Modification of oxidized activated carbon surface by fe and mn for arsenic removal from aquerous solution - Pham Thi Hai Thinh

Vietnam Journal of Science and Technology 56 (2C) (2018) 80-87 MODIFICATION OF OXIDIZED ACTIVATED CARBON SURFACE BY Fe AND Mn FOR ARSENIC REMOVAL FROM AQUEROUS SOLUTION Pham Thi Hai Thinh1, 2, *, Tran Hong Con3, Phuong Thao3 1Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi 2Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi 3VNU, University of Science, 19 Le Thanh Tong, Ha Noi *Email: phamhaithinh1979@gmail.com Received: 3 May 2018; Accepted for publication: 21 August 2018 ABSTRACT Carboxylate groups on oxidized activated carbon surface were transformed to the forms of Mn2+ and Fe3+ (signed as OAC-Mn and OAC-Fe respectively) through multi-step procedure. This modified activated carbon then was used as an adsorption material for arsenic removing from aqueous solution. Synthetic water containing As(III) and As(V) was used for study of arsenic adsorption capacities of OAC-Fe and OAC-Mn. The similar study had also been done with original granular activated carbon for comparison. The effects of modified metals onto oxidized activated carbon, metals doses and initial arsenic concentration on the removal of As(III), As(V) have been surveyed and discussed. Batch adsorption experiments were carried out with arsenic concentration in the range of 1 – 50 mg/l. Langmuir models were used for the adsorption isotherm screening. The results showed that both of OAC-Fe and OAC-Mn have good adsorption capacities for As(III) but OAC-Fe has a greater removal capacity for As(V) than OAC-Mn. OAC-Mn was identified as a good material for the of As(III) removal, because of its oxidation efficiency of As(III) to As(V) during adsorption process. Keywords: oxidized activated carbon, Fe and Mn modificaton, arsenic removal. 1. INTRODUCTION Activated carbons (AC) have been proven to be effective adsorbents for the removal of a wide variety of organic and inorganic pollutants. However, AC is relatively less effective in removing metal species from aqueous solution as compared to removing organic compounds [1]. Because AC has nonpolar characteristic and poor adsorption selectivity so somewhat inhibits attraction between charged metal species and its surface [2, 3]. To enhance sorption capacity for cationic and oxyanionic metal species, modification and impregnation techniques have been performed [4, 5]. The oxidation of AC can significantly enhance the adsorption capacity of these adsorbents by improving their ion-exchange properties. Iron-impregnated activated carbon (Fe- Modification of oxidized activated carbon surface by Fe and Mn for Arsenic removal 81 AC) and/or manganese-impregnated activated carbon (Mn-AC) are considered potential multifunctional reaction media because the AC possessing a large surface area and the surface can be modified. Activated carbon that impregnated with Fe-oxides or Mn-oxides can be applied to the treatment of both cationic and anionic states of heavy metals via adsorption and oxidation process, respectively [6]. Surface-modified AC by metal impregnation is becoming a recent research field for the development of adsorption material. The use of iron and manganese impregnated on AC has been reported by some researches [7, 8, 9] for arsenic removing from water environment. Arsenic is generally found as a contaminant in soil and water systems due to various anthropogenic sources, such as mining activity, discharges of industrial wastes and agricultural application and geochemical reactions [10]. Although arsenic has multiple oxidation states (+5, +3, 0 and −3), arsenite As(III) and arsenate As(V) are the most common in natural environments. Arsenic removal technologies are wide applied. However, some of these processes are expensive or require the control of pH and/or other parameters to achieve the optimum arsenic removal capacity. In addition, most of the processes that have been identified as promising techniques in the treatment of As(V) [11] are also partly effective for the treatment of As(III), thus require a further simple and cost-effective technique for the oxidation of As(III) to As(V). Therefore, as one of the promising techniques, manganese and iron impregnated AC was applied for the treatment of both As(III) and As(V). The objective of this study is to develop a method to impregnate OAC for the treatment of both As(III) and As(V). 