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Distribution of Al, Ca, Fe and Mg in weathering extracts from Campanian Ignimbrite (yellow facies)
Zeolites and Related Materials: Trends, Targets and Challenges Proceedings of 4th International FEZA Conference A. Gédéon, P. Massiani and F. Babonneau (Editors) © 2008 Elsevier B.V. All rights reserved.
525
Distribution of Al, Ca, Fe and Mg in weathering extracts from Campanian Ignimbrite (yellow facies) A. Buondonnoa, A. Colellab, E. Coppolaa, M. de Gennarob, E. Grillia, A. Langellac, M. Rubinoa a
Dipartimento di Scienze Ambientali, Seconda Università degli Studi di Napoli, Via Vivaldi 43, 81100 Caserta, Italy b Dipartimento di Scienze della Terra, Università Federico II, Via Mezzocannone 8, 80134 Napoli, Italy c Dipartimento di Studi Geologici e Ambientali, Università del Sannio, Via Port’Arsa 11, 82100 Benevento, Italy
Abstract A study was started aiming at assessing the pedogenic potential of zeolitized tuffs as possible substrates to soil formation, especially for soil rebuilding in degraded lands. This paper deals with Ca, Al, Mg and Fe distribution in leachates obtained by a sequence of experimental weathering cycles of Campanian Ignimbrite (yellow facies) by water (W) and Na-humate (Na-Hu). The cation amounts were Al>Ca>Mg>Fe in W and Ca>Al>Mg>Fe in Na-Hu extracts, the latter being more efficient. Keywords: experimental pedology, zeolitized tuff, weathering, Na-humate.
1. Introduction A very few information is available on the pedo-mineralogical evolution of zeolitized tuffs, notwithstanding the world-wide outcrop occurrence of such rocks and their relevant presence as soil substrates in volcanic districts. An experimental pedology program was started aiming at modeling the weathering of zeolitized tuffs and the subsequent cations release [1]. This paper deals with Al, Ca, Fe and Mg distribution in leachates obtained by an experimental sequence of weathering cycles of Campanian Ignimbrite by water and Na-humate.
2. Experimental methods A commercial product, marketed by IZ - Italiana Zeoliti company as CAB 70 (Pigneto, Modena, Italy), coming from an outcrop of the Campanian Ignimbrite formation (yellow facies) located in Comiziano (Napoli), was used in the present investigation. The chemical analysis, made by X-ray Fluorescence Spectrometry (Philips PW1400 apparatus, equipped with a W tube), was: SiO2 = 53.75, TiO2 = 0.40, Al2O3 = 16.45, Fe2O3 = 3.91, MnO = 0.14, MgO = 1.11, CaO = 5.98, K2O = 6.98, Na2O = 1.35, P2O5 = 0.06, H2O = 10.10. The mineral composition, estimated by the Reference Intensity Ratio (RIR) procedure [2] was: phillipsite 38%, chabazite 13%, smectite 4%, biotite 1%, feldspar 33% and calcite 1%; amorphous phases were also present. Weathering treatment cycles (WTC) were performed as it follows: 5 gram of representative samples, crushed and sieved at 0.3 ∅ 2.0 mm, was periodically shaken at 25°C in polypropylene stoppered tubes with 100 mL of deionized water (W) or of a solution containing 2 g L-1 commercial Na-humate (Na-Hu), by Fluka, pH =
526
A. Buondonno et al.
7.1 ± 0.1. The Na-Hu concentration, 2 g L-1, has been used by analogy with literature investigations on clay minerals [3]. After 7 days suspensions were centrifuged and the supernatant carefully removed, quantitatively replaced by fresh W or Na-Hu, and analyzed for Al, Ca, Fe and Mg concentrations. A total of 20 WTC was performed.
3. Results and Discussion Figure 1 reports the amounts of cations determined after each WTC. 5 Ca
Mg
Fe
Al
mmol kg-1 tuff
4 3 2 1 0 0
2
4
6
8 10 12 WTC by water
14
16
18
20
25 20
Ca
Mg
Fe
Al
mmol kg-1 tuff
15 10 5 0 0
2
4
6
8
10
12
14
16
18
20
WTC by Na-Hu
Figure 1. Amounts of cations determined in W (upper) and Na-Hu (lower) extracts.
