Kinetics and mechanism of the reductive ammonia leaching of ocean nodules by manganous ion

The kinetics of reductive ammonia leaching of ocean nodules by manganous ion were found to be chemically controlled. The rates of Cu, Ni and Co extraction all show an order of dependence of 0.5 each on total ammonia and manganous ion. The logarithm of metal ion extraction rates vs. pH shows a maximum at about pH 9.0 to 9.5. The orders with respect to [H+] are −0.5 and 0.5, respectively, in the pH ranges of 7.0 to 9.0 and 9.5 to 11.0, due to various protolytic equilibria involving ammonia and Mn(II). The rates of metal ion extraction have the order Cu > Ni > Co. A chemical surface-leaching reaction mechanism is proposed, involving adsorption of manganous ammine on the nodule lattice, thereby liberating Cu, Ni and Co minerals, which are subsequently dissolved due to metal ammine formation.