removal of copper from aqueous solutions by adsorption on activated carbons

Colloids and Surfaces

A: Physicochemical and Engineering Aspects 190 (2001) 229–238

Removal of copper from aqueous solutions by adsorptionon activated carbons

Meenakshi Goyal *, V.K. Rattan, Diksha Aggarwal, R.C. BansalDepartment of Chemical Engineering and Technology, Punjab Uni�ersity, Chandigarh 160014, India

Received 12 April 2000; accepted 24 January 2001

Abstract

The adsorption isotherms of Cu(II) ions from aqueous solutions in the concentration range 40–1000 mg l−1 ontwo samples of granulated and two samples of activated carbon fibres containing varying amounts of associatedoxygen have been reported. The adsorption isotherms are type I of BET classification showing initially a rapidadsorption tending to be asymptotic at higher concentrations. The amounts of oxygen associated with the carbonsurface has been enhanced by oxidation with nitric acid and ammonium persulphate in the solution phase and withoxygen gas at 350°C and decreased by degassing of the oxidized carbon samples at 400, 650 and 950°C. Theadsorption of Cu(II) ions increases on oxidation and decreases on degassing. The increase in adsorption on oxidationdepends on the nature of the oxidative treatment while the decrease in adsorption on degassing depends on thetemperature of degassing. This has been attributed to the increase in the carbon–oxygen acidic surface groups onoxidation and their decrease on degassing. Suitable mechanisms consistent with the results have been proposed.© 2001 Elsevier Science B.V. All rights reserved.

Keywords: Activated carbon; Adsorption; Surface groups; Adsorption isotherm

www.elsevier.nl/locate/colsurfa

1. Introduction

Copper is present in the waste water of severalindustries. It is also a micronutrient in agricultureand can, therefore, accumulate in surface waters.The excessive intake of copper results in its accu-mulation in the liver and produces gastrointestinalproblems. Consequently, it is essential thatpotable waters be given some treatment to removecopper and other heavy metals before domestic

supply. Activated carbons, because of their largesurface area, a microporous structure and a highdegree of surface reactivity, have been consideredto be very good adsorbents for the adsorption oforganics and inorganics from water. Thus a con-siderable amount of work is being carried out forthe removal of metal ions from aqueous phaseusing activated carbons.

Petrov et al. [1] studied the adsorptive removalof several metal ions such as Zn, Cd, Pb and Cufrom aqueous solutions on anthracite prepared bythermal oxidation in air. The metal uptake in-creased with increasing pH of the solution. The

* Corresponding author. Tel.: +91-541441, ext. 4905.E-mail address: [email protected] (M. Goyal).

0927-7757/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S0927-7757(01)00656-2

M. Goyal et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 190 (2001) 229–238230

uptake was found to be only slight at a solutionpH of 1 but it increased considerably in the pHrange 3–4. The oxidation of the carbon enhancedthe uptake of metal ions because of the creationof oxygen surface groups on the anthracite sur-face. The presence of electrolytes in the solutiondecreased the uptake of the metal ions. Man-galardi et al. [2], and Andreevo et al. [3], whilestudying the removal of Cu(II) ions from waterusing a powdered activated carbon at differentpH values of the solution, observed that the re-moval of Cu(II) ions was considerable at pHvalues lower than 7 and that the effluent was leftwith only 0.1 mg l−1 of copper. Activated carbonwas found to be a better adsorbent of coppercompared with Fuller’s earth or bentonite.Fuller’s earth and bentonite absorbents were ef-fective moderately only at pH greater than 8.Mathur and coworkers [4] observed that fly ashfrom power plants was also quite effective in theremoval of heavy metal ions including copperfrom sewerage waste water.

