International Journal of Environment ISSN 2091-2854 9 | P a g e INTERNATIONAL JOURNAL OF ENVIRONMENT Volume-1, Issue-1, Jun-Aug 2013 ISSN 2091-2854 Received: 9 June Revised: 14 August Accepted: 16 August METHOD FOR ESTIMATION OF CALCIUM CARBONATE IN SOILS FROM IRAQ Jabbar K. Kassim Department of Soil and Water Science, Faculty of Agriculture Sciences, University of Sulaimani, Kurdistan, Iraq Corresponding author: jabbar_50@yahoo.com Abstract Attempts have been made to evaluate four methods of quantitative determination of soil carbonates. Calcium carbonates equivalent were determined by the acid neutralization, calcimeter and acetic acid methods. Also, it obtains by the fourth methods when the acid neutralization method is corrected against proton adsorption. The acid neutralization method gave significantly higher estimates of total carbonates and different from each of the others. The calcimeter method gave the lower estimates of CaCO3 equivalent. The results showed that the corrected values of CaCO3 equivalent did not differ significantly from other three methods but the overall mean tended to be higher than the acetic acid and calcimeter methods. It may be concluded that the acetic acid method is simple, can reasonably estimate the carbonate content and requires only a pH meter. It can be used for routine determination of soil carbonate. Keywords: Calcium carbonate equivalent, calcimeter, acid neutralization, Acetic acid Introduction Carbonate is a natural constituent of many soils occurring as sparingly soluble, alkaline earth carbonate, chiefly as calcite and dolomite. Most carbonate minerals found in local soils are calcite and account 90% of total soil carbonates (Al-Kasyi,1989). Soil properties play a major role in planning land use activities such as agriculture, erosion control, environmental protection and nature conservation. The determination of total carbonate such as CaCO3 in soil is of great interest on account of high usefulness for diagnosing soil status in terms of structure, texture, biological activity or nutrient content. In calcareous soils carbonates exert a major influence on the chemical properties. Also carbonate content is used as a differentiating criterion for some classes at the family level of Soil Taxonomy (Soil Survey Staff, 2006). Few attempts have been made to evaluate methods of quantitative determination of carbonates in arid and semiarid soils. So, numerous methods mailto:jabbar_50@yahoo.com International Journal of Environment ISSN 2091-2854 10 | P a g e have been used for quantitative determination of soil carbonates (U.S. Salinity Laboratory Staff, 1954; Derimains, 1962; Hassan and Al- Tawil, 1973; Bullok, 1975; Loeppert et al., 1974; Nelson, 1982, El Mahi et al.,1987, Moore et al.,1987 and Ashworth, 1977). The most commonly used procedures involve dissolution of the solid phase carbonates by reaction with acid. Quantitation is commonly achieved by measurement of evolved CO2 volumetrically, gravimetrically, manometrically, titrimetrically. Also, it may be achieved quantitatively by measurement of acid consumed during the neutralization reaction. A Fourier transform infrared spectrometer, is employed to determine automatically the total inorganic carbonate in solid and waters based on active photoacoustic absorption of infrared light by carbon dioxide (Wenxin et al., 1999). On the other hand, Zougagh et al., (2005) used two methods for determination of total carbonate soils by continuous flow piezoelectric detection. Several of the specific procedures are outlined below .The acid neutralization procedure, is probably the most commonly used, due to its simplicity which involves addition of excess acid and back titration with standard base (U.S. Salinity Laboratory Staff ,1954 ).Another widely used method is quantitative volumetric procedure, in which volume of CO2 is determined fallowing addition of excess HCl (Derimains,1962 and Bullock,1974).The pressure-calcimeter in which increase in pressure is measured atconstant temperature and volume following addition of excess acid (Martin and Reeve, 1955; Hassan and Al- Tawil,1973 and Presley,1975) provides an alternative procedure for determination of soil carbonate. It is applicable in straight