527
Al, Ca, Fe and Mg in weathering extracts from Campanian Ignimbrite 12 Ca/Al, W 10 Mg/Fe, W Cation ratio
8 6 4 2 0 0
2
4
6
8 10 WTC by water
12
14
16
18
20
14
16
18
20
12 Ca/Al, Na-Hu
8
Mg/Fe, Na-Hu
Cation ratio
10
6 4 2 0 0
2
4
6
8
10
12
WTC by Na-Hu
Figure 2. Cation ratios determined in W (upper) and Na-Hu (lower) extracts. On the average, the cation concentration decreased as Al>Ca>Mg>Fe in water extracts (Fig. 1, upper), and Ca>Al>Mg>Fe in Na-Hu extracts (Fig. 1, lower). In any case, the Na-Hu was an extractant more effective than W. For both extractants, the solubilization patterns of all the investigated cations widely fluctuated during the experiment, especially for aqueous extracts, and in particular for Ca and Al. It is also apparent that the Ca-W and Al-W patterns were more frequently out of phase than the respective Na-Hu patterns, thus suggesting that discontinuous and uncoupled dissolution/release of Ca- and Al-phases occurred during the different weathering cycles.
528
A. Buondonno et al.
The patterns for Mg and Fe were more flat and uniform with respect to Ca and Al, although the Mg-W and Fe-W distribution still showed clear, out of phase fluctuations. The different trends in cation dissolution/release could be also linked to the different pH values found in the leachates [1]. The pH of water extracts was prevailingly alkaline, and widely ranged from 6.9 to 8.6, with a mean value equal to 7.8 ± 0.1. Differently, the pH of Na-Hu extracts was somewhat more buffered around the neutrality, ranging from 6.8 to 7.5, and with a mean value of 7.1 ± 0.1, corresponding to that of the weathering Na-Hu solution. Figure 2 reports the ratios Ca to Al, and Mg to Fe, determined in water (upper graph) or in Na-Hu (lower graph) extracts, respectively, during the weathering treatment cycles. For W extracts, the Ca to Al ratio usually was less than 1.0, and gently increased, with a discontinuous trend, during the final phases of the experiment, reaching the maximum 1.4 at the 19th WTC; on the contrary, the Mg to Fe ratio dramatically increased after the 5th WTC, with peak ratio values equal to 4.7, 7.3, and 8.0 at the 8th, 12th, and 18th WTC. The cations ratios in Na-Hu extracts showed totally different trends. The Ca to Al ratio immediately exhibited two peaks values equal to 10.3 and 10.7 at the 1st and the 2nd WTC, respectively. Subsequently, the Ca/Al ratio values rapidly and unevenly decreased at 4.0 ÷ 1.0, with a final increase at 5.4. A further distinct trend was observed for the Mg to Fe ratio, which erratically varied from 0.7 to 2.6.
4. Conclusion The different cation release from the investigated tuff was clearly depending on the nature of both cations and leaching solutions. The prevailing reactions appear to be dissolution and hydrolysis in water, and etching/chelating and cation exchange in Nahumate, this latter being more efficient. In particular, it must be considered the obvious influence of zeolites phases on cation exchange processes, which mostly affect the dynamics of monovalent cations such as Na+ and K+. Such exchange reaction seems to occur mainly for Ca when WTC by Na-Hu are considered. On the other hand, sidereactions as secondary precipitation/complexation likely influenced the uneven cations distribution, in both the aqueous alkaline and in the humate-rich environments. The synoptic examination of the experimental data suggest that, as a general rule, cations were first sourced from soluble phases, exchange sites, and from the weathering of i) amorphous Al,Fe-oxi-hydroxides, ii) glass, and, iii) less stable silicates such as pyroxenes. Further research steps will be aimed at balancing the cationic exchange budget, including Na+ and K+, and at casting light on the possible mineralogical alterations connected to the weathering phenomena. The achieved results provide further useful information to plug a gap in knowledge on the weathering potential of the zeolitized tuffs as geolithologic substrate for soil formation, highlighting their possible use as pedogenetic parent material for soil rebuilding in degraded areas.
References [1] A. Buondonno, A. Colella, C. Colella, E. Coppola, B. de’ Gennaro, M. de’ Gennaro, N. Gargiulo, E. Grilli, A. Langella, M. Rubino, Studies in Surface Science and Catalysis, 170B (2007) 2092. [2] S.J. Chipera D.L. Bish, Powder Diffraction, 10 (1995) 47. [3] P.M. Huang, M. Schnitzer, Interactions of Soil Minerals with Natural Organics and Microbes, Soil Sci. Soc. Am., Inc., Madison, WI (1986) 606 pp.
