Abstract

The cation exchange capacity (CEC) of seven well characterized halloysite nanotubes (HNTs) in the dehydrated 7 angstrom form has been measured using a method based on cobalt hexammine exchange. In addition to unbuffered measurements, which varied between 2.9 and 9.3 cmol(+)kg(-1), CECs were also determined over a wide pH range and proton titration measurements were conducted on two samples. The data were fitted using a constant capacitance model based on the presence of two sites: permanently charged sites and pH-dependent variable charged sites. Normalization of CEC to the average specific surface area (BET) of the halloysite samples reduces considerably the variation of CEC values for the different samples particularly over the intermediate pH range (5-9) with the average value at pH 7 equal to 8.5 cmol(+)kg(-1) and a standard deviation of 1.17. Overall the CEC behaviour of the seven samples appears reasonably consistent throughout the set. Calculations based on proton titrations suggest a ratio of variable charge to basal sites for the dehydrated halloysite nanotubes of similar to 3:1.

Keywords

Halloysite; Nanotube; HNT; Cation exchange capacity; pH; Constant Capacitance Model

Published in

Clay Minerals
2016, Volume: 51, number: 3, pages: 373-383
Publisher: MINERALOGICAL SOC

SLU Authors

• Hillier, Stephen

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    
  • The James Hutton Institute

UKÄ Subject classification

Soil Science


Publication identifier

DOI: https://doi.org/10.1180/claymin.2016.051.3.04

Permanent link to this page (URI)

https://res.slu.se/id/publ/82948