution pH value for each metal. This critical solution pH value was found to be lower than the pH value associated with the formation of hydrolysis products. Of the ten commercially available activated carbons evaluated in these experiments, Barney Cheney NL 1266 was found to adsorb the largest percentage of lead, copper and cobalt. The adsorption of any single metal (lead, copper and cobalt) was hindered by the presence of the other metals; the metals apparently competed for adsorption sites. Key words---copper, lead, cobalt, aqueous solution, removal, activated adsorption
INTRODUCTION The concept of adsorption of metals by activated carbon was first demonstrated in 1929 (Watanabe and Ogawa, 1929). Up until approximately 1970 the use of activated carbon for metal removal was confined to improving the efficiency of metallurgical recovery. In 1970 the United States became alarmed about the widespread contamination of surface waters by mercury. Mercury cell chlorine/caustic plants were found to be discharging large quantities of mercury into streams used for potable water sources. Filters were subsequently developed that were effective in removing mercury form caustic solutions. One component of these filters was activated carbon (Smith et al., 1971). This was reported to be the first use of carbon for the sole purpose of trace metal removal from water (Smith, 1973). In 1971 Sigworth and Smith reported on the correlation of solution pH and the adsorption of inorganics by activated carbon. They reported that metal adsorption is inversely proportional to metal solubility in aqueous solutions--"better adsorption can be expected when conditions render the compound less soluble" (Sigworth and Smith, 1971). Most metals become less soluble and form hydroxides and oxides as the solution pH is increased. In 1975 and 1977 the results of extensive pilot plant studies conducted by the Environmental Protection Agency on metal removal by physical and chemical W.R. 18/~-A
927
treatment were issued. The effectiveness of the unit process of coagulation, sedimentation, filtration and carbon adsorption to remove 23 common and uncommon trace metals from wastewater was evaluated. The overall process was found to be very efficient in removing most of the trace metals. Activated carbon increased the efficiency of metal removal by as much as 80% for certain metals (Maruyama et al., 1975; Hannah et al., 1977). The object of this research was to conduct a study of the phenomenon of metal adsorption by activated carbon from aqueous solution. Lead, copper and cobalt were chosen to be studied in detail. The parameters affecting adsorption (i.e. carbon type, solution pH, equilibrium time and carbon dose) were optimized and the possible mechanisms involved were probed. EXPERIMENTAL Metal solutions Aqueous solutions with 10 mg I- ~concentrations of lead, copper and cobalt were prepared. The solution pH was adjusted with reagent grade nitric acid or sodium hydroxide. The solution was then filtered through Whatman No. t filter paper. A control sample was taken at this point to determine the exact metal concentration before contact with activated carbon. Exactly 100 ml of the sample solutions were placed into the 125 ml glass bottles containing previously weighed samples of activated carbon. The bottles were then capped with Teflon-lined screw caps and shaken for specific periods of time. After agitation the samples were filtered through Whatman No. 1 filter paper and the final metal concentrations
928
A. NETZER and D. E HUGHES
were determined. So[utions containing identical metal concentrations but `*ithout any carbon were tested simultaneously to determine if metal was removed by filtration or some other mechanism except contact with activated carbon. .4ctitated carbon selection Samples of ten activated carbons were obtained from Barney Cheney, Calgon. ICI America. West,,aco and Witco (Table 1). The carbons were evaluated for their specific ability to adsorb the individual metals from aqueous solutions. These experiments were conducted at the original pH of the solutions. The activated carbon with the greatest metal adsorption was selected and utilized for the remaining tests.
_-~ -= - - -
-.5 -~ ,.z
2
.>>
,7,-!
---
-~
'~E?_.
E:
Optimum pH determination Solutions containing 10rag l ~ lead. copper or cobalt were adjusted to various integral pH values ranging from 2 to 10. The ability of the previously selected activated carbon to adsorb the metals as a function of solution pH was then determined. The lowest solution pH for maximum metal adsorption was then selected and utilized for the remaining tests. Minimum contact time determ#u~tion Solutions at the optimum pH containing lead, copper or cobalt and constant doses of the previously selected carbon were agitated on a wrist shaker. Various periods of agitation were employed to determine the minimum contact time required for complete or maximum metal adsorption. A second series of tests with all three metals in the sarne solution and with varying doses of the previously selected activated carbon were also conducted to determine the minimum contact time. The minimum contact time ,*as determined and utilized in the remaining tests.
,~°_ _c~.
`5 .~=
z Y.
..z
~-1 {
=
:=
e --
g
-q,,,
=
Metal adsorption studies The remaining tests to study the metal adsorptive properties of the selected carbon were conducted at the optimum solution pH and minimum contact time determined in the preliminary tests. Solutions containing one, two or all three metals at concentrations of 10mgl -~ with varying carbon doses were evaluated.
~a
RESULTS
The results o f the tests to evaluate the ability o f the ten carbons to adsorb lead, copper and cobalt from aqueous solutions are s h o w n by Figs t, 2 and 3, C a r b o n No. 1 (Barney Cheney N L 1266) was determined to be superior; it is a h a r d w o o d - b a s e d granular carbon. The results o f the experiments performed to determine the o p t i m u m pH for metal a d s o r p t i o n are summarized in Figs 4, 5 and 6. A pH of 4 was determined to be the lowest pH for m a x i m u m adsorption and was utilized for the remaining tests. Figures 7, 8 and 9 illustrate the initial tests performed to determine the m i n i m u m contact time. Due to the variation in contact time required for cobalt vs that required for lead and copper, additional tests were performed with all metals in the same solution and with varying carbon doses. The results o f these tests are s h o w n in Figs 10, 11 and 12. The m i n i m u m contact time required for complete a d s o r p t i o n was determent to be 120 rain.
2
.-:,a
~Z
~r ~a =g_,..= ,~ .~ ~a E a=.a . _
=-
*
= g =
i
,Adsorption of copper, lead and cobalt b? activated carbon
,00
.'OFgF 96
92
90
I CARBON A3DED : 0 2 ~ Z SOLUT,ON VOLUME :,OOml 3 INITIALLE~,3 CONCENTR~,TIOr'~ = 9 6 mg/i ( 4 7 x tO'Sin) 4 CONT~.CTT, 'AE : 2 HOURS B{
96 9.0
I.C~RBON ADDE0 : 05g 2 SOLUTION VOLUME= 100rnl 31NITIAL LEAD CONCENTRATION=IOrnq/I
SC
> 7C 0
929
;8F
o f t e r pH
7
6.9
87
•
0 ~o
°ddit,on
4B
_J ~- 40 r~
21
20
15
i
ii
0 ~4 #5
~2 #3
ltl
~0
~6
iI
i2
7
n ~7
08
#9
i,O --~i f
:
~10
,
3
ACTIVATED CARBONS
I n0n'10
04
,
,
,
,
o o , _ o
DO
8'~"s'~',o"
5
SOLUTION
Fig. I. Activated charcoal comparison {'or lead removal at pH 2.7 and contact time of 2 h.
o,,
0.8
..,
pH
Fig. 4. Lead concentration after (1)pH adjustment and (2) carbon adsorption vs solution pH.