Tarkovskaya et al. [5] examined the adsorptiveand cation exchange properties of several car-bonaceous materials such as activated oxidizedanthracite, semi coke, brown coal and severalmodified coals and found these materials to beeffective to varying degrees for the removal ofcations from solution. Urmani et al. [6] found thatusing eucalyptus wood charcoal, pH of the metalsolution was the principal variable affecting theremoval of copper and zinc. These metal ionscould not be adsorbed significantly at pH valueslower than 4. Kahn and Khattak [7,8] studied theadsorption of copper from copper sulphate solu-tions on carbon black Spheron-9 under varyingconditions of time, pH and concentration. Ad-sorption equilibrium was established within 1 h inthe concentration range 10–1000 ppm. Increase inpH increased the extent of adsorption. The datawas found to obey Langmuir and Freundlichadsorption except for adsorption at higher pHvalues where precipitation was thought to takeplace. Removal of copper, lead and zinc fromaqueous solutions by synthetic geothite was mea-sured as a function of pH at several temperatures.It was found that the adsorption was closelyrelated to cation hydrolysis. Low et al. [9] exam-

ined the ability of coconut husk and its reactivedye-coated forms for the removal of copper fromaqueous solutions at different concentrations andpH values. The equilibrium data was found toobey the Langmuir isotherm. The dye coating ofthe husk enhanced the removal of copper. De-orkar and Tavlarides [10] used inorganic chemi-cally active adsorbent beds for the removal ofcopper and nickel from dilute aqueous streams.The adsorption of both Cu(II) and Ni(II) ionsincreased with pH while that of copper cyanidewas maximum at pH 5–5.5. At breakthroughpoint the removal capacity was between 13 and 33mg g−1 for Ni(II) ions and about 20 mg g−1 forcopper cyanide.

Above perusal of the literature indicates thatseveral types of adsorbents have been used for theremoval of copper from aqueous solutions. Butoxidized carbons possess some unique propertiesdue mainly to the large amount of oxygen con-taining functional groups on their surface. Thesesurface groups make the carbon surface hy-drophilic and enhance its ion exchange capacityso that these carbons are potential adsorbents forthe removal of metal ions from industrial anddomestic waste water. Thus the present work wasundertaken.

2. Experimental

Two samples of granulated activated carbons(GAC-S and GAC-E) obtained from Norit N.V.,The Netherlands and two samples of activatedcarbon fibres (ACF-307 and ACF-310) obtainedfrom Ashland Petroleum company, Kentucky,USA have been used in these investigations. Theactivated carbons have been oxidized with nitricacid and ammonium persulphate in solutionphase and with gaseous oxygen at 350°C to en-hance the amount of carbon–oxygen surfacefunctional groups [11–13]. The oxidized carbonswere then degassed at 400, 650 and 950°C togradually eliminate varying amounts of these car-bon–oxygen surface groups [14–16].

The procedures for degassing and oxidationhave been described elsewhere [14,15] but briefdescriptions are given below.

M. Goyal et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 190 (2001) 229–238 231

2.1. Degassing of the carbons

About 5 g of each of the activated carbonsample was spread in thin layer about 5 incheslong in a tube furnace. It was kept in positionby means of porous copper gauge plugs. Thetube furnace was connected to a Hyvac. Cencovacuum pump capable of giving a vacuum tothe order of 3×10−3 mmHg. The temperatureof the furnace was raised to the required levelslowly. The gases begun to be evolved soon af-ter. The temperature was allowed to rise gradu-ally and before it was raised by another 50°Ccomplete elimination of the gases, at the pro-ceeding temperature was ensured. After de-gassing at the required temperature, the samplewas allowed to cool in vacuum to room temper-ature to avoid reformation of the carbon–oxy-gen surface groups and was then transferred tostoppered bottles flushed with nitrogen. Thesesamples are refereed to as ‘degassed samples’ inthe text.

2.2. Oxidation with nitric acid

The activated carbon sample (5 g) was heatedwith 150 ml of pure nitric acid in borosil beakerof 250-ml capacity in a water bath maintained14

at about 80°C. When all but about 10 ml of theacid had evaporated, the contents were cooled,diluted with water and transferred over a filterpaper. The carbon sample was washed exhaus-tively with hot distilled water until the filtratewas free of nitrate ions. This oxidation andwashing resulted in the loss of some carbon.Some of the oxidized carbon also passedthrough the filter paper. The washed carbonsample was dried first in air and then in anelectric oven at 120°C outgassed at 150°C andthen stored in stoppered glass bottles flushedwith nitrogen.

2.3. Oxidation with gaseous oxygen

Five grams of each carbon sample was spreadin a platinum boat. The mouth of the platinumboat was covered with a platinum lid havingholes so that oxygen gas could make contact

with the carbon. The boat containing the carbonsample was placed in a resistance tube furnace.The temperature of the furnace was maintainedat 350°C. Pure and dry oxygen was passed overthe sample at the rate of 2 l h−1 for 4 h. Thesample was then cooled in oxygen gas andtransferred to reagent bottles and stored undernitrogen.

