Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1991-01-23
1992-08-04
Tung, T.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204105R, C25C 120
Patent
active
051356244
ABSTRACT:
An efficient hydrometallurgical refining method is disclosed for the production of high purity silver. The method comprises: casting an anode of raw silver; subjecting the cast anode to an electrorefining stage wherein the raw silver is directly electrorefined in a suitable electrolyte solution; leaching the anodic residue with an appropriate lixiviant to dissolve impurities and precipitate silver in the form of a silver compound that is suitable for conditioning the electrolyte; treating the leach liquor to recover dissolved silver and recycling recovered silver to the leaching or anode casting stage; and treating the anolyte in a conditioning stage with an appropriate silver compound prior to recycle to the electrorefining stage as catholyte. The process is fast and simple to operate since the sequencing of steps has been rationalized and the reagent requirements and harmful emissions are low. The life of the electrolyte extends over many electrode cycles and valuable byproducts are also recovered. In the preferred embodiment, raw silver anodes with major arsenic and antimony impurities are electrorefined directly; e.g., in a silver nitrate medium using a diaphragm cell. The major impurities form a porous, thick and adherent layer which is spalled off periodically. Pure silver is deposited at the cathode as a dense powder at a high current efficiency. The anolyte is pumped to an external conditioning circuit where Ag.sub.2 SO.sub.4 and lime are added to maintain a stable electrolyte composition. The treated electrolyte is then recycled to the cathode compartment. Silver sulphate (Ag.sub.2 SO.sub.4) is produced by leaching the anodic residues and/or other suitable materials in a separate step.
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Dinardo Orlando
Tan Khay Gie J.
Her Majesty the Queen in right of Canada as represented by the
Ryser David G.
Tung T.
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