IO0
~3
I. CARBON ADDED = 0 . 5 ( ] 2. SOLUTION VOLUME • IOOml 3. INITIAL COPPER CONCENTRATION = IOmq/I
90
j 80 > O 70 :E
71 66
ILl rr 60
60
57 I-
== 5o
4s
O L) 4(
.n
2c
#1
0 3 #'4 0 5 ACTIVATED
02
#`B 0 7 #`8 CARBONS
#`9
5 I-3 #`10
Figure 13 illustrates the % lead removal vs the carbon dose for solutions containing only lead; lead and cobalt; lead and copper; and lead, cobalt and copper. The amount of lead adsorbed when other metals were present was less than when only lead was in solution. The shapes of all lead curves were similar. Figure 14 indicates the °% copper removal vs the carbon dose for solutions containing only copper; copper and cobalt; copper and lead; and copper, cobalt and lead. The amount of copper adsorbed when other metals were present was slightly less than when only copper was in solution. The shapes of all copper curves were similar. Figures 15 shows the % cobalt removal vs the carbon dose for solutions containing only cobalt; cobalt and lead; cobalt and copper; and cobalt, lead
Fig. 2. Activated charcoal comparison for copper removal at pH 3.3 and contact time of 2 h.
IO.3
10.3
IOO -
9,8
I.CARBON ADDED • 1.0~ ;>.SOLUTION VOLUME = IOOml 3. INITIAL COBALT CONCENTRATION = IOmq/I
90
-J 80-
!8
>
~ 70~: 6 0 -
,°I
58
F-
i
so0 u 40z w u
~_9
30-
i,E I
u'J 20 ~_ n
~oL
! i
!
#1
I.I #2
54
44
41
oili
#`3
04
#5
#`6
#7
i:I U IF , 08
#9
~iO
ACTIVATED CARBONS
Fig. 3. Activated charcoal comparison ofcobah removal at pH 3.0 and contact time of 2 h.
9.5
I 8.3 • l •
I I •
U I It I
•
[I I
I
I CARBONADDED=O.2g 2 SOLUTIONVOLUME,lO0ml 3.tNITIALCOPPERCONCENTRATION= 10"3 mg/I ( l ' 6 x 10"Sin)
after pH
•
I
.
odio~,m,o,
Illl
IllI on'.
3
v,°i , o,oo DO
4 5 6 SOLUTION
7
8
9
I0
pH
Fig. 5. Copper concentration after (I) pH adjustment and (2) carbon adsorption vs solution pH.
930
A. NETZER a n d D. E. HLGHES
C. 3
I 0 0 100
IOO
IO0 9.2
iI E B
.z
• after p;'i iadlustmen r
U
F] ofter carbon U addition
}
I CARBON ADDED = 0.3g 2. SOLUTION VOLUME. lOOrnl 3 I N I T I A L COBALT CONCENTRATION:9 1 ~ g , ' i
{3:3 O 6 (o
Z O 4 i,,< m 3
z
? ~Z
24 L,) 2 Z
Z © u
g,
I
I 15 SOLUTION
I 30
I 60 CONTACT
pH
I 120 (rain)
1 150
,__J
Fig. 9. Cobalt concentration vs contact time with carbon at pH 4.0
C-'RBON ADDED = O 4 g 2 S0..UTION VOLUME= I 0 0 ml 3 INITIAL COBALT CONCENTRATION:IO 0 m g / I H 7xfO -5m) 4CONTACT T I M E : 2 H O U R S
Fig. 6. C o b a l t c o n c e n t r a t i o n a f t e r ( l ) p H adjustment (2) c a r b o n a d s o r p t i o n vs s o l u t i o n p H .
I , 90 T~ME
and IO l-- I.CARBON ADDED =O. O 0 2 , 0 0 ! , O O S , A N D 0 2 G 2. SOLUTION VOLUME = l O O m l 3.1NITIAL METAL CONCENTRATION: L E A D = ?.6rnq/~ COPPER: IO OrngM
-- 9
10 I
'8~-
COBALT ~ 1 1 . 4 m q / I
9i CARBON ADOED = O.O2q 2 SOLUTION VOLUME = lOOmJ
7 ~~\',. " ~ O ~
TIAL LEAD CONCENTRATION= 9 5 m g / I
E
~
"0
..........
l i "i"x
c~ uJ .J • --13--
z O
3
::-.
Z
O
0 . 0 0 2 g Carbon 0,01 g C o ~ b o n
----&,- - - 0 . 0 5 Q C o r b o n -.---.O. . . . . 0 . 2 O g C o r b o n
"Q.
rr
~
Z O L)
/ I 45
I 30
I 60 CONTACT
1 90 TIME
I t20
I, 150
(rain)
Fig. 7. Lead concentration vs contact time with carbon at pH 4.0,
o~
E
O c)
*"**'---,o
~
I CARBON AODED = 0 O5q 2 SOLUTION VOLUME = IOOml 3.1NITI AL COPPER CONCENTRATION=98mg/l
:
9
~
7
O.
1 90 TIME
~ .... 120
O 150
( rain )
.
""
.
.
.
.
.
.
.
.
.
.
--
I CARBON ADDED =O. OO2.0. O i , O 0 5 , ~ , N D 3 Z ~
~:, 2 SOLUTION VOLUME = 100 ml O 6 - '-. 3. INITIAL METAL CONCENTRATION:COPPER: l 0 0 m g / i U \\ LEAD: ?" 6 m g M ) 5 COBALT- !~ 4 m g / I 4
~h-Z w
uJ
Z 0 ~o
0 L) I 15
I 60 CONTACT
. . . . . . . . . . . . . .
Fig. 10. Lead concentration vs contact time vdth carboii (copper and cobalt also in solution) at pH 4.0.
z O
....