2.4. Base neutralization capacity (surface acidity)

Surface acidity of each carbon sample was de-termined by mixing 0.25 g of each carbon sam-ple with 25 ml of 0.2 N NaOH solution in aborosil flask of 100-ml capacity. The suspensionwas heated by placing the stoppered bottle in awater bath maintained at about 70°C for 8 h.The amount of unused alkali was determined bytitrating an aliquot of the clear supernatant liq-uid against a standard acid solution. A blankwas run every time and the necessary correc-tions were applied.

2.5. Determination of pH of the carbon

Portion (0.2 g) of the carbon sample wasplaced in contact with 20 ml CO2 free distilledwater in a borosil glass bottle.

The suspension was shaken mechanically for 6h and the pH of the suspension determined us-ing a glass electrode pH water.

3. Adsorption of copper

The adsorption of Cu(II) ions was determinedby contacting a known weight (0.1 g) of eachcarbon sample, dried in an electric oven at120°C and cooled in a desciator, with 20 mlsolution of copper chloride of different concen-trations. The suspensions were placed in a ther-mostat with occasional shaking. After 24 h analiquot portion of the solution was pipetted outand the concentration determined spectrophoto-metrically at a wavelength of 595 nm by makinga complex with Bis (cyclohexanone) and oxyldi-hydrazone using standard analytical procedures[16].


4. Results and discussion

The effect of pH of the solution on the adsorp-tion of Cu(II) ions on the four samples of activatedcarbons was determined. The results for the fourcarbon samples are shown in Fig. 1 (a) and (b). ThepH of the solution was controlled by the additionof HCl or NaOH. The uptake of Cu(II) ions at pHbelow 2 was small in both the granulated as wellas fibrous activated carbons but more so in the caseof granulated carbons. However, when the pH ofthe solution was increased, a maximum in uptakewas obtained at pH 3 in the case of fibrous carbonsand at pH 4 for the granulated carbons. Theslightly low range in pH of maximum adsorptionof copper ions in the case of fibrous activatedcarbons may be attributed to the fact that thefibrous carbon suspensions in water show slightlylower pH values than the granulated carbon sus-pensions. At pH value higher than 6, the adsorp-tion studies could not be carried out because of theprecipitation of Cu(OH)2.

It appears that a change in pH of the solutionresults in the formation of different ionic species[17]. At pH values lower than 3, there is excessiveprotonation of the carbon surface resulting in adecrease in the adsorption of Cu(II) ions. This isin consonance with the results obtained earlier byPetrov et al. [1]. At pH of the solution beyond 4,the preponderance of OH− generates a competi-tion between the carbon surface and the solutionOH ions for Cu(II) ions, which causes a decreasein the adsorption of Cu(II) ions on the carbonsurface.

The adsorption isotherms of Cu(II) ions of thefour carbon samples from aqueous solution ofcupric chloride in the concentration range 20–1000mg l−1. are presented in Fig. 2. The pH of eachsolution was maintained at pH 5 by the additionof hydrochloric acid. It is seen that the adsorptionisotherms are type I of the BET classificationshowing initially a rapid adsorption tendingto be asymptotic at higher concentrations.

Fig. 1. (a, b) Adsorption isotherms of Cu(II) ions on carbons as a function of pH of the solution.


Fig. 2. Adsorption isotherms of Cu(II) ions on different asreceived activated carbons.

tion of the associated oxygen as CO2 and CO onevacuation at 950°C is different in the two groupsof carbons. Granulated activated carbons havelarger amount of oxygen evolved as CO2 while thefibrous carbons have larger amounts of oxygenevolved as CO. It appears that it is not the totaloxygen but its disposition into CO2 and CO,which may be a factor in determining the adsorp-tion of Cu(II) ions by carbons. However, a clearconclusion cannot be drawn because these car-bons do not differ very significantly in theiramounts of associated oxygen evolved as CO2.

