Evaluation of Heavy Metals Removal Using Some Egyptian Clays

Transcription

1 211 2nd International Conference on Environmental Science and Technology IPCBEE vol.6 (211) (211) IACSIT Press, Singapore Evaluation of Heavy Metals Removal Using Some Egyptian Clays H. A. Talaat 1, N.M. El Defrawy 1, A.G. Abulnour 1 and H.A. Hani 1 1 Engineering Research Division National Research Centre (NRC), Giza, Egypt hataat@yahoo.com A. Tawfik 2 2 Inorganic Chemical Industries and Mineral Resources Research Division National Research Centre (NRC), Giza, Egypt tawfik_omar76@yahoo.com Abstract Heavy metals are toxic to health and environment. Extensive endeavors are mandatory to economically remove them from contaminated water. Among viable options, clays of different characteristics are considered for the removal of heavy metals from polluted effluents. In this paper, raw and treated Egyptian kaolin as well as Ca and Na-bentonites ( and ) are investigated for heavy metals removal. The treatment includes acid washing and calcination. The characterization of the clays was performed using XRF, XRD and DTA. Adsorption of Cr(III), Ni(II), Cd(II), Cu(II), Zn(II) and Pb(II) salts at low concentrations were investigated in batch mode. The clay dose was.5 g/l with metal concentrations from.3 mg/l to 1.3 mg/l. In a case study, the experimental results showed that raw kaolin gave better performance as compared to acid washed or calcined kaolin. The highest adsorption capacity for Cd(II), Cu (II), Zn(II), Ni(II) and Pb(II) was achieved using. was the most favorable for Cr(III) adsorption. The adsorption of Cd(II), Cu(II) and Ni(II) were well represented using Freundlich isotherm, while that of Pb(II) and Zn(II) fitted well with Langmuir isotherm. The results indicate that the use of bentonite could provide a cheap and technically viable option for heavy metals removal from polluted water. Keywards- Egyptian kaolin; bentonite; adsorption; heavy metals; isotherms I. INTRODUCTION Egyptian kaolin is found as alternating beds within thick sandstone succession or as a matrix for sand grains. It is composed of mainly kaolinite mineral (5-95%) with some free quartz and some clay minerals and feldspar [1,2]. Bentonite is an adsorbent aluminum phyllosilicate and is mainly composed of montmorillonite (smectite) with some other clays and inorganic minerals. Types of bentonites depend on their dominant elements (K, Na, Ca and Al). Such clay minerals in soil play the role of natural scavenger by removing and accumulating contaminants in water passing through the soil through exchange adsorption mechanism. The high specific area and the ability of holding water in the interlayer sites gave clays excellent adsorbent capacity which could be increased by acid activation and/or thermal treatment [3]. Adsorption is an important physicochemical process that occurs at the solid-liquid interface. It is considered a preferred method for removal, recovery and recycling of toxic heavy metals. Natural and modified clay minerals have been studied as adsorbents for the removal of various toxic and hazardous pollutants of major concern to the environment. Kaolinite and montmorillonite showed good adsorbance for removal of toxic heavy metals as (Cd, Cr, Co, Cu, Fe,Pb, Mn,Ni and Zn). The reported results showed that clays could be effectively used as liner in water treatment plants [-6]. Also, raw kaolin has been used in Egypt to remove heavy metals (Cd,Cr,Cu,Pb,Sr,Ni and Zn) as a post treatment stage in wastewater treatment plants comprising three consecutive processing namely; aeration, addition of alum and adsorption at kaolin surface. The treated waste water complied with the Egyptian discharge limits for surface water and irrigation [7]. The adsorption characteristics of Cd(II) and Cu(II) onto natural bentonite have been reported based on its adsorption ability as a function of temperature, particle size, ph, metal concentrations and shaking time. The results verified the possibility of substituting activated carbon with bentonites for some adsorption applications due to its cheapness, availability and low cost recovery processes in water purification []. Comparison between adsorption of Cu(II) and Pb(II) onto natural and modified bentonite revealed that the adsorption on Na-bentonite is better and is affected by increasing ph with maximum adsorption in the range of [9]. The sorption data have been found to be applicable