Characterization of activated carbons from different

Separation and Purification Technology 122 (2014) 421–430

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Characterization of activated carbons from different sources and the simultaneous adsorption of Cu, Cr, and Zn from metallurgic effluent Liliane Schier de Lima a,⇑, Sueli Pércio Quináia a, Fabio Luiz Melquiades b, Gabriel E.V. de Biasi b, Jarem R. Garcia c,d a

Department of Chemistry, Universidade Estadual do Centro-Oeste, Rua Camargo Varela de Sá, 3, 85040-080 Guarapuava, PR, Brazil Department of Physics, Universidade Estadual do Centro-Oeste, Rua Camargo Varela de Sá, 3, 85040-080 Guarapuava, PR, Brazil Department of Engineering, Universidade Estadual de Ponta Grossa, Av. Carlos Cavalcanti, 4748, 84030-900 Ponta Grossa, PR, Brazil d Department of Chemistry, Universidade Estadual de Ponta Grossa, Av. Carlos Cavalcanti, 4748, 84030-900 Ponta Grossa, PR, Brazil b c

a r t i c l e

i n f o

Article history: Received 27 March 2013 Received in revised form 26 November 2013 Accepted 29 November 2013 Available online 4 December 2013 Keywords: Activated carbon Simultaneous sorption Metal ions Metallurgic effluent

a b s t r a c t Activated carbon is often used in metal ion adsorption processes due to the large surface area it provides. In addition, activated carbon is an inexpensive and environmentally friendly material that provides good cost-benefit for the industries that use it. In this study, activated carbons from different sources were characterized physically and chemically. For example, surface area, thermogravimetric analysis, scanning electronic microscopy, energy dispersive X-ray fluorescence, zeta potential, surface basic and acid groups, iodine number, and ash content were determined. Principal components analysis (PCA) was also used to evaluate the relationship between these characteristics and the origin of the activated carbons examined. The capacity for these adsorbents to simultaneously remove Cu(II), Cr(VI), and Zn(II) from a metallurgic effluent were also evaluated, with some of the adsorbents being able to remove these ions very efficiently. Ó 2013 Published by Elsevier B.V.

1. Introduction Activated carbons are porous adsorbents and are used in several industrial processes. These carbons have often been used in the adsorption of pollutants present in gas or liquid phases in order to control environmental pollution, to remove organic compounds, or to remove toxic metallic species [43,11,3]. For industries such as leather, textile, metal plating, battery, pigments, and metallurgic, toxic metallic ions are widely used, and these can affect the environment. Moreover, toxic metallic ions can accumulate in microorganisms, flora, and aquatic fauna, thereby introducing these metals into the food chain and increasing the risk for health problems in humans [21,30]. The removal of metallic ions can be achieved using various methodologies, including precipitation, adsorption, ion exchange, membrane processes, eletrodialysis, and reverse osmosis [29,24,22,39,16]. Among them, activated carbon adsorption is a very effective method due to the large surface area available and the characteristics of activated carbon. In addition, activated carbon can be produced from several naturally carbonaceous materials at a relative low cost [1,32,20,14]. Porous materials such as activated carbons are often characterized by several chemical and physical parameters, including surface

⇑ Corresponding author. Tel./fax: +55 42 36291244. E-mail address: [email protected] (L.S. de Lima). 1383-5866/$ - see front matter Ó 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.seppur.2013.11.034

functional groups, surface area, pore volume, adsorption capacity, pH, and zeta potential. These properties are very important because they directly influence the performance of the activated carbon [31]. Principal components analysis (PCA) is a statistic tool that graphs whole data sets in order to identify correlations among the data [6,33]. In addition, PCA can be used to examine the presence or absence of natural groupings among samples using two- and three-dimensional graphs. This type of presentation helps visualize the relationship among variables [33,13]. The present work aims to characterize activated carbons available from different sources in order to examine correlations that may exist among these characteristics according to a PCA. The activated carbons characterized were also evaluated for their potential to provide simultaneous adsorption of metallic ions in an effluent produced in the metallurgic industry.