forward manner to soils in low organic matter and containing no dolomite and no appreciable quantity of MnO The calcimeter method is widely used locally to determine soil carbonates. Another proposed procedure was used to determine soil carbonate which is based on the following reaction: CaCO3 + 2HC2 H2 O2 → Ca +2C2 H2 O2 +H2 O +CO2 The neutralization of acetic acid expressed in the reaction HC2 H2 O2 → H + + C2 H2 O2 - It was based on that a known quantity of acetic acid was added to a known quantity of soils. Then the pH of reaction mixture was determined fallowing complete dissolution of CaCO3 and equilibrium (Loeppert et al., 1974). Also, El Mahi et al., (1987) reported that the values of carbonate equivalent estimated by acid neutralization were corrected as: CaCO3 equivalent = acid neutralization % CaCO3 - 0.05 CEC. International Journal of Environment ISSN 2091-2854 11 | P a g e The objective of this investigation is to evaluate and compare the common available procedure for quantitative determination of local soil carbonate with the objective of finding a rapid method that is reasonably accurate and simple. Materials and methods The studied soil samples were collected from different profile horizon of different parts of Iraq. Soils were air – dried, ground by hand and sieved through a 2 mm sieve. The lime content (CaCO3 equivalent) was determined by dissolution of carbonate with 0.5 M HCl and titration of excess acid with 0.2 MNaOH as described by Allison and Moodie (1965). In addition to the calcimeter method described by Bullock (1975) the carbonate was determined by procedure proposed by Loeppert et al., (1974). It was based on adding a known quantity of 0.4 M acetic acid to a known quantity of soil samples (<2 mm fraction). Then the pH of the mixtures was experimentally determined. 2.000 g samples were weight into 50 mL polypropylene centrifuge tubes and 25 mL aliquot of 0.400 M acetic acid was added to each tube. Tubes were shaken for 8 h and the samples were allowed to sit overnight with cap loosed to allow escape of CO2 produce during the dissolution of CaCO3. Tubes were centrifuged and then pH of the superannuate was accurately determined + 0.01 pH units with a combination pH electrode which was allowed to equilibrate for exactly 5 min before recording the value. Also, some tubes were allowed to sit over a period of 7 days. Kaolinite and bentonite (smectite group) deposit from Al – Anbar Province was initially fractionated to obtain the > 2 mm particle size separated and was Ca- saturated by titration to pH 8.0 with Ca(OH)2 . Calcium carbonate (0.25, 0.50, 1.0 and 1.50 g of Ca- saturated kaolinite and / or smectite. The pH of the solution was determined and experimental CaCO3 contents calculated as previously described for soil samples. Precaution was taken to ensure that all soil samples were treated identically during pH determination. Results and discussion The soils were selected from a collection of calcareous soils of different parts of Iraq, to give a wide range in carbonate (30 to 4967 g CaCO3 kg soils. These soils were very low in organic matter (5.45 to 27.85 g organic matter kg soil) and free Fe – oxides and oxyhydroxide (1.13 to 9.57 g kg soil ) content ( Kassim et al., 1993 ). The soils and their classification were given in Table (1). International Journal of Environment ISSN 2091-2854 12 | P a g e Table 1. Location and classification of 21 soils profiles used in the study. ----------------------------------------------------------------------------------------------- Profile numbers Location Classification P1,P2 Al-Nassriah Typic Fluvaqents P3,P4 Al-Nassriah Vertic Fluvaqents P5,P6 Tikrit Cambic Gypsiorthids P7 Mosul Cambic Gypsiorthid P8,P9 Tikrit Calcic Gypsiorthids P10 Rabiah Calcic Gypsiorthids P11 South of Mosul Calcic Gypsiorthid P12,P13 Tikrit Typic Torripsammen P14,P15 Rabiah Typic Calciorthids P16,P17 Rabiah Typic Calcixerolls P19,20 Rabiah Calcixerollic Xerochrepts P20 Mosul Calcixerollic Xerochrepts P21 Aski Kalaic Mollic Calciorthids Eight two -soil samples were taken from different depths from 21 profiles. All samples were analyzed for lime (CaCO3equivalent) using three different methods. These methods were acid neutralization (HCl), calcimeter