4TH International Congress on Technology - Engineering & SCIENCE - Kuala Lumpur - Malaysia (2017-08-05)

Rubidium Extraction From Seawater Brine By An Integrated Membrane Distillation-selective Sorption System
An ideal scenario for seawater reverse osmosis (SWRO) brine management is to achieve minimal liquid discharge while recovering valuable resources [1]. Membrane distillation (MD) is able to concentrate SWRO brine (reducing brine volume) while producing additional water [2]. Concentrating valuable elements in SWRO brine by MD is another advantage. Rubidium (Rb) in SWRO brine (0.19-0.22 mg/L) is a trace alkali metal with a high market price (USD14720/kg), used for laser technology and fiber optics[3]. A lab produced polymer (polyacrylonitrile, PAN) encapsulated potassium copper hexacyanoferrate (KCuFC) sorbent (KCuFC(PAN)) exhibited high Rb selectivity [4]. For the first time, the suitability of an integrated system of MD with KCuFC(PAN) sorbent (MD-KCuFC(PAN)) (Figure 1a,b) for Rb recovery and simultaneous SWRO brine volume reduction was evaluated. The results showed that KCuFC(PAN) sorbent exhibited 10 to 15% increment of Rb sorption at 55 °C (Langmuir Qmax = 125.11 ± 0.20mg/g) compared to at 25 °C (Langmuir Qmax = 108.71± 0.20mg/g). This endothermic feature makes it beneficial to integrate KCuFC(PAN) into MD system, which operates at 55 °C. The integrated MD-KCuFC(PAN) system with periodic membrane cleaning, enabled to concentrate the SWRO brine by up to a volume concentration factor (VCF) of 2.9 (65% water recovery) (Figure 2). Repeated cycles of MD-KCuFC(PAN) sorption with SWRO brine enabled the extraction of 2.26 mg Rb from 12 L of brine (equivalent to 1.9 kg of Rb/day, or 0.7 tonne/yr in a 10 MLD plant). NH4Cl air stripping followed by resorcinol formaldehyde (RF) resin filtration (Figure 1 b) enabled to recover Rb from the desorbed solution. In summary, the novel approach to extract Rb by an integrated MD-KCuFC(PAN) is promising as this process enables extraction of Rb directly from the MD feed tank while simultaneously producing fresh water. The 20 to 40 h time duration to concentrate the SWRO brine by VCF of 2.9, was suitable for a long contact time of Rb sorption by the encapsulated cores of KCuFC(PAN).
Gayathri Danasamy, Sanghyung Jeong, Mohd. Abu Hassan Johir, Saravanamuthu Vigneswaran