It is well known [11–15,18–21] that associatedoxygen on the carbon surface is present in theform of two types of surface groups: one whichare evolved on evacuation as CO2 in the tempera-ture range 350–700°C. These surface groups areacidic in character and are postulated as carboxylsor lactones [11–13,18–21]. The other oxygengroups are evolved as CO on evacuation in thetemperature range 500–950°C. These groups arepostulated to be quinones, which tend to makethe carbon surface hydrophobic and neutral incharacter. Furthermore, the amounts of theseboth types of surface groups can be enhanced byoxidation of the carbon surface.

In order, therefore, to examine the influence ofthese carbon oxygen surface groups more clearlyon the adsorption of copper ions, two samples ofcarbons viz. ACF-307 and GAC-E were oxidizedwith nitric acid and ammonium persulphate insolution phase and with O2 at 350°C in thegaseous phase. The adsorption isotherms ofCu(II) ions on the oxidized samples are shown inFigs. 3 and 4. The adsorption isotherms on theas-received samples are reproduced in thesefigures for the sake of easy comparison. It is

The uptake of Cu(II) ions is smaller in the case offibrous carbons compared with granulated car-bons, the difference being a factor of 3. Thiscannot be explained on the basis of surface areaalone because ACF-310, which has about thesame BET surface area as GAC-E (cf. Table 1)adsorbs smaller amounts of Cu(II) ions thanGAC-E. This can also not be explained on thebasis of the total amount of oxygen associatedwith these carbons because fibrous activated car-bons, which show lower adsorption have largeramounts of oxygen associated with them (cf.Table 1). It can, however, be seen that the disposi-

Table 1Surface area and gases evolved on degassing different as-received activated carbons at 950°C

BET (N2) surface area (m2 g−1)Sample identification Oxygen evolved as (g 100 g−1)

CO TotalCO2 H2O

910ACF-307 1.305.30 7.601.001184 1.90ACF-310 4.20 1.40 7.50

1.24 4.39GAC-S 1256 2.10 1.051.33GAC-E 5.121190 2.13 1.66


Fig. 3. Adsorption isotherms of Cu(II) ions on ACF-307before and after oxidation with different oxidizing agents.

This receives support from the adsorptionisotherms of Cu(II) ions on the oxidized carbonsamples after degassing them at 400, 650 and950°C. This treatment eliminates varying amountsof the carbon oxygen surface groups. The adsorp-tion isotherms on the degassed samples are pre-sented in Figs. 5–8. It is seen that the uptake ofCu(II) ions decreases gradually as the temperatureof degassing is increased. The decreases in Cu(II)ions uptake is only slight between 0.2 and 0.5%for both ACF-307 and GAC-E when degassed at400°C. However, the decrease in uptake is appre-ciably larger for the 650° degassed samples (cf.Figs. 5–8). This can be attributed to a smaller(�15%) elimination of the acidic surface groupsin case of the 400° degasssed samples and larger(�85%) elimination of the acidic surface groupsin case of the 650° degassed samples (cf. Tables 3and 4). In case of the samples outgassed at 950°C,the adsorption of Cu(II) ions is even smaller.These samples are almost completely free of anyoxygen groups, which provide sites for the ad-sorption of Cu(II) ions.

Fig. 4. Adsorption isotherms of Cu(II) ions on GAC-E beforeand after oxidation with different oxidizing agents.

interesting to note that for both the carbons, theadsorption of Cu(II) ions increases on oxidation,the magnitude of increase being different for thedifferent oxidative treatments. The uptake ofCu(II) ions is considerably larger when the oxida-tion is carried out with nitric acid. Incidentallythis treatment is a stronger oxidative treatmentand results in the fixation of considerably largeramounts of oxygen on the surface of both thecarbons (cf. Table 2). The amount of associatedoxygen increases from 5–7% to 20–22% on oxi-dation of the two samples with nitric acid andonly to between 10 and 12% on oxidation withammonium persulphate and oxygen gas Further-more, Table 2 also shows that the oxidation withnitric acid enhances the amount of surface acidicgroups appreciably while the increase on oxida-tion with oxygen is only small. It appears fromthe above results that the uptake of Cu(II) ions bycarbons is influenced largely by the presence ofacidic surface groups.


