AbstractAqueous two‐phase extraction systems were developed to separate intracellular proteins from cell debris. To economize on the use of chemicals as well as to minimize environmental pollution, a closed mode of operation was sought. Various approaches to achieve recycling of salt from the primary lower phase containing 30–60% (w/w) of the added salt together with cell debris, proteins and nucleic acids were studied. Techniques assessed included microfiltration, heat treatment and the extraction with phase systems formed by aliphatic alcohols. With 20% (w/w) primary lower phase it was found to be possible to separate 95% of the salt in 3–4 theoretical steps using counter‐current ext