During the development of a solvent extraction process for the separation of nickel and cobalt from ocean nodule sulphate leach liquor, there was a need for fast and accurate analytical method for determination of these elements in various process streams. For the determination of copper, nickel and cobalt which are present in gm/litre level, simultaneous visible spectrophotometric method developed in our laboratory was employed. Iron which is present at <0.2 g/l was estimated by atomic absorption spectrophotometry. It has been found that Iron (III) seriously interferes with the determination of nickel giving almost 10% higher values as, confirmed by classical gravimetric method. Therefore, an attempt has been made to develop a first and accurate method for the simultaneous determination of copper, cobalt, nickel and iron by visible spectrophotometry. The method developed eliminates the need for separate estimation of iron by atomic absorption spectrophotometry and nickel by gravimetry.
Leach liquor obtained from manganese sea nodules contain base metals such as copper, cobalt, nickel as the major constituents with iron at 0.2g/l level. The analytical methods for simultaneous determination of base metals based on complex formation and applicable at trace level concentrations are reported in literature (Garcia et al (1995), Jaywant D.V and Murthy T.K.S (1971), Pradhan V, Singh RP (1988) and Ren S.X (1995)). However, we have adopted the method developed in our laboratory by Jaywant D.V and Murthy T.K.S (1971) as this is applicable for most of our process samples having concentrations of metals in g/l range and also has the advantage of avoiding the use of any chromogenic reagent. While using this method, it was found that Fe (III) at about 0.2g/l seriously interferes in the determination of nickel giving almost 10% higher values as compared to the determination by classical gravimetry.