Table 2Surface acidity and gases evolved on degassing different oxidized activated carbons at 950°C

Sample identification Base neutralization capacityOxygen evolved as (g 100 g−1)or surface acidity (mquiv 100 g−1)

CO H2O TotalCO2

ACF-3075.30 1.301.00 7.60Original 24

12.90Oxidized with HNO3 7.47 2.40 22.77 8705.40(NH4)2S2O8 7.51 1.90 12.81 390

7.71 1.203.11 11.02O2 3057.42 2.10H2O2 12.072.55 95

GAC-E1.66Original 1.302.13 5.12 486.20 1.92 20.52 583Oxidized with HNO3 12.405.61 1.854.63 12.09(NH4)2S2O8 156

3.17O2 5.97 1.26 10.40 122H2O2 – – – – –

The surface acidity (base neutralization capac-ity) of the carbon surface was determined bytitration with 0.1 N sodium hydroxide solution[20]. The results are recorded in Table 5. It is

evident that the carbon samples oxidized withnitric acid have the maximum surface acidity. Theamounts of surface oxygen groups evolved as CO2

expressed in similar units are also included in

Fig. 6. Adsorption isotherms of Cu(II) ions on oxygen-oxi-dized ACF-307 before and after degassing at different temper-atures.

Fig. 5. Adsorption isotherms of Cu(II) ions on HNO3-oxidizedACF-307 before and after degassing at different temperatures.


Fig. 7. Adsorption isotherms of Cu(II) ions on HNO3-oxidizedGAC-E before and after degassing at different temperatures.

Table 3Gases evolved on degassing different oxidized and degassedACF-307 carbon samples at 950°C

Sample identification Oxygen evolved as (g 100 g−1)

H2OCO2 TotalCO

ACF-3077.47 22.7712.90 2.40HNO3 oxidized

Oxidized and then degassed at (°C)19.050.85400 10.85 7.35

650 2.15 6.86 0.12 9.13– –Traces–9501.208.21 12.023.11Oxygen oxidized

Oxidized and then degassed at (°C)11.92400 0.828.152.95

7.810.42 0.21650 8.44Traces –– –950

Table 4Gases evolved on degassing different oxidized and degassedGAC-E carbon samples at 950°C

Oxygen evolved as (g 100 g−1)Sampleidentification

TotalCO2 CO H2O

GAC-EHNO3 oxidized 20.521.926.2012.40

Oxidized and then degassed at (°C)10.85400 5.92 1.02 17.14

6.86 0.12 9.13650 2.15TracesTracesTraces950 Traces

5.97 1.26 10.40Oxygen oxidized 3.17

Oxidized and then degassing at (°C)9.421.005.56400 2.86

650 5.980.58 4.78 0.62– –950 –Traces

Fig. 8. Adsorption isotherms of Cu(II) ions on oxygen-oxi-dized GAC-E before and after degassing at different tempera-tures.

Table 5. It is seen that the surface acidity asdetermined by titration with sodium hydroxide isdirectly related to the amount of oxygen evolvedas CO2 when expressed in similar units.

A relationship between the surface acidity andthe uptake of Cu(II) ions on GAC-E and ACF-307 at 1000 mg l−1 concentration of the solutionbefore and after oxidation and degassing treat-ments is shown in Fig. 9. It is seen that the pointsfor the two carbons cannot be collected along a


Table 5Surface acidity and CO2 evolved for different samples of activated carbons

Sample identification Surface acidity CO2 evolved on out gassing at 950°C(mequiv 100 g−1)(base neutralization capacity mquiv 100 g−1)

ACF-307As-received 24 62

806HNO3, oxidized 870194305O2, oxidized680HNO3, oxidized and degassed at 400°C 728134140HNO3, oxidized and degassed at 650°C

O2, oxidized and degassed at 400°C 1841652628O2, oxidized and degassed at 650°C

GAC-E13348As-received

583HNO3, oxidized 775198122O2, oxidized638HNO3, oxidized and degassed at 400°C 505157102HNO3, oxidized and degassed at 650°C

O2, oxidized and degassed at 400°C 17910336O2, oxidized and degassed at 650°C 34

single straight line. However, the plots for a givencarbon show a linear variation of adsorption withsurface acidity thus giving rise to two linear plotsone for each carbon. The difference in behavior ofthe two carbons in giving two different straightlines may be attributed to the difference in themicroporous character of the two carbons.

