Scholarly article on topic 'Enhanced Copper (II) Removal from Acidic Water By Granular Activated Carbon Impregnated with Carboxybenzotriazole'

Enhanced Copper (II) Removal from Acidic Water By Granular Activated Carbon Impregnated with Carboxybenzotriazole Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
APCBEE Procedia
OECD Field of science
Keywords
{"Granular Activated Carbon (GAC)" / Benzotriazole / Copper / "Acidic water"}

Abstract of research paper on Chemical sciences, author of scientific article — Muna A. AbuDalo, Svetlana Nevostrueva, Mark T. Hernandez

Abstract Under acidic conditions (<pH 4.0) common granular activated carbons (GACs) exhibit declining affinity and capacity for many heavy metal cations in treating industrial wastewaters. The adsorption capacities of four types of granular activated carbon (GACs) were significantly increased by oxidation with boiling nitric acid. Column and breakthrough experiments results demonstrated that carboxybenzotriazole (CBT) enhanced the ability of activated carbon to sequester copper to remarkable level: up to 10% by mass. Hard and soft acid/base behavior (HSAB), metal stability and complexation constants, benzotriazoles dissociation constants and point of zero charge for the carbon, as well as triazole precipitation on the GAC surface were attributed to the differences in metal affinity and associated immobilization potential.

Academic research paper on topic "Enhanced Copper (II) Removal from Acidic Water By Granular Activated Carbon Impregnated with Carboxybenzotriazole"

Available online at www.sciencedirect.com

SciVerse ScienceDirect

APCBEE Procedia 5 (2013) 64 - 68

ICESD 2013: January 19-20, Dubai, UAE

Enhanced Copper (II) Removal from acidic Water By Granular Activated Carbon Impregnated with Carboxybenzotriazole

Muna A. AbuDaloa*, Svetlana Nevostruevab and Mark T. Hernandezc

aChemistry Department, Faculty of Science and Arts, Jordan University of Science and Technology, P.O Box 3030 22110 JORDAN ^Environmental Engineer at Intel Corporation, 5000 W. Chandler Blvd. CH7-336, Chandler AZ 85226, USA c Department of Civil and Environmental Engineering, University of Colorado at Boulder, Campus Box 428, Boulder, CO 80309-0428,

Abstract

Under acidic conditions (<pH 4.0) common granular activated carbons (GACs) exhibit declining affinity and capacity for many heavy metal cations in treating industrial wastewaters. The adsorption capacities of four types of granular activated carbon (GACs) were significantly increased by oxidation with boiling nitric acid. Column and breakthrough experiments results demonstrated that carboxybenzotriazole (CBT) enhanced the ability of activated carbon to sequester copper to remarkable level: up to 10% by mass. Hard and soft acid/base behavior (HSAB), metal stability and complexation constants, benzotriazoles dissociation constants and point of zero charge for the carbon, as well as triazole precipitation on the GAC surface were attributed to the differences in metal affinity and associated immobilization potential.

© 2013 The Authors. Published by Elsevier B.V.

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Granular Activated Carbon (GAC); Benzotriazole; Copper; Acidic water

1. Introduction

Copper is a relatively noble metal and widely used in circuit board printing industry. Large amount of acidic wastewater containing relatively high concentration Cu2+ is produced, which requires proper treatment before discharge into the environment to meet regulation standard. Coagulation and precipitation is a

* Corresponding author. Tel.: +962 2 720 1000 Ext. 23557.+; fax:+962 2 720 1071 E-mail address: maabudalo@just.edu.jo.

2212-6708 © 2013 The Authors. Published by Elsevier B.V.

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.012

common treatment method. However, it produces excessive sludge that needs additional treatment and also wastes precious copper resource. Sometimes it is also difficult to meet effluent Cu2+ standard only by the means of coagulation and precipitation. Recovery of copper by adsorption before its discharge into the water body might be a better alternative. Application of processes such as ion exchange, reverse osmosis, ceramic filtration, and adsorption are often required for many industries to meet regulatory discharge requirements.

