Characterization and prevention of interfacial crud produced during the extraction of vanadium and chromium by primary amine

In this study, the interfacial crud produced during the extraction of vanadium and chromium by primary amine N1923 was investigated from the leaching solution containing heavy metals. Effect of pH values of the leaching solution on the percentage of the crud produced and the emulsion type of the crud were studied. X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD) and Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) have been employed for the physiochemical characterizations of the crud. Our results indicate that the percentage of the crud produced is greatly affected by the pH value of the real leaching solution, and the crud is more stable in the acidic solution. The crud is an oil-in-water emulsion with many fine solid particles in the water phase. The particles, which are from the real leaching solution, have been proved to be the main cause for the crud formation. Particles in the cruds are normally composed of a large number of the crystals of Na2SO4, a few SiO2 and oxides or hydroxids of Fe and Al. However, component proportions of the solids are dependent on the pH values. Possible mechanism of the crud formation is put forward. The solids present in the real leaching solution exert a stabilizing effect on the emulsion, based on which Na2SO4 crystallizes at the interface of the emulsion. Furthermore, the Na2SO4 crystals strengthen the stability of the emulsion, and thereafter the interfacial crud forms. Three effective methods to prevent the crud formation are proposed, i.e. clearing the real leaching solution by membrane filtration, increasing of the amount of the modifier, and applying of hexane as the diluent.