2. MATERIALS AND METHODS 2.1. Material preparation All AC samples in this study were from Tra Bac Joint Stock Corporation in Tra Vinh province. Details of preparation of oxidized activated carbon and treatment surface by NaOH (OAC) are reported elsewhere [12]. The results of BET surface area of AC and OAC are 785 and 761 m2/g. Preparation of OAC-Mn: Manganese (II) sulfate (MnSO4.H2O) was used as a manganese precursor. Manganese content were changed at 3, 5, 7 and 10 wt%. 5 g of OACNa were added into 200 mL of MnSO4.H2O solution at the concentration of 3, 5, 7 and 10 wt%. After being stirred at 125 rpm for 24 h at pH about 8, modified carbon was filtered and dried at 100 oC for 12 h to allow stabilization of the coating process. To remove traces of uncoated manganese on the OAC, the dried OAC-Mn was rinsed several times with distilled water and then dried again at 105 oC for 24 h. The sample was signed as OAC-Mn. Preparation of OAC-Fe: 500 mL of 0.1; 0.3 and 0.5 M FeCl3/HCl 0.01 M solutions were adjusted to pH 3 by HCl 0.1 M, after that it was mixed with OAC with ratio of 1:20 (solid: liquid) in a flask. This mixture was put on a vacuum pump to let iron fill into the pores about 2 hour. It was carried out thermal hydrolysis at 70 oC, with the water in the suspension continuously removed until approximately 10 – 20 % of the water remained. After that, the suspension was decanted and the solid phase was mixed with deionized water. The mixtures were kept for 24 hours at 25 oC to allow the diffusion of iron ions into the AC pore spaces. After that, to remove any non-impregnated iron the samples were filtered and dried at 70 oC for 12 hours. The product was then washed with distilled and dried again at 105 oC for 24 h. The sample was signed as OAC-Fe. 2.2. Methods Pham Thi Hai Thinh, Tran Hong Con, Phuong Thao 82 2.2.1. pHpzc determination The initial pH value (pHi) of 0.1 M NaCl solution was adjusted from pH 2 to pH 11 by adding 0.5 M NaOH or 0.5 M HCl, 50 ml of this solution was transferred to a series of Erlenmeyer flasks and 0.1 g AC was added to each flask. The flasks were securely sealed immediately and suspensions were then shaken at 150 rpm for 24 h before the final pH value (pHf) of the supernatant was recorded. The difference between pHi and pHf (∆pH = pHi – pHf) was plotted against pHi and the point of the intersection of the resulting curve and pHi was pHpzc [13]. 2.2.2. Measurement of manganese and iron content The manganese and iron content of the OAC-Mn, OAC-Fe composites, 0.1 g samples were acid digested in concentrated HNO3 and 30 % H2O2 (as described in EPA Method 3050B) and then analyzed using inductively coupled plasma (ICP) emission spectroscopy. 2.2.3. Batch equilibrium study Arsenate (As(V)) and arsenite (As(III)) stock solutions (1000 mg/L) were prepared from Na2HAsO4·7H2O and NaAsO2, respectively. Working solutions were prepared fresh daily for each batch test. The batch experiments were carried out by adding 100 mL of As(V) or As(III) solution into 250 mL Erlenmeyer flasks that each contained 0.5 g of OAC-Mn or OAC-Fe. The flasks were shaken at 150 rpm for 24 h. After 24 h of contact time, samples from each flask were decanted, filtered and analyzed for the residual arsenic in the solution. 2.2.4. Calculation of As(III) and As(V) adsorption capacity Adsorption isotherms of AOCNa-Mn, OACNa-Fe for arsenite and arsenate adsorption were described by the Langmuir models. The Langmuir isotherm [14] is given by equation: where: qe is equilibrium adsorption capacity (mg/g); qm is the maximum adsorption capacity (mg/g); Ce is equilibrium concentration (mg/L) and KL is Langmuir constant (L/mg). 