Removal of Mn(II) from hydrochloric acid leach liquors of nickel laterite ore through microbubble oxidation and acid leaching

Leach liquor obtained from atmospheric acid leaching of nickel laterite with HCl solution contain large concentrations of Mn and Mg. This paper presents a method for separating large amounts of Mn and Mg from Ni and Co chloride solution by microbubble aeration oxidation and acid leaching processes. Such methods utilize the multiple advantages of the microbubble technology, such as large specific surface area, negatively charged surface, long stagnation, high oxygen mass transfer efficiency, and the ability to generate active oxygen. The effects of aeration pore size, oxygen flow rate, reaction temperature, stirring speed, and pH were studied. Under optimal experimental conditions (bubbling O-2 flow = 0.4 L/min, aeration aperture = 0.45 mu m, speed of agitation = 400 rpm, temperature = 50 ?, pH = 7), the recovery efficiency of Ni and Co were 99.3% and 89.0%, and the removal efficiency of Mn and Mg were 99.5% and 97.7%, respectively. Through XRD, XPS, and FTIR, it was found that soluble Mn was first oxidized to Mn3O4 and MnO2.H2O. In the acid dissolution process, Mn3O4 reacted with dilute sulfuric acid to form MnO2, which is insoluble in dilute acid, and was thus easily separated from Ni and Co. Analysis of the mass transfer process showed that the microbubble aeration method can greatly increase the oxygen mass transfer coefficient (0.073 s-1), accelerate the dissolution of O-2, and create conditions for the generation of active oxygen species.