2.3 Multi-stage countercurrent extraction
procedures
The three-stage countercurrent extraction as shown in Figure 1 was
performed using a separatory funnels
at a laboratory scale[26]. 0.4 mol/L TMPD
dissolved in CCl4 and the SL brine without acidification
(pH=4.60) was used as organic phase and feed brine, respectively.
Firstly, the prepared fresh organic (20 mL) and feed brine (20 mL) were
added to the second funnel. After the mixture reached a balance, the
phase separation was set. Then, the aqueous phase (A2) was poured into
the first funnel and the organic phase (O2) into the third funnel. Equal
volumes of the fresh organic and brine were then added to the first and
the third stage for the mixture and separation, respectively. Then, the
organic phase (O1) and aqueous phase (A3) were simultaneously poured
into the second funnel, and both the raffinate and the loaded organic
samples were obtained. In this way, the whole countercurrent extraction
process could be recycled by introducing the feed brine and organic
intermittently. After a series of extraction and product removal cycles,
the system stabilized. The
whole
five-stage extraction and stripping process experiment (section 3.10)
was carried out in the same way.