3. RESULTS AND DISCUSSION 3.1. Materials characterization pHpzc indicates the net zero charge of AC, this parameter describes the overall contribution of the groups operating on the activated carbons and their ability for attracting charged ions to their surface. Table 1 provides the pHpzc of the activated carbons studied before and after manganese and iron modification. pHpzc of OAC-Mn was a slight increase (from 6.8 to 7.3). Given the conditions of the impregnation, the increase in the pHpzc might be the adjust pH of solution by NaOH. Otherwise, pHpzc of OAC-Fe was light decrease (from 6.8 to 6.4) because the impregnated process was carried out of pH 3 so might be increases acidic functional groups on OAC surface. The iron and manganese content of the raw materials and modified activated carbons is summarized in Table 1. The iron and manganese content of raw AC was very low. The manganese and iron impregnated on OAC caused a remarkable change to its iron and manganese Modification of oxidized activated carbon surface by Fe and Mn for Arsenic removal 83 content. The highest iron content was observed in the OAC-Fe 0.3 M, and the lowest in the AC- Fe 0.1 M. The highest manganese content was in the OAC-Mn 7%. Additionally, the oxidation process by HNO3/NaOH caused modify the carbon surfaces and lead to an increased amount of surface groups, and hence to a higher level of iron and manganese fixed at equilibrium. It can be seen that the use of OAC increased the final Fe and Mn content on the OAC, as compared with what was obtained using AC with Mn, Fe impregnated similar concentrations. Table 1. Physicochemical characteristics of OAC, OAC-Mn and OAC-Fe. Characteristics OACNa AC- Mn7 OAC- Mn3 OAC- Mn5 OAC- Mn7 OAC- Mn10 AC- Fe5 OAC- Fe1 OAC- Fe3 OAC- Fe5 pHpzc 6.8 7.5 7.4 7.3 7.3 7.2 6.5 6.4 6.4 6.3 Mn content (mg/kg) 67.5 883 5647 8079 10500 9970 61.2 56.5 60.2 50.5 Fe content (mg/kg) 78.3 75 68 60 65 73 1079 6030 9860 7661 Where: AC is origin activated carbon; AC-Mn7; AC-Fe5 are origin activated carbon that were impregnated with MnSO4.7H2O 7 wt% and 0.5 M FeCl3/HCl 0.01 M solutions; OAC-Mn3, OAC-Mn5, OAC-Mn7, OAC-Mn10 were oxidized and impregnated with MnSO4.7H2O solution at the concentration of 3, 5, 7 and 10 wt%, respectively. OAC-Fe1, OAC-Fe3, OAC-Fe5 were oxidized and impregnated with 0.1; 0.3; and 0.5 M FeCl3/HCl 0.01 M solutions. 3.2. Effect of pH on arsenite and arsenate adsorption pH is one of the most important factors affecting arsenate adsorption in the liquid phase [15,16]. The impact of pH on arsenate removal was studied with pH values ranging from 2 to 11 using 100 mg OAC-Mn7 or OAC-Fe3 with and 35 mL 5 mg/L arsenate solution. As shown in Fig. 1, arsenic removal rate maintained close to 100 % at pH 3 – 6 and declined slightly at pH 6.0 – 7.0. When pH was above 7.0, arsenic removal rate declined quickly. OAC-Mn and OAC-Fe becomes more positively charged when pH is less than 7.3 and 6.4 (pHpzc) and more negatively charged when pH is above 7.3 and 6.4. As pH increased, the attractive force between OAC-Mn and OAC-Fe and arsenate became less and changed to repulsive force when pH above 7.3 and 6.4. For As(III) the percentage removal is maximum in the pH range of 6 – 10 for OAC-Mn and OAC-Fe. The pH of the solution determines chemistry and speciation of As and it also effects the surface charge of the adsorbent. Below pH 9 As (III) typically exists in non ionic form i.e., H3AsO3 (arsenous acid) but pH greater than 9 it exists in two anionic forms H2AsO3- and HAsO32-. At higher pH > 11 the arsenic removal is declined for OAC-Mn and OAC-Fe. 3.3. Effect of initial concentration and manganese, iron content doping on As (III) removal OAC with five different manganese and four iron contents were used in arsenite adsorption tests to determine the adsorption capacities. AC has little arsenate adsorption capacity (0.19 mg/g) Figure 1. Effect of pH on arsenite and arsenat adsoption 0 0.3 0.6 0.9 1.2 1.5 2 4 6 8 10 12 14 Ad so pt io n ca pa cit y ( m g/ g) pH OAC-Mn7 AsIII OAC-Fe3 AsIII OAC-Mn7 AsV OAC-Fe3 AsV Pham Thi Hai Thinh, Tran Hong Con, Phuong Thao 84 while impregnated iron and manganese enhanced the adsorption capacity considerably. The Langmuir model was used to interpret the arsenite adsorption on OAC-Mn and OAC-Fe. As shown in Figure 2, Langmuir model fits arsenite adsorption isotherm curves very well with R2 between 