Method for producing high grade reduced silver
US5749940A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 11, 1997 |
| Grant date | May 12, 1998 |
| Priority date | — |
| Expiry date | Mar 11, 2017 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY02P10/20
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
The known method comprises the following steps. (1) the de-copperized anode slime is chlorination-leached with HCl and H.sub.2 O.sub.2. (2) Na.sub.2 CO.sub.3 is added to the chlorination-leach residue of (1). (3) NH.sub.3 is added to the residue of (2). (4) Distillation of NH.sub.3 to remove NH.sub.3 contained in the ammonia leach solution of (3). (5) Distillation residue is washed with water to yield refined AgCl. (6) Conversion of AgCl to Ag.sub.2 O. (7) Reduction of Ag.sub.2 O to Ag. In order to enhance the purity of the reduced silver, the present invention provides the following improvements (a) to (d). (a) Dechlorination (2) with the use of Na.sub.2 CO.sub.3 is carried out at ambient temperature. (b) After dechlorination, the residue is washed with hot water. (c) Sulfuric acid is added instead of carrying out distillation (4). (d) Prior to conversion (6), the chlorination is again carried out.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.