Acid-base properties of Na-sepiolite and Na-palygorskite were studied by potentiometric titrations at 298 K and two ionic strength I = 0.1 and I = 0.002. Intrinsic constants of deprotonation were calculated by two different methods: a) Stumm method, by extrapolating to zero the function that relates surface charge with the logarithms of apparent acidity constants and b) with MINTEQ program by minimizing the differences between surface H+ concentration data and the values obtained from deprotonation constants proposed according to the Diffuse-Double-Layer Model (DDLM). Hydroxyl groups located at the broken edges of these fibrous clay minerals (SOH) and permanent charge sites (X-) were considered as reactive sites. The determined values of the acid-base constants for Na-sepiolite and Na-palygorskite were intermediate between those for SiO2 and Al2O3, which is in agreement with minerals that contain moderately strong-acidity and weak-acidity surface groups. The SOH groups showed an initial increase (after SOH2+ deprotonation), forming a plateau with a slight de-crease at high pH values (8-9) due to the formation of SO- sites. X- sites ad-sorbed H+, Na+ or Mg2+ ions.
References
[1]
Brindley, G.W. and Pedro, G. (1972) Report of the AIPEA Nomenclature Committee. AIPEA Newsletter, 4, 3-4.
[2]
Bradley, W.F. (1940) The Structural Scheme of Attapulgite. American Mineralogist, 25, 405-410.
[3]
Brauner, K. and Preisinger, A. (1956) Struktur und Enstehund des Sepioliths. Tschermaks Mineralogische und Petrographische Mitteilungen, 6,120-140.
https://doi.org/10.1007/BF01128033
[4]
Jones, B.F. and Galán, E. (1988) Sepiolite and Palygorskite. In: Bailey, S.W., Ed., Reviews in Mineralogy. Hydrous Phyllosilicates, Vol. 19, Mineralogical Society of America, Michigan, 631-674.
[5]
Singer, A. (2002) Palygorskite and Sepiolite. In: Dixon, J.B. and Schulze, D.G., Eds., Soil Mineralogy with Environmental Applications, Soil Science Society of America, 555-583.
[6]
Singer, A. (1989) Palygorskite and Sepiolite Group Minerals. In: Dixon, J.B. and Weed, S.B., Eds., Minerals in Soil Environment, Soil Science Society of America, 829-872.
[7]
Cao, E., Bryant, R. and Williams, D.J.A. (1996) Electrochemical Properties of Na- Attapulgite. Journal of Colloid and Interface Science, 179, 143-150.
https://doi.org/10.1006/jcis.1996.0196
[8]
Lu, W. and Smith, E.H. (1996) Modelling potentiometric titration behavior of glauconite. Geochimica et Cosmochimica Acta, 60, 3363-3373.
[9]
Bradbury, M.H. and Baeyens, B. (1997) A Mechanistic Description of Ni and Zn Sorption on Na-Montmorillonite. Part II: Modelling. Journal of Contaminant Hydrology, 27, 223-248.
[10]
Baeyens, B. and Bradbury, M.H. (1997) A Mechanistic Description of Ni and Zn Sorption on Na-Montmorillonite. Part I: Titration and Sorption Measurements. Journal of Contaminant Hydrology, 27, 199-222.
[11]
Baeyens, B. and Bradbury, M.H. (2005) Experimental Measurements and Modeling of Sorption Competition on Montmorillonite. Geochimica et Cosmochimica Acta, 69, 4187-4197.
[12]
Spathariotis, E. and Kallianou, C. (2001) Adsorption of Copper, Zinc, and Cadmium on Clay Fraction of Two Acid Soils: Surface Complexation Modeling. Communications in Soil Science and Plant Analysis, 32, 3185-3205.
https://doi.org/10.1081/CSS-120001115
[13]
Duc, M., Gaboriaud, F. and Thomas, F. (2005) Sensitivity of the Acid-Base Properties of Clays to the Methods of Preparation and Measurement: 1. Literature Review. Journal of Colloid and Interface Science, 289, 139-147.
[14]
Duc, M., Gaboriaud, F. and Thomas, F. (2005) Sensitivity of the Acid-Base Properties of Clays to the Methods of Preparation and Measurement: 2. Evidence from Continuous Potentiometric Titrations. Journal of Colloid and Interface Science, 289, 148-156.