5. Mechanism of copper adsorption

The carbon surface has unsaturated c�c bonds,which on oxidation can add oxygen causing thecreation of acidic chemical structures which havebeen postulated as carboxyls and lactones[11– 13,18–21]. These acidic surface groups onhydrolysis in aqueous solution produce H+ ions,which are directed towards the liquid phase, leav-ing the carbon surface with negatively charged�COO− sites. These �COO− sites generate a com-petition between the H+ ions and the Cu(II) ionsfor the carbon surface. Thus the availability ofrelatively high concentration of COO− sites incase of the oxidized carbons results in an increasein the adsorption of Cu(II) ions. On degassing atgradually increasing temperatures, these oxygen

Fig. 9. Relationship between the maximum amount of Cu(II)ions adsorbed and base adsorption capacity.

.


surface groups are eliminated in increasingamounts from the carbon surface. This causes adecrease in the concentration of surface COO−

sites thereby decreasing the adsorption of Cu(II)ion. When the oxygen groups are removed almostcompletely by degassing at 950°C, the concentra-tion of surface �COO− sites is reduced to almostnil resulting in a further decrease in the adsorp-tion of Cu(II) ions. The adsorption of Cu(II) ionsin case of the 950°, degassed carbon sample maybe attributed to take place in pores.

Acknowledgements

R.C. Bansal is thankful to the All Indian Coun-cil for Technical Education (AICTE) for theaward of Emeritus Fellowship.

References

[1] H. Petrov, T. Budinova, I. Khovesov, Carbon 30 (1992)135.

[2] T. Mangalardi, A.E. Paolini, F. Pellorca, Russ. Chim. 42(1990) 2570.

[3] I.Y. Andreevo, I.L. Minko, I. Yu Kaka Kevich, Zh.Prakl. Khim 64 (1991) 1276.

[4] A. Mathur, S.K. Khare, D.C. Rupainwar, J. Indian Pol-lut. Control 5 (1989) 52.

[5] I.A. Tarkovskaya, A.N. Tomashevskaya, U.E. Goba,O.E. Nagorskaya, L.A. Shurupova, B.S. Povazhnyi,Ukr. Khim.Ali. 57 (1991) 480.

[6] H. Urmani, T.W. Ahmed, S.Z. Ahmed, Pak. J. Sci. Ind.Res. 34 (1991) 26.

[7] M.A. Kahn, Y.I. Khattak, Carbon 30 (1992) 957.[8] M.A. Kahn, Y.I. Khattak, J. Chem. Soc. Pak. 12 (1990)

213.[9] K.S. Low, C.K. Loe, S.L. Wong, Environ. Technol. 16

(1995) 877.[10] N.V. Deorkar, L.L. Tavlarides, Met. Mater. Waste

Reduct. Recov. Remov. Process Symp. (1994) 3.[11] R.C. Bansal, J.B. Donnet, F. Stoeckli, Activated Car-

bon, Marcel Dekker, New York, 1988.[12] R.C. Bansal, J.B. Donnet, in: R.C. Bansal, J.B. Donnet,

F. Wang (Eds.), Carbon Black, Marcel Dekker, NewYork, 1993.

[13] R.C. Bansal, N. Bhatia, T.L. Dhami, Carbon 16 (1978)65.

[14] R.C. Bansal, T.L. Dhami, S. Parkash, Carbon 16 (1978)289.

[15] B.R. Puri, R.C. Bansal, Carbon 1 (1964) 451.[16] I.M. Vogel, in: Text Book of Qualitative Inorganic

Analysis (Revised by J.Bassel, R.C. Donney, G.H. Jaf-fery and J. Mendham), fouth ed., ELBS Publication,1986, M XVIII-26.

[17] M.O. Corpacioglu, C.P. Huang, Carbon 21 (1987) 1031.[18] S.S. Barton, D.H. Gellispie, B.H. Harrison, W. Kemp,

Carbon 16 (1978) 363.[19] J.B. Donnet, A. Voet, Carbon Black, Marcel Dekker,

New York, 1976, p. 20.[20] H.P. Boehm, Advances in Catalysis, vol. 16, Academic

Press, New York, 1966, p. 179.[21] B.R. Puri, R.C. Bansal, Carbon 1 (1964) 457.

removal of copper from aqueous solutions by adsorption on activated carbons

Documents