Granular activated carbon (GAC) has some advantages over polymeric resin including lower manufacturing cost, higher mechanical strength, and higher stability in extreme environments. Major industrial application of GAC includes sorption of a wide array of organic compounds primarily for water treatment. However, with respect to the adsorption of heavy metals by activated carbon, there is a relatively small body of bench-scale research [1-4]. The surface chemistry of activated carbon in response to the metal-bearing solution condition affect both the affinity and capacity of heavy metals; pH being one of the key parameters. Many researchers found that the adsorption of metals by activated carbon dramatically decreases as pH reduced [1-2]. Other researchers investigated the applicability of the specialty GAC sorbents to treat metal-laden industrial wastewater [5]. In this paper, a commercial granular active carbon (GAC), Calgon MRX-P, was used to demonstrate the effectiveness of oxidized activated carbon impregnated with carboxybenzotriazole (CBT) on copper removal from acidic water.

2. Materials and Methods

2.1. Reagents and solutions

Commercial Carboxybenzotriazole (CBT) contains two isomers: 4-CBT (45% by weight) and 5-CBT (55% by weight) was obtained from PMC Specialty Group Inc. (Cincinnati OH, USA). It has low water solubility and was first prepared by dissolution in concentrated NaOH at pH >12.0, then pH of the solution was brought back to the value of 5.0 by slowly adding droplets of 1M HNO3. All other chemicals were reagent grade and purchased from Fisher Scientific or Sigma-Aldrich companies.

2.2. Adsorbent

Granular activated carbon (GAC) Calgon MRX-P of bituminous origin was obtained from Calgon Carbon Corporation (Catlettsburg KY, USA). The properties of MRX-P were shown in Table 1

Table 1. Common engineering properties of Calgon MRX-P

Properties

Surface area (m2/g) 900

Apparent density(g/ml) 0.5

pHpzc (The point of zero charge) 7.2

Mesh size 10x30

3. Procedure and Experimental Design

3.1. GAC oxidation treatment

Modification of the commercial granular activated carbons MRX-P involved oxidation by 20% HNO3 at 90-95°C for 8 hours with consequent washing in pure deionized H2O until the effluent had reached pH>3.0. Subsequently, the oxidized versions of Calgon GACs MRX-P (referred to herein as MRX-Pox ) were dried in

the oven at 90 °C for 2 days and kept in a desiccator for batch experiments.

3.2. Measurement of point zero charge for the carbons

The point of zero charge of GACs was determined by indirect mass titration (drift) method as described by Summers [6] with sodium chloride as an inert electrolyte. Prior to measurement of pH drift, each carbon was thoroughly washed with water followed by dilute sodium hydroxide (~pH 10) to neutralize any free acid that may have remained after oxidation

3.3. Column and breakthrough experimental design

One gram of dehydrated MRX-P or MRX-Pox was packed into a Teflon tube with an internal diameter of 4.86 mm and the length of the carbon bed 120 mm, which resulted in pore volume of 2.22 mL. Both ends of these mini-columns were then sealed with a glass wool. Four types of columns were used for observing metal removal capacity in low pH environments (1.0<pH<4.5): 1) columns packed with 1g of MRX-P, 2) columns packed with 1g of MRX-Pox, 3) columns packed with 1g of MRX-P saturated with CBT (MRX-P+CBT) and, 4) columns packed with 1g of MRX-Pox saturated with CBT (MRX-Pox+CBT). 125 mL of 10 g/L CBT solution pH of 5.0 was pumped through the mini-column by peristaltic pump at a flow rate of 10 mL/hr. The columns were dried at 90 °C for 2 days and the glass wool used to seal the columns was replaced with a fresh glass wool to avoid any CBT residue.

The column breakthrough behaviour for copper was obtained by pumping 0.5 mmol/L of Cu(II) containing solution in an upflow mode through the above-prepared four types of columns at 0.27mL/min flow rate (EBCT of 8.3 min). To enhance the removal efficiency, 5mmol of either chloroacetic or maleic acids was used and the solution was adjusted to the different pH values by 1M NaOH or 1M HNO3. The effluent samples were constantly gathered by the fraction collector for the determination of the breakthrough point. Effluent concentrations of the metals and CBT vs. bed volumes were established through ICP/AES and HPLC, respectively.

