Selective recovery of mercury(II) from industrial wastewaters I. Use of a chelating ion exchanger regenerated with brine

An iminodiacetic acid chelating ion exchanger is able to remove mercury(II) selectively from solutions containing iron, zinc, cadmium and lead in sulfuric acid at pH 1.5. At an initial Hg concentration of 10–12 mg/l, mercury leakage is below 50 μ/l over at least 200 bed volumes. Leakages are higher in the presence of chloride because of complexation; a combination of chloride and fluoride results in even higher leakages. Mercury is only partly eluted from the resin with nitric acid, but is readily eluted with sodium chloride solution and can be recovered in pure form by reduction to Hg(I) or Hg(0). The extent of desorption depends on NaCl concentration, pH and flow rate. At 3 M and pH 7, desorption of mercury in the first cycle averages 70–80% in ten bed volumes of eluate. Recovery of mercury taken up in subsequent cycles is close to 100% provided that the resin was loaded to more than 10% of its capacity.