Eco-Friendly Recovery of Copper-Aluminum Oxide Spent Catalyst Via Oxalic Acid

Recovery of Copper-Aluminum Oxide Spent Catalyst

Abstract

Ranging from petroleum to food industries, catalysts hold significant value in facilitating thousands of chemical reactions every day. The continuous use of these catalysts over a number of cycles declines their performance due to carbon deposition and sulphur poisoning, resulting in their disposal as hazardous waste ultimately. This disposal leads to a considerable loss of valuable metals and resources. To address this concern and promote sustainable practices, by virtue of organic acids’ relative friendliness to the environment, the recovery of Cu and Al from spent (wasted) catalysts has been studied. Oxalic acid, an efficient bidentate ligand, has the ability to leach out metals from spent catalysts, have them in the metal oxalate complex form, which are later calcined to re-generate mixed metal oxides (MMO). The chelating efficiency of oxalic acid was investigated for used Cu-Al mixed oxide catalysts obtained from layered double hydroxide (LDH) precursors as a function of pH (2-4), concentration of oxalic acid (0.1 M, 0.5 M, 1 M) and temperature (45 ℃, 65 ℃ and 85 ℃). Citric acid in combination with oxalic was also studied for leaching, however, it was not proceeded due to inefficient leaching. After the leaching procedure, the sample was analyzed by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). In order to reobtain the metal precursor, the leached solution was precipitated in the pH range of 9-11 by the addition of 2 M NaOH and characterized by X-ray Diffraction (XRD). This precursor can later on be calcined at >600 ℃ to obtain fresh mixed oxides.