Thermodynamic Analysis of Acid Leaching of Base Metals from Oil Fly Ash with Emphasis on Inorganic Acids

Oil fly ash (OFA) contains significant amounts of V, Ni, Fe, Si, and Al. The presence of the mentionedelements makes this solid waste valuable as well as hazardous to the environment. There are two mainhydrometallurgical approaches for the leaching of OFA: selective recovery of target metals, and coextractionof most metals. Regarding leaching parameters studied in the literature, solid-to-liquid ratio (S/L)and acid concentration are two important factors that are dependent, showing the importance of leachantselection. Inorganic acid leaching was found a proper approach since; ۱): the leaching residue remainsdestitute of valuable metals, ۲): inorganic acids provide more acidity, and ۳): are less expensive than manyother leachants. This study investigated the use of thermodynamic software to assess the behavior of basemetals leaching from oil-based fly ashes with inorganic acids. Based on the results, among the major OFAcomponents, the metals of value namely V, Ni, and Al, as well as impurity metals such as Fe, Na, and Mg, areleachable in acidic media provided by inorganic acids. However, achieving a good recovery of thementioned elements has always been found difficult. V is soluble in a wide range of Eh-pH and thisdissolution behavior can be fruitful in precipitation steps, where with the change of pH or Eh the V content ofthe solution remains as soluble ions. According to the thermodynamic assessments, Si cannot be dissolved inacidic media and will remain in the residue and this might bring about further usage of leaching residue assupplementary cementitious materials.

Keywords:

Thermodynamic Assessment , Inorganic Acid , Oil Fly Ash , Leaching