2. Materials and methods 2.1. Selection and preparation of activated carbons Table 1 shows the activated carbons selected for this study. They were obtained from different raw materials, including those of vegetal and mineral origin. Samples of PIN (Pinus Wood – Pinus taeda), EUC (Eucalyptus Wood – Eucalyptus grandis), BRA (Bracatinga Wood – Mimosa scrabella), DEN (Dende coconut shell – Elaeis guianeensis),

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L.S. de Lima et al. / Separation and Purification Technology 122 (2014) 421–430 Table 1 Activated carbons samples: origin and activation process. Sample

Activated carbon origin

Activation process

1 2 3 4 5 6 7 8 9 10 11 12 13

PIN – Pinus wood – Pinus taeda EUC – Eucalyptus wood – Eucalyptus grandis BRA – Bracatinga wood – Mimosa scrabella BAB – Babassu coconut shell – Orbignya phalerata DEN – Dende coconut shell – Elaeis guianeensis CP – Peach stones TUC – Tucumã shell – Astrocaryum tucuma BAM – Bamboo – Bambusa vulgares MAÇ – Maçaranduba – Manilkara huberi BET – Mineral Betuminous charcoal LIG – Mineral lignite charcoal CT1 – China – Type 1 – Vegetal origin CT2 – China – Type 2 – Vegetal origin

Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Physical (steam) Chemical (ZnCl2) Chemical (H3PO4)

Table 2 Surface characterization and zeta potential of activated carbons. Sample

Activated carbon

Basic groups (mEq/g)

1 2 3 4 5 6 7 8 9 10 11 12 13

PIN EUC BRA BAB DEN CP TUC BAM MAÇ BET LIG CT1 CT2

0.437 1.172 1.197 0.693 0.776 0.628 0.451 1.179 1.345 0.855 2.892 0.000 0.000

A

Acid groups (mEq/g)

B

1.0

Zeta potential

Carboxilic acids

Lactones

Phenolics

0.278 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.173 1.067 0.725

0.153 0.000 0.000 0.000 0.000 0.026 0.025 0.000 0.000 0.000 0.324 0.427 0.373

0.148 0.077 0.124 0.000 0.388 0.211 0.101 0.102 0.225 0.124 0.143 0.402 0.324

7.09 9.01 9.20 8.39 7.66 7.11 7.35 8.96 9.02 8.33 9.20 2.68 3.75

3 GROUP 3 2

1

TUC BAB CP DEN PIN EUC BAM BRA MA«

GROUP 1

0.5

CT2

Phenolic groups 0.0 vation Activation Process Carboxilic xilic acid groups

Zeta potential poten

Factor 2: 21.84%

Factor 2 : 21.84%

0

CT1 BET

-1

-2

-3 -0.5

LIG

Lactones groups

-4

Basic Groups Origin

GROUP 2

-5

-1.0

-6 -1.0

-0.5

0.0

0.5

1.0

-7

Factor 1 : 63.98%

-6

-5

-4

-3

-2

-1

0

1

2

3

4

Active

Factor 1: 63.98%

Fig. 1. Scores (A) and loadings (B) on the plane defined by the PCA analysis performed for activated carbons from different sources.

CP (Peach stones), TUC (Tucumã shell – Astrocaryum tucuma), and MAÇ (Maçaranduba – Manilkara huberi) were activated using a steam of water and oxygen as activating agents at 800 °C. High vapor pressure was also applied in a vertical refractory furnace. Samples CT1 (China – Type 1, vegetal origin, CT2 (China – Type 2, vegetal origin), and BAM (Bamboo – Bambusa vulgares) were imported from Shanghai Activated Carbon (China). Activated carbon

CT1 was chemically activated using ZnCl2, while CT2 was activated with H3PO4. BET (Mineral Bituminous charcoal) was imported from Xanxi Xinxidai (China) and LIG (Mineral Lignite charcoal) was imported from Norit, an American Company. Samples were dried at 120 °C to achieve a constant weight, then were ground using a Raymond mill model 3036 until >90% of the particles were smaller than 45 lm.

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2.2. Equipments, reagents, and samples

