Lead adsorption characteristics of selected calcareous soils of Iran and their relationship with soil properties

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1 Symposium no. 47 Paper no Presentation: poster Lead adsorption characteristics of selected calcareous soils of Iran and their relationship with soil properties GHARAIE H.A. (1), MAFTOUN M. and KARIMIAN N. (2) (1) Assist. Prof. IROST, P.O. Box , Shiraz, Iran (2) Prof. Soil Sci. Dept. College of Agri. Shiraz Univ. Shiraz, Iran Abstract Most of soils of Iran are calcareous in nature.high ph and carbonate levels are common characteristics of these soils.in these conditions the heavy metals tend to occur in insoluble forms,mainly precipitates as carbonates or oxides.the heavy metal Pb contaminates soils,plants,water,the atmosphere,animals and humans,especially in areas of heavy traffic.this experiment was conducted to find the relationship between the Pb adsorption and selected properties of calcareous soils. Twenty surface (0-20 cm) soil samples with ph ranging from 7.6 to 8.2 and calcium carbonate equivalent (CCE) ranging from 27 to 64% were used in the Pb adsorption study. Two-gram subsamples of each soil were equilibrated with 50 ml of 0.01 M KNO 3 solution initially containing 30,000 to 300,000 mg Pb L -1. The Pb that disappeared from solution (after 2 h shaking at 25 o c) was considered as adsorbed Pb. The adsorption data showed a highly significant fit to Freundlich and Langmuir adsorption isotherm. The coeficients of both isotherms showed significant positive correlations with CCE, OM and clay, except for A Freundlich and OM for which the correlation is negative. Distribution coefficient (also called maximum buffering capacity) calculated as the product of Langmuir K and b, was also found to be significantly related to CCE and OM. Keywords: calcareous soils, lead adsorption, contamination, heavy metals, pollution, lead, soils of Iran Introduction Heavy metals such as Pb, Cd, Cr and Ni have been studied for their effects on soil and plants. The accumulation and persistence of many heavy metals creates an important ecological problem (Andrcu and Garcia, 1996) An increase in the content of Cd, Cu, Mo, Ni, Pb or Zn could produce serious hazards in the soil- plant-animal system. High ph and carbonate levels are common chemical characteristics of Mediterranean soils. In these conditions the heavy metals tend to occurr in insoluble forms (Neilsen et al., 1988) mainly precipitates of carbonates (Andreu and Garcia, 1996; Brown and Elliott, 1992) or oxides. These conditions is dominant in soils of Iran. Due to environmental protection in the industerial world, the study of fate of heavy metals is highly necessary. Lead is adsorbed by soil colloids. The available data affirm the importance of ph, Fe and Al oxide, exchangeable bases and vermiculite on the adsorption of Pb by noncalcareous soils (Hole and Stume, 1976; Harter, 1979; Benjamin et al., 1991)

2 The adsorption of Pb by calcareous soils is poorly understood in contrast with adsorption by noncalcareous soils (Elkatib et al., 1991). Carbonate minerals are major components of calcareous soils of Iran and may have a high potential for surface adsorption of heavy metals. This is supported by McBride (1980). According to Elkhatib (1990), the presence of carbonate minerals can have a great effect on Pb mobility and reactivity through their surface interaction with Pb and thier effect on ph. Retention of nutrients by soils usually studied by adsrption isotherms (Karimian and Moafpourgan, 1999). This is despite the objection raised by some workers (Harter and Smit, 1987; Sposito, 1989) to use the fit of data to isotherm,as a proof that a particular mechanism has occurred. Harter, 1991) in a review of the subject, concluded that,contrary to this objections, adsorption isotherms have provided the majority of information about micronutrient adsorption by soils; and that the equation coefficient can be used to compare data set. This is also supported by Karimian and Moafpourian 1999). The adsorption reactions affects on mobility and availability of trace elements, including Pb.Adsorption isotherms most frequently used are Freundlich and Langmuir (i.e., equation [1] and[2], respectively). X=A.C B [1] X=(K.b.C)/(1+K.C) [2] Where; X is Pb adsorption, mg kg -1 ; A and B are Freundlich coefficients; C is concentration of Pb in equilibrium solution, mg L -1 ; K is Langmuir coefficient related to binding energy of Pb to soil solids; and b is Langmuir adsorption maximum, i.e., the maximum amount of Pb adsorbed on soil solids as a monolayer, mg kg -1. Adsorption characteristics of calcareous soils of Iran have been reported by several workers (Angooty and Negaresan, 1994; Fekri et al., 1994; Ghanbari et al., 1998; Mohammadi, 1996; Samar, 1996) for phosphorous (P), and by karimian and Gholamalizadeh Ahabgar (1999) for manganese (Mn); Karimian and Moafpourian, (1999), Maftoun et al. (2000), for zinc (Zn). The aims of this study were to: A. Investigate the Pb adsorption characteristics of some calcareous soils of Iran. B. Determine the quantitative relationship between these characteristics and properties of selected soils. Materials and Methods Twenty surface soil samples (0-20 cm) from Fars province, Southern Iran with different physical and chemical properties (Table 1) were used for this experiment to study the Pb adsorption isotherm characteristics of calcareous soils under laboratory condition.the soil samples were air dried and passed through a 2-mm sieve after collection and the physicochemical soil properties were determined according to the following procedures: Clay content by hydrometer method, Day, (1965); ph of saturated paste by glass electrode; electrical conductivity (Ec) of saturation extract by conductivity meter ;organic matter (OM) by Walkley-Black (1965)

