Concentrating phosphoric acid by direct contact membrane distillation using a low-cost polyethylene separator

Abstract

The ability to recycle phosphorus (P) components in reusable strength from wastewaters presents a promising opportunity to meet the increasing consumption demand. In this paper, the concentration of a dilute stream of phosphoric acid from 15 to 60 wt% was demonstrated using a high-performing PE separator in direct contact membrane distillation (DCMD), benchmarking against commercial PVDF and PTFE membranes. Combining with morphological/structural/material characterization, the membrane performance and energy efficiency were analyzed in-depth based on a combined heat and mass transfer model, which coupled the effects of both concentration and temperature polarization. The interplay of membrane flux, operating conditions and energy indicators was examined, indicating the significant influence of feed temperature, membrane characteristics and the trade-off relationship between Evaporation Efficiency/ Gained Output Ratio and Specific Energy Consumption. The concentration of 15 wt% H3PO4 stream using the PE separator was operated continuously for 100 h with minimal change in flux (> 40 kg/m2·h at 65 °C). The long-time stability was confirmed by membrane autopsy before and after experiments. The results demonstrated the PE separator as a promising low-cost membrane for acid concentration, providing an alternative for resource recovery from harsh solutions.