A 6200

2.3. Characterization of adsorbents The Brunauer–Emmett–Teller (BET) method was used to determine surface area, pore volume, and pore diameter for all samples. This methodology employs nitrogen adsorption at different pressures at 77 K. Surface area was determined by applying isothermal BET, and total pore volume was estimated by the volume of N2 adsorbed at a high relative pressure [9]. The Hovarth-Kawazoe (HK) method was applied to determine the volume and surface area of micropores [19]. The Boehm methodology was used to determine the chemical characteristics of the activated carbon surfaces [23,7,8]. The method is based on a back titration with sodium hydroxide to obtain the amount of acidic and basic groups in the adsorbents [17,37,15,28,38]. For example, bases of different strengths are used to determine acidic groups present, including carboxylic acids, lactones, and phenols, while hydrochloric acid is used to determine basic groups present. Aliquots (50 mL) of hydrochloric acid or different bases were added to 500 mg activated carbon samples to detect basic or acid groups present. Mixtures were kept in suspension with stirring for 24 h at room temperature, then were filtered and titrated with sodium hydroxide (0.1 mol/L). Acid and basic groups were determined as mEq/g of adsorbent. The equilibrium method in the batch system was used to obtain zeta potential values for the activated carbons by analyzing different pHs [35]. Adsorbent (200 mg) in 20 mL sodium chloride (0.1 mol/L) at a pH ranging from 1 to 12 was used. After 1 h of stirring at room temperature, samples were filtered and the final pH was determined. Analyses of TG/DTA were made with a heating rate of 10 °C/min from room temperature to 900 °C, in a flow of N2, and using a platinum crucible. Approximately 10 mg of adsorbent were used for the measurements. The pores and surface of the activated carbons studied were observed using scanning electron microcopy (SEM) at 20 °C. All of the activated carbons were also characterized in the presence of other metallic species using EDXRF. For this, 2–3 g of

6000

Weight loss, ug

5800

5600 5400 5200 5000 4800 4600 0

100

200

300

400

500

600

700

800

900

1000

800

900

1000

Temperature (degree Celsius)

B 7600 7400 7200

Weight loss, ug

The QUANTITACHROME AUTOSORB was used to determine the surface area, pore diameter, and pore volume of the activated carbons. A Scanning Electron Microscope (SEM) was obtained from SHIMADZU (model Superscan SSX-550) and was used to observe activated carbon pores. Measurements of Thermogravimetric Analysis and Differential Thermal Analysis (TG/DTA) were performed using a thermogravimetric analyzer (SEIKO EXSTAR 6000 series equipment). Ash content was determined by using a Furnace QUIMIS. Energy Dispersive X-ray Fluorescence (EDXRF) measurements used a portable X-ray tube (target Ag, Ag filter 50 lm, 4 W) to excite samples and a Si-PIN detector (221 eV resolution, 5.9 keV energy, 25 lm Be window) with electronic devices. Adsorption studies were carried out using an incubator with orbital stirring (Tecnal model TE-420) and a Varian (model SpectraAA-220) equipped with hollow cathode lamps and a deuterium lamp for background correction. Metallic ion content was determined through the integration area. Measurements were performed using air/C2H2. Samples were prepared in duplicate and their white aspects were discounted. Calibration curves were generated using analytical standards prepared from 1000 mg/L stock solutions (BIOTEC) and deionized water (HUMAN 900Ò). The effluent sample used was collected from a metallurgical company that produces parts for chainsaws. The initial pH of this effluent was very low (1), and the concentrations of Cr(VI), Cu(II), and Zn(II) were approximately 10, 5, and 12 mg/L, respectively.

7000 6800 6600 6400 6200 6000 0

100

200

300

400

500

600

700

Temperature (degree Celsius)

Fig. 2. TG/DTA activated carbons.

activated carbon were placed in a container covered with Mylar film in order to ensure that the absorption coefficient would be 1. The measurements conditions used were: 28 kV, 10 lA, Ag filter of 50 lm, Ag collimator, and 500 s. The ash content of adsorbents was determined using an oven furnace at 750 °C for 8 h, according to ASTM 2866-94 methodology. The iodine number adsorption was also used according to ASTM D 4607-94 methodology [4,5]. This method is a relative indicator of the porosity of an activated carbon and is widely used by industries as a gauge of the level of activation. However, the method does not necessarily indicate the adsorption capacity for other species. 2.4. Adsorption studies using a metallurgic effluent Various doses (2, 4, 10, 20, 30, and 40 g/L) of adsorbents were used to evaluate the simultaneous adsorption of metallic ions from a metallurgic effluent. The pH of the effluent was adjusted to 4 for the adsorption studies according to preliminary studies previously performed [26]. Briefly, adsorbents were added into a 250 mL conical flask containing 25 mL effluent. The suspensions were agitated at 160 rpm in a rotary shaker for 30 min at room temperature. Cu(II), Cr(VI), and Zn(II) residual content was determined by Flame Atomic Absorption Spectrometry (FAAS). The data presented are

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the average of three replicates and the standard deviation (SD) for each data point was determined and shown.