3 Cation exchange capacity (CEC) by replacing exchangeable cation with sodium acetate (NaOAc), removal of excess sodium (Na) by alcohol, exchanging Na by ammonium acetate (NH 4 OAc), and determining Na concentration by flame photometry (Chapman, 1965); and CaCO 3 equivalent (CCE) by neutralization with hydrochloric acid (HCl) (Allison, 1965). Table 1 Some physicochemical properties of selected soils. Soil No. ph CEC OM CCE Clay cmol kg -1 g kg CCE : Calcium Carbonate Equivalent; OM : Organic Matter; CEC : Cation Exchange Capacity For each sample, 0.25 g subsamples were placed in ten plastic centrifuge tube and mixed with 50 ml of lead nitrate which was prepared in 0.01 M KNO 3 with initial concentration of 30,000, 60,000, 90,000, 120,000, 150,000, 180,000, 210,000, 240,000, 270,000 and 300,000 mg L -1. KNO 3 were used to adjust ionic strength. The tubes were stoppered and shaked continuously for 2 hours in a mechanical shaker at room temprature and then centrifuged for ten minutes. The supernatants were filtered through Whatman No. 42 filter paper and used for determination of Pb concentration by Shimadzu AA-670 atomic adsorption. The difference between the Pb concentration of initial solution and the filtered supernatant was taken as the Pb retained by the soil. This retention may be due to precipitation of lead carbonates (Nriago, 1973a). Freundlich and Langmuir equations (1and 2, respectively) were used to interpret the equilibrium adsorption data and respective adsorption coefficients were calculated. From the data attained the K d (distribution coefficient) (Bolt and Bruggcn wert, 1976) or maximum buffering capacity (Iycngar and Raja, 1983) or M (Karimian and moatpouryan, 1999), were calculated. Stepwise regression procedure was used to study the relationship between the coefficients and the soil properties

4 Result and Discussion The adsorption data showed a highly significant fit to the Freundlich adsorption isotherm (Table 2). The amount of Freundlich coefficient (A) varies from 2109 to for different soils. This coefficient represents the amount of lead adsorbed per unit of soil by one unit of lead concentration in equilibrium solution and can be used for investigation of lead adsorption properties. This finding is supported by Karimian and Moafpouryan (Karimian and Moafpuuryan, 1999), for zinc in calcareous soils of Iran. Table 2 Coefficients of Freundlich adsorption isotherm (X=AC B ) and coefficients of determination (r 2 ) for the fit of data. Soil No. A B r ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** : Highly significant (p<0.01). According to the results CCE, OM and clay are significantly (p<0.05) related to A freundlich (equation 3), A= CCE OM+ C R 2 =0.317 [3] Where A is Freundlich coefficient (mg Pb kg -1 ), OM is soil organic matter (g kg -1 ) and CCE is calcium carbonate equivalent (g kg -1 ). The amount of B freundlich varies from to and has a highly significant (p<0.01) relationship with soil organic matter, B= OM R 2 =0.356 [4] Where B is the freundlich coefficient and OM were defined in equation [3] (equation 4). The fit of data to Langmuir adsorption isotherm (equation 2) was highly significant (p<0.01) (Table 3). Langmuir K was found to be significantly (p<0.05) related to CCE and OM (equation 5), and varies from to (Table 3). K= (10-6 )CCE +3.22(10-6 ) OM R 2 =0.245 [5]