[15]
Arda, D., Hizal, J. and Apak, R. (2006) Surface Complexation Modeling of Uranyl Adsorption onto Kaolinite Based Clay Minerals Using FITEQL 3.2. Radiochimica Acta, 94, 835-844. https://doi.org/10.1524/ract.2006.94.12.835
[16]
Bourg, I.C., Sposito, G. and Bourg, A.C.M. (2007) Modeling the Acid-Base Surface Chemistry of Montmorillonite. Journal of Colloid and Interface Science, 312, 297- 310.
[17]
Gaskova, O.L. and Bukaty, M.B. (2008) Sorption of Different Cations onto Clay Minerals: Modelling Approach with Ion Exchange and Surface Complexation. Physics and Chemistry of the Earth, 33, 1050-1055.
[18]
Serrano, S., O’Day, P.G., Vlassopoulos, D., García-González, M.T. and Garrido, F. (2009) A Surface Complexation and Ion Exchange Model of Pb and Cd Competitive Sorption on Natural Soils. Geochimica et Cosmochimica Acta, 73, 543-558.
[19]
Malamis, S. and Katsou, E. (2013) A Review on Zinc and Nickel Adsorption on Natural and Modified Zeolite, Bentonite and Vermiculite: Examination of Process Parameters, Kinetics and Isotherms. Journal of Hazardous Materials, 252-253, 428- 461.
[20]
Carter, D.L., Heilman, M.C. and González, C.L. (1965) Ethylene Glycol Monoethyl Ether for Determining Surface Area of Silicate Minerals. Soil Science, 100, 356-360.
https://doi.org/10.1097/00010694-196511000-00011
[21]
Sumner, M.E. and Miller, W.P. (1996) Methods of Soil Analysis. Part 3. Chemical Methods. In: Spark, D.L., Ed., Cation Exchange Capacity, and Exchange Coefficients, Soil Science Society of America and American Society of Agronomy, Madison, 65-94.
[22]
Hossner, L.R. (1996) Methods of Soil Analysis. Part 3. Chemical Methods. In: Spark, D.L., Ed., Dissolution for Total Elemental Analysis, Soil Science Society of America and American Society of Agronomy, Madison, 49-64.
[23]
Charlet, L., Schindler, P.W., Spadini, L., Furrer, G. and Zysset, M. (1993) Cation Adsorption on Oxides and Clays: The Aluminum Case. Aquatic Science, 55, 291- 303. https://doi.org/10.1007/BF00877274
[24]
Stumm, W., Hohl, H. and Dalang, F. (1976) Interaction of Metal Ions with Hydrous Oxide Surfaces. Croatica Chemica Acta, 48, 491-504.
[25]
Gustafsson, J.P. (2004) Visual MINTEQ ver. 2.30, KTH. Royal Institute of Technology, Sweden.
[26]
Vico, L.I. and Acebal, S.G. (2008) Adsorption of Manganese (II) from Aqueous Solutions by Na-Sepiolite and Na-Palygorskite. Agrochimica, 52, 209-225.
[27]
Schindler, P.W., Lietchti, P. and Westall, J.C. (1987) Adsorption of Copper, Cadmium and Lead from Aqueous Solution to the Kaolinite/Water Interface. Netherlands Journal of Agricultural Science, 35, 231-240.
[28]
Parker, J.C., Zelazny, L.W., Sampath, S. and Harrris, W.G. (1979) A Critical Evaluation of the Extension of Zero Point of Charge (ZPC) Theory to Soil Systems. Soil Science Society America Journal, 43, 668-674.
https://doi.org/10.2136/sssaj1979.03615995004300040008x
[29]
Sposito, G. (1981) The Operational Definition of the Zero Point of Charge in Soils. Soil Science Society America Journal, 45, 292-297.
https://doi.org/10.2136/sssaj1981.03615995004500020013x
[30]
Skipper, N.T. (2003) Molecular Modeling of Clays and Mineral Surfaces. CMS Workshop Lectures Vol. 12.
[31]
Cygan, R.T. (2003) Molecular Modeling of Clays and Mineral Surfaces. CMS Workshop Lectures Vol. 12.
![\"\"](\"Edit_63057df7-1e0c-497e-a765-7c2b46c1b8df.bmp\")
Al2O3, which is in agreement with minerals that contain moderately strong-acidity and weak-acidity surface groups. The SOH groups showed an initial increase (after SOH2+ deprotonation), forming a plateau with a slight de-crease at high pH values (8-9) due to the formation of SO- sites. X- sites ad-sorbed H+, Na+ or Mg2+ ions.
