The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

doi:10.1016/S0169-1317(99)00006-X

Applied Clay Science

Volume 14, Issues 5–6, July 1999, Pages 319-327

https://doi.org/10.1016/S0169-1317(99)00006-X Get rights and content

Abstract

The effect of the Na₂CO₃ activation on the rheological properties of a bentonite from Kütahya (Turkey) was investigated. The bentonite was activated with Na₂CO₃ at different dosages (1–15 g Na₂CO₃/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na₂CO₃/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na₂CO₃ (bentonite concentrations 2–6% w/w). At 2.5 g Na₂CO₃/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l⁻¹. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.

Introduction

Bentonite dispersions are widely used in industrial processes because of their exceptional rheological behaviour. In order to increase the viscosity and to improve the thixotropic behaviour of bentonite suspensions, Na₂CO₃, NaOH, Mg(OH)₂ are added to bentonite suspensions (Szanto et al., 1967; Bleifuss, 1973; Lagaly et al., 1981; Alther, 1982).

Lagaly (1989)investigated the effect of soda addition on the rheological properties of bentonites. Addition of soda increased the viscosity and the thixotropy. Further addition of soda reduced these values again. Volzone and Garrido (1991)studied the effect of Na₂CO₃ on several Argentine bentonites. They observed an increase of the gel strength and of the apparent viscosity at 160 s⁻¹. This increase was related to the content of the particles 0.5≤μm and the Na⁺/Ca⁺² ratio.

The type of flow, the viscosity and the yield value of clay suspensions are affected by the following factors: (i) the clay concentration, (ii) the size and shape of clay particles, (iii) the electrostatic properties of clay particles, (iv) the exchangeable ions, (v) the concentration of the electrolytes in suspensions and (vi) the type of bentonite (Brandenburg and Lagaly, 1988; Keren, 1989; Chen et al., 1990). Generally, the flow of bentonite dispersions is very sensitive to the Na⁺/Ca⁺² ratio. In practical applications the properties of bentonites can be improved by changing the Na⁺/Ca⁺² ratio (Alther, 1986). The rheological properties of dispersed bentonites depend on the cation that is originally present in the bentonite. A Ca-bentonite dispersed in a sodium salt solution behaves differently from a dispersion of a bentonite in its sodium form in a calcium salt solution, even though the Na⁺/Ca⁺² ratio is the same (Brandenburg and Lagaly, 1988; Tombacz et al., 1989).

The objective of the present study is to determine the influence of NaCl, Na-hexametaphosphate and pH on the rheological behaviour of the original and the activated Kütahya bentonite suspensions.

Section snippets

Experimental methods

Fractions of white colour Kütahya Ca-bentonite smaller than 36 μ were used in this study. A locality map for the bentonite sample is provided in Fig. 1. The total reserve of this bentonite area is estimated to be about 1 million ton (The Mineral Research and Exploration Report, 1972, 1996 Seyhan, 1972; Akbulut, 1996). The chemical analysis of the bentonite is given in Table 1. The activated samples were analyzed for Ca⁺² and Na⁺ by a Unicom 939 AAS and JENWAY PFP7 model flame photometer,

Results and discussion

The basal spacing decreased from 1.504 nm to 1.209 nm by Na₂CO₃ addition (Table 2). The strong increase of the Na₂O compared with the decreasing amounts resulted from the excess Na₂CO₃. Since the activated samples were washed only twice, the excess Na₂CO₃ was not completely removed. When 2.5% Na₂CO₃ was added, 74% of the Ca⁺² ions were exchanged by Na⁺ ions. Further addition of Na₂CO₃ increased the degree of exchange of Ca⁺² ions to 90%.

The shear stress–shear curves of the activated bentonites

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The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

Abstract

Introduction

Section snippets

Experimental methods

Results and discussion

Appl. Clay Sci.

Appl. Clay Sci.

Appl. Clay Sci.

Appl. Clay Sci.

Appl. Clay Sci.

Appl. Clay Sci.

The role of bentonite in soil sealing applications

Bull. Assoc. Eng. Geol.

Activation of non-swelling bentonite

Clay Miner.

Rheological behaviour of Na-montmorillonite suspensions at low electrolyte concentration

Clays Clay Miner.

The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na₂CO₃-activated Kütahya bentonite