number of acid groups and low zeta potential values. The mineral activated carbons, BET and LIG, formed Group 2 and they contained high basic group content. They distinguished themselves from the other only by the origin. The remaining activated carbons constituted Group 3, and they had similar zeta potential values and a large amount of basic groups on their surface. The adsorbents all had a vegetal origin and were physically activated. Moreover, Factor 1, which accounts for 63.98% of the data, correlated the following variables: origin, amount of basic groups, and zeta potential. Conversely, the amounts of acid groups and the process of activation were inversely correlated. Factor 2 accounted for 21.84% of the data. Phenolic groups were present in all of the samples studied, except in the BAB activated carbon, and this is consistent with previous studies. The activated carbons produced by surface oxidation with steam and air were found to be less acidic compared to the

3. Results and discussion 3.1. Characterization of adsorbents The chemical characteristics of the surfaces used in this study, including functional groups and zeta potential, are listed in Table 2. PCA was employed to analyze the relationship among basic and acid groups, zeta potential, origin of activated carbons, and the process of activation for the surfaces studied. It was observed that three groups strongly separated according to the type of activation process and origin (Fig. 1A and B). One distinct group included the activated carbons, CT1 and CT2 (Group 1), and these had a high

BRA

CP

CT2

DEN

EUC

LIG

MAÇ

TUC

Fig. 3. Scanning electron microscopic images.

450

800

A

700

400

B

350

600

400

Volume, cc/g

Volume, cc/g

300 500

CT2 CT1

300

250 LIG

200

BET

150 200

100

100

50

0

0 0

0.1

0.2

0.3

0.4

0.5

P/Po

0.6

0.7

0.8

0.9

1

0

0.1

0.2

0.3

0.4

0.5

P/Po

Fig. 4. BET isotherms for (A) CT1 and CT2 activated carbons and (B) BET and LIG activated carbons.

0.6

0.7

0.8

0.9

1

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chemically activated carbons. Furthermore, several surface groups could be formed on the activated carbons, and at high temperatures, the carboxylic groups are typically less stable than phenolic groups [38,12]. The vegetal activated carbons also contained high basic group content, and exhibited high zeta potential values when activated by steam [10,28] caracterizaram carvões de madeira ativados fisicamente, e quimicamente. The TG/DTA values for the adsorbents evaluated are shown in Fig. 2. In all cases, the first endothermic event was due to water loss and the second event was due to loss of mass. The evolution of volatiles as temperature increased resulted in a broad exothermic band. Previously, it has been shown that when carbon is activated in the presence of oxygen (a physical process), levels of gases containing oxygen such as H2O, CO, CO2, and SO2 increase [40,41]. A high thermal stability was observed for all activated carbons, and loss of mass was detected at higher temperatures. The pore characteristics of the different activated carbons studied were analyzed using SEM. Clear differences in porosity

and particle shape were observed, and representative images are shown in Fig. 3. These differences are very important primarily when adsorbents are applied, since the pores can be selective. In general, the pores of mineral and chemically activated carbons were more difficult to observe by SEM. BET, CT1, and CT2 showed a large number of micropores present. Maybe these micropores are leaving directly from the surface of the particle, and it was not possible to be seen. These images also show the particles that formed during the milling process and their different physical characteristics. Figs. 4 and 5 show the BET isotherms of activated carbons. Valladares et al. previously demonstrated that the application of activated carbon is dependent on pore distribution, and the determination of this distribution is very complex due to the structural and energetic heterogeneity of these materials [42]. Thus, the methods applied for determining pore distribution and pore volume assume different positions in the calculations and relationships between key features of heterogeneity. Among these, the

600

500

PIN

400

BAB BAM 300

CP Bambu MAÇ

200

BRA

100

0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

P/Po

Fig. 5. BET isotherms for PIN, EUC, BAB, DEN, BRA, MAÇ, BAM, and CP.

300

250

Cumulated Surface Area, m2/g

Volume, cc/g

EUC

200

150

100

50

0 0

0.02

0.04

0.06

0.08

0.1

0.12

Cumulated Pore Volume, cc/g Fig. 6. Cumulative surface area as a function of total pore volume calculated using the DFT method for TUC activated carbon.