and acetic acid reaction (US Salinity Laboratory Staff, 1954, Allison and Moodie, 1965 and Loeppert et al 1974). In case of acetic acid method, an addition of a known amount of pure calcite (CaCO3) was added to excess quantity of acetic acid and the pH of the reaction was experimentally determined. The pH vs. initial CaCO3 weight is plotted and shown in Fig (1). The results indicated that the pH rang is 2.98 to 5.74 and the relative change in pH was great at low CaCO3, generally when it was > 75 mg CaCO3. The standard curve for soil samples was obtained by the procedure proposed by Loeppert et al., (1974). A plot of pH vs. log [mgCaCO3/ (T – mg CaCO3)] was obtained to serve as standard curve for soil samples and was approximately linear with an r =0.996 (Fig 2). Fig 1: The effect of pure calcium carbonate on pH International Journal of Environment ISSN 2091-2854 13 | P a g e In case of acetic acid method, the relative change in pH was great at low CaCO3 levels and it was sensitive to small changes in CaCO3 content. The errors due to consumption of protons by ion exchange complex were very high at low carbonate levels. It may be reduced by manipulating condition to result in an increase final equilibrium pH. It may be accomplishes by increasing soil sample size and /or reducing concentration or volume of acid reactant. However, it was preferred increasing soil samples to reduce the error. Also, the soils under investigation showed that only few soil samples where low in carbonate content (Fig 3). Fig 2: The relationship between the log amount of pure calcium carbonate and pH The major sources of error in the procedure for determination of soil carbonates were clay minerals, organic matter, incomplete dissolution of CaCO3 and error in pH determination. Addition of acetic acid to different quantity of CaCO3 in the presences of different levels of clay minerals, the CaCO3level was experimentally determined. The results were shown in Table ( 2). It was indicated that the levels of experimentally determined CaCO3 were higher in presences of clay minerals especially at lower added CaCO3. Upon addition of 25 mL of 0.40 M acetic acid to 25.0 of pure CaCO3 in presence of 0.250, 0.500, 1.00 and 1.50 g of kaolinite or smectite, the experimentally determined CaCO3 levels were approximately 26,26, 28, and 29; 26,28,30 and 32 respectively (Table 2). Table 2- Influence of Ca-saturated clay on determination of CaCO3 equivalent by acetic acid Actual Kaolinite Experimentaly Bentonite Experimentaly CaCO3 determined (smectite) determined CaCO3 CaCO3 mg mg mg mg mg 250 26 250 26 500 26 500 27 25 1000 28 1000 39 International Journal of Environment ISSN 2091-2854 14 | P a g e 1500 29 1500 31 ------------------------------------------------------------------ 250 50 250 51 500 52 500 53 50 1000 52 1000 53 1500 53 1500 56 ------------------------------------------------------------------- 250 100 250 101 500 102 500 104 100 1000 102 1000 106 1500 107 1500 107 ------------------------------------------------------------------- 250 150 250 150 500 154 500 156 150 1000 155 1000 158 1500 153 1500 158 ---------------------------------------------------------------------- 250 200 250 200 500 203 500 206 200 1000 204 1000 207 1500 204 1500 207 Also, the experimentally determined CaCO3 was higher in the presence of smectite than kaolinite. Therefore it is evident that the clay mineral consumed protons predominantly via a mechanism of ion exchange onto the clay surface or interlayer. So, it could be concluded that relative experimental or actual error generally increased as the clay contents were increased for a given CaCO3 level. For example with actual CaCO3 quantity of 25, 50,100 and 200 mg, relative percentage errors in presence of 1.50 g of kaolinite were 16, 6, 4.7,3 and 2 respectively. But the relative percentage errors in the presence of 1.50 of smectite were 24, 13, 7, 5.3 and 3.5 respectively. It was well known that the dissolution of CaCO3, Ca +2 was released into the reaction mixture. The proportion of H +1 on the exchange complex was controlled largely by Ca +2 / H +1 exchange equilibrium relationships. The amount of adsorbedH +1 being influenced by the quantity and cation exchange capacity of the