At present, there are about three major technologies that can be applied to silver recovery, including electrolytic recovery, metal displacement, and chemical precipitation. Among them, the recovery rate of silver recovered by electrolysis is 90-95%, and the metal replacement and chemical precipitation silver recovery rate can be greater than 99%. The electrolysis method inserts two electrodes into the solution and turns on the direct current, and silver is plated on the cathode. Electrolysis can be divided into low current density devices and high current density devices. The fixer fluid has a low current density of less than 3 amps/sq. ft. and a high current density of greater than 10 amps/sq. ft. When using high current densities, the cathode surface must be increased in agitation. Bleached fixatives require high current densities of 60-90 amps/sq. ft. due to the blocking of electrolytics by bleach. The cathode is a rotating cylinder to increase the agitation rate. The voltage between the electrodes is very low, about 0.5 to 0.7 volts. Anode materials are all made of carbon (due to the fact that carbon can conduct electricity while resisting corrosion), and cathodes are made of stainless steel.
Metallic silver can be directly obtained by electrolysis, but the choice of electrolytic equipment and control of electrolysis conditions have a great influence on the quality and recovery of silver. In the fusing and bleaching/fixing waste liquids, silver ions exist as Ag(S2O3) 2-3 complexes. If the current density is too high or the concentration of silver in the recovery liquid is too low, black silver sulfide precipitates easily and the quality of recycled silver is affected. The only equipment needed is to use a carbon rod of a dry cell as a simple anode (graphite is better, but it is not easy to obtain), then use a stainless steel plate as a cathode, adjust the electrode distance, and apply a voltage of 2 to 5 volts; the solution can be stirred more effectively it is good. Initially, silver at 90 to 98% purity can be obtained at the cathode, and blacker, dirtier silver can be obtained as it continues. At the end of the operation, the silver concentration in the solution is reduced to 100 ppm, and there will be silver sulfate sludge. The bleaching fixer solution requires a higher voltage, and the higher the final concentration is, the approximately 500 ppm silver residual solution cannot be discharged into the sewer.
Chemical hazards include: H2S generated when the current is high, or ammonia when mixed with the developing liquid. The silver can be recovered to about 300 mg/L by the general plate electrolysis equipment, and the silver can be recovered to 100 mg/L or less by the high quality electrolysis system (including the rotating cathode and fluidized bed electrolysis system), in which the fluidized bed electrolysis recovery system is the largest The unit can provide up to 1,000 Ampere. The recovery of single device silver can exceed 20 kilograms per day. The stainless steel plate is used as the cathode and the silver is recovered to 100 mg/L or less. The metallic silver metal can still be obtained very well. It is easy to use the stainless steel plate. Stripping is currently the preferred silver recycling facility. After the electrolytic recovery, the remaining silver ions (less than 100 mg/L) can be recovered by using the reagent (code TMT) developed by Kodak Co., USA, and the silver can be treated to 0.5 mg/L or less, which can meet the standard of releasing water. The metal substitution method uses a ferrous material and puts waste liquid to precipitate silver due to substitution. This method causes iron in the fixer and must be discarded. However, as long as the bleach fixer discards 20 percent of waste liquid and reduces iron content, it can still be reused. Chemical displacement method can use sodium sulfide or sodium borohydride (NaBH4) to remove the silver in the waste solution. Sulfide reacts to obtain silver sulfide, and sodium borohydride gives metallic silver. The advantages of chemical treatment are rapid, the reaction rate can reach over 99%, and the purity of silver is above 95%.