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most used are: (i) adsorption hysteresis is negligible for microporous materials as opposed to mesoporous materials; (ii) it is assumed that the shape of the pores is described by a simple model; (iii) sorbate–sorbent interactions neglect the effects of the possible heterogeneity of the energy surface, considering an ideal graphite structure; (iv) some methods take into account the sorbate–sorbent interactions in the adsorption process and others

A

neglect it completely; and (v) some methods depend on a particular mechanism of micropore filling [36]. Furthermore, it is expected that different types of real deviations exist for microporous materials and these assumptions are not completely satisfied. Fig. 4A shows the adsorption isotherms of N2 for activated carbons from Group 1 (e.g., CT1 and CT2). These activated carbons showed a high BET surface area and the largest number of micropores when

0.16 0.14 0.12

Dv(w)

0.1 0.08 0.06 0.04 0.02 0 0

2

4

6

8

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20

12

14

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18

20

Pore diam eter, A

B

0.20000 0.18000 0.16000 0.14000

Dv(w)

0.12000 0.10000 0.08000 0.06000 0.04000 0.02000 0.00000 0

2

4

6

8

10

Pore diam eter, A

C

0.2 0.18 0.16 0.14

Dv(w)

0.12 0.1 0.08 0.06 0.04 0.02 0 0

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4

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Pore diam eter, A

Fig. 7. The HK method for pore distribution was applied to: (A) CT1 and CT2, (B) BET and LIG, and (C) BAB, BAM, DEN, MAÇ, PIN, EUC, BRA, and CP.

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compared with the other activated carbons. Consequently, a greater number of mesoporous also are present on the above mentioned carbons. Moreover, the mesoporous in these carbons can be observed from the hysteresis curve. Fig. 4B shows the BET isotherms obtained for mineral activated carbons (Group 2). It was observed that LIG differs from BET primarily due to a large desorption hysteresis, which is characteristic of mesoporous materials. Group 3 (PIN, EUC, BAB, DEN, CP, BAM, MAÇ, and BRA) isotherms are shown in Fig. 5. A higher relative micropore volume was observed for BAB, DEN, BAM, and MAÇ, while the other activated carbons exhibited a microporosity less than 70% when compared with the total volume. Furthermore, TUC activated carbon did not exhibit microporosity. Therefore, it was not possible to plot the BET isotherm. Instead, the area was calculated using Density Functional Theory (DFT), and the cumulative volume plot was used as shown in Fig. 6 [25]. The surface area determined for BET was 768.20 m2/g, while for LIG it was 6.16 m2/g, according to the BET method. Previously, the BET method has been applied successfully to microporous materials [34]. However, if the material has a relatively significant

amount of mesoporous and macroporous properties, the method is not appropriate [34]. The HK method was used to evaluate the development of microporosity (Fig. 7). In all of the analyses, the value obtained was always less than 10 Å. Although, a significant mesopore volume greater than 10 Å was calculated for CT1 and CT2. For LIG, two broad peaks were found in the region representing volumes greater than 10 Å due to the presence of mesopores. A narrower range and well-defined microporosity was detected for BAB, BAM, DEN, and MAÇ. PIN, EUC, BRA, and CP activated carbons had a little wider range, although their values were still less than 10 Å. Table 3 summarizes the surface area, pore volume, and average pore diameter calculated for the activated carbons investigated. Iodine number is a classical and relatively simple method, widely used by the industry to evaluate the degree of activation. The correlation between iodine number and surface area for each activated carbon was strong (r2 = 0.8934). This result was of particular interest since the BET technique requires more time and has a higher cost associated with it.

Table 3 Characteristics of activated carbons as a function of surface area and pore volume, iodine sorption and ash content.

a

Activated carbon

BET surface area (m2/g)

Total pore volume (cm3/g)

Micropore volume (cm3/g)

Mesopore volume (cm3/g)

Pore diameter (Å)

Iodine number (mg/g)

Ash content (%)

PIN EUC BRA BAB DEN CP TUCa BAM MAS BET LIGa CT1 CT2

783.90 574.10 660.20 588.10 623.60 500.70 255.60 1016.00 790.90 768.20 484.50 1129.00 1051.00

0.4965 0.3159 0.3934 0.3386 0.4473 0.2740 0.1021 0.5178 0.6784 0.5554 0.4815 0.9645 0.9070

0.3225 0.2191 0.2608 0.3075 0.3291 0.1746 0.00 0.4299 0.5746 0.4234 0.1928 0.6886 0.6184

0.1740 0.0968 0.1326 0.0311 0.1182 0.0994 0.1021 0.0879 0.1038 0.1320 0.2887 0.2759 0.2886

5.225 5.875 5.875 5.375 5.175 5.125 – 5.475 7.775 5.375 17.27 5.875 5.425

843.54 499.28 561.53 546.14 593.41 331.57 342.20 943.28 708.50 776.71 480.14 918.99 952.45

6.98 12.30 19.80 18.00 10.28 10.70 2.23 6.53 6.05 20.50 26.45 5.90 6.25

Surface area and pore volume calculated by DFT method.

