期刊
COLLOIDS AND INTERFACES
卷 4, 期 2, 页码 -出版社
MDPI
DOI: 10.3390/colloids4020016
关键词
colloid stability; CCC; FEBEX bentonite; DLVO; zeta potential
资金
- Federal Ministry of Economics and Technology (BMWi) [02E11203B, 02E11456A]
- Federal Ministry of Economics and Technology (BMWi) through European Commission (7th Euratom Framework Programme for Nuclear Research and Training Activities
- FP7/2007 2013) [295487]
- Federal Ministry of Economics and Technology (BMWi) through HGF PoF-III program NUSAFE
In this study, the critical coagulation concentration (CCC) for FEBEX bentonite colloids is determined by colloid coagulation studies under variation of pH, electrolyte concentration, and fulvic acid (GoHy-573FA) content. For CaCl(2)electrolyte solution, a pH-independent Ca-CCC of 1 mmol L(-1)is found. In the case of NaCl background electrolyte, a pH-dependent Na-CCC can be determined with 15 +/- 5 mmol L(-1)at pH 6, 20 +/- 5 mmol L(-1)at pH 7, 200 +/- 50 mmol L(-1)at pH 8, 250 +/- 50 mmol L(-1)at pH 9, and 350 +/- 100 mmol L(-1)at pH 10, respectively. The addition of 1 mg L(-1)dissolved organic carbon in the form of fulvic acid (FA) increases the Ca-CCC to 2 mmol L-1. An association of FA with FEBEX bentonite colloids as surface coating can clearly be identified by scanning transmission X-ray microscopy (STXM). The experimental bentonite stability results are described by means of an extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach summing up hydration forces, short-range Born repulsion, van der Waals attraction, and electrical double layer repulsion. The measured zeta (zeta)-potential of the bentonite colloids is applied as platelet face electrokinetic potential and the edge electrokinetic potential is estimated by the combination of silica and alumina zeta-potential data in the ratio given by the FEBEX bentonite structural formula. Adjusting the montmorillonite face electrokinetic potential by a maximum of +/- 15.9 mV is sufficient to successfully reproduce the measured stability ratios. Due to the uncertainty in the zeta-potential measurement, only semiquantitative calculations of the stability ratio can be given.
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