1 30
o......................... O
I
50
I 60 CONTACT
I 90 TIME
I
I
120
150
( rain )
Fig. 8. Copper concentration vs contact time with carbon at pH 4.0.
O ''.
O
"'%..
' • --D----&--....... 0 ...... .I 30
0
0 . 0 0 2 g Carbon
.......
. . . . . . . . . . . . . . o .............
0.O I (j C a r b o n
O . 0 5 q Car b a n U.-'Uq {.0r b0n I l 60 90 CONTACT TIME (rain)
J t20
_ _ J !50
Fig. 1 l. Copper concentration vs contact time with carbon (lead and cobalt also in solution) at pH 4 0
90
Adsorption of copper, lead and cobalt by activated carbon
'oo r II
~ll---i--------- I - -
-
-
-
-
--t: .....
/',~
90
/
",.,%,
IO
=.,.
b
• O.O02gCorbon --0O.Ol g Carbon ---&--- O . 0 5 g Carbon ..... o ....... 0 . 2 0 g Carbon
0
=
o
F i
Z lad u z 0 u
I
I
30
I,
60 CONTACT
90 TIME (rain)
I
h'i/ #,(i. L,'/-~
//.11:
, sO.OT,ON VOL~ME=,O0.,
2.INITIAL METAL CONCENTRATION: (A)g.6mg/I COPPER (B) 9.6mg/I COPPER&9.3mqlICOBALT (C) 9.3 mg/I COPPER &B.I mg/I LEAD {O) 9.9 mg/I COPPER. 11.6 rag/ICOBALT 7.7 mg/I LEAD _l I I i J5 o.i o.2 o.s o.,~ o. CARBON ADDED (g)
~J 201-" ]1/.: O_ ' l O f t { : I .~.:' I0t~..~¢ [~i o~
•
120
I
rr
1 71 <
I
'a ,or. fill
I. CARBON ADDED = 0 . 0 0 2 , 0.01, 0.05, ANDO,29 2 SOLUTION VOLUME = I 0 0 ml :3 INITIAL METAL CONCENTRATION: COBALT= I I.Amq/I LEAD, 7.6 mg/I COPPER= I0.0 mg/I
...
/ !/ :" / , , / # / .." / ~ ' / :"
l / BOp
" ,ok z 0
A
/,'/'
o ,0L I
..-
..l"
~> eo
...................
0 "~'O. .... .........0 ...............................~
o,
93l
Fig. 14, ~o Copper removal vs carbon added (with or without lead and/or cobalt in solution) at pH 4.0 and contact time of 2 h.
i50
Fig. 12. Cobalt concentration vs contact time with carbon (lead and copper also in solution) at pH 4.0.
and copper. The amount of cobalt adsorbed when other metals were present was significantly less than when only cobalt was in solution. The shapes of the four cobalt curves were dissimilar. Figure 16 compares the removal of all three metals from a single solution vs the carbon dose. The cobalt removal was depressed when the lead and copper adsorption was less than 100%.
(Barney Cheney NL 1266) was superior in every test, the remaining nine carbons demonstrated a large variation in their ability to adsorb the three metals from their aqueous solutions. Due to the large number of variables in the adsorption of metals by activated carbon and the complexity of the surface and water chemistry, no single carbon property appears to be dominant in determining its metal adsorptive characteristics from aqueous solutions.
Solution pH The experiments with solution pH as a variable
DISCUSSION
Activated carbon =oo
There was a significant difference in the ability of the ten activated carbons to adsorb lead, copper and cobalt from aqueous solutions. Although one carbon
90
/.
A) - - - 0 - - - COBALT ~ ( 8 ) - - O - - C O B A L T WITH LEAD / / (C) ---A---- COBALT WiTH COPPER ~ (D) " ' " l ' " " COBALT WITH LEAD / et COPPER o
/ /-l--
/ '~
~
>
70
3,o t7 ,, ............
/
60
/
/
,,
/
so 0
(B) i 0 - LEAD WITH COBALT {C) - - ~ - - - LEAD wiTH COPPER
= 60hi;,/I 50
LI/4'
e
(O) - - ' - I .... &LEADcoPPERWITHCOBALT
40
/~/
,.u 30
~.=2c
Z1
J/;
// //,;
x ..-..... _ / ' ........ . ~ ' : .........
<~ IPli:
,c
~' U ,o1.17i Irlll:
0 = ~--.~/'-'T 1 0.1
"°tldi..'i
I.BOLUTION VOLUME = IOOml 2.INITIAL METAL CONCENTRATION: (A) g.Omg/I LEAD (B) 8.2 mg/I LEAD I~ 9. Bmg/I COBALT (C)8.1 mq/I LEAD B 9 3 mq/ICOPPER (0) 7.Tmg/I LEAD.~II.Bmp/ICOBALT 8~ B.9 mg/I COPPER
E O~L!///": ~- 2 ~. ~ I 0.1
0.2 0.3 CARBON ADDED (g)
0.4
0.5
Fig, 13. ~o Lead removal vs carbon added (with or without copper and/or cobalt in solution) at pH 4.0 and contact time of 2h.
Z/F,
,,' ..... ,,-,; ...-. l
0.2 CARBON
I
0.3 ADOED
I
I
O.A
05
(g)
I.SOLUTION VOLUME = IOOrnl 2,INITIAL METAL CONCENTRATION: (A) B.Sm(}/I COBALT (B) 9.Bmq/I COBALT& 8.2 mq/| LEAD {C) 9.3m~/I COBALT & 9.6 mp/ICOPPER (D}ll.Bmg/I COBALT, 7.7mp/t LEAD 9.Pmg/I COPPER
Fig. 15. % Cobalt removal vs carbon added (with or without lead and/or copper in solution) at pH 4.0 and contact time of 2 h.
"932
¢ ,NETZERand D.
E. HUGHES
Cont(.ic[
~oip ' 70L
/
0:
//
/i
a'
//
¢9
//
/l /
/
El:
¢.)
//
LO .,J
/I
/
LEA0 ~Z
/~/"
e,_
_ 0. I
0,2 CARBON
COPPER
--I--
1 0.3 ADDED
I. SOLUTION VOLUME = I00 m I 2.1NITIAL METAL C0NCENTI=!~TION
1
I
04
0 5
(~) LE&D: 7.7mgll COPPER= 9 9mg/I COBALT' II 6rag/!