predominantly to the Langmuir and Freundlich sorption isotherm [1, 11]. Kamel et al [] showed that the affinity of Egyptian kaolinitic clay for ion sorption is in the order: Cu>Fe>Pb> Mn>Zn. The sorption mechanism by kaolinite clay takes place mainly through the formation of single monolayer. The efficiency of clay ores, modified clays and bentonites for heavy metals removal has been discussed by several authors [, 13-15]. The physicochemical parameters involved during this adsorption were investigated. This work is concerned with the adsorption of heavy metals on natural and treated Egyptian kaolin and bentonite. II. MATERIALS AND METHODS A. Materials 1) Adsorbent Two structurally different Egyptian clays were utilized in this study namely; raw kaolin (K r ) and raw bentonite of Al/Si total ratio 1:1.67 and 1:2.7 by weight, respectively. Bentonite has two different forms of calcium-bentonite (Ca- V1-37

2 B) and sodium-bentonite () treated by soda ash as delivered. Raw kaolin was supplied from Abu Zeneima (Sinai) by Normeetec Company for Building Materials, while bentonites were supplied by the International Company of Mining and Investment from Wadi- Elnatron area. 2) Adsorbate Salts of chromium nitrate, cadmium, nickel, zinc, copper and lead sulfate were used as a source of heavy metal ions. Dilute hydrochloric or nitric acid and sodium bi-carbonate were used for ph adjustment. Chemicals used were of analytical/laboratory grade procured from Merck, fine Chemicals and Aldrich. Distilled water was used for all experimental investigations. B. Methods 1) Pretreatment of kaolin Treatment of kaolin was carried-out through acid washing and/or calcinations from 5 to 9 o C for different time intervals. Kaolin has been subjected to acid washing on a pilot scale where, 1 kg of kaolin was fed in a reactor and agitated with 5 liter distilled water acidified with HCl.The ph was adjusted to 5 and the mixture was continuously stirred for 3 hours, then centrifuged using pilot scale basket centrifuge and the filtrate was recycled twice to ensure maximum solids recovery. The filter cake was washed/centrifuged with 5 L distilled water, then dried for 2 hours at ºC in a pilot scale shelf tray dryer. The previously acid washed kaolin sample was calcined at different temperatures between 5 to 9 o C for different time intervals from 1 hr to 5 hrs. Also, raw kaolin was calcined at o C for 6,,1 and hrs. 2) Characterization of clay samples The chemical and mineralogical compositions of raw and treated kaolin as well as bentonites were characterized by X- ray fluorescence (XRF) using AXIOS PANalytical 25, X- ray diffraction (XRD) BRUKER and differential thermal analysis (DTA/ TG LAB system SETARAM. The initial and residual metal ion concentration in aqueous solutions has been determined using Atomic Absorption Spectrometer (AAS) operating with an air-acetylene flame. 3) Adsorption performance and isotherms The experimental tests to determine the adsorption capacity of the raw and treated Egyptian kaolin and bentonite samples for the removal of some heavy metals from their solutions were conducted in batch mode using a 1 L beaker salt solution. Metal removal studies have been investigated using kaolin in different forms: raw kaolin (), acid washed kaolin (KA), acid washing followed by calcination (KT51- KT95) and calcined without acid washing as well as raw Na and Ca-bentonites. Prior to each experiment, a predetermined amount of sieved adsorbent (.5 g) with particle size of less than 1 µm was added to each beaker, then the prepared salt solution with the desired concentration (Ci, mg/l) was added and ph was adjusted using dilute NaHCO 3 or HCl solutions. Stirring was kept at 25 rpm for 2 minutes followed by two hours at 7 rpm for each run throughout the experiment to ensure homogeneous mixing. Settling was performed for 3 minutes followed by filtration through Whatman filter paper no.. The concentrations of heavy metal ions before and after the treatment were determined by the atomic absorption spectrophotometer. The adsorption isotherms of raw clays (kaolin, Ca and Na-bentonites) for the removal of some heavy metals have been evaluated. Experiments were performed with single metal solutions (Cr(III), Ni(II), Cd(II), Cu(II), Zn(II) and Pb(II)). Both Langmuir and Freundlich isotherms have been studied using the following equations [1, 11]. The Langmuir isotherm could be represented by