Search

Particles size distribution (PSD) is introduced as a tool for analysis of bentonite aggregation and swelling kinetics. Raw Ca-bentonite was purified using a combined wet sieving and sedimentation processes, followed by thermochemical treatment with Na2CO3 to increase its swelling capacity. The detailed analysis of the PSD shows a strong correlation between the PSD and the swelling process. For the chemically treated raw bentonite, PSD revealed two different peaks representing unswelled and swelled particles along with some aggregates. The swelling is shown to be a kinetically controlled process that depends on time, temperature, and bentonite chemical composition. At the beginning of the chemical treatment, the effect of aggregates was more dominant; therefore, the viscosity did not increase much with particle size. However, the combined chemical and thermal treatment has enhanced the Na-activation process and boosted bentonite swelling. The rheological measurements have shown enhancement in the viscosity and confirmed the PSD findings. The same optimal treatment conditions are obtained from both rheological measurements and PSD analysis. A model is developed based on classical reaction rate kinetics and used to describe the conversion from unswelled to swelled particles. The PSD has a strong correlation with the physical properties of the suspension such as the viscosity. The swelling rate fits a second order model with a rate constant, k, in the range 0.002 to 0.124 h−1 and an activation energy, E, of 87 kJ/mol. PSD analysis together with the developed kinetic model are powerful tools for studying the swelling kinetics of bentonites. [ABSTRACT FROM AUTHOR]

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-bentonite 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 increase in particle size is likely due to improved swelling and the existence of some of weak particle-particle interactions bentonite (aggregates). [ABSTRACT FROM AUTHOR]

Steelmaking is an energy-intensive process that generates considerable amounts of by-products and wastes, which often pose major environmental and economic challenges to the steel-making industry. One of these by-products is steel dust that is produced during the separation of impurities in the smelting and refining of metals in steel-making furnaces. In this study, electric arc furnace (EAF) dust has been evaluated as a potential, low-cost additive to increase the viscosity and weight of drilling muds. Currently, the cost of drilling operations typically accounts for 50 to 80% of the exploration costs and about 30 to 80% of the subsequent field development costs. Utilization of steelmaking waste in drilling fluids formulations is aimed to produce new and optimized water-based drilling formulations, which is expected to reduce the amount of bentonite and other viscosifier additives used in the drilling formulations. The results showed that in a typical water-based drilling fluid of 8.6 ppg (1030.51 kg/m3), the amount of standard drilling grade bentonite could be reduced by 30 wt.% with the addition of the proposed new additive to complete the required mud weight. The mixture proved to be stable with no phase separation. [ABSTRACT FROM AUTHOR]

In this study, the influence of a hybrid coagulation/flocculation process on the electrokinetic of highly stable bentonite suspension has been examined. Choline chloride (ChCl) based natural deep eutectic solvent (NADES) was utilized as coagulant coupled with polyacrylamide (PAM) with different charge types and densities used as a flocculant. Turbidity, zeta potential, and floc size analysis were used to evaluate the changes in the flocculation efficiency of hybrid systems relative to the single NADES and PAM systems. The study revealed a clear impact on the flocculation behavior of cationic and anionic PAMs in the presence of NADES. The addition of NADES as a coagulant aid reversed the flocculation activities of the PAMs due to the presence of positively charged NADES that enhances the adsorption of the anionic polyacrylamide (APAM) over the cationic polyacrylamide (CPAM). Low flocculation efficiency was observed for the hybrid systems of NADES/CPAM as indicated by the highly positive zeta potential (ζ > + 25 mV) and small flocs ( D 50 < 50 μ m). Hybrid systems of NADES/ APAMs, on the other hand, significantly improved the flocculation efficiency by achieving a zeta potential within the instability region (− 10 mV < ζ < + 10 mV) and relatively large flocs D 50 > 50 μ m. Aside from the charge type, the molecular weight (MW) and charge density (CD) of the PAM had a significant impact on the flocculation behavior of bentonite suspension. High PAM adversely impacted the flocculation parameters for APAMs. Therefore, a hybrid system of NADES/ AN 923 SH at an APAM dosage of 15 mg L − 1 with residual turbidity of 0.3 NTU, ζ -potential of − 3.9 mV and D 50 of 70.4 μ m was the optimum system with the most significant enhancements compared to single systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• Hybrid coagulation-flocculation on the flocculation of bentonite is investigated. • Compared to single PAM, hybrid systems performed exceptionally well. • Hybrid systems were able produce bigger flocs than single systems. In this study, the influence of the hybrid coagulation-flocculation system on the flocculation and shear resistivity of bentonite suspension has been investigated. Two short-chained coagulants, polyamine and polyDADMAC, accompanied with low and high Molecular Weight (Mw) long-chained anionic Polyacrylamide (PAM) flocculants have been used to enhance the size and mechanical properties of the produced flocs. Four characterization techniques were used as evaluation criteria of degree of flocculation including turbidity, zeta potential (ζ), floc size analysis and rheology. Optimum dosages between 5 and 10 mg/L were obtained for flocculants and between 20 and 30 mg/L for coagulants in hybrid systems. Compared to single systems, hybrid systems performed exceptionally well. Removal efficiency of 99% was achieved using hybrid systems producing water with turbidity as low as 1.05 NTU. Although differences were insignificant in the treatment quality, significant improvement was achieved in floc size and rheological behavior. Hybrid systems were able to produce large flocs of more than 400 µm, five times bigger than flocs from the single cationic coagulant systems. Most importantly, rheological testing of produced slurries revealed the remarkable advancement achieved by hybrid systems. Hybrid systems were able to increase the elastic modulus (G′) by more than ten times resulting from the compacted flocs present in the system. Furthermore, resistivity toward shear and oscillations were improved. Ultimately, hybrid systems have surpassed the single cationic systems by achieving slightly better treatment besides producing larger, denser and more resistive flocs. Generally, polyDADMAC performed better than polyamine in hybrid systems. The combination of polyDADMAC with high Mw PAM gave the best separation as well as the largest flocs, while the combination with low Mw PAM resulted in the best rheological properties. [ABSTRACT FROM AUTHOR]