Fig. 16. (';; Lead, copper and cobalt remo~,al vs carbon added at pH 2 and contact time of 2 h.
were conducted to determine the lowest pH range for maximum metal adsorption by activated carbon. The overall effect of solution pH on the ability of the activated carbon to adsorb the three metals was similar. At pH = 2 the metal adsorption by activated carbon was insignificant for all three metals. At pH = 3 there was a slight improvement in metal adsorption. At pH = 4 and above there was a dramatic increase in metal adsorption. As solution pH is increased from a low value metal adsorption by activated carbon (at metal concentrations of approx. 10 -4 N) began at a pH of approx. 3 for copper, lead and cobalt, In 1976 Baes and Mesmer reported that as solution pH is increased, the onset of metal hydrolysis and precipitation (at a metal concentration of 10-SN) began at a pH of 6 for lead and copper and a pH of 8 for cobalt (Baes and Mesmer, t976). As solution pH is increased the onset of adsorption therefore occurs before the beginning of hydrolysis (and precipitation) for all three metals. Adsorption preceded hydrolysis by approx. 5pH units for cobalt and approx. 3 pH units for copper and lead. This finding that the onset or adsorption occurs at a lower pH than the beginning of hydrolysis agrees with that of James and Healey (1972) in their experiments with adsorption of cobalt, iron, chromium and calcium on SiO2 and TiO2. The hydrolysis of metal cations occurs by the replacement of water ligands in the inner coordination sphere with hydroxo groups (James and Healey, 1972). This replacement occurs after the removal of the outer hydration spheres of the metal cation. Adsorption may not be related directly to the hydrolysis of the metal ion, but instead to the loss of the outer hydration spheres that precedes hydrolysis.
:i;~it'
The first series of tests indicated that }t)min appeared to be sufficient for complete adsorption of lead and copper, but 2 h ~*as required &,v cobalt (Figs. 7. 8 and 9). It ',,,'as noted that the carbon do.,c utilized for the cobalt solution adsorbed a higher percentage of cobalt from solution thar~ was adsorbed in the lead or copper solution, l o further investigate this finding, new set of experiments varxing the contact time and carbon dose ~as performed with solutions containing all three metals {Figs 10. i i and 12). The results of these tests indicated that the required contact time for complete adsorption of the metals was affected by the ratio of metal species to adsorption sites, The adsorption process appears to proceed rapidb when the number of available adsorption sites i:, much larger than the number of metal species that can be adsorbed. The required contact time increases with increased loading (mass of metal ma,~s oF carbon). The contact time required to reach equilibrium appears to be proportional to the ratio of the number of adsorption sites to the number of metai species as shown on Figs 10, I I and 12. Two or three different metals in the same ~oluti(m
Tests were conducted to study the adsorption process when two or three different metals were in the same solution. Figures 13, 14. 15 and 16 suggest that the metals are adsorbed on the same sites. When tv~-o or three metals are present in solution the~ seem to compete for adsorption sites. Lead adsorption was hindered by the presence of the other metals. Copper had a greater effect on lead adsorption than cobalt. Copper adsorption was only slightly affected by the presence of the other metals The presence of the other metals had a pronounced effect on cobalt adsorption. Cobalt removal was significantly reduced when copper, or copper and lead were in solution. Figure 16 best illustrates the effect copper and lead had on cobalt adsorption. Significant cobah adsorption did not begin until approx. S0'~i of the copper and lead had been adsorbed. Lead and copper appeared to compete more aggressively for the available adsorption sites or displace previousI.,, adsorbed cobalt.
CONCLUSIONS
The major findings of these studies are summarized below. (1) There was a significant difference in the ability of different commercially available activated carbons to adsorb copper, lead and cobalt from aqueous solutions. (2) The solution pH was the single most important parameter affecting adsorption. The lowes~ optimum
Adsorption of copper, lead and cobalt b? activated carbon solution pH for maximum adsorption was determined to be 4 for cobalt, copper and lead. (3) Solution pH is also related to the loss of hydration sheaths, hydrolysis and precipitation of metal ions. As solution pH is increased from a low value, the onset of adsorption precede metal hydrolysis and precipitation and appeared to coincide with the loss of the outer hydration sheaths of the metal ion. (4) The contact time required for equilibrium of the metal species between the carbon and solution appeared to be dependent on the ratio of the number of adsorption sites to the number of metal species that can be adsorbed. A 2 h contact time was required for complete copper, cobalt and lead adsorption. (5) Approximately twice as much Lead was removed than copper and approx. 10 times more lead was removed than cobalt, by the same amount of activated carbon. (6) The adsorption of any single metal studied (copper, cobalt or lead) was hindered by the presence of the other metals. Cobalt adsorption was particularly dampened by the presence of copper.
933
REFERENCES
Baes G. B. Jr and Mesmer R. E. (1976) Hydrolysis of Cations. Wiley. New York. Hannah S. A.. Jelus M. and Cohen J. R. (19771 Removal of uncommon trace metals by physical and chemical treatment processes. J. War. Poll,a. Control Fed. 49, 2297-2309. James R. O. and Healey R. W. (1972) The adsorption of hydroiyzable metals at oxide solution interface. J. colloid interface Sci. 40, 42. Maruyama T., Hannah S. A. and Cohen J. R. (1975) Metal removal by physical and chemical treatment processes. J. War. Pollut. Control Fed. 47, 962-965. Sigworth E. A. and Smith S. B. (1972) Adsorption of inorganic compounds by activated carbon. J. Am. War. Wks Ass. 64, 386-391. Smith S. B. (1973) Trace metals removal by activated carbon. Paper presented at the Conference on Traces oj" Heat,y Aletals in Water: Rernoral Processes and Monitoring. Princeton University, NJ.
Smith S. B., Hyndshaw A. Y., Laughlin H. F. and Maynard S. C. (1971) Mercury pollution control by activated carbon: a review of field experience. Paper presented at 44th Water Pollution Control Federation, San Francisco, CA. Watanabe T. and Ogawa K. (1929) Activated carbon for purifying copper electrolytes--Collected Lectures. Chem. Abst. 24, 1037.