the following equation: 1 / Qe = (1/Qm) + (1/Ce) * (1/Qm*b) (1) where Ce is the equilibrium aqueous metal ions concentration (mg/l), Qe the amount of metal ions adsorbed per gram of adsorbent at equilibrium (mg/g), Qm and b are the Langmuir constants related to the maximum adsorption capacity and energy of adsorption, respectively. The Freundlich adsorption isotherm is mathematically expressed as follows: log Qe = log K + (1/n) * log Ce (2) Where, K is an indicator of the adsorption capacity and 1/n is the adsorption intensity. By plotting log Qe versus log Ce, values of K and n can be determined from the intercept and slope of the plot, respectively. III. RESULTS AND DISCUSSION A. Characterization of Raw Clay Samples 1) Chemical and mineralogical compositions Table (1) shows the oxides constituents of the studied clay samples using XRF analysis for raw kaolin () and two types of bentonites; ( and ). Raw kaolin has low alumina content (3.31%) and contains slightly less silica contents. Bentonites show higher distribution of alkali oxides especially Fe 2 O 3 (1.2% & 1.9%) and lower alumina content (1-2%) compared to the studied kaolin. There is general agreement between the current obtained values for both major oxide contents and the high loss on ignition percentage (-15%) with the calculated values and recorded results previously obtained for Egyptian kaolin and bentonite [7,15,]. The mineralogical compositions of the studied clays obtained from XRD analysis are presented in Table (1) and Fig. 1. The results show that kaolinite is the sole clay mineral found in the studied kaolin. The kaolinite mineral content (56%) obtained is much less than the percentage from reported for other locations in Egypt like Kalabsha kaolin (%). In the same context, the high percentage (3.5%) of free quartz is comparable to the value recorded in the literature for free quartz of Kalabsha (7%) [2]. The XRD pattern for Na-bentonite reveals that it contains 2.3 %, 15.5% kaolin, 33.9% quartz and 3.5% K-feldspar (as microcline) as compared to Egyptian bentonite of El-Fayoum area which contains -6% montmorillonite and 2-3 % V1-3

3 kaolinite, while bentonite of Abu Tartour contains 5% kaolinite, 56% montmorillonite, 9% illite and 11% free quartz [17,1]. Thus, the bentonites are considered as low grade as far as montmorillonite is concerned, although its percentage is higher than the used kaolin. 2) Differential thermal analysis (DTA) Fig. 2 shows the thermal behavior of kaolin and Nabentonite. DTA curve of kaolin revealed endothermic peaks at about o C and at about 326 o C referring to the removal of moisture content and to the de-hydration process of water in spacing layers, respectively. Another endothermic effect around 56 o C is attributed to the removal of hydroxyl group for kaolinite mineral. An exothermic peak at about 9 o C refers to the start of kaolinite structure transformations. The thermal behavior of bentonite samples by DTA shows endothermic peaks at about 9 o C and 29 o C. These peaks indicate the removal of absorbed water and to the dehydration process of re-absorbed water during heating. Another endothermic effect around 517oC is attributed to the removal of hydroxyl group from montmorillonite mineral. TABLE I. CHEMICAL AND MINERALOGICAL COMPOSITIONS OF RAW CLAYS Chemical composition Constituents (%) K r SiO TiO Al 2 O Fe 2 O MgO CaO Na 2 O Others L.O.I Moisture content Mineralogical compositions kaolinite Quartz Montmorillonit e Others Anatase ; Microclin e; 3.5 Figure 1. XRD patterns for raw Na and Ca-bentonites and kaolin B. Characterization of Treated Kaolin XRD pattern for the investigated washed kaolin is presented in Fig. 3 which shows an increase in the quartz content (.%) with a notable decrease in both kaolinite (7.2%) and.5% anatase contents. C. Adsorption of Heavy Metals The adsorption of Cr(III), Ni(II), Cd(II), Cu(II), Zn(II) and Pb(II) have been thoroughly studied in batch mode onto raw, acid washed and/or calcined kaolin as well as raw bentonites. V1-39