4. Results and discussion

4.1. Effect of oxidation on the point zero charge for the carbons

Oxidation played a significant role in altering the surface charge of the carbon that was notable for pHpzc values of MRX-P and MRX-Pox, 7.2 to 3.1, respectively. The outcome highlighted the importance of surface charge through oxidation and would ultimately influence the ability of the candidate GACs to hold metal-coordinating benzotriazoles. Analogous effect was observed by Strelko and co-workers [7] for oxidized activated carbons derived from commercially available Filtrasorb 400 and apricot stones.

The results of elemental analysis performed at Elemental Analysis, Inc. (Lexington KY, USA on activated carbons MRX-P and MRX-Pox, are reported in Table 2. It was demonstrated that for oxidized version of MRX-P the fraction of O2 considerably increased by 11%. At the same time results showed a decrease in carbon content, which had reduced from 84% to 65%. The outcome was comparable to that observed by Puri et al. [8] for activated sugar and coconut based GAC before and after oxidation. Obviously, some of the carbon, containing surface substances, was transformed by oxidation in boiling nitric acid which significantly increases carbon capacity to adsorb organics and remove charged metal cations from water. On the other hand, hydrogen, nitrogen and sulfur fractions of GACs did not significantly change with the oxidation process. That phenomenon might be explained by the nature of the carbon and initial activation method, which define the

carbon surface chemistry and cannot be notably altered by oxidation. Ash content of MRX-P was found to decrease from 6.8% to 4.8% by oxidation. Residual metals, which are often a major component of ash, were present in a highly insoluble form at high pH , and thus were likely not available to interact with aqueous benzotriazoles when introduced.

Table 2: Summary of elemental analysis (wt%) for selected carbons

GAC sample Oxygen Carbon Hydrogen Nitrogen Sulfur Ash

MRX-P 1.34 83.89 0.71 0.42 0.30 6.80

MRX-Pox 12.97 65.43 1.57 0.74 0.30 4.84

4.2. Breakthrough behaviour and copper sorption capacity

The sorption capacity of the four types of columns tested vs. influent pH was shown in Fig 1a. Generally, copper adsorption capacity increased with solution pH increment for all four types of columns tested. For the same pH point, MRX-P has the lowest adsorption capacity while MRX-P-OX is much better than MRX-P, indicating oxidation treatment of active carbon under strong acid condition can greatly improve copper adsorption ability. Impregnating MRX-P or MRX-P-OX carbon bed with CBT can further enhance their copper adsorption capacity. Capacity reached a maximum of 69 mgCu/ gGAC for MRX-P+CBT at pH of 4.0 compared to 9.8 mg Cu/gGAC for MRX-P alone. It was observed that Cu(II) sorption capacity increased when the pH level of the solution was above GAC's pHPZC threshold of 3.1. The difference in copper (II) removal effectiveness became more distinct at pH 4.0 with the maximum of 105 mg Cu/gGAC for MRX-Pox+CBT. Elevating the level of oxygen-containing functional groups on the carbon surface from 1.34% to 12.97% proved to enhance elimination of copper cations from the solution. Moreover, addition of the benzotriazole derivatives to the pores of granular activated carbon improved Cu (II) removal even further by increasing electronegativity. Analogous progress in Cu(II) ions elimination was achieved using oxidized carbon Chemviron F400 in column experiments at pH 4.7 by Saha et al. [9]. Shukla et al. [10] also demonstrated that oxidized coir stripped with 0.25N HCl recovered more copper cations from acidic solutions with the maximum of 6.99 mgCu/gGAC versus to 0.3 lmgCu/gGAC in the case of non-oxidized coir.

# Hiil \ ilium*1-, ml ml

(a) (b)

Fig 1 Sorption Capacity (a) and breakthrough curves (b) for all tested carbon, n=3

A significant shift in metal removal potential was observed for oxidized carbon loaded with CBT (442BV) compared to its non-oxidized counterpart under otherwise identical conditions (125BV) as shown in Fig 1b. CBT addition considerably enhanced the capacity of oxidized GAC for selected Cu (II) ion due to the increase in GAC hardness (according to HSAB concept). Pre-adsorption of MRX-P carbon with CBT enhanced the

removal capacity of copper ion to some extent, because pHPZC (7.2) for MRX-P carbon was well above the solution pH (3.5), its surface was likely electropositive and would not attract metal cations. In addition, some removal of Cu(II), could be attributed to precipitation on GAC surfaces. Previous investigations by Abu-Dalo showed that 18 and 40% of the copper removal was associated with MeBT precipitate at pH 3.0 and 4.0, respectively [11]. Results were in general agreement with the magnitude of enhancements observed by Lee et al.[12] and Yin et al. [13] for the removal of metal ions on chitosan-deposited activated carbon and on polyethyleneimine-impregnated palm shell activated carbon, respectively.