0.981 and 0.99. Figure 2. Linear curve with Langmuir model for As (III) adsorption (a. For Mn; b. For Fe). Impact of the amount of iron impregnated and initial concentration on arsenic adsorption capacity is shown in Figure 2b. The relationships between four iron contents and maximum adsorption capacity (qm) were evaluated. As shown in Figure 2b, arsenite adsorption capacity increased as more iron was impregnated and reached a highest capacity of 3.15 mg/g when iron content increased to 0.3 M. Further increase of iron content resulted in capacity decreasing gradually. Surface unmodified activated carbon obtained used for removal of arsenic generally have low efficiency as the carbon surface is predominantly negatively charged at neutral pH and is thus not suitable for adsorption of these arsenic species. Impact of the amount of manganese impregnated and initial concentration on arsenic adsorption capacity is shown in Figure 2a. OAC-Mn7 has highest ion exchange capacity, while AC-Mn 7 has minimum one (4.08 mg/g and 2.07 mg/g, respectively). Mn-AC was identified as a good material for the removal of As(III). Oscarson et al. [17] reported that type of MnO2 can effectively remove As(III) through oxidation and adsorption. As the redox potentials of Mn(IV)/Mn2+ (+1.23V) is greater than that of As(III)/As(V) (+1.18V), As(III) can be thermodynamically oxidized to As(V) by Mn(IV). From the reaction of MnO2 coated OAC with As(III), the release of Mn(II) was observed [7]. This is described in equation: MnO2 + H3AsO3 + 2H+ ↔ H3AsO4 + Mn2+ + H2O Ion Mn2+ was reacted with H3AsO4 to form precipitate Mn3(AsO4)2 on surface OAC. OAC was impregnated with Fe3+ that it was formed FeOOH as per the following equation [18]: Fe3+ + 3OH- → FeOOH + H2O When As (III) was removed at pH > 6, H3AsO3 may be reacted with FeOOH as following equation: FeOOH + H3AsO3 → FeO.H2AsO3 + H2O FeO.H2AsO3 is of weak interaction between As-O- and Fe so OAC-Fe is less effective in removing As (III) than OAC-Mn. 3.4. Effect of initial concentration and manganese, iron content doping on As (V) removal 0 5 10 15 20 25 0 10 20 30 40 50 C e/q e (g /L ) Ce (mg/L) OAC-Mn3 OAC-Mn5 OAC-Mn7 OAC-Mn10 AC-Mn7 0 10 20 30 40 0 10 20 30 40 50 C e/q e (g /L ) Ce (mg/L) OAC-Fe1 OAC-Fe3 OAC-Fe5 AC-Fe5 a b Modification of oxidized activated carbon surface by Fe and Mn for Arsenic removal 85 The effect of initial concentration was carried out by changing the initial concentration from 1.0 to 50.0 mg/L for As(V) at 25°C and at pH ~ 5.5. The adsorption isotherm of As (V) of different OAC-Mn and OAC-Fe were presented by Langmuir model (Figure 3). Raw activated carbons (AC) with low manganese, iron content and acidic surfaces had low arsenic capacities (about 0.17 mg/g). The basic treatment of AC also reduced the arsenic uptake, which is attributed to the slight change in surface charge. After manganese and iron modification on OAC, all activated carbons increased their As(V) adsorption capacity. The highest arsenic adsorption capacities were obtained by OAC-Mn7 (1.95 mg/g) and OAC-Fe3 (4.27 mg/g). The maximum adsorption amount of As(V) onto OAC-Fe was 4.27 mg/g, which was approximately two times lower than that onto OAC-Mn. OAC-Fe was reacted with As (V) that it was formed precipitate such as FeAsO4 or FeOH2AsO4 depend on pH solution. Mn on OAC-Mn was existed in the form of MnO2. Adsorption mechanism of OAC-Mn with As (V) was valence bond between anion arsenate and Mn. Consequently, OAC-Fe was adsorbed As (V) better than OAC-Mn. Figure 3. Linear curve with Langmuir model for As (V) adsorption (a. For Mn; b. For Fe). 