The commonly used method is to add a saturated solution of sodium sulfide. The silver ions in the waste water turn into black silver sulfide powder, which is precipitated as "silver mud." The black lacquer silver paste is heated and dissolved with nitric acid to give silver nitrate crystals which are then reduced to silver in the electrolytic cell. This method is simple, but the resulting precipitates must be purified to obtain pure metallic silver. The added chemicals are expensive and have low economic benefits. If you want to recover silver from black and white films or X-ray discarded films, you must Silver is first dissolved into a solution. Unwashed waste sheets can be dissolved in silver halide by the fixer. The washed waste sheets must first be made of silver compounds with an oxidant (such as potassium ferricyanide, ferric EDTA, or copper chloride), and the silver compounds should be dissolved in the fixer solution. . The resulting fixing solution can be taken out of the silver metal by the aforementioned electrolytic method.
Related new technologies and new methods: According to overseas media reports, the United States CSRS company launched the recovery of film machine fixer in the "silver" equipment. The electrolytic silver recovery system manufactured by CSRS is one of the world’s most advanced recycling systems. It uses intelligent microprocessor technology to recover the “silver†that is being applied to the liquid at the first time. Not only high recovery rate, but also can effectively extend the life of the fixer. The operating panel of the system adopts the touch-sensitive keys marked by the international mark. When the machine is running, a warning light “Recover Now†will appear to remind the operator that the machine will enter the “sleep†state when it is not running. The entire recycling machine adopts a closed loop and a closed design to protect the operator from chemicals. At present, the product has obtained UL, FCC, TUV, CE and other safety signs. Electrolytic extraction of silver in four steps: 1. Electrolysis 2. Purification 3. Replacement 4. Purification The presence of silver in the fixative is sulfur complex with sulphate and can not be used directly in the displacement reaction. 1. Electrolysis to find two carbon rods, clean, then connect the positive and negative poles of the adjustable voltage supply (DC power supply, current should be more than 10A). Insert two carbon rods into the fixer as far apart as possible. The wires connected to the carbon rods are not allowed to come in contact with the liquid, and they are energized and the voltage is adjusted so that the carbon rods connected to the positive electrode generate a slight gas. Silver will slowly deposit on the carbon rod of the negative electrode. When I ended, I forgot. 2. Purification The carbon rod of the negative electrode was placed in excess dilute nitric acid to thoroughly dissolve the deposited metallic silver to form a mixed liquid of silver nitrate and nitric acid. Filter the solid magazine with filter paper. 3. Displace excess iron powder in the mixture. After the reaction is completed, the remaining solid is a mixture of metallic silver and metallic iron. Filter solids with filter paper and rinse with light water. 4. Purification Add excess dilute hydrochloric acid to the solid and dissolve the iron powder. The remaining solid is relatively pure metal silver.
Metallic silver can be directly obtained by electrolysis, but the choice of electrolytic equipment and control of electrolysis conditions have a great influence on the quality and recovery of silver. In the fusing and bleaching/fixing waste liquids, silver ions exist as Ag(S2O3) 2-3 complexes. If the current density is too high or the concentration of silver in the recovery liquid is too low, black silver sulfide precipitates easily and the quality of recycled silver is affected. The only equipment needed is to use a carbon rod of a dry cell as a simple anode (graphite is better, but it is not easy to obtain), then use a stainless steel plate as a cathode, adjust the electrode distance, and apply a voltage of 2 to 5 volts; the solution can be stirred more effectively it is good. Initially, silver at 90 to 98% purity can be obtained at the cathode, and blacker, dirtier silver can be obtained as it continues. At the end of the operation, the silver concentration in the solution is reduced to 100 ppm, and there will be silver sulfate sludge. The bleaching fixer solution requires a higher voltage, and the higher the final concentration is, the approximately 500 ppm silver residual solution cannot be discharged into the sewer.
