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MAY 2022 I PCB007 MAGAZINE 83 the copper into the organic phase. Other unit operations equipment used for LLE are sieve tray and bubble-cap towers, but the mixer-separator is the simplest and easiest to maintain. Figure 3 shows diagrams of an LLE system for printed circuit etching of either alkaline or acid types of etchants with copper recov- ery. Many of these have been installed over the years. Figure 3a is the mixer-separator unit that Figure 3a: The copper etcher with rinse water and the primary mixer-separator for removal of copper and regeneration of the etchant. Figure 3b: Once the copper is in the organic phase, a mixer-separator strips the copper out of the kerosene and into the sulfuric acid aqueous phase. Figure 3c: Now back into the electrolyte, the copper is plated onto stainless steel cathodes and sold as scrap copper. Figure 3d: A smaller mixer-separator is used to remove copper from the etcher's rinse waters. strips the copper out of the etchant. In Figure 3b, another mixer-separator unit can strip the copper into the acid electrolyte, whereas in Figure 3c, the copper is plated out as sheets from the copper sulphate electrolyte. Figure 3d is the final mixer-separator that removes cop- per from the etcher's rinse water and returns it to the cascade etcher rinses while the organic phase is combined with the etchant extract. All streams are 100% recycled.