Petroleum coke slags: characterization and dissolution
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Slags are crystalline to vitreous by-product materials generated in many high temperature industrial processes. This study presents a general technique for the identification of the phases present in petroleum coke gasification slags. documents the phase assemblages and textures, and finally determines the dissolution of vanadium from these slags as part of the considerations of potential resource reclamation. The general identification procedure utilizes (1) recognition of separate phases using optical microscopy and scanning electron microscopy; (2) electron probe microanalysis (EPM) of chemical compositions of individual phases; (3) statistical analysis of the EPM data to eliminate spurious data; (4) estimation of valence states of transition metals using thermodynamic and computational methods; (5) derivation of chemical formulae for the phases using computational methods and chemistry of ionic substitutions; (6) verification of phase identity using X-ray diffraction analysis.
More than twenty phases were determined in petroleum coke slags including oxides, silicates. vanadates, sulfate. sulfides and alloys. The reduced slags are rich in V2>03 with silicates and minor amounts of sulfides and native metals whereas the oxidized slags are composed of V2>04, nickel aluminum spinels. various vanadates and glass. Textural analysis provided information on the crystallization process, reaction with gasifier refractory lining materials, sulfide exsolution processes, glass devitrification. and the development of chemical zonation in some spinels. This infonnation offers some perspectives on the potential of resource reclamation.
Resource reclamation for petroleum coke slags is best assessed with a knowledge of phases, phase assemblages, textures and dissolution behavior of the material. The dissolution of vanadium. the most significant element. was examined using long tenn dissolution experiments. These demonstrate that vanadium concentrations are pH dependent ranging from 1500 ppm to 5000 ppm with a minimum concentration near pH 6. Vanadium dissolution rates range from L28xlO-4 mol m-2 sec-1 to 3.08xlO-6 mol m-2 sec-1. In view of the strategic nature of vanadium and the fact that the concentration of vanadium in slags is almost two orders of magnitude higher than the current mining grades, petroleum coke slags offer significant potential to serve as resources for vanadium.
- Doctoral Dissertations