4 Figure 2. DTA of raw Na- and Ca-bentonite as well as Kaolin [13] which showed that untreated kaolin reveals better adsorption for Cd(II) removal than treated kaolin. It has been thus concluded that acid washing alone or that followed by calcination have a detrimental effect on the adsorption of raw kaolin. 2) Thermally treated kaolin As an alternative, thermally treated kaolin, not preceded by acid washing, has been studied. Fig. represents the adsorption capacities (Qe,mg/g) for Cr(III), Cu(II) and Ni(II) using raw kaolin and calcined at C for (6,,1 and hours) at initial concentrations of Cr(III) (.3mg/g), Cu(II) (.1mg/g) and Ni(II) (2.9mg/g). It is observed that the maximum attained adsorption capacities using raw kaolin for Cu(II) and Ni(II) were 3.1 mg/g and 2.3 mg/g, respectively. For these two metal ions, lower values of Qe have been obtained for calcined kaolin. However, comparable Qe values for Cr(III) (.1,.2 mg/g) have been obtained respectively for raw and calcined kaolin at C for 6 hours. Lower Qe values have been observed for Cr(III), Cu(II) and Ni(II) at longer calcination time intervals. TABLE II. ADSORPTION OF CHROMIUM (III) AND CADMIUM (II) ONTO RAW AND TREATED EGYPTIAN KAOLIN Cr (III) Cd (II) Sample Ce (mg/g) % Removal Ce (mg/g) % Removal KA KT51* KT53* KT2* KT9* : raw kaolin KA: acid washed kaolin Cr (.3mg/l) Cu(.1mg/l) Ni(2.9mg/l) 3 Qe(mg/g) Figure 3. XRD patterns for acid washed kaolin 1) Acid washed and calcined kaolin The adsorption capacities of Cr(III) (Ci=.66 mg/l) and Cd(II) (Ci=1.69 mg/l) onto raw kaolin, acid washed kaolin (KA) and washed kaolin followed by calcination at temperatures ranging from 5 to 9 C for different intervals of 1 to 5 hrs are presented in Table (2). It is observed that the removal efficiencies of the tested metals for acid washed kaolin and calcined samples were lower than raw kaolin which may be attributed to the increase in the quartz content and the decrease in kaolinite content after acid washing. This result is in agreement with that of Gupta et al K/6 K/ K/1 K/ Figure. Adsorption capacities of raw and calcined kaolin at different temperatures and times *KT: Kaolin sample acid washed and calcined; values in the first column represent the calcination temperature 1 о C, while those in the second are for the calcination time in hours. V1-

5 D. Comparative Adsorption Performance of Raw Kaolin, Na and Ca Bentonites Adsorption performance of the studied clays is depicted in Fig. 5" for Cr (III), Ni(II), Cd(II), Cu(II), Zn(II) and Pb(II). Investigating the effect of initial ion concentrations leads to the following results: - The maximum attained Cr(III) adsorption capacities for the tested clays are 9.2 mg/g, 1.7 and 15.7 mg/g for, and, respectively. - As for Ni(II) adsorption, shows best results reaching 11.6mg/g adsorption capacity. - It is concluded that had the highest adsorption capacities for Cu, Cd, Pb, Zn and Ni. It is also observed that the selectivity of metals adsorbed is in the order of Pb>Cr>Cd>Cu>Zn>Ni. This may be attributed to the affinity of combination of each metal on the clay [1 and 19]. Table III compiles maximum and minimum removal efficiencies for the tested metal ions over the experimental initial concentration range (up to 1 mg/l). TABLE III. METALS REMOVAL EFFICIENCIES USING DIFFERENT TYPES OF EGYPTIAN CLAYS Metal % Removal Cr (III) Cd (II) Cu(III) Pb (II) Zn (II) Ni (II) ) Adsorption isotherms for the tested heavy metals Isotherm studies have been conducted for adsorption of Ni, Cd, Cu, Zn and Pb using kaolin, Ca and Na-bentonites. The fitting results for Langmuir and Freundlich isotherms along with the relevant contents presented in Table (). As shown in Table (), the adsorption of Ni onto, Cu onto and, Zn and Pb onto all samples was best represented using Langmuir isotherm which is in agreement with previously reported results [5 and 11]. On the other hand, the adsorption of Ni(II) onto and, Cu(II) onto and Cd(II) onto all clays was well fitted using Freundlich isotherm. TABLE IV. LANGMUIR AND FREUNDLICH ISOTHERMS FOR ADSORPTION OF NI, CD, CU, ZN AND PB USING KR, CA-B AND NA-B Clay Langmuir constants Freundlich constants bce Qe = Qm 1 Type log( Qe ) = log( K) + log( Ce) 1 + bce n Qm b R 2 n K R 2 Nickel (ph=5-5.7, Ci=.-7.9 mg/l) Cadmium (ph= 5-5.5, Ci=1-1.3 mg/l) Copper (ph=5-5.3, Ci= mg/l) Zinc (ph=5-5., Ci= 1-1. mg/l) Lead (ph=.5-5, Ci=3-.9 mg/l) mg Cr/g mg Ni/g mg Cu/g mg Zn/g 2 mg Pb/g V1-1

