From ore? From waste liquid? From the movie? From a thermos? From the mirror? From used electrical appliances? Or from somewhere else?
Each method is different.
Take the extraction of silver from "three wastes" as an example:
The main thing is to have the conditions to collect the "three wastes" and to buy a certain amount of raw materials. Of course, too little means less. The so-called "three wastes" refer to: waste photographic fixing solution (film processing wastewater from photo studio, hospital radiation room, printing plate, etc.) and waste silver plating solution. Waste liquid from the treatment of semiconductor production molds, waste semiconductor components, electrical connectors, silver-plated waste and waste from mirror-making industry (broken mirrors and thermos bottles, etc.). ) can be used to withdraw silver.
Raw materials: contact and purchase in photo studio, hospital radiation room, printing factory, electroplating factory, wireless power plant, electrical appliance Kai Guanchang, semiconductor component factory, mirror factory, waste recycling station and other units. Broken glass, waste thermos bottles and other silver-plated scraps should be broken, soaked in nitric acid solution for 2-3 hours until there is no silver shell on the glass, and then filtered to take the filtrate. Usage is the same as that of waste fixing solution. Generally, there are three extraction methods, which are described as follows:
1. replacement method: replace the silver in the waste fixing solution with metals with high chemical activity, such as zinc, iron and aluminum. This method is very simple. Metal powder, metal obsidian or metal strips can be directly added or inserted into the waste fixing solution, and silver will be replaced and attached to the metal surface. However, the substituted products are impure and need further purification.
2. Precipitation method: Silver in fixing solution is precipitated with sodium sulfide in the form of silver sulfide, and then silver sulfide precipitate is added into hot concentrated hydrochloric acid and excessive iron powder to obtain 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-
Because hydrogen sulfide (H2S) is toxic, the operation must be carried out in a ventilated place to ensure safety.
3. Electrolysis: It is a good method to directly extract silver by electrolysis, which can be treated at one time, and the quality of silver produced is very pure.
It is very important to use two electrodes correctly in electrolysis. When electrified, the cation, namely silver ion, moves to the cathode, and the obtained electrons are reduced to silver atoms and accumulated on the surface of the cathode. Anions move to the anode, lose electrons and are oxidized. If the electrode is used improperly, it will cause electrode corrosion and pollute the solution. Therefore, the graphite rod (that is, the central carbon rod of dry battery) should be connected to the positive pole of DC power supply as the anode; Silver bars or stainless steel plates are connected to the negative pole of DC power supply as cathode, and inserted into waste stationary liquid for electrolysis. The PH value of the solution is generally adjusted at 2-4 (adjusted by dropping nitric acid), the voltage is 1V, and the current density is 03A/cm2. In this way, in the process of electrolysis, the silver bars on the cathode will change from small to large due to the accumulation of silver, and the color is pure white. If the current is high and the silver precipitates too quickly, it will turn black. When the electrolytic product is brown, it shows that the silver content in the solution is very small (silver content per kilogram is less than 1g), which is not suitable for further electrolysis.
Determine how much silver is contained in the waste fixing solution and whether it can be electrolyzed. You can also insert a clean copper wire into the solution. After 2 minutes, the copper wire did not turn silvery white, indicating that silver had been extracted from the solution.