00-13-135484 S300 + 0.00 Copyright ~') 1984 Pergamon Press Ltd
ADSORPTION OF COPPER, LEAD AND COBALT BY ACTIVATED CARBON A. NETZERt and D. E. HUGHES" tEnvironmental Sciences,The University of Texas at Dallas, Richardson, TX 75080 and '- Western Electric Company, Mesquite, TX 75149, U.S.A. (Received March 1982)
Abstract--The phenomena of lead, copper and cobalt adsorption by activated carbon from aqueous solution was studied in detail. Laboratory studies were conducted to evaluate and optimize the various process variables (i.e. carbon type, solution pH, equilibrium time and carbon dose). A quantitative determination of the adsorptive capacity of activated carbon to remove these metals was also determined. Significant differences were found in the ability of different types of activated carbons to adsorb lead, copper and cobalt from aqueous solution. Solution pH was found to be the most important parameter affecting the adsorption. It was found that there was practically no adsorption of lead, copper and cobalt by activated carbon below a well defined solution pH value for each metal. This critical solution pH value was found to be lower than the pH value associated with the formation of hydrolysis products. Of the ten commercially available activated carbons evaluated in these experiments, Barney Cheney NL 1266 was found to adsorb the largest percentage of lead, copper and cobalt. The adsorption of any single metal (lead, copper and cobalt) was hindered by the presence of the other metals; the metals apparently competed for adsorption sites. Key words---copper, lead, cobalt, aqueous solution, removal, activated adsorption
INTRODUCTION The concept of adsorption of metals by activated carbon was first demonstrated in 1929 (Watanabe and Ogawa, 1929). Up until approximately 1970 the use of activated carbon for metal removal was confined to improving the efficiency of metallurgical recovery. In 1970 the United States became alarmed about the widespread contamination of surface waters by mercury. Mercury cell chlorine/caustic plants were found to be discharging large quantities of mercury into streams used for potable water sources. Filters were subsequently developed that were effective in removing mercury form caustic solutions. One component of these filters was activated carbon (Smith et al., 1971). This was reported to be the first use of carbon for the sole purpose of trace metal removal from water (Smith, 1973). In 1971 Sigworth and Smith reported on the correlation of solution pH and the adsorption of inorganics by activated carbon. They reported that metal adsorption is inversely proportional to metal solubility in aqueous solutions--"better adsorption can be expected when conditions render the compound less soluble" (Sigworth and Smith, 1971). Most metals become less soluble and form hydroxides and oxides as the solution pH is increased. In 1975 and 1977 the results of extensive pilot plant studies conducted by the Environmental Protection Agency on metal removal by physical and chemical W.R. 18/~-A
927
treatment were issued. The effectiveness of the unit process of coagulation, sedimentation, filtration and carbon adsorption to remove 23 common and uncommon trace metals from wastewater was evaluated. The overall process was found to be very efficient in removing most of the trace metals. Activated carbon increased the efficiency of metal removal by as much as 80% for certain metals (Maruyama et al., 1975; Hannah et al., 1977). The object of this research was to conduct a study of the phenomenon of metal adsorption by activated carbon from aqueous solution. Lead, copper and cobalt were chosen to be studied in detail. The parameters affecting adsorption (i.e. carbon type, solution pH, equilibrium time and carbon dose) were optimized and the possible mechanisms involved were probed. EXPERIMENTAL Metal solutions Aqueous solutions with 10 mg I- ~concentrations of lead, copper and cobalt were prepared. The solution pH was adjusted with reagent grade nitric acid or sodium hydroxide. The solution was then filtered through Whatman No. t filter paper. A control sample was taken at this point to determine the exact metal concentration before contact with activated carbon. Exactly 100 ml of the sample solutions were placed into the 125 ml glass bottles containing previously weighed samples of activated carbon. The bottles were then capped with Teflon-lined screw caps and shaken for specific periods of time. After agitation the samples were filtered through Whatman No. 1 filter paper and the final metal concentrations
928
A. NETZER and D. E HUGHES
were determined. So[utions containing identical metal concentrations but `*ithout any carbon were tested simultaneously to determine if metal was removed by filtration or some other mechanism except contact with activated carbon. .4ctitated carbon selection Samples of ten activated carbons were obtained from Barney Cheney, Calgon. ICI America. West,,aco and Witco (Table 1). The carbons were evaluated for their specific ability to adsorb the individual metals from aqueous solutions. These experiments were conducted at the original pH of the solutions. The activated carbon with the greatest metal adsorption was selected and utilized for the remaining tests.
_-~ -= - - -
-.5 -~ ,.z
2
.>>
,7,-!
---
-~
'~E?_.
E:
Optimum pH determination Solutions containing 10rag l ~ lead. copper or cobalt were adjusted to various integral pH values ranging from 2 to 10. The ability of the previously selected activated carbon to adsorb the metals as a function of solution pH was then determined. The lowest solution pH for maximum metal adsorption was then selected and utilized for the remaining tests. Minimum contact time determ#u~tion Solutions at the optimum pH containing lead, copper or cobalt and constant doses of the previously selected carbon were agitated on a wrist shaker. Various periods of agitation were employed to determine the minimum contact time required for complete or maximum metal adsorption. A second series of tests with all three metals in the sarne solution and with varying doses of the previously selected activated carbon were also conducted to determine the minimum contact time. The minimum contact time ,*as determined and utilized in the remaining tests.
,~°_ _c~.
`5 .~=
z Y.
..z
~-1 {
=
:=
e --
g
-q,,,
=
Metal adsorption studies The remaining tests to study the metal adsorptive properties of the selected carbon were conducted at the optimum solution pH and minimum contact time determined in the preliminary tests. Solutions containing one, two or all three metals at concentrations of 10mgl -~ with varying carbon doses were evaluated.
~a
RESULTS
The results o f the tests to evaluate the ability o f the ten carbons to adsorb lead, copper and cobalt from aqueous solutions are s h o w n by Figs t, 2 and 3, C a r b o n No. 1 (Barney Cheney N L 1266) was determined to be superior; it is a h a r d w o o d - b a s e d granular carbon. The results o f the experiments performed to determine the o p t i m u m pH for metal a d s o r p t i o n are summarized in Figs 4, 5 and 6. A pH of 4 was determined to be the lowest pH for m a x i m u m adsorption and was utilized for the remaining tests. Figures 7, 8 and 9 illustrate the initial tests performed to determine the m i n i m u m contact time. Due to the variation in contact time required for cobalt vs that required for lead and copper, additional tests were performed with all metals in the same solution and with varying carbon doses. The results o f these tests are s h o w n in Figs 10, 11 and 12. The m i n i m u m contact time required for complete a d s o r p t i o n was determent to be 120 rain.
