The process of removing impurities from coarse silver and producing pure silver is one of the main processes for silver extraction. Crude silver from copper, lead, zinc and other non-ferrous metal production of byproducts and industrial waste recovery, including silver50%~99.5%, Gold 0.01%~10%, platinum 0%~0.15%, palladium 0%~0.3% and residual base metal. In addition to silver electrolytic refining widely used in industry, there are fire, generalization and solvent extraction methods.Silver Filler Metals
The method of fire is to oxidize and remove impurities from the coarse silver melts at high temperature to produce pure silver. The general practice is, in the melting furnace at 1423K temperature will be the rough silver melt, to melt the surface of the molten oxygen melting 32h, add sodium carbonate remelting, get silver 96.8%, copper 0.8% and a small amount of gold and platinum Group of metal Silver. The fire method has the characteristics of fast speed and can deal with the complex and low grade silver, but the purity of the product is not high, only as the pretreatment work of electrolytic refining method.Silver Filler Metals
Silver Electrolytic Refining is a silver containing more than 79% of silver as anode, in the silver nitrate solution electrolysis, so that impurities into the anode mud or electrolyte, from the cathode precipitation purity of 99.99% silver method.
Generalized method is to dissolve the coarse silver in nitric acid or concentrated sulfuric acid, then from the solution to precipitate the silver chloride, and then use reducing agent iron, zinc, copper, hydrazine hydrate, formic acid and other reduction of silver chloride, the purity of 99.9% ~ 99.99% Silver method. The silver-ammonia complexes [AG (NH3) 2]cl were produced by reaction of ammonia and silver chloride, and then reduced by reducing agent, which could improve the purity of silver. The process of reducing AGCL by water hydrazine (N2H4·H2O) is: agcl sediment water slurry, adding nh4oh adjusting grout to ph1o~11, and slowly adding twice times of theoretical volume at room temperature and agitation, hydrazine hydrate concentration of 40% or 80%. Each kilogram of silver is about to add hydrated hydrazine 0.3~0.4h, ammonia 1.2~1.6kg. After 30min reduction can be obtained gray-white sponge silver, the reaction is: 4agcl+n2h4+4oh-==4ag↓+n2↑+4h2o+4cl-silver reduction rate of 99.9%, purity of more than 99%.
Solvent extraction is a method for separating silver into organic phase and impurity by mixing the silver solution containing impurities with the organic phase of solvent extractant (see Jinge extraction and purification). The organic phase, which is composed of 40% sulfur ether residue as kerosene, is compared to 1:1 conditions. From the ag-containing 16g/l, Cu 70g/l, ni 5.07g/l and nitric acid 0.26mol/l in the solution of the extraction of silver, using ammonia reverse extraction, and then hydrazine to reduce the reverse extraction of silver, the purity of more than 99.9% silver powder, ag recovery rate of 99%.Silver Filler Metals