525
Distribution of Al, Ca, Fe and Mg in weathering extracts from Campanian Ignimbrite (yellow facies) A. Buondonnoa, A. Colellab, E. Coppolaa, M. de Gennarob, E. Grillia, A. Langellac, M. Rubinoa a
Dipartimento di Scienze Ambientali, Seconda Università degli Studi di Napoli, Via Vivaldi 43, 81100 Caserta, Italy b Dipartimento di Scienze della Terra, Università Federico II, Via Mezzocannone 8, 80134 Napoli, Italy c Dipartimento di Studi Geologici e Ambientali, Università del Sannio, Via Port’Arsa 11, 82100 Benevento, Italy
Abstract A study was started aiming at assessing the pedogenic potential of zeolitized tuffs as possible substrates to soil formation, especially for soil rebuilding in degraded lands. This paper deals with Ca, Al, Mg and Fe distribution in leachates obtained by a sequence of experimental weathering cycles of Campanian Ignimbrite (yellow facies) by water (W) and Na-humate (Na-Hu). The cation amounts were Al>Ca>Mg>Fe in W and Ca>Al>Mg>Fe in Na-Hu extracts, the latter being more efficient. Keywords: experimental pedology, zeolitized tuff, weathering, Na-humate.
1. Introduction A very few information is available on the pedo-mineralogical evolution of zeolitized tuffs, notwithstanding the world-wide outcrop occurrence of such rocks and their relevant presence as soil substrates in volcanic districts. An experimental pedology program was started aiming at modeling the weathering of zeolitized tuffs and the subsequent cations release [1]. This paper deals with Al, Ca, Fe and Mg distribution in leachates obtained by an experimental sequence of weathering cycles of Campanian Ignimbrite by water and Na-humate.
2. Experimental methods A commercial product, marketed by IZ - Italiana Zeoliti company as CAB 70 (Pigneto, Modena, Italy), coming from an outcrop of the Campanian Ignimbrite formation (yellow facies) located in Comiziano (Napoli), was used in the present investigation. The chemical analysis, made by X-ray Fluorescence Spectrometry (Philips PW1400 apparatus, equipped with a W tube), was: SiO2 = 53.75, TiO2 = 0.40, Al2O3 = 16.45, Fe2O3 = 3.91, MnO = 0.14, MgO = 1.11, CaO = 5.98, K2O = 6.98, Na2O = 1.35, P2O5 = 0.06, H2O = 10.10. The mineral composition, estimated by the Reference Intensity Ratio (RIR) procedure [2] was: phillipsite 38%, chabazite 13%, smectite 4%, biotite 1%, feldspar 33% and calcite 1%; amorphous phases were also present. Weathering treatment cycles (WTC) were performed as it follows: 5 gram of representative samples, crushed and sieved at 0.3 ∅ 2.0 mm, was periodically shaken at 25°C in polypropylene stoppered tubes with 100 mL of deionized water (W) or of a solution containing 2 g L-1 commercial Na-humate (Na-Hu), by Fluka, pH =
526
A. Buondonno et al.
7.1 ± 0.1. The Na-Hu concentration, 2 g L-1, has been used by analogy with literature investigations on clay minerals [3]. After 7 days suspensions were centrifuged and the supernatant carefully removed, quantitatively replaced by fresh W or Na-Hu, and analyzed for Al, Ca, Fe and Mg concentrations. A total of 20 WTC was performed.
3. Results and Discussion Figure 1 reports the amounts of cations determined after each WTC. 5 Ca
Mg
Fe
Al
mmol kg-1 tuff
4 3 2 1 0 0
2
4
6
8 10 12 WTC by water
14
16
18
20
25 20
Ca
Mg
Fe
Al
mmol kg-1 tuff
15 10 5 0 0
2
4
6
8
10
12
14
16
18
20
WTC by Na-Hu
Figure 1. Amounts of cations determined in W (upper) and Na-Hu (lower) extracts.