5. Summary

In this study, nitric acid oxidation improved the steric surface characteristics of candidate GACs (such as pore composition, oxygen content, and pHPZC) and made them more suitable and stable for metal-ligand sorption under acidic conditions. The experiments demonstrated that 4,5-CBT might be used to enhance selected metal removal potential of GACs at low pH by adsorbing benzotriazoles onto activated carbon surfaces which subsequently complex metal ions. Impregnating active carbon column with CBT can greatly enhance its Cu2+ uptake capacity from acidic solution. This metal treatment approach may offer flexibility and economic advantages over conventional alkaline precipitation and ion exchange columns.

References

[1] Netzer, A. and Hughes, D.E. Adsorption of copper, lead and cobalt by activated carbon. Water Research 1984; 18 (8): 927-933.

[2] Reed, B. E. and Nonavinakere, S.K. . "Metal adsorption by activated carbon: Effect of complexing ligands, competing adsorbates, ionic strength, and background electrolyte." Separation Science and Technology 1992; 27 (14): 1985-2000.

[3] Strelko, V. J., Malik, D.J. and Streat, M. Interpretation of transition metal sorption behaviour by oxidized active carbons and other adsorbents. Separation Science and Technology 2004; 39(8): 1885-1905.

[4] Doss, V. and Natarajan, G.S. Granular activated carbon Filtrasorb-400 loaded with five different complexing agents as adsorbed chelating species, an innovative adsorbent for the removal of copper ions in aqueous solutions. Research Journal of Chemistry and Environment 2006; 10 (3): 83-89.

[5] Ajmal, M., Rao, R.A.K., Ahmad, R., Ahmad, J. and Rao, L.A.K. Removal and recovery of heavy metals from electroplating wastewater by using Kyanite as an adsorbent. Journal of Hazardous Materials 2001; B87: 127-137.

[6] Summers, R.S. Activated carbon adsorption of humic substances: effect of molecular size and heterodispersity (Ph.D. thesis). Dept. of Civil Engineering, Stanford University, Stanford, CA; 1986

[7] Strelko, V. J., Malik, D.J. and Streat, M. The influence of active carbon oxidation on the preferential removal of heavy metals. Separation Science and Technology_2001; 36(15): 3367-3383.

[8] Puri, B.R., Singh, D.D, Nath, J. and Sharma, L.R. Chemosorption of oxygen on activated charcoal and sorption of acids and bases. Industrial and Engineering Chemistry 1958; 50(7): 1071-1073.

[9] Saha, B., Tai, M.H. and Streat, M. Metal sorption performance of activated carbon after oxidation and subsequent treatments. Trans IChemE 2001; 79(B): 345-487.

[10] Shukla, S.R., Gaikar, V.G., Pai, R.S. and Suryavanshi, U.S. Batch and column adsorption of Cu(II) on unmodified and oxidized coir. Separation Science and Technology 2009; 44: 40-62.

[11] Abu-Dalo, M. (2003). Electrochemical characterization of benzotriazole derivatives and their behaviour in industrial waste treatment (Ph.D. thesis). Department of Civil, Environmental and Architectural Engineering. Boulder, University of Colorado

[12] Lee, J.M., Palanivelu, K. and Lee, Y.S. Removal of hexavalent chromium on chitosan-deposited activated carbon. 8th International Symposium on Nanocomposited and Nanoporous Materials, February 22-24; 2007

[13] Yin, C.Y., Aroua, M.K. and Daud, W.M.A.W. Fixed-bed adsorption of metal ions from aqueous solution on polyethyleneimine-impregnated palm shell activated carbon. Chemical Engineering Journal 2009;148: 8-14.