Abstract: This invention relates to the recovery of molybdenum, vanadium, and aluminum, as well as of cobalt and nickel, from the residues of hydrodesulfurization catalysts.PRIOR ARTMolybdenum-containing catalysts are used in the petroleum industry for the hydrodesulfurization of hydrocarbons. The hydrodesulfurization treatment consists in contacting petroleum or a petroleum fraction with hydrogen in the presence of a catalyst so as to remove the sulfur as gaseous hydrogen sulfide. The catalysts used for said purpose generally comprise a support material made of alumina containing, as active components, either molybdenum and cobalt or molybdenum and nickel. Sometimes catalysts in which the support consists of silica in place of alumina are also used.The active components, i.e. molybdenum, cobalt and/or nickel, are present as oxides in the fresh catalysts. The percentages of active components are variable. In most cases, these percentages are of about 10-15% for molybdenum oxide (MoO.sub.

Abstract: A process for preparing manganese nitrate solution by leaching manganese ore containing manganese dioxide in an aqueous slurry containing dissolved nitrogen dioxide gas. The reaction is controlled by monitoring the pH of the aqueous slurry, and adjusting the relative concentration of the manganese ore containing manganese dioxide and/or the rate of addition of nitrogen dioxide containing gas, to establish and maintain the leaching reaction.