6 Figure 5. Adsorption capacities of the studied heavy metals onto, and IV. CONCLUSIONS Raw kaolin and bentonites obtained from Egyptian quarries manifested acceptable adsorption performance regarding the removal of low concentration metal ions namely; Cr(III), Cd(II), Cu(II), Pd(II),Zn(II) and Ni(II) in polluted water. Acid washing and/or calcination at various temperatures and time, as conducted on pilot scale, had detrimental effect on adsorption performance of kaolin as compared to its raw form. However, the low grade raw kaolin used in the present study was found to be an effective cheap source of scavenging material for heavy metal removal. manifested highest adsorption capacity and removal efficiency for almost all the studied metal ions although gave comparable results. Adsorption of Ni(II) on, Cu(II) on and, Zn(II) and Pd(II) on all clay samples follows Langmuir isotherm. Adsorption of Ni(II) onto and Cd(II) on all clay samples are well represented by Freundlich isotherm. Bentonite used in this work represents a cheap and viable option for the removal of low concentration metal ions from polluted water. ACKNOWLEDGMENT This work is funded by STDF, Egypt project No. 13 entitled "Development of Novel Zeolite for the Removal of Soluble Hazardous Pollutant". REFERENCES [1] H. Baioumy, H.Gilg, E. Holzl, S. Taubald and L. Warrs, Source and origin of sedimentary kaolin deposits in Egypt, 6th Annual Meeting of the Clay Minerals Society, Billings, Montana, June 29, pp [2] N. Abdel-Khalek," The Egyptian kaolin: an outlook in the view of the new climate of investment, "Applied Clay Science, vol. 15, 1999, pp [3] S. Abd-Allah, O. El Hussaini and R.Mahdy, "Towards a more safe environment: characterization of some clay sediments in Egypt for safe environmental applications," Australian Journal of Basic and Applied Sciences, vol., 27, pp [] O. Yauvz, Y.Altunkaynak and F.Guzel, Removal of copper, nickel, cobalt and manganese from aqueous solution by kaolinite, Water Research, vol. 37, 23, pp [5] K.Bhattacharyya and S.Gupta," Adsorption of a few heavy metals on natural and modified kaolinite and montmorillonite: A review," Advance in colloid and interface science, vol. 1, 2, pp [6] S.Veli and B. Alyuz, "Adsorption of copper and zinc from aqueous solution by using natural clay," Journal of Hazardous Materials, vol. 19, 27, pp [7] M.Rashed and M.Soltan, "Removal of nutrients and heavy metals from urban wastewater using aeration, alum and kaolin Ore.," Proceeding EPCOWM, Jan. 22, pp [] N. Karapinar and R. Donat, " Adsorption behaviour of Cu2+ and Cd2+ onto natural bentonite," Desalination, vol. 29, 29, pp [9] L.Yun, S. Xing, X. Qiming, C. Haidong, Z. Huixian and G. Shixiang, "Adsorption of copper and lead in aqueous solution onto bentonite modified by -methylbenzo-15-crown-5,"journal of Hazardous Materials, vol. B137, 26, pp [1] E.Unuabonah, K.Adebowale, B.Olu-owolabi,L.Yang and L.kong," Adsorption of Pb (II) and Cd (II) from aqueous solutions onto sodiumtetraborate-modified kaolinite clay: Equilibrium and thermodynamic studied," Hydrometallurgy, vol. 93, 2, pp [11] J. Hizal and R. Apak, "Modeling of copper (II) and lead (II) adsorption on kaolinite-based clay minerals individually and in the presence of humic acid," Journal of Colloid and Interface Science, vol. 295, 26, pp [] M.Kamel, M.Ibrahm, A.Ismael and M.El-Motaleeb, "Adsorption of some heavy metal ions from aqueous solutions by using kaolinite clay," Ass. Univ. Bull. Environ. Vol. 7, no. 1, 2, pp [13] S.Gupta and K. Bhattacharyya, "Removal of Cd (II) from aqueous solution by kaolinite, montmorillonite and their poly (oxo zirconium) and tetrabutylammonium derivatives,"journal of Hazardous Materials, vol. B, 26, pp [1] A. Mansri, K.Benabadji, J. Desbrières and J. François, "Chromium removal using modified poly(-vinylpyridinium) bentonite salts," Desalination,vol. 25, 29, pp [15] O. Abollino, M. Aceto, M. Malandrino, C. Sarzanini and E. Mentasti, Adsorption of heavy metals on Na-montmorillonite. Effect of ph and organic substances, Water Research, vol. 37, 23, pp [] M.M. Wahba and A.M. Zaghloul, Adsorption characteristics of some heavy metals by some soil minerals, Journal of Applied Sciences Research, vol. 3, no. 6, 27, pp [17] M.Essa and M. Farragallah, Clay minerals and their interaction with heavy metals and microbes of soils irrigated by various water resources at Assiut, Egypt," Ass. Univ. Bull. Environ. Res., vol. 9, no. 2, 26, pp [1] C. Appel and L. Ma," Concentration, ph and surface charge effects on cadmium and lead adsorption in three tropical soils," J. Envirom. Qual., vol. 31, 22, pp [19] U. Saha, S. Taniguchi and K. Sakurai, "Simultaneous adsorption of cadmium, zinc, and lead on hydroxyalumimun and hydroxyaliminosilicate-montmorillonite complexes, "Soil Sci. Soc. Am. J., vol. 66, 22, pp V1-2