527
Al, Ca, Fe and Mg in weathering extracts from Campanian Ignimbrite 12 Ca/Al, W 10 Mg/Fe, W Cation ratio
8 6 4 2 0 0
2
4
6
8 10 WTC by water
12
14
16
18
20
14
16
18
20
12 Ca/Al, Na-Hu
8
Mg/Fe, Na-Hu
Cation ratio
10
6 4 2 0 0
2
4
6
8
10
12
WTC by Na-Hu
Figure 2. Cation ratios determined in W (upper) and Na-Hu (lower) extracts. On the average, the cation concentration decreased as Al>Ca>Mg>Fe in water extracts (Fig. 1, upper), and Ca>Al>Mg>Fe in Na-Hu extracts (Fig. 1, lower). In any case, the Na-Hu was an extractant more effective than W. For both extractants, the solubilization patterns of all the investigated cations widely fluctuated during the experiment, especially for aqueous extracts, and in particular for Ca and Al. It is also apparent that the Ca-W and Al-W patterns were more frequently out of phase than the respective Na-Hu patterns, thus suggesting that discontinuous and uncoupled dissolution/release of Ca- and Al-phases occurred during the different weathering cycles.
528
A. Buondonno et al.
The patterns for Mg and Fe were more flat and uniform with respect to Ca and Al, although the Mg-W and Fe-W distribution still showed clear, out of phase fluctuations. The different trends in cation dissolution/release could be also linked to the different pH values found in the leachates [1]. The pH of water extracts was prevailingly alkaline, and widely ranged from 6.9 to 8.6, with a mean value equal to 7.8 ± 0.1. Differently, the pH of Na-Hu extracts was somewhat more buffered around the neutrality, ranging from 6.8 to 7.5, and with a mean value of 7.1 ± 0.1, corresponding to that of the weathering Na-Hu solution. Figure 2 reports the ratios Ca to Al, and Mg to Fe, determined in water (upper graph) or in Na-Hu (lower graph) extracts, respectively, during the weathering treatment cycles. For W extracts, the Ca to Al ratio usually was less than 1.0, and gently increased, with a discontinuous trend, during the final phases of the experiment, reaching the maximum 1.4 at the 19th WTC; on the contrary, the Mg to Fe ratio dramatically increased after the 5th WTC, with peak ratio values equal to 4.7, 7.3, and 8.0 at the 8th, 12th, and 18th WTC. The cations ratios in Na-Hu extracts showed totally different trends. The Ca to Al ratio immediately exhibited two peaks values equal to 10.3 and 10.7 at the 1st and the 2nd WTC, respectively. Subsequently, the Ca/Al ratio values rapidly and unevenly decreased at 4.0 ÷ 1.0, with a final increase at 5.4. A further distinct trend was observed for the Mg to Fe ratio, which erratically varied from 0.7 to 2.6.
4. Conclusion The different cation release from the investigated tuff was clearly depending on the nature of both cations and leaching solutions. The prevailing reactions appear to be dissolution and hydrolysis in water, and etching/chelating and cation exchange in Nahumate, this latter being more efficient. In particular, it must be considered the obvious influence of zeolites phases on cation exchange processes, which mostly affect the dynamics of monovalent cations such as Na+ and K+. Such exchange reaction seems to occur mainly for Ca when WTC by Na-Hu are considered. On the other hand, sidereactions as secondary precipitation/complexation likely influenced the uneven cations distribution, in both the aqueous alkaline and in the humate-rich environments. The synoptic examination of the experimental data suggest that, as a general rule, cations were first sourced from soluble phases, exchange sites, and from the weathering of i) amorphous Al,Fe-oxi-hydroxides, ii) glass, and, iii) less stable silicates such as pyroxenes. Further research steps will be aimed at balancing the cationic exchange budget, including Na+ and K+, and at casting light on the possible mineralogical alterations connected to the weathering phenomena. The achieved results provide further useful information to plug a gap in knowledge on the weathering potential of the zeolitized tuffs as geolithologic substrate for soil formation, highlighting their possible use as pedogenetic parent material for soil rebuilding in degraded areas.
References [1] A. Buondonno, A. Colella, C. Colella, E. Coppola, B. de’ Gennaro, M. de’ Gennaro, N. Gargiulo, E. Grilli, A. Langella, M. Rubino, Studies in Surface Science and Catalysis, 170B (2007) 2092. [2] S.J. Chipera D.L. Bish, Powder Diffraction, 10 (1995) 47. [3] P.M. Huang, M. Schnitzer, Interactions of Soil Minerals with Natural Organics and Microbes, Soil Sci. Soc. Am., Inc., Madison, WI (1986) 606 pp.