5 Where K is Langmuir coefficient, OM and CCE are defined in equation [3]. Correlation of Langmuir coefficient; b,mg Pb Kg 1 soil; with OM and CCE found to be highly significant (p<0.01), equation [6], B= CCE OM R 2 =0.378 [6] Supposing the Langmuir adsorption isotherm (equation [2]) is the one describing the relationship between adsorbed Pb and that remained in the solution, it could be shown by Bolt and Bruggenwert,1976, that at very low equilibrium concentration the term 1+KC approach 1 and equation [2],thus, convert to equation [7] X=K.b.C [7] If the two side of equation [7] divided by C, the equation [8] attained: X/C=K.b [8] Table 3 Coefficients of Langmuir adsorption isotherm X = (K.b.C)/(1+K.C)], distribution coefficients (K d ), maximum buffering capacities (M), and coefficients of determination (r 2 ) for the fit of data. Soil No. K(10 6 ) b K d =M* r ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** * : Kd=M=K.b ** : Highly significant(p<0.01) Where all terms are defined before and X/C represents the amount of Pb adsorbed by unit weight of solid phase relative to that remained in unit volume of solution phase, which is called distribution coefficient and showed by Kd (26), X/C is termed maximum buffering capacity by Iyengar and Raja,(27) and designated by Karimian and Moafpouryan, (10);so: X/C=Kd=M=K.b [9]

6 Where, K d is distribution coefficient, M is maximum buffering capacity and X, C, K and b are defined before. The amount of K d varies from 403 to 956. This means that for soil No. 9, one unit concentration of Pb in equilibrium solution may correspond to as high as 403 units of adsorbed Pb by the solid phase, whereas the similar value for soil No. 2 is 956, about 2.3 times. The K d values found to be significantly (p<0.05) related to soil properties (CCE and OM) (equation [10] ); Kd = CCE 5.1 OM R2 =0.215 [10] Where K d in equation [9], CCE and OM in equation [4] were defined. Equation 3, 4, 5 and 6 show that clay, calcium carbonate equivalent (CCE). And organic matter (OM) content of soil plays significant roles in adsorption characteristics of calcareous soils under study. According to Elkhatib et al. (1992) when Pb; as an absorbate ion is added to a system containing mineral absorbents it may form a stable surface compound in equilibrium with the solution (adsorption), or crystal growth and finally precipitation takes place. He also states that adsorption of Pb in calcareous soils is due to high amount of calcium carbonate. Soldatini et al. (1976), states that in calcareous soils, Pb precipitates as Pbcarbonate and since all components of soil are responsible for adsorption of Pb and also have interaction, it is difficult to say which component has the most effect on Pb adsorption. It is concluded from the study that carbonates can act as a sink for decontamination of this heavy metal. This is in agreement with the other worker (McBride, 1980; Elkhatib et al., 1991, 1992). References Allison, L.E Organic carbon, pp In C.A. Black (ed.). Methods of Soil Analysis. Part 2. American Society of Agronomy, Madison, WI. Allison, L.E. and C.D. Moodie Carbonate, pp In C.A. Black (ed.). Methods of Soil Analysis. Part 2. American Society of Agronomy, Madison, WI. Andreu,V., Gimeno-Garcia Total content and extractable fraction of cadmium, cobalt, copper, lead, and zinc in calcareous orchard soils. Commun. Soil Sci. Plant Anal. 27(13, 14): Angooty, M. and A. Negarestan Phosphorous adsorption studies in three soil series from Shahriar region using adsorption isotherms. In 4 th Soil Science Congress of Iran, Shiraz, Iran (in Farsi). date? Benjamin, M.M. and J.O. Leckie Multiple-site adsorption of Cd, Cu, Zn and Pb on amorphous iron oxyhydroxide. J. Colloid Interface Sci. 79: Bolt, G.H. and M.G.M. Bruggenwert Soil chemistry. Part A. In Basic Elements. Eisevier Scientific Publishing Co., Amsterdam, The Netherlands. Brown, G.A. and H.A. Elliott Influence of electrolytes on EDTA extraction of Pb from polluted soils. Water, Air and Soil Pollu. 62: Chapman, H.D Cation exchange capacity, pp In C.A. Black (ed.). Methods of Soil Analysis. Part 2. American Society of Agronomy, Madison, WI