2
.-:,a
~Z
~r ~a =g_,..= ,~ .~ ~a E a=.a . _
=-
*
= g =
i
,Adsorption of copper, lead and cobalt b? activated carbon
,00
.'OFgF 96
92
90
I CARBON A3DED : 0 2 ~ Z SOLUT,ON VOLUME :,OOml 3 INITIALLE~,3 CONCENTR~,TIOr'~ = 9 6 mg/i ( 4 7 x tO'Sin) 4 CONT~.CTT, 'AE : 2 HOURS B{
96 9.0
I.C~RBON ADDE0 : 05g 2 SOLUTION VOLUME= 100rnl 31NITIAL LEAD CONCENTRATION=IOrnq/I
SC
> 7C 0
929
;8F
o f t e r pH
7
6.9
87
•
0 ~o
°ddit,on
4B
_J ~- 40 r~
21
20
15
i
ii
0 ~4 #5
~2 #3
ltl
~0
~6
iI
i2
7
n ~7
08
#9
i,O --~i f
:
~10
,
3
ACTIVATED CARBONS
I n0n'10
04
,
,
,
,
o o , _ o
DO
8'~"s'~',o"
5
SOLUTION
Fig. I. Activated charcoal comparison {'or lead removal at pH 2.7 and contact time of 2 h.
o,,
0.8
..,
pH
Fig. 4. Lead concentration after (1)pH adjustment and (2) carbon adsorption vs solution pH.
IO0
~3
I. CARBON ADDED = 0 . 5 ( ] 2. SOLUTION VOLUME • IOOml 3. INITIAL COPPER CONCENTRATION = IOmq/I
90
j 80 > O 70 :E
71 66
ILl rr 60
60
57 I-
== 5o
4s
O L) 4(
.n
2c
#1
0 3 #'4 0 5 ACTIVATED
02
#`B 0 7 #`8 CARBONS
#`9
5 I-3 #`10
Figure 13 illustrates the % lead removal vs the carbon dose for solutions containing only lead; lead and cobalt; lead and copper; and lead, cobalt and copper. The amount of lead adsorbed when other metals were present was less than when only lead was in solution. The shapes of all lead curves were similar. Figure 14 indicates the °% copper removal vs the carbon dose for solutions containing only copper; copper and cobalt; copper and lead; and copper, cobalt and lead. The amount of copper adsorbed when other metals were present was slightly less than when only copper was in solution. The shapes of all copper curves were similar. Figures 15 shows the % cobalt removal vs the carbon dose for solutions containing only cobalt; cobalt and lead; cobalt and copper; and cobalt, lead
Fig. 2. Activated charcoal comparison for copper removal at pH 3.3 and contact time of 2 h.
IO.3
10.3
IOO -
9,8
I.CARBON ADDED • 1.0~ ;>.SOLUTION VOLUME = IOOml 3. INITIAL COBALT CONCENTRATION = IOmq/I
90
-J 80-
!8
>
~ 70~: 6 0 -
,°I
58
F-
i
so0 u 40z w u
~_9
30-
i,E I
u'J 20 ~_ n
~oL
! i
!
#1
I.I #2
54
44
41
oili
#`3
04
#5
#`6
#7
i:I U IF , 08
#9
~iO
ACTIVATED CARBONS
Fig. 3. Activated charcoal comparison ofcobah removal at pH 3.0 and contact time of 2 h.
9.5
I 8.3 • l •
I I •
U I It I
•
[I I
I
I CARBONADDED=O.2g 2 SOLUTIONVOLUME,lO0ml 3.tNITIALCOPPERCONCENTRATION= 10"3 mg/I ( l ' 6 x 10"Sin)
after pH
•
I
.
odio~,m,o,
Illl
IllI on'.
3
v,°i , o,oo DO
4 5 6 SOLUTION
7
8
9
I0
pH
Fig. 5. Copper concentration after (I) pH adjustment and (2) carbon adsorption vs solution pH.
930
A. NETZER a n d D. E. HLGHES
C. 3
I 0 0 100
IOO
IO0 9.2
iI E B
.z
• after p;'i iadlustmen r
U
F] ofter carbon U addition
}
I CARBON ADDED = 0.3g 2. SOLUTION VOLUME. lOOrnl 3 I N I T I A L COBALT CONCENTRATION:9 1 ~ g , ' i
{3:3 O 6 (o
Z O 4 i,,< m 3
z
? ~Z
24 L,) 2 Z
Z © u
g,
I
I 15 SOLUTION
I 30
I 60 CONTACT
pH
I 120 (rain)
1 150
,__J
Fig. 9. Cobalt concentration vs contact time with carbon at pH 4.0
C-'RBON ADDED = O 4 g 2 S0..UTION VOLUME= I 0 0 ml 3 INITIAL COBALT CONCENTRATION:IO 0 m g / I H 7xfO -5m) 4CONTACT T I M E : 2 H O U R S
Fig. 6. C o b a l t c o n c e n t r a t i o n a f t e r ( l ) p H adjustment (2) c a r b o n a d s o r p t i o n vs s o l u t i o n p H .
I , 90 T~ME
and IO l-- I.CARBON ADDED =O. O 0 2 , 0 0 ! , O O S , A N D 0 2 G 2. SOLUTION VOLUME = l O O m l 3.1NITIAL METAL CONCENTRATION: L E A D = ?.6rnq/~ COPPER: IO OrngM
-- 9
10 I
'8~-
COBALT ~ 1 1 . 4 m q / I
9i CARBON ADOED = O.O2q 2 SOLUTION VOLUME = lOOmJ
7 ~~\',. " ~ O ~
TIAL LEAD CONCENTRATION= 9 5 m g / I
E
~
"0
..........
l i "i"x
c~ uJ .J • --13--
z O
3
::-.
Z
O
0 . 0 0 2 g Carbon 0,01 g C o ~ b o n
----&,- - - 0 . 0 5 Q C o r b o n -.---.O. . . . . 0 . 2 O g C o r b o n
"Q.
rr
~
Z O L)
/ I 45
I 30
I 60 CONTACT
1 90 TIME
I t20
I, 150
(rain)
Fig. 7. Lead concentration vs contact time with carbon at pH 4.0,
o~
E
O c)
*"**'---,o
~
I CARBON AODED = 0 O5q 2 SOLUTION VOLUME = IOOml 3.1NITI AL COPPER CONCENTRATION=98mg/l
:
9
~
7
O.
1 90 TIME
~ .... 120
O 150
( rain )
.
""
.
.
.
.
.
.
.
.
.
.