clay. Therefore, at low carbonate levels and high clay levels, errors due to retention of H +1 on the exchange complex were greatest especially in presence of smectite. The relative errors may be reduced by manipulating conditions to results in an increase in final equilibrium pH. Increasing soil sample size and /or reducing concentration or volume of acetic acid reactant could be accomplished this. Also, the errors in experimentally determination of actual CaCO3 in presence of kaolinite and smectite by the two other methods (acid – base titration and calcimeter methods). The results in Table (3) showed that the relative percentage errors were the highest in acid base titration than the other methods. For example with actual CaCO3 quantity of 25,50,100 and 200 mg the relative percentage errors in presence International Journal of Environment ISSN 2091-2854 15 | P a g e of 1.5 g of kaolinite or smectite were 24,16,13,6.6 and 4.5 for kaolinite and 40,28,18,12 and 8 for smectite respectively in acid base titration method. But they were negligible in the calcimeter method even in the presence of high percentage of clays. So, it is evident that the clay consumed protons predominantly via mechanism of ion exchange on the clay surface. Also, it could be due to decomposition of the clay mineral especially in acid base titration methods. Generally, the relative experimental error increased as the clay content was increased for a given CaCO3 level. Another error may be due to presence of organic matter especially at high organic matter (Martin, 1955), which may be attributed to large number of potential proton binding sites. But these errors could be negligible simply because the studied soils were very low in organic matter content (Al – Janbi et al., 1989 a,b and Kassim et al.,1989 ). These results are in agreement with the results reported by Hassan and Al – Tawil (1973) that organic matter could not be considered are limiting factor for application especially for calcimeter methods. Table 3 - Influence of Ca-saturated clay on determination of CaCO3 -------------------------------------------------------------------------------------------------------------------------------------- Acid titration Calcimeter Actual Kaolinite Experimentaly Bentonite Experimentaly Kaolinite Experimentaly bentonite Experimentaly CaCO3 determined (smectite) determined determined (smectite) determined CaCO3 CaCO3 CaCO3 CaCO3 mg mg mg mg mg mg mg mg mg 250 27 250 27 250 25 250 26 500 27 500 29 500 25 500 26 25 1000 31 1000 35 1000 26 1000 26 1500 32 1500 36 1500 26 1500 27 ---------------------------------------------------------------------------------------------------------------------------- 250 54 250 57 250 50 250 50 500 56 500 60 500 50 500 52 50 1000 56 1000 63 1000 51 1000 52 1500 58 1500 64 1500 51 1500 52 ---------------------------------------------------------------------------------------------------------------------------- 250 103 250 108 250 100 250 100 500 104 500 109 500 100 500 100 100 1000 109 1000 116 1000 101 1000 102 1500 113 1500 119 1500 101 1500 103 ---------------------------------------------------------------------------------------------------------------------------- 250 152 250 153 250 150 250 150 500 154 500 155 500 150 500 150 150 1000 157 1000 166 1000 150 1000 151 1500 160 1500 168 1500 151 1500 151 ---------------------------------------------------------------- ----------------------------------------------------------- 250 201 250 204 250 200 250 200 500 202 500 208 500 200 500 201 International Journal of Environment ISSN 2091-2854 16 | P a g e 200 1000 207 1000 212 1000 201 1000 202 1500 209 1500 216 1500 201 1500 202 The soils under investigation were high in carbonate content and the results were shown in Fig (3). The histograms showed that more than 80% of these soils were high in carbonate exceed 200 g CaCO3kg soil. It had been found that the rate of reaction of CaCO3 was linearly and inversely related to pH within the range 3.00 to 5.00 (Berner and Morse, 1974). The condition employed in these experiments i.e. addition of 25 mL of 0.40 M acetic acid to 2.0 g soil samples. It has been found that the maximum working limit is 200 g CaCO3 kg soil, which results in final equilibrium