NaCl recovery from organic pollutants-containing salt waste via dual effects of aqueous two-phase systems (ATPS) and crystal regulation with acetone

Abstract

A large amount of salt waste accompanied with contaminants (e.g., organic pollutants) is produced in chemical production process, causing serious environmental hazards and waste of salt resources. However, there have been few satisfactory treatments for this hazardous waste until now. In this work, a novel strategy for NaCl recovery and organic pollutants removal from the salt waste containing pyridine derivatives was developed by using acetone in salt waste solution. The results showed NaCl was effectively recovered (recovery rate, 99.12%), and the TOC value of its saturated solution was reduced from 806.2 to 145.4 mg/L, below the limits (200 mg/L) for chlorine gas and caustic soda production in chlorine alkali plant. Moreover, no pyridine derivatives can be identified through Fourier transform infrared spectroscopy (FTIR) test. Mechanism analysis demonstrated the dual effects of acetone as following: 1) acetone and NaCl formed aqueous two-phase systems (ATPS) to remove organic pollutants; 2) acetone, as a crystal regulator, induced NaCl crystals to recrystallize in cubic morphology with a smooth surface, which enhanced the removal of pollutants. Besides, the acetone-water phase split facilitated the separation of organic pollutants as well as the reuse of acetone. This work proposes a promising and feasible method for salt waste to remove organic pollutants and recover recrystallized NaCl solids, and also provides new insights into the function of acetone on the crystal regulation of salts.