NICKEL EXTRACTION FROM ACIDIC CHLORIDE SOLUTIONS WITH ALIPHATIC OXIMES

The U.S. Bureau of Mines investigated the use of aliphatic oximes to extract nickel from acidic nickelous-chromic chloride solutions. Batch solvent-extraction tests were conducted to characterize nickel extraction and stripping. The oximes tested, heptanal, octanal, 2-ethylhexanal, decanal and dodecanal, selectively extracted nickel over chromium by an ion pair transfer mechanism. Nickel was stripped from the loaded oxime extractants with dilute acid. When subjected to acidic processing conditions, the oximes partially degraded to their parent aldehydes by hydrolysis but were regenerated by contacting the solvent with a neutralized hydroxylamine-hydrochloride solution. Decanal oxime (DOX) was successfully used in a continuous countercurrent solventextraction circuit that incorporated three loading, six stripping and one regeneration stage. At steady state, the circuit produced raffinates, strip liquors and loaded solvents containing 0.002, 27.2 and 10.3 g/l Ni, respectively. The DOX degraded 12% per loading and stripping cycle but was effectively regenerated prior to recycling to the head of the circuit. Additional testing, in closed reactors, indicated that the stability of the DOX extractant could be improved by adding decyl aldehyde to the solvent and by stripping the solvent with a dilute solution of HCl and hydroxylamine hydrochloride; however, additional research is needed to determine long-term DOX stability in a process solvent-extraction circuit. © 1990.