The paper presents the results of a pilot-scale study investigating the efficiency of an ion exchange resin system in the removal of Ni, Hg, and Cr from flue gas desulphurisation wastewater, in the presence of competitive metals such as Ca, Mg, Al, Fe, and Mn. The core part of the ion exchange installation consisted of two columns that were filled with ion exchange resin with iminodiacetic functional groups (Purolite S930) and one column filled with resin with isothiouronium functional groups (Purolite S920). The results showed that Ni, Hg, and Cr were almost completely removed from the wastewater with nearly 100% efficiency. Purolite S930 almost totally removed Ni, reducing its content from 89.3 ± 35 μg dm-3 to below 0.1 μg dm-3, while Purolite S920 reduced the remaining Cr content from 2.2 ± 0.6 μg dm-3 and most of the Hg content, from 23.5 ± 6.6 μg dm-3 to below 0.1 μg dm-3. The competitive metals Ca, Mg, Mn, and Al showed low affinity to the studied ion exchange resins. The study also assessed speciation of ion forms and sorption mechanisms. Breakthrough curve analysis was also carried out, which revealed that the selectivity sequence of iminodiacetic resin was Ni > Cr > Hg > Fe > Al > Mn > Ca, Mg. Elution studies were performed on S930 resins that allowed the separation of two streams: one containing mostly Ni and Fe which can be subjected to Ni recovery and the other containing mostly Cr and Hg which can be separated.
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