--
I CARBON ADDED =O. OO2.0. O i , O 0 5 , ~ , N D 3 Z ~
~:, 2 SOLUTION VOLUME = 100 ml O 6 - '-. 3. INITIAL METAL CONCENTRATION:COPPER: l 0 0 m g / i U \\ LEAD: ?" 6 m g M ) 5 COBALT- !~ 4 m g / I 4
~h-Z w
uJ
Z 0 ~o
0 L) I 15
I 60 CONTACT
. . . . . . . . . . . . . .
Fig. 10. Lead concentration vs contact time vdth carboii (copper and cobalt also in solution) at pH 4.0.
z O
....
1 30
o......................... O
I
50
I 60 CONTACT
I 90 TIME
I
I
120
150
( rain )
Fig. 8. Copper concentration vs contact time with carbon at pH 4.0.
O ''.
O
"'%..
' • --D----&--....... 0 ...... .I 30
0
0 . 0 0 2 g Carbon
.......
. . . . . . . . . . . . . . o .............
0.O I (j C a r b o n
O . 0 5 q Car b a n U.-'Uq {.0r b0n I l 60 90 CONTACT TIME (rain)
J t20
_ _ J !50
Fig. 1 l. Copper concentration vs contact time with carbon (lead and cobalt also in solution) at pH 4 0
90
Adsorption of copper, lead and cobalt by activated carbon
'oo r II
~ll---i--------- I - -
-
-
-
-
--t: .....
/',~
90
/
",.,%,
IO
=.,.
b
• O.O02gCorbon --0O.Ol g Carbon ---&--- O . 0 5 g Carbon ..... o ....... 0 . 2 0 g Carbon
0
=
o
F i
Z lad u z 0 u
I
I
30
I,
60 CONTACT
90 TIME (rain)
I
h'i/ #,(i. L,'/-~
//.11:
, sO.OT,ON VOL~ME=,O0.,
2.INITIAL METAL CONCENTRATION: (A)g.6mg/I COPPER (B) 9.6mg/I COPPER&9.3mqlICOBALT (C) 9.3 mg/I COPPER &B.I mg/I LEAD {O) 9.9 mg/I COPPER. 11.6 rag/ICOBALT 7.7 mg/I LEAD _l I I i J5 o.i o.2 o.s o.,~ o. CARBON ADDED (g)
~J 201-" ]1/.: O_ ' l O f t { : I .~.:' I0t~..~¢ [~i o~
•
120
I
rr
1 71 <
I
'a ,or. fill
I. CARBON ADDED = 0 . 0 0 2 , 0.01, 0.05, ANDO,29 2 SOLUTION VOLUME = I 0 0 ml :3 INITIAL METAL CONCENTRATION: COBALT= I I.Amq/I LEAD, 7.6 mg/I COPPER= I0.0 mg/I
...
/ !/ :" / , , / # / .." / ~ ' / :"
l / BOp
" ,ok z 0
A
/,'/'
o ,0L I
..-
..l"
~> eo
...................
0 "~'O. .... .........0 ...............................~
o,
93l
Fig. 14, ~o Copper removal vs carbon added (with or without lead and/or cobalt in solution) at pH 4.0 and contact time of 2 h.
i50
Fig. 12. Cobalt concentration vs contact time with carbon (lead and copper also in solution) at pH 4.0.
and copper. The amount of cobalt adsorbed when other metals were present was significantly less than when only cobalt was in solution. The shapes of the four cobalt curves were dissimilar. Figure 16 compares the removal of all three metals from a single solution vs the carbon dose. The cobalt removal was depressed when the lead and copper adsorption was less than 100%.
(Barney Cheney NL 1266) was superior in every test, the remaining nine carbons demonstrated a large variation in their ability to adsorb the three metals from their aqueous solutions. Due to the large number of variables in the adsorption of metals by activated carbon and the complexity of the surface and water chemistry, no single carbon property appears to be dominant in determining its metal adsorptive characteristics from aqueous solutions.
Solution pH The experiments with solution pH as a variable
DISCUSSION
Activated carbon =oo
There was a significant difference in the ability of the ten activated carbons to adsorb lead, copper and cobalt from aqueous solutions. Although one carbon
90
/.
A) - - - 0 - - - COBALT ~ ( 8 ) - - O - - C O B A L T WITH LEAD / / (C) ---A---- COBALT WiTH COPPER ~ (D) " ' " l ' " " COBALT WITH LEAD / et COPPER o
/ /-l--
/ '~
~
>
70
3,o t7 ,, ............
/
60
/
/
,,
/
so 0
(B) i 0 - LEAD WITH COBALT {C) - - ~ - - - LEAD wiTH COPPER
= 60hi;,/I 50
LI/4'
e
(O) - - ' - I .... &LEADcoPPERWITHCOBALT
40
/~/
,.u 30
~.=2c
Z1
J/;
// //,;
x ..-..... _ / ' ........ . ~ ' : .........
<~ IPli:
,c
~' U ,o1.17i Irlll:
0 = ~--.~/'-'T 1 0.1
"°tldi..'i
I.BOLUTION VOLUME = IOOml 2.INITIAL METAL CONCENTRATION: (A) g.Omg/I LEAD (B) 8.2 mg/I LEAD I~ 9. Bmg/I COBALT (C)8.1 mq/I LEAD B 9 3 mq/ICOPPER (0) 7.Tmg/I LEAD.~II.Bmp/ICOBALT 8~ B.9 mg/I COPPER
E O~L!///": ~- 2 ~. ~ I 0.1
0.2 0.3 CARBON ADDED (g)
0.4
0.5
Fig, 13. ~o Lead removal vs carbon added (with or without copper and/or cobalt in solution) at pH 4.0 and contact time of 2h.
Z/F,
,,' ..... ,,-,; ...-. l
0.2 CARBON
I
0.3 ADOED
I
I
O.A
05
(g)
I.SOLUTION VOLUME = IOOrnl 2,INITIAL METAL CONCENTRATION: (A) B.Sm(}/I COBALT (B) 9.Bmq/I COBALT& 8.2 mq/| LEAD {C) 9.3m~/I COBALT & 9.6 mp/ICOPPER (D}ll.Bmg/I COBALT, 7.7mp/t LEAD 9.Pmg/I COPPER
Fig. 15. % Cobalt removal vs carbon added (with or without lead and/or copper in solution) at pH 4.0 and contact time of 2 h.
"932
¢ ,NETZERand D.
E. HUGHES
Cont(.ic[
~oip ' 70L
/
0:
//
/i
a'
//
¢9
//
/l /
/
El:
¢.)
