Two, precipitation method: the silver in the fixing solution with sodium sulfide, silver sulfide precipitation out of the form of silver sulfide, and then add the silver sulfide precipitate into the hot concentrated hydrochloric acid, and add an excess of iron powder, you can get silver, but the product needs to be purified again. The relevant reaction formula is as follows: ?
2[Ag(S2O3)2]3+S--→Ag2S↓＋4S2O32?
Ag2S＋2HG＋fe--→2Ag↓＋FeGl2＋H2S2
Ag2S+2HG+fe--→2Ag↓+FeGl2+H2S2.
Because hydrogen sulfide (H2S) is toxic, so the operation should be carried out in the wind to ensure safety.
Three, electrolysis: electrolysis is used to directly extract silver, is a better method, can be a one-time treatment, produced by the silver quality is very pure.
The correct use of the two electrodes in the electrolysis method is very important, when the electricity is energized, the cation that is, the silver ions to the cathode to move, get the electron is reduced to silver atoms in the cathode surface buildup; the anion to the anode to move, lose the electron is oxidized. If the electrode is not used properly, it will cause corrosion of the electrode and contamination of the solution. Therefore, graphite rods (i.e., the center of the dry cell carbon rods) should be connected to the positive electrode of the DC power supply as the anode; silver rods or stainless steel plate connected to the negative electrode of the DC power supply as the cathode, together with the insertion of the waste solution for electrolysis. The PH of the solution is generally adjusted at 2-4 (adjusted with drops of nitric acid), the voltage is 1 Volt, and the current density is 0?3A/Cm2. so that in the electrolysis process. The silver bar on the cathode will be due to the accumulation of silver from small to large, pure white color. If the current is high and the silver precipitates too quickly, it is black in color. When the electrolysis product appears brown, indicating that the silver content of the solution has been very little (less than 1 gram of silver per kilogram), should not be electrolyzed.
Determination of how much silver in the fixing solution, can electrolysis, you can also take a clean copper wire, inserted into the solution, 2 minutes after the copper wire is not yet seen turned silver-white, indicating that the silver in the solution has been difficult to extract. Extracted gold and silver, can be sent to the People's Bank of various places to buy .