Sedimentation characteristics of two commercial bentonites in aqueous suspensions

Abstract

The sedimentation characteristics of two commercial bentonites, Tixoton (organically treated) and Montigel-F (untreated), were investigated using a 3% w/v clay suspension at different concentrations (1, 3.5 and 10%) of NaCl and pH values (2, 7 and 12). Settling rates, floc diameters and sediment volumes were derived from changes in light transmittance using a Turbiscan Ma 2000 instrument.Both bentonite suspensions were unstable (flocculated) in NaCl solutions. The settling rate increased with increasing concentration of NaCl and was directly related to floc diameter. The sediment volume reduced with increasing NaCl concentrations, a result of greater double layer compression caused by increased ionic strength. At comparable salt concentrations, the organically-treated bentonite (Tixoton) settled at a much slower rate and had a greater sedimentation volume. The suspensions of both organically-treated and untreated bentonites were stable (dispersed) above pH 7 and unstable in acidic conditions. The settling rate for Tixoton under acid conditions was much smaller than that for the Montigel-F. Differences in sedimentation characteristics between the two bentonite samples are probably due to the presence of an anionic polymer (carboxymethyl cellulose: CMC) in Tixoton.The viscosity of the bentonite suspensions was also studied. The viscosity of the clay suspension is closely related to clay dispersivity in solution. The CMC was highly effective in increasing the viscosity of the bentonite suspensions, but only under neutral and alkaline conditions.

Salinity effects on sedimentation behavior of kaolin, bentonite, and soda ash mine tailings

“…The effect of salinity on particle sedimentation was more pronounced in bentonite compared to kaolinite, and aluminum sulfate (Al 2 (SO 4 ) 3 ) was most effective in enhancing bentonite sedimentation. These effects of salinity on bentonite sedimentation are in agreement with an investigation by Akhter et al (2008). Gumaste et al (2014) investigated the effects of NaCl and SrCl 2 on sedimentation behavior of a white clay (70% kaolinite), bentonite clay (90% montmorillonite), and natural marine clay (liquid limit = 79%).…”

“…Bentonite consists of considerably smaller clay particles compared to kaolin, which have a larger specific surface area and DDL (Mitchell and Soga, 2005). Increasing the salt concentration within a range from 0.1 to 1000 mM can continuously suppress the DDL thickness in bentonite (Akhter et al, 2008) and enhance particle flocculation (Ohtsubo and Ibaraki, 1991) via reduction in repulsive forces between particles, which contribute to the increase in sedimentation rate observed in this study (Fig. 5a).…”

Optimizing the solar water disinfection (SODIS) method by decreasing turbidity with NaCl

“…The flocculating behaviour of different types of clay in saline solutions has been documented (Akther et al 2008;Gibbs 1983;1985;Hsi & Clifton, 1960;Panayiotopoulos et al 2004). Furthermore, there is potential for the well-known flocculating behaviour of clays to apply to complex clay and mud combinations (Mietta et al 2009).…”

Surface properties of bentonite and illite complexes with humus acids

“…The bentonite contained about 61% montmorillonite, 30% mica, 5% chlorite and 4% feldspar (Stawiński et al, 1990). Due to their layer charge and specific surface area, smectites significantly affect the physicochemical properties of soils (Allen & Hajek, 1989;Borchardt, 1989;Józefaciuk, 1998;Akther et al, 2008;Christidis, 2009;Faghihian & Nejati-Yazdinejad, 2009;Cordorio et al, 2010). Due to their low stability, smectites often occur in soils as mixed-layer mica-smectite or kaolinitesmectite (Borchardt, 1989).…”