Acid dissolution of cupric oxide
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dissolution reaction of m e t a l oxides in acidic solutions is widely utilized industrially. The leaching of bauxite ore and of oxidized copper ore, the upgrading of ilmenite ore, and the pickling of rolled steel are typical examples. In the review paper written by W a r r e n and Devuyst~ an approximate g e n e r a l mechanism of the leaching of oxides was proposed based on the results observed for iron oxides, beryllium oxide, aluminum oxides, cuprous oxide and others. However, very little information is available in a form suitable for determining the mechanism of dissolution for individual m e t a l oxide-solution systems. In o r d e r to verify the g e n e r a l applicability of the mechanism proposed by W a r r e n and Devuyst~ for the leaching of m e t a l oxides, it is necessary t o extend the kinetic study t o other systems. The present study is concerned with the dissolution of cupric oxide in solutions containing perchloric, sulfuric, n i t r i c or hydrochloric a c i d . EXPERIMENTAL Materials Synthetic cupric oxide was prepared by oxidizing copper powder of high purity (99.99 pct Cu) at 850°C in an electric furnace for 20 h. The product obtained by this oxidation treatment was identified as cupric oxide by means of X-ray diffractometry, and was assayed 79.48 pct Cu.* After cooling the sample in *Theoretical content ofCuin CuOis 79.89 pct Cu. the furnace, the oxidation product was ground t o pass through 400 mesh Tyler screen, pelletized at 16 ton/ cm 2, and then sintered at 850~C for 50 h, followed by slow cooling in the furnace t o room temperature. The disks thus prepared were mounted in epoxy r e s i n in H. MAJIMA and Y. AWAKURA are Professor and Instructor, respectively, Department o f Metallurgy, Kyoto University, Kyoto, Japan 606. T. YAZAKI is ResearchEngineer, Yamaha Motor Co. Ltd., IwataCity, Japan438. Y. CHIKAMORI is Research Engineer, Titan Kogyo K. K., Ube City, Japan 755. Manuscript submitted June 4, 1979. METALLURGICAL TRANSACTIONS B
such a manner that only the mechanically polished surfaces were presented t o the dissolution medium. The disks of cupric oxide were about 6 mm thick and 20 mm in diam; the exposed polished surface area was 3.14 cm2. The apparent density was 5.3 g / c m ~ which is about 83 pet of the theoretical density of 6.4 g / c m 3. A stirring rod made of stainless steel was fastened t o each epoxy r e s i n mount containing the cupric oxide disk. All other chemicals used were of reagent g r a d e . Deionized water was used in the preparation of all the solutions. Experimental Procedure A 500 ml glass separable flask was used for all the dissolution experiments. A sintered cupric oxide disk, facing downward, was rotated in the solution in the flask. The temperature within the reaction vessel was maintainedat +0.5°C of the desired value by a water bath. In typical experiments, the disk was rotated at 1200 rpm in a 500 ml acidic solution at a given temperature unless otherwise stated. Analytical The concentration of cupric ion in solution was estimated continuous
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