Chemical hazards include: H2S generated when the current is high, or ammonia when mixed with the developing liquid. The silver can be recovered to about 300 mg/L by the general plate electrolysis equipment, and the silver can be recovered to 100 mg/L or less by the high quality electrolysis system (including the rotating cathode and fluidized bed electrolysis system), in which the fluidized bed electrolysis recovery system is the largest The unit can provide up to 1,000 Ampere. The recovery of single device silver can exceed 20 kilograms per day. The stainless steel plate is used as the cathode and the silver is recovered to 100 mg/L or less. The metallic silver metal can still be obtained very well. It is easy to use the stainless steel plate. Stripping is currently the preferred silver recycling facility. After the electrolytic recovery, the remaining silver ions (less than 100 mg/L) can be recovered by using the reagent (code TMT) developed by Kodak Co., USA, and the silver can be treated to 0.5 mg/L or less, which can meet the standard of releasing water. The metal substitution method uses a ferrous material and puts waste liquid to precipitate silver due to substitution. This method causes iron in the fixer and must be discarded. However, as long as the bleach fixer discards 20 percent of waste liquid and reduces iron content, it can still be reused. Chemical displacement method can use sodium sulfide or sodium borohydride (NaBH4) to remove the silver in the waste solution. Sulfide reacts to obtain silver sulfide, and sodium borohydride gives metallic silver. The advantages of chemical treatment are rapid, the reaction rate can reach over 99%, and the purity of silver is above 95%.
The commonly used method is to add a saturated solution of sodium sulfide. The silver ions in the waste water turn into black silver sulfide powder, which is precipitated as "silver mud." The black lacquer silver paste is heated and dissolved with nitric acid to give silver nitrate crystals which are then reduced to silver in the electrolytic cell. This method is simple, but the resulting precipitates must be purified to obtain pure metallic silver. The added chemicals are expensive and have low economic benefits. If you want to recover silver from black and white films or X-ray discarded films, you must Silver is first dissolved into a solution. Unwashed waste sheets can be dissolved in silver halide by the fixer. The washed waste sheets must first be made of silver compounds with an oxidant (such as potassium ferricyanide, ferric EDTA, or copper chloride), and the silver compounds should be dissolved in the fixer solution. . The resulting fixing solution can be taken out of the silver metal by the aforementioned electrolytic method.
Related new technologies and new methods: According to overseas media reports, the United States CSRS company launched the recovery of film machine fixer in the "silver" equipment. The electrolytic silver recovery system manufactured by CSRS is one of the world’s most advanced recycling systems. It uses intelligent microprocessor technology to recover the “silver†that is being applied to the liquid at the first time. Not only high recovery rate, but also can effectively extend the life of the fixer. The operating panel of the system adopts the touch-sensitive keys marked by the international mark. When the machine is running, a warning light “Recover Now†will appear to remind the operator that the machine will enter the “sleep†state when it is not running. The entire recycling machine adopts a closed loop and a closed design to protect the operator from chemicals. At present, the product has obtained UL, FCC, TUV, CE and other safety signs. Electrolytic extraction of silver in four steps: 1. Electrolysis 2. Purification 3. Replacement 4. Purification The presence of silver in the fixative is sulfur complex with sulphate and can not be used directly in the displacement reaction. 1. Electrolysis to find two carbon rods, clean, then connect the positive and negative poles of the adjustable voltage supply (DC power supply, current should be more than 10A). Insert two carbon rods into the fixer as far apart as possible. The wires connected to the carbon rods are not allowed to come in contact with the liquid, and they are energized and the voltage is adjusted so that the carbon rods connected to the positive electrode generate a slight gas. Silver will slowly deposit on the carbon rod of the negative electrode. When I ended, I forgot. 2. Purification The carbon rod of the negative electrode was placed in excess dilute nitric acid to thoroughly dissolve the deposited metallic silver to form a mixed liquid of silver nitrate and nitric acid. Filter the solid magazine with filter paper. 3. Displace excess iron powder in the mixture. After the reaction is completed, the remaining solid is a mixture of metallic silver and metallic iron. Filter solids with filter paper and rinse with light water. 4. Purification Add excess dilute hydrochloric acid to the solid and dissolve the iron powder. The remaining solid is relatively pure metal silver.
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