Choline chloride based natural deep eutectic solvent for destabilization and separation of stable colloidal dispersions

In solid-liquid separation processes, coagulation/flocculation is one of the most popular techniques in treating wastewater, as it is efficient, simple, and economical. Consequently, the formation of a new environment friendly destabilizing agent needed for the development of this processes. Hence, the aim of this paper is to introduce a new green and cheap choline chloride (ChCl) based natural deep eutectic solvent (NADES) as a coagulant for clay-based dispersions which are known to be a highly stable colloidal systems. For the NADES preparation, lactic acid (LA) and ChCl were used as the hydrogen bond donor and acceptor, respectively with a 1:1 ratio. Furthermore, the individual components of the NADES; ChCl and LA were also separately tested as coagulants as well as a binary mixture of both. Zeta potential, turbidity, floc size distribution, settling behavior, and viscosity measurements were conducted to study the potential of NADES in destabilizing and separating of high-stable bentonite dispersions and determine the strength of the resultant flocs. Initially, at pH 10, bentonite suspension had a high turbidity of 347 NTU and zeta potential of -45 mV. At optimum concentration the reduction in turbidity and zeta potential were as follows: 5.32 NTU with -30.6 mV, and 4.3 NTU with -22 mV was achieved using ChCl alone and mixture of ChCl and LA (ChCl-Cl), respectively. NADES showed the most efficient performance with almost 100% turbidity removal and a significant reduction in the zeta potential of -18 mV. For the three tested coagulants (ChCl, ChCl-LA, and NADES), produced flocs ranged in size from 5 mu m to 36 mu m depending on the coagulant type and dosage were achieved. NADES produced the largest flocs followed by ChCl-LA and ChCl. The obtained results were also confirmed through settling rate and sediment volume in addition to the viscosity measurements of the resultant flocs.

Automated summary

In this study, a ChCl-based NADES was successfully used as a coagulant to treat highly stable bentonite dispersions, achieving effective clarification and separation. The results showed that NADES had better coagulation performance compared to ChCl and ChCl-LA.