%0 Journal Article
%T Acid-Base Properties of Aqueous Suspensions of Homoionic Sepiolite and Palygorskite
%A Silvia G. Acebal
%A Leticia I. Vico
%J Natural Resources
%P 432-444
%@ 2158-7086
%D 2017
%I Scientific Research Publishing
%R 10.4236/nr.2017.86028
%X 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<sup>-</sup>) were considered as reactive sites. The determined values of the acid-base constants for Na-sepiolite and Na-palygorskite were intermediate between those for SiO<sub>2</sub> and <img src=\"Edit_63057df7-1e0c-497e-a765-7c2b46c1b8df.bmp\" width=\"18\" height=\"15\" alt=\"\" />Al<sub>2</sub>O<sub>3</sub>, which is in agreement with minerals that contain moderately strong-acidity and weak-acidity surface groups. The SOH groups showed an initial increase (after SOH<sub>2</sub><sup>+</sup> deprotonation), forming a plateau with a slight de-crease at high pH values (8-9) due to the formation of SO<sup>-</sup> sites. X<sup>-</sup> sites ad-sorbed H<sup>+</sup>, Na<sup>+</sup> or Mg<sup>2+</sup> ions.
%K Fibrous Clay Minerals
%K Sorption Properties
%K Surface Speciation
%U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=77117