Separation of rare earth elements from mixed-metal feedstocks by micelle enhanced ultrafiltration with sodium dodecyl sulfate

Micelle enhanced ultrafiltration (MEUF) is a surfactant-based membrane separation process that may be used to separate target ions from mixed metal aqueous solutions, such as leachates of coal ash and other geological wastewaters. The ability of MEUF to separate rare earth elements (REEs) was evaluated using sodium dodecyl sulfate (SDS) as the sorbent in surfactant micelle phase, which was subsequently separated using ultrafiltration, acidification, and ferricyanide precipitation. Separation experiments were performed with a synthetic coal ash leachate feedstock as an example mixed-metal feedstock. Experiments tested the influence of surfactant concentration, pH, and co-existing competitive ions on REE recoveries, and also tested methods for SDS recovery and reuse. Membrane rejection efficiencies of REEs were 97% and 71% respectively for synthetic and real leachate under optimized operating conditions. A two-step process of precipitation with CaCl(2)and Na(2)CO(3)following membrane separation was the best for recovering SDS with a yield of 99.7%.

Automated summary

Micelle enhanced ultrafiltration (MEUF) is an effective membrane separation process for separating target ions from mixed metal aqueous solutions. This study evaluates the separation efficiency of MEUF for rare earth elements (REEs) using sodium dodecyl sulfate (SDS) as the sorbent. The results show that under optimized conditions, the membrane rejection efficiency of REEs is high and SDS can be efficiently recovered using a two-step precipitation method.