Selective elution of nickel and cobalt from iminodiacetic acid cation exchange resin using ammoniacal solutions

Nickel and cobalt were eluted from iminodiacetic acid functionalized ion exchange resin by ammoniacal eluents. The highest recovery of nickel and cobalt was achieved using a mixture of aqueous ammonia, ammonium sulphate, and magnesium sulphate. The use of ammonium sulphate yielded a higher extent of nickel desorption than the use of ammonium carbonate. The presence of a divalent metal salt such as magnesium sulphate, calcium sulphate, or manganese sulphate was found to increase the extent of nickel desorption. Magnesium was found to be most suitable for this purpose. Nickel and cobalt on the resin are displaced by magnesium during this process. The selectivity of this elution process varies by metal. Aluminium and iron show little or no affinity for ammoniacal elution. Calcium and manganese desorb to a limited extent. The kinetics of nickel desorption in aqueous ammonia–ammonium sulphate–magnesium sulphate solution are slower than that of sulphuric acid elution. When resin loaded with magnesium is contacted with aqueous nickel sulphate, nickel sulphate will displace magnesium on the resin. This reaction occurs on a similar time scale as that of protonated resin.