pH of approximately 4.85. So, if the soil carbonate minerals (Kassim and Haba, 1989), it would not be preferred increasing the acid concentration especially with soil containing readily decomposable minerals example soil chlorite may be subjected to severe errors due to decomposition of soil components. On the other hand, contact time must be sufficient to allow for complete dissolution of solid phase CaCO3. The distribution of soil carbonate contents are summarized in Fig 3 and present values of CaCO3 equivalents determined by three methods. The acid neutralization method gave significantly higher estimates of total carbonate (p 0.001) than the other methods. But the calcimeter method gave the lowest estimates value of total carbonate. Also, it is interesting to note that the 5% CaCO3 equivalent as the lower limit for calcareousness (Hodgson, 1976) only 7 out of the 82 soil samples could not be classified as than 5% CaCO3 equivalent. On the other hand, the acid neutralization was the only method calcareous soil by the calcimeter method, while none of the other methods gave values less gave values 40% CaCO3 equivalent and 25 soils samples were CaCO3 values above 350 mg CaCO3 kg soil. The acetic acid and / or calcimeter methods gave only 7 and 3 soils have values of 350 mg CaCO3 kg soil respectively. The results showed that the majority of soil samples were within the range of 200 to 300 mg CaCO3 kg soil. The mean CaCO3 content for all soil samples studied were 209, 246, and 287 mg CaCO3 kg soil estimated by calcimeter, acetic acid and acid neutralization methods respectively. The mean values indicated that the results of acid neutralization method were significantly different from each other and gave the highest mean values for CaCO3content. This could be attributed to the fact that the acid neutralization method suffers from the reaction of acid with soil constituents other than carbonate and the consumption by the exchange complex that lead to overestimate of carbonate. These results were in agreement International Journal of Environment ISSN 2091-2854 17 | P a g e with results found by many workers (Bundy and Bremmer, 1972; Nelson and Summer, 1982; Loeppert et al., 1984 and El Mahi et al., 1987). The acid neutralization method suffers from the reaction of the acid with soil constituent other than carbonates and the consumption of protons by the exchange complex. The latter error was corrected by assuming that protons occupied the entire exchange complex (El Mahi et al.,1987). The corrected values of CaCO3 equivalent using acid neutralization did not differ significantly from the other three methods. On the other hand, the overall mean values (272 mg CaCO3 kg ) were higher than those of the others, suggesting that the acid may be reacted with noncarbonated soil minerals. Fig 3: Frequency distribution of carbonate in soils determined by the calcimeter, acetic acids and hydrochloric acids Generally, it may be concluded that the calcimeter method gave the lowest CaCO3equivalent estimate while the acid neutralization method gave the highest CaCO3 equivalent content. The results in Table (4) shown that there were highly significant correlation between the methods. The acetic acid method was higher correlated with the calcimeter method (r = 95.1). Also, the acetic acid method may be reasonably used to determine CaCO3 equivalent in the local soils of arid and semiarid. In addition to its simplicity, it required only a pH meter. International Journal of Environment ISSN 2091-2854 18 | P a g e Table 4. Simple correlation coefficients(r values) between different methods of estimation of CaCO3 equivalent -------------------------------------------------------------- Methods Calcimeter Acetic acid -------------------------------------------------------------- Acetic acid 0.975 Acid neutralization 0.963 0.974 Corrected 0.963 0.973 ------------------------------------------------------------- A further investigation will needed to developed methods for evaluating the particle size distribution and reactivity of soil carbonate. Also, it is important to study carbonate mineralogy to quantify carbonate minerals phases present in local soils. 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