Fig. 8. EDXRF for activated carbons.

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A

110 100

% Cu (II) removal

90 80 70 60 50 40 30 20 0

5

10

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25

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45

Dosage, g/L

B

120

100

% Cr(VI) removal

80

60

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0

-20 0

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Dosage, g/L

C

120

100

% Zn(II) removal

80

60

40

20

0

-20 0

5

10

15

20

25

Dosage, g/L Fig. 9. Adsorption studies performed using a metallurgic effluent for the simultaneous removal of: (a) Cu(II), (b) Cr(VI), and (c) Zn(II).

Energy Dispersive X-ray Fluorescence (EDXRF) is a technique that allows several elements to be simultaneously determined without prior preparation of a solid sample. In addition, it is not a destructive technique. In this study, it was used to qualitatively determine the metals present in activated carbons samples. All activated carbons were found to have high levels of Fe, Ni, and

Mn according to the EDXRF analysis performed (Fig. 8). However, Fe contamination may have occurred during the preparation and grinding of the activated carbon samples. Copper (Cu) metal was also detected in the BAB and TUC activated carbon samples, while zinc (Zn) metal was present in activated carbons obtained from BAM, BRA, and CT1. The levels of Zn detected were high, possibly


due to the type of activation the materials were subjected to (e.g., ZnCl2). Lastly, activated carbons from CT1 and CT2, which were obtained from China, had arsenic (As) present. In addition, these were the only samples that did not have calcium (Ca) counts detected.

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were applied to a metallurgic effluent, they were very efficient at concomitantly removing the metallic ions, Cu(II), Cr(VI), and Zn(II), at the studied doses. At lower doses, the best activated carbon was LIG. However, the other activated carbons also exhibited adsorption capacities that could be optimized.

3.2. Adsorption studies Acknowledgments All of the samples examined in this study were applied to a metallurgic effluent to evaluate their capacity to remove metallic ions such as Cu(II), Cr(VI), and Zn(II) (Fig. 9). LIG activated carbon was the best at removing all three ions simultaneously. BRA activated carbon was also efficient at removing the three ions. Overall, Cu(II) adsorption was the most efficient for all of the activated carbons studied compared with Cr(VI) and Zn(II) adsorption. Furthermore, at a dose of 20 g/L adsorbent, there was no significant difference among the most sorbents (Fig. 9a). On the other hand, Cr(VI) and Zn(II) adsorption by the activated carbons exhibited differing efficiencies. For example, CT1, CT2, and PIN did not efficiently remove Cr(VI). However, LIG, BRA, BAM, and TUC in doses up to 10 g/L were found to efficiently remove this ion. In contrast, the other carbons were effective only at doses greater than 30 g/L (Fig. 9b). Regarding the removal of Zn(II) (Fig. 9c), LIG was the most efficient, while BRA and BET were efficient at doses greater than 10 g/L. The remaining carbons showed improvement with increased doses. Hazlík et al. [18] studied the adsorption of Ag, Cd, and Cu from aqueous solutions by natural carbonaceous materials in single, binary, and ternary solutions. It was observed that the adsorption of metals was significantly affected by the presence of other ions in solution, and that removal of metals was considerably higher in a mixed solution compared to a single solution. Furthermore, according to the authors, the adsorption capacity of Cu was higher than Cd for all of the adsorbents tested. A preference for adsorbing metals may be strongly related to ionic properties, such as eletronegativity, ionic radius, and ionic potential. Regarding these factors, the Cu(II) ion has great potential and is strongly removed by an adsorbent [27,2]. It was observed that the adsorption of metal ion Cu(II) was the best when we compare with another metals (Zn(II) and Cr(VI)) for all activated carbons studied. This better capacity could be related with the size of this ion. The ion Cu(II) is the smallest ion and it have a high eletronegativity while the others one are more voluminous ions. The porous distributions for the activated carbons could not be related directly with this capacity, once the best adsorption occurred with the LIG activated carbon, which showed a mesoporous surface. On the other hand, this LIG activated carbon showed a more heterogeneous surface, with major quantity of acid and basic groups of surface when compared with other activated carbons. 4. Conclusions The characterization of activated carbons performed in this study, and the subsequent PCA performed, identified a relationship between the origin, activation process, surface basic and acid groups, and zeta potential of these carbons. Three groups were identified and these exhibited similar characteristics. In addition, the BET isotherms showed large surface areas for all adsorbents, except for LIG and TUC. For these activated carbons, it was not possible to determine the surface area from the BET isotherm. Thus, for these cases, the DFT method was used to calculate the cumulative surface area. LIG also showed a large amount of mesoporous when it is compared with the other carbons. For most of the adsorbents, the porosity that developed was always less than 10 Å. Furthermore, the iodine number was found to directly correlate with the surface area in m2/g. When the activated carbons examined

