Preparation of Low-Salt-Rejection Membrane by Sodium Hypochlorite Chlorination for Concentration of Low-Concentration Magnesium Chloride Solution
Year: 2025
Type: article
Abstract: The process of magnesium bicarbonate precipitation for rare earths yields a dilute MgCl2 solution. The solution can only be concentrated to a maximum of about 70 g/L by reverse osmosis (RO), which is insufficient for recycling. low-salt-rejection reverse osmosis (LSRRO) allows for a higher concentration of brine while operating at moderate pressures. However, research on LSRRO for MgCl2 enrichment are still at an early stage. In this study, polyamide RO membranes were treated with sodium hypochlorite (NaClO) to prepare low-salt-rejection membranes. The effects of sodium hypochlorite concentration, pH, and chlorination time on membrane properties were investigated. Under alkaline chlorination conditions, the membrane's salt rejection decreased and water flux increased. This should be resulted from the hydrolysis of polyamide (PA), which forms carboxyl and amine groups. The carboxylic acids were dissolved in the alkaline solution, which reduces the crosslinking degree of the PA. In addition, the salt rejection decreased and water flux increased with increasing sodium hypochlorite concentration and treatment time. The low-salt-rejection membrane prepared by exposing the membrane to NaClO at a concentration of 15 g/L and a pH of 11 for a duration of 3 h, exhibited a salt rejection of 50.7%. The mult-stage LSRRO was utilized to concentrate the 40 g/L solution of magnesium chloride at the pressure of 5 MPa. The concentration of the concentrated brine reached 120 g/L, which is 70% higher than the theoretical maximum concentration of 70 g/L for conventional RO. This proved to some extent the superiority of LSRRO.
Source: Materials
DOI: 10.3390/ma18122824
Authors: Zhengyang Wu, Zongyu Feng, Longsheng Zhao, Zheng Li, Meng Wang, Chao Xia
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,137
OpenAlex ID: W4411353442