7 Day, P.R Particle fractionation and particle-size analysis, pp In C.A. Black (ed.). Methods of Soil Analysis. Part 2. American Society of Agronomy, Madison, WI. Elkhatib, E.A., G.M. Elshebiny, A. Balba and M. Lead sorption in calcareous soils. Environ. Pollut. 69: Elkhatib, E.A., G.M. Elshebiny and A.M. Balba Kinetics of lead sorption in calcareous soils. Arid Soil Research and Rehabilitization 64: Fekri-Koohbanani, M., M. Kalbasi and Sh. Hajrasuliha Comparison of single and double- Langmuir, Freundlich and Temkin adsorption isotherm in selected soils form Isfahan. In 4 th Soil Science Congress of Iran, Shiraz,I ran (in Farsi). Ghanbari, A., M. Maftoun and N. Karimian Phosphorous adsoption-desorption characteristics of selected highly calcareous soils of Fars province. Iran J. Agric. Sci. 29(1). Harter, R.D Adsorption of copper and lead by Ap and B2 horizons of several north-eastern United State soils. Soil Sci. Soc. Am. J. 55: Harter, L.D. and G. Smith Langmuir equation and alternate methods of studying adsorption reaction in soils, pp In M. Stelly (ed.) Chemistry in the Soil Environment. ASA Spec. Publ. 40, American Society of Agronomy Madison WI. Harter, R.D Micronutrient adsorption-desorption reactions in soils, pp In J.J. Mortvedt, F.R. Cox, L.M. Shuman and R.M. Welched. (eds.). Micronutrients in Agriculture, 2 nd ed. No. 4. Soil Science Society of America, Madison, WI. Hole, H. and W. Stumm Interaction of Pb 2+ with hydrous Y-Al 2 O 3. J. Colloid Interface Sci. 55: Iyengar, B.R.V. and M.E. Raja Zinc adsorption as related to its availability in some soils of Karnataka. J. Indian Soc. Soil Sci. 31: Karimian, N. and A. Gholamalizadeh Ahangar Manganese retention by selected calcareous soils as related to soil properties. Commun. Soil Sci. Plant Anal. 29: Karimian, N. and G.R. Moafpouryan Adsorption characteristics of selected calcareous soils of Iran and their relationship with soil properties. Commun. Soil Sci. Plant Anal. 30(11, 12): Maftoun, M., H. Haghighat Nia and N. Karimian Charactrization of Zn Adsorption in some calcareous paddy soils from Fars province. J. Sci. Tech. Agric. Nat. Resour. 4: McBride, M.B Chemisorption of Cd on calcite surfaces. Soil Sci. Soc. Am. J. 44: Mohammadi, A., M. Kalbasi, M.H. Roozitalab and M.J. Malakouti Phosphorous adsorption isothem in relation to predominant clay type percent lime of selected soils of Iran. In 5 th Soil Science Congress of Iran, Shiraz, Iran (in Farsi). Neilsen, D.P., B. Hoyt and A.F. McKenzie Comparision of soiltests and leaf analysis as methods of diagnosing Zn deficiency in British Columbia apple orchards. Plant Soil 105:

8 Nriago, J.O. 1973a. Lead ortophosphate: II. stability of chlorpromorphite at 25 o C. Geoderma Cosmochem Acta 37: Sadiq, M Solubility and speciation of zinc in calcareous soils. Water, Air and Soil Pollut. 57,58: Samar, S.M Desorptoin kinetics of phosphorous in selected soils of Damavand and Karaj. In 5 th Soil Science Congress of Iran, Shiraz, Iran (in Farsi). Sposito, G The Chemistry of Soils. Oxford University Press, New York, NY. Soldatini, G.F., R. Riffaldi and R.L. Minzi Pb adsorption by soil.water,air and Soil Pollut. 22,

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