Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Research paper Effects of sodium carbonate addition, heat and agitation on swelling and rheological behavior of Ca-bentonite colloidal dispersions Musaab I. Magzoub a , Mustafa S. Nasser a,⁎ , Ibnelwaleed A. Hussein a , Abdelbaki Benamor a , Sagheer A. Onaizi b , A.S. Sultan c , M.A. Mahmoud c a Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar b Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31216, Saudi Arabia c Department of Petroleum Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31216, Saudi Arabia ARTICLE INFO Keywords: Ca-bentonite Sodium carbonate Rheology Swelling ABSTRACT The effects of the addition of sodium carbonate (Na 2 CO 3 ) and the subsequent simultaneous heating and stirring on the rheological behavior of Ca-bentonite colloidal dispersions have been investigated in this study. Ca-ben- tonite dispersions were treated with Na 2 CO 3 at various ratios (2, 4, 12 g/100 g bentonite), and then subjected to heating and stirring for variable periods. It was found that the swelling and the viscosity of the treated bentonite samples increased with increasing Na 2 CO 3 content and the optimal Na 2 CO 3 level (relative to the bentonite content) was found to be 4 g/100 g of Ca-bentonite (4%). The results also showed that simultaneous heating and stirring enhanced the bentonite swelling and ion exchange processes for sodium activation. The rheological properties of the Ca-bentonite suspensions depend on the strength of the bentonite gel structure and the inter- particle interactions. Although the treated and untreated bentonite samples showed gel and solid-like behavior in the linear viscoelastic region (LVR), the region where the storage (G′) and loss (G″) moduli are independent of applied strain and/or stress, the G′ values of the Na 2 CO 3 treated bentonite samples were higher than those of untreated samples. All bentonite samples (whether Na 2 CO 3 treated or untreated) showed more elastic than viscous response (i.e., G′ >G″) within the LVR. The results showed that bentonite dispersions treated with 4% Na 2 CO 3 displayed the highest elastic behavior. The relationship between zeta potential and pH for the untreated and Na 2 CO 3 treated Ca-bentonite dispersions were investigated. Bentonite colloids were stable in the examined range of pH (3 -12); such wide pH range stability is essential for many industrial applications. Finally, the effect of heat treatment on the swelling behavior of 4% Na 2 CO 3 treated bentonite dispersions was extracted from particle size measurements using a laser scattering particle size analyser. The results showed that the particle size increased with the combined heating and stirring treatment for the first 3 h then remained constant. This in- crease in particle size is likely due to improved swelling and the existence of some of weak particle-particle interactions bentonite (aggregates). 1. Introduction The commercial value of bentonites as raw materials is high due to their applications in many industries such as cosmetics and medical products, paints, water treatment (de Figueirêdo et al., 2014; Vipulanandan and Mohammed, 2014; Zhuang et al., 2015), pharma- ceuticals (Cara et al., 2000a,b; Viseras et al., 2010), dyes (Bergaya and Lagaly, 2013; Al-Hussaini and Eldars, 2014; Chang et al., 2014; Wang et al., 2014) and papermaking (Li et al., 2011; Wu et al., 2013; Yoon et al., 2013). Bentonites are also used in drilling fluids because of their exceptional rheological properties. In drilling applications, good quality bentonite provides the required viscosity and acceptable filtration loss (Lebedenko and Plée, 1988; Yildiz et al., 1999; Falode et al., 2008). Bentonite consists mainly of montmorillonite [(Al,M- g) 2 (OH) 2 (Si,Al) 4 O 10 (Ca) x × nH 2 O] and different amounts of other mi- nerals such as quartz (SiO 2 ), calcium and sodium feldspar [(CaAl 2 Si 2 O 8 ), (NaAl 3 Si 2 O 8 )] (Abu-Jdayil, 2011; Mierczynska-Vasilev and Smith, 2016). There are two types of bentonites: sodium bentonite (Na-bentonite), which has a high swelling capacity, and calcium ben- tonite (Ca-bentonite), which is a non-swelling clay and spontaneously forms colloidal dispersions in water (Hassan and Abdel-Khalek, 1998; Dill, 2016; Yan et al., 2016). Bentonite is mainly composed of layers including silica and alumina sheets linked together and arranged on top of each other. Bentonite lamellar platelets are packed together by http://dx.doi.org/10.1016/j.clay.2017.07.032 Received 1 March 2017; Received in revised form 26 July 2017; Accepted 27 July 2017 ⁎ Corresponding author. E-mail address: m.nasser@qu.edu.qa (M.S. Nasser). Applied Clay Science xxx (xxxx) xxx–xxx 0169-1317/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Magzoub, M.I., Applied Clay Science (2017), http://dx.doi.org/10.1016/j.clay.2017.07.032