We thank Alphacarbo Industrial Ltd. for their donation of activated carbons, and Capes for their financial support. References [1] D. Aggawal, M. Goyal, R.C. Bansal, Adsorption of chromium by activated carbon from aqueous solution, Carbon 37 (1999) 1989–1997. [2] S.J. Allen, P.A. Brown, Isotherm analyses for single component and multi component metal sorption onto lignite, J. Chem. Tech. Biotechnol. 62 (1995) 17–24. [3] Z.A. Al-Othman, R. Ali, M. Naushad, Hexavalent chromium removal from aqueous medium by activated carbon prepared from peanut shell: adsorption kinetics, equilibrium and thermodynamic studies, Chem. Eng. J. 184 (2012) 238–247. [4] ASTM D 2866-94 – (Reapproved 1999) – Standard Test Method for Total Ash Content of Activated Carbon. [5] ASTM D 4607-94 – (Reapproved 1999) – Standard Test Method for Determination of Iodine Number Activated Carbon. [6] K.R. Beebe, J.R. Pell, M.B. Seasholtz, Chemometrics: A Practical Guide, John Wiley & Sons, New York, 1997. [7] H.P. Boehm, Chemical identification of surface groups, Adv. Catal. 16 (1966) 179–197. [8] H.P. Boehm, Some aspects of the surface chemistry of carbon blacks and other carbons, Carbon 32 (1994) 759–764. [9] S. Brunauer, P.H. Emmet, E. Teller, Surface area measurements of activated carbon, silica gels and other adsorbents, J. Am. Chem. Soc. 60 (1938) 309–319. [10] C.I.C. Bueno, W.A. Carvalho, Remoção de Chumbo (II) em Sistemas Descontínuos por Carvões Ativados com Ácido Fosfórico e Vapor, Quím. Nova 30 (8) (2007) 1911–1918. [11] M.O. Corapcioglu, C.P. Huang, The adsorption of heavy metals onto hydrous activated carbons, Water Res. 21 (1987) 1031–1044. [12] M.O. Corapeioglu, C.P. Huang, The surface acidity and characterization of some commercial active carbons, Carbon 25 (4) (1987) 569–578. [13] P.R.M. Correia, M.M.C. Ferreira, Reconhecimento de padrões por métodos não supervisionados: explorando procedimento quimiométricos para tratamento de dados analíticos, Quim. Nova 30 (2) (2007) 481–487. [14] P. Galiatsatou, M. Mataxas, V. Kasselouri-Rigopoulou, Mesoporous activated carbon from agricultural byproducts, Mikrochim. Acta 136 (2001) 147–152. [15] L. Giraldo, J.C. Moreno-Piraján, Pb2+ adsorption from aqueous solutions on activated carbons obtained from lignocellulosic residues, Brazilian J. Chem. Eng. 25 (1) (2008) 143–151. [16] P.K. Gosh, Hexavalent chromium [Cr(VI)] removal by acid modified waste activated carbons, J. Hazard. Mater. 171 (2009) 116–122. [17] V.V.S. Guilarduci, J.P. Mesquita, P.B. Martelli, H.F. Gorgulho, Adsorção de fenol sobre carvão ativado em meio alcalino, Quím. Nova 29 (6) (2006) 1226–1232. [18] J. Hanzlík, J. Jehlicka, O. Sebek, Z. Weishauptova, V. Machovic, Multicomponent adsorption of Ag(I), Cd(II) and Cu(II) by natural carbonaceous materials, Water Res. 38 (2004) 2178–2184. [19] G. Hovarth, K.J. Kawazoe, Method for the calculation of effective pore size distribution in molecular sieve carbon, Chem. Eng. Jpn. 16 (1983) 470. [20] Z. Hu, L. Lei, Y. Li, Y. Ni, Chromium adsorption on high-performance activated carbons from aqueous solution, Separat. Purif. Technol. 31 (2003) 13–18. [21] L. Khezami, R. Capart, Removal of chromium(VI) from aqueous solution by activated carbons: kinetic and equilibrium studies, J. Hazard. Mater. B123 (2005) 223–231. [22] M. Kobya, Removal of Cr(VI) from aqueous solutions by adsorption onto hazelnut shell activated carbon: kinetic and equilibrium studies, Bioresour. Technol. 91 (2004) 317–321. [23] J. Lahaye, The chemistry of carbon surfaces, Fuel 77 (6) (1998) 543–547. [24] S.B. Lalvani, T. Wiltowski, A.H. Hubner, A. Weston, N. Mandich, Removal of hexavalent chromium and metal cations by a selective and novel carbon adsorbent, Carbon 36 (1998) 1219–1226. [25] C. Lastoskie, K.E. Gubbins, N.J. Quirke, Pore size distribution analysis of microporous carbons: a density functional theory approach, Phys. Chem. 97 (1993) 4786. [26] L.S. Lima, M.D.M. Araujo, S.P. Quináia, D.W. Migliorini, J.R. Garcia, Adsorption modeling of Cr, Cd and Cu on activated carbon of different origins by using fractional factorial design, Chem. Eng. J. 166 (2011) 881–889. [27] G. Mackay, J. Porter, Equilibrium parameters for the sorption of copper, cadmium and zinc ions onto peat, J. Chem. Tech. Biotechnol 69 (1997) 309– 320. [28] D. Malik, V. Strelko, M. Streat, A.M. Puziy, Characterization of novel modified active carbons and marine algal biomass for the selective adsorption of lead, Water Res. 36 (2002) 1527–1538.

