Deposition of cobalt on iron powder.

The cementation reaction [chemical formula] although theoretically possible, is not normally considered to be of significance since the negative electrode potential of the reaction is very small and the rate of deposition is usually extremely low. However, a previous investigation of the corresponding reaction between nickel and iron suggests that such reactions may occur at a relatively rapid rate, provided the specific surface area of the iron is very high, as in the case of a fine powder. In the present work the cementation reaction has been followed in a three phase fluidized bed, which maintained the powder in suspension in the solution and ensured that all particles had an equal chance of contact with cobalt ions. An investigation was made of the effect on the reaction of certain process variables including temperature, PH, type of anion in the solution and concentration of iron powder in the cell and cobalt ions in the solution. This has allowed, under optimum conditions, cobalt deposition at a relatively high rate. In view of the relative cost of iron and cobalt this reaction may be a suitable way of extracting cobalt from waste solutions. An examination of the morphology of the deposit suggested that deposition always took place irregularly, so that some parts of the iron powder remained in contact with the solution. Thus the cementation reaction did not come to a rapid conclusion, on account of the formation of a continuous layer of cobalt on the iron surface. This irregular deposit was maintained even when electrodeposition occurred simultaneously with the cementation reaction.