Rhenium extraction from dilute solution by precipitation flotation and oxidative volatilization techniques

The low mass transfer effect of dilute solution results in low recovery efficiency of critical metal Re ions from ultralow-concentration metallurgical industrial effluents. Bubble driving was an effective measure to enhance the mass transfer in the dilute solution, and bubble flotation technology was adapted to enrich and recover metal ions. In this work, the extraction of critical metal Re from dilute solutions by a precipitation flotation process was investigated. The precipitation flotation process includes ion precipitation by CTAB and ammonium salt, flocculation by PAM and air bubble flotation separation. The effects of technical parameters on Re recovery were systematically investigated. In the precipitation stage, NH4+ with a positive charge firstly reacts with the rhenate (ReO4-) with a negative charge via electrostatic action and then further reacts with CTAB to form fine CTAB(NH4ReO4) precipitate through complexation coordination. In the flocculation procedure, the particle size of precipitate flocs is elevated due to the physical polymerization of PAM polymer. In the flotation procedure, the long carbon chains on the surface of the flocs have a foaming effect due to their strong hydrophobicity, and they are trapped by the upfloated bubbles and rapidly enriched in the foams. Under the optimized conditions, the recovery efficiency of Re is 99.5% and qualified circulating water with a turbidity of 9.8 is obtained. Eventually, highly purified Re oxides (99.8%) are prepared from the Re froth product via oxidizing volatilization since the utilized organic CTAB and PAM can be burned completely during the oxidizing calcination process.