430


[29] L. Monser, N. Adhoum, Modified activated carbon for the removal of copper, zinc, chromium and cyanide from wastewater, Sep. Purif. Technol. 26 (2002) 137–146. [30] S.A. Nabi, R. Bushra, Z.A. Al-Othman, M. Naushad, Synthesis, characterization and analytical applications of a new composite cation exchange material acetonitrile stannic(IV) selenite: adsorption behavior of toxic metal ions in nonionic surfactant medium, Sep. Sci. Technol. 46 (2011) 847–857. [31] C.A. Nunes, M.C. Guerreiro, Estimation of surface area and pore volume of activated carbons by methilene blue and iodine numbers, Quim. Nova 34 (3) (2011) 472–476. [32] M. Pérez-Candela, J.M. Martín-Martínez, R. Torregrosa-Maciá, Chromium (VI) removal with activated carbons, Water Res. 29 (9) (1995) 2174–2180. [33] M.A. Sharaf, D.L. Illman, B.R. Kowalski, Chemometrics, John Wiley & Sons, New York, 1986. [34] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol, T. Siemieniewska, Pure Appl. Chem. 57 (1985) 603. [35] I.D. Smiciklas, S.K. Milonjic, P. Pfendt, The point of zero charge and sorption of cadmium (II) and strontium (II) ions on synthetic hydroxyapatite, Separat. Purif. Technol. 18 (2000) 185–194.

[36] W.A. Steele, The Interaction of Gases with Solids Surfaces, Pergamon Press, New York, 1974. 53. [37] V. Strelko, D.J. Malik, Characterization and metal sorptive properties of oxidized active carbon, J. Colloid Interf. Sci. 250 (2002) 213–220. [38] V. Strelko, D.J. Malik, M. Streat, Characterisation of the surface of oxidized carbon adsorbents, Carbon 40 (2002) 95–104. [39] A.H. Sulaymon, B.A. Abid, J.A. Al-Najar, Removal of lead copper chromium and cobalt ions onto granular activated carbon in batch and fixed-bed adsorbers, Chem. Eng. J. 155 (2009) 647–653. [40] H. Teng, J.-A. Ho, Y.-F. Hsu, Preparation of activated carbons from bituminous coals with CO2 activation – influence of coal oxidation, Carbon 35 (2) (1997) 275–283. [41] H. Teng, T.-S. Yeh, L.-Y. Hsu, Preparation of activated carbons from bituminous coal with phosphoric acid activation, Carbon 36 (9) (1998) 1387–1395. [42] D.L. Valladares, F. Rodriguez Reinoso, G. Zgrablich, Characterization of active carbons: the influence of the method in the determination of the pore size distribution, Carbon 36 (10) (1998) 1491–1499. [43] W.C. Ying, E.A. Dietz, G.C. Woehr, Adsorptive capacities of activated carbon for organic constituents of wastewaters, Environ. Prog. 9 (1990) 1–9.