Utilization of green solvents for boron removal in water and wastewater treatment

Abstract

Boron, an element with essential role in plant growth, human health maintenance and industrial processes, often require intensive planning and costing to have its level calibrated. The incentives for boron removal from water and wastewater streams could be either as a preventive measure, such as meeting drinking water regulations in desalination plants and protecting boron-sensitive agricultural crops, or as a productive measure, such as recovering boron form industrial wastewater in order to make use of the resource. From the various techniques for boron removal, solvent extraction, or liquid-liquid extraction (LLE), have been long experienced for the extraction of boron through different types of alcohols. The aim of this project is to improve the solvent extraction process of boron with different extractants such as ionic Liquids (IL) and Deep Eutectic Solvents (DES). Different hydrophobic ILs have been tested for the extraction of boric acid from aqueous environment. In addition, Four hydrophobic deep eutectic solvents have been developed from a combination of menthol (Men) and thymol (Thy) as Hydrogen Bond Acceptors (HBA) with decanol (Dec) and 2-methyl-2,4-pentanediol (MPD) as Hydrogen Bond Donors (HBD).The DES were characterizes in terms of their physical properties, thermal properties (using TGA, DSC and FTIR) and critical properties (using group contribution method based on the modified Lydersen-Joback-Reid and Lee-Kesler mixing rules. In order to evaluate their performance, the hydrophobic DESs were used to extract boric acid from aqueous solutions. The extraction efficiencies and distribution coefficients were used as the evaluation criteria, and different parameters were investigated. The hydrophobic DESs made with MPD showed high efficiency of boric acid extraction for up to 90.1%. Additionally, the extraction for the DESs was stable in a range of pH from 2 to 7. Boric acid extraction from a synthetic seawater and a synthetic brine was enhance by almost 2% and 5% for Thy:MPD and Men:MPD respectively. FTIR spectra was recorded before and after extraction of boric acid in order to have a better understanding on the extraction mechanism. Stabilization of the hygroscopic MPD in the eutectic mixtures enabled its used in water treatment applications.

Date of Award	Dec 2019
Original language	American English