4. CONCLUSIONS In order to improving adsorption properties of AC for arsenic, manganese and iron were impregnated on oxidized activated carbon. . From this research, the effect of pH is significant on adsorption capacities of As (III) and As (V). The OAC-Fe, OAC-Mn gives more adsorption capacity of all types of arsenic species than that of AC-Fe, AC-Mn. OAC-Mn and OAC-Fe were identified as good filter materials for the removal of As(III) through the promising oxidation efficiency of As(III) to As(V) by the OAC-Mn and the adsorption of As(V) by both the OAC-Fe and OAC-Mn. In a batch experiment, the adsorption capacity of OAC-Mn7, OAC-Fe3 for As (III) and As (V) adsorption were highest. The maximum adsorption capacity of As (III) and As (V) was calculated from Langmuir isotherm and found to be 4.08; 1.95 and 3.15; 4.27 mg/g, respectively, for OAC-Mn7 and OAC-Fe3. These comparisons clearly indicate that OAC-Fe has greater capacity in the removal of As(V) than As(III) and also in the removal of As(V) compared with OAC-Mn. OAC-Fe was shown to have an important capacity for the removals of As(III) and As(V) through adsorption. OAC-Mn showed a good oxidation capacity for As(III). 0 20 40 60 80 100 0 10 20 30 40 50 C e/q e (g /L ) Ce (mg/L) OAC-Mn3 OAC-Mn5 OAC-Mn7 OAC-Mn10 AC-Mn7 0 5 10 15 20 25 0 10 20 30 40 50 C e/q e (g /L ) Ce (mg/L) OAC-Fe1 OAC-Fe3 OAC-Fe5 Ac-Fe5 a b Pham Thi Hai Thinh, Tran Hong Con, Phuong Thao 86 REFERENCES 1. Adhoum N., Monser L. - Removal of cyanide from aqueous solution using impregnated activated carbon,Chem. Eng. Process. 41 (2002) 17–21. 2. Yin C. Y., Aroua M. K., Wan Daud W. M. A. - Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions, Sep. Purif. Technol. 52 (2007a) 403–415. 3. Yin C. Y., Aroua M. K., Wan Daud W. M. A. - Impregnation of palm shell activated carbon with polyethyleneimine and its effects on Cd2+ adsorption, Colloids Surf. A: Physicochem. Eng. Aspects 307 (2007b) 128–136. 4. Monser L., Greenway G. M. - Liquid chromatographic determination of methylamines using porous graphitic carbon, Anal. Chim. Acta 322 (1996) 63–68. 5. Monser L., Adhoum N. - Modified activated carbon for the removal of copper, zinc, chromium and cyanide from wastewater, Sep. Purif. Technol. 26 (2002) 137–146. 6. Reed B.E., Vaughan R. L., and Jiang L. - As(III), As(V), Hg, and Pb removal by Fe-oxide impregnated activated carbon, J. Environ. Eng. 126 (2000) 869–873. 7. Chang Y. Y., Kim K. S., Jung J. H., Yang J. K. and Lee S. M. - Application of iron-coated sand and manganese-coated sand on the treatment of both As(III) and As(V), Water Science & Technology 55 (1–2) (2007) 69–75. 8. Chang Y. Y., Song K. H., Yang J. K. - Removal of As(III) in a column reactor packed with iron-coated sand and manganese-coated sand, Journal of Hazardous Materials 150 (2008) 565–572 9. Qigang C., Wei L., Wei-chi Y. - Preparation of iron-impregnated granular activated carbon for arsenic removal from drinking water, Journal of Hazardous Materials 184 (2010) 515–522. 10. Kim M.J., Nriagu J., Haack S. - Arsenic species and chemistry in groundwater of southeast Michigan, Environ. Pollut. 120 (2002) 379–390. 11. Chen H.W., Frey M.M., Clifford D., McNeill L.S., Edwards M. - Arsenic treatment considerations, J. Am. Water Works Assoc. 91 (1999) 74–85 12. Pham Thi Hai Thinh, Tran Hong Con, Phuong Thao, Phan Do Hung - Research on ion exchangre capacity of oxidized activated carbon, Vietnam Journal of Science and Technology 55 (4C) (2017), 245-250. 13. Hai Nguyen Tran, Sheng-Jie You, Huan-Ping Chao – Effect of pyrolysis temperatures and times on the adsorption of cadimium onto orange pell derired biochar, Waste Management and research 34 (2) (2016) 129 - 138 14. Langmuir I. - The sorption of gases on plane surface of glass, mica, and platinum, J. Am. Chem. Soc. 40 (9) (1918) 1361 - 1403. 15. Payne K., Abdel-Fattah T. - Adsorption of arsenate and arsenite by iron-treated activated carbon and zeolites: effects of pH, temperature, and ionic strength, J. Environ. Sci. Health A 40 (2005) 723–749.; 16. Jang M., Chen W. F., Cannon F. S. - Preloading hydrous ferric oxide into granular activated carbon for arsenic removal, Environ. Sci. Technol. 42 (2008) 3369–3374. Modification of oxidized activated carbon surface by Fe and Mn for Arsenic removal 87 17. Oscarson D. W., Huang P. M., and Liaw W. K. - Role of manganese in the oxidation of arsenite by freshwater lake sediments, Clays Clay Miner. 29 (1981) 219–225. 18. Mondal P., Majumder C. B., Mohanty B. - Effects of adsorbent dose, its particle size and initial arsenic concentration on the removal of arsenic, iron and manganese from simulated ground water by Fe3+ impregnated activated carbon, Journal of Hazardous Materials 150 (2008) 695–702.