//
LO .,J
/I
/
LEA0 ~Z
/~/"
e,_
_ 0. I
0,2 CARBON
COPPER
--I--
1 0.3 ADDED
I. SOLUTION VOLUME = I00 m I 2.1NITIAL METAL C0NCENTI=!~TION
1
I
04
0 5
(~) LE&D: 7.7mgll COPPER= 9 9mg/I COBALT' II 6rag/!
Fig. 16. (';; Lead, copper and cobalt remo~,al vs carbon added at pH 2 and contact time of 2 h.
were conducted to determine the lowest pH range for maximum metal adsorption by activated carbon. The overall effect of solution pH on the ability of the activated carbon to adsorb the three metals was similar. At pH = 2 the metal adsorption by activated carbon was insignificant for all three metals. At pH = 3 there was a slight improvement in metal adsorption. At pH = 4 and above there was a dramatic increase in metal adsorption. As solution pH is increased from a low value metal adsorption by activated carbon (at metal concentrations of approx. 10 -4 N) began at a pH of approx. 3 for copper, lead and cobalt, In 1976 Baes and Mesmer reported that as solution pH is increased, the onset of metal hydrolysis and precipitation (at a metal concentration of 10-SN) began at a pH of 6 for lead and copper and a pH of 8 for cobalt (Baes and Mesmer, t976). As solution pH is increased the onset of adsorption therefore occurs before the beginning of hydrolysis (and precipitation) for all three metals. Adsorption preceded hydrolysis by approx. 5pH units for cobalt and approx. 3 pH units for copper and lead. This finding that the onset or adsorption occurs at a lower pH than the beginning of hydrolysis agrees with that of James and Healey (1972) in their experiments with adsorption of cobalt, iron, chromium and calcium on SiO2 and TiO2. The hydrolysis of metal cations occurs by the replacement of water ligands in the inner coordination sphere with hydroxo groups (James and Healey, 1972). This replacement occurs after the removal of the outer hydration spheres of the metal cation. Adsorption may not be related directly to the hydrolysis of the metal ion, but instead to the loss of the outer hydration spheres that precedes hydrolysis.
:i;~it'
The first series of tests indicated that }t)min appeared to be sufficient for complete adsorption of lead and copper, but 2 h ~*as required &,v cobalt (Figs. 7. 8 and 9). It ',,,'as noted that the carbon do.,c utilized for the cobalt solution adsorbed a higher percentage of cobalt from solution thar~ was adsorbed in the lead or copper solution, l o further investigate this finding, new set of experiments varxing the contact time and carbon dose ~as performed with solutions containing all three metals {Figs 10. i i and 12). The results of these tests indicated that the required contact time for complete adsorption of the metals was affected by the ratio of metal species to adsorption sites, The adsorption process appears to proceed rapidb when the number of available adsorption sites i:, much larger than the number of metal species that can be adsorbed. The required contact time increases with increased loading (mass of metal ma,~s oF carbon). The contact time required to reach equilibrium appears to be proportional to the ratio of the number of adsorption sites to the number of metai species as shown on Figs 10, I I and 12. Two or three different metals in the same ~oluti(m
Tests were conducted to study the adsorption process when two or three different metals were in the same solution. Figures 13, 14. 15 and 16 suggest that the metals are adsorbed on the same sites. When tv~-o or three metals are present in solution the~ seem to compete for adsorption sites. Lead adsorption was hindered by the presence of the other metals. Copper had a greater effect on lead adsorption than cobalt. Copper adsorption was only slightly affected by the presence of the other metals The presence of the other metals had a pronounced effect on cobalt adsorption. Cobalt removal was significantly reduced when copper, or copper and lead were in solution. Figure 16 best illustrates the effect copper and lead had on cobalt adsorption. Significant cobah adsorption did not begin until approx. S0'~i of the copper and lead had been adsorbed. Lead and copper appeared to compete more aggressively for the available adsorption sites or displace previousI.,, adsorbed cobalt.
CONCLUSIONS
The major findings of these studies are summarized below. (1) There was a significant difference in the ability of different commercially available activated carbons to adsorb copper, lead and cobalt from aqueous solutions. (2) The solution pH was the single most important parameter affecting adsorption. The lowes~ optimum
Adsorption of copper, lead and cobalt b? activated carbon solution pH for maximum adsorption was determined to be 4 for cobalt, copper and lead. (3) Solution pH is also related to the loss of hydration sheaths, hydrolysis and precipitation of metal ions. As solution pH is increased from a low value, the onset of adsorption precede metal hydrolysis and precipitation and appeared to coincide with the loss of the outer hydration sheaths of the metal ion. (4) The contact time required for equilibrium of the metal species between the carbon and solution appeared to be dependent on the ratio of the number of adsorption sites to the number of metal species that can be adsorbed. A 2 h contact time was required for complete copper, cobalt and lead adsorption. (5) Approximately twice as much Lead was removed than copper and approx. 10 times more lead was removed than cobalt, by the same amount of activated carbon. (6) The adsorption of any single metal studied (copper, cobalt or lead) was hindered by the presence of the other metals. Cobalt adsorption was particularly dampened by the presence of copper.
933
REFERENCES
Baes G. B. Jr and Mesmer R. E. (1976) Hydrolysis of Cations. Wiley. New York. Hannah S. A.. Jelus M. and Cohen J. R. (19771 Removal of uncommon trace metals by physical and chemical treatment processes. J. War. Poll,a. Control Fed. 49, 2297-2309. James R. O. and Healey R. W. (1972) The adsorption of hydroiyzable metals at oxide solution interface. J. colloid interface Sci. 40, 42. Maruyama T., Hannah S. A. and Cohen J. R. (1975) Metal removal by physical and chemical treatment processes. J. War. Pollut. Control Fed. 47, 962-965. Sigworth E. A. and Smith S. B. (1972) Adsorption of inorganic compounds by activated carbon. J. Am. War. Wks Ass. 64, 386-391. Smith S. B. (1973) Trace metals removal by activated carbon. Paper presented at the Conference on Traces oj" Heat,y Aletals in Water: Rernoral Processes and Monitoring. Princeton University, NJ.
Smith S. B., Hyndshaw A. Y., Laughlin H. F. and Maynard S. C. (1971) Mercury pollution control by activated carbon: a review of field experience. Paper presented at 44th Water Pollution Control Federation, San Francisco, CA. Watanabe T. and Ogawa K. (1929) Activated carbon for purifying copper electrolytes--Collected Lectures. Chem. Abst. 24, 1037.