Oxime degradation chemistry in copper solvent extraction plants

摘要

The oximes used as extractants in copper solvent extraction plants slowly undergo chemical degradation under normal operational conditions. The degradation reactions involve both the oximine group and the aromatic ring. The hydrolysis of oxime generates either an aldehyde or a ketone, which accumulates in the organic phase thereby steadily deteriorating the phase disengagement behaviour. The nitration of the aromatic ring is another important degradation reaction which involves the attack of an electrophilic nitronium NO_2~+ to the o-position of the phenolic ring. The presence of nitrate ions may also enhance the decomposition towards carbonylic products, particularly in the stripping circuit. The alcoholysis, induced by tridecanol and p-nonyl phenol, the formation of oxazole by photochemical degradation and the sulphonation of the aromatic ring often by the accidental contact between the organic and concentrated sulphuric acid, are discussed. Experimental evidence shows that equilibrium modifiers significantly affect the oxime stability. The degradation products, which have polar characteristics, promote slow phase disengagement at the plant and, hence, an accelerated decomposition rate because of the increased liquid-liquid contact area.