What is the recycling price of fixing wastewater and developing wastewater?

At present, there are three main technologies that can be applied to silver recovery, including electrolytic recovery, metal replacement and chemical precipitation. The recovery rate of electrolytic silver is 90 ~ 95%, and the recovery rate of metal replacement and chemical precipitation of silver can be greater than 99%. During electrolysis, two electrodes are inserted into the solution, and direct current is applied to make the cathode silver plated. Electrolysis can be divided into low current density equipment and high current density equipment. The low current density of fixing solution is less than 3 amps/square foot, while the high current density is greater than 10 amps/square foot. When high current density is used, the stirring rate must be increased on the cathode surface. Bleaching fixer must use ultra-high current density, that is, 60 ~ 90 amps/square. The phenomenon that bleaching agent hinders electrolysis is caused. The cathode is a rotating cylinder to improve the stirring speed. The voltage between the electrodes is very low, about 0.5 to 0.7 volts. All anode materials are made of carbon (because carbon can conduct electricity and resist corrosion at the same time), and cathode materials are made of stainless steel. Metallic silver can be obtained directly by electrolysis, but the selection of electrolysis equipment and the control of electrolysis conditions have great influence on the quality and recovery rate of silver. In fixing and bleaching/fixing waste liquid, silver ions exist as complexes of Ag(S2O3)2-3. When the current density is too high or the silver concentration in the recovery solution is too low, it is easy to produce black silver sulfide precipitation, which affects the quality of recovered silver. The only equipment needed is to use the carbon rod of dry battery as a simple anode (graphite is good, but it is not easy to obtain), then use stainless steel sheet as a cathode, adjust the electrode distance, and apply a voltage of 2 to 5 volts; It is best to be able to stir the solution. At first, you can get 90-98% pure silver at the cathode, and then you will get darker and dirtier silver. The end point of operation is that the silver concentration in the solution drops to 100 ppm, and there will be silver sulfate mud. The treatment of bleaching fixer requires high voltage and high final concentration. In the residual silver solution of about 500 ppm, this kind of wastewater cannot be discharged into the sewer. Chemical hazards include: hydrogen sulfide produced when the current is high, or ammonia gas produced when mixed with developer. General plate electrolysis equipment can recover silver to about 300 mg/L, and high-quality transfer electrolysis system (including rotating cathode and fluidized bed electrolysis system) can recover silver to below 1000 mg/L, in which the largest unit of fluidized bed electrolysis recovery system can provide 1000 ampere, and the daily recovery of silver by a single equipment can exceed 20 kg, and the stainless steel plate can be used as cathode to recover silver to/kloc-0. The residual silver ions (less than 100 mg/L) after electrolytic recovery can be recovered by precipitation with the reagent (code TMT) developed by Kodak Company in the United States, and the silver can be treated below 0.5 mg/L, which can meet the discharge standard. The metal replacement method uses iron material, and because of the replacement, the waste liquid is put into it to precipitate silver. This method makes the fixing solution contain iron, so it must be discarded. However, as long as 20% of the waste liquid is discarded and the iron content is reduced, the bleaching fixer can still be reused. In the chemical replacement method, silver can be removed from the waste liquid by sodium sulfide or sodium borohydride (NaBH4). Silver sulfide can be obtained by the reaction of sodium sulfide, and metallic silver can be obtained by sodium borohydride. The advantages of chemical treatment are high speed, the reaction rate can reach above 99%, and the purity of silver is above 95%. Common methods: adding saturated solution of sodium sulfide, the silver ions in wastewater become black silver sulfide powder and precipitate into "silver mud". This dark silver mud is heated and dissolved with nitric acid to obtain silver nitrate crystals, which are then reduced to silver in an electrolytic cell. This method is simple, but the precipitate must be purified to obtain pure metallic silver, and the added chemicals are expensive and have low economic benefits. If silver is to be recovered from waste black-and-white films or X-rays, it must be dissolved in the solution first. The unwashed leftover bits and pieces can be dissolved with fixing solution, while the cleaned leftover bits and pieces must be made into compounds with oxidant (such as potassium ferricyanide, ferric EDTA or copper chloride), and then silver compounds is dissolved with fixing solution. As described above, silver metal can be extracted from the obtained fixing solution by electrolysis. Related new technologies and methods: According to overseas media reports, CSRS Company of the United States introduced equipment to recover "silver" from the fixing solution of the printer. The electrolytic silver recovery machine system produced by CSRS company is one of the advanced recovery and treatment systems in the world at present. It uses intelligent micro-processing technology to recover the "silver" to be used in the liquid medicine at the first time, which not only has high recovery rate, but also can effectively prolong the service life of the fixing agent. The system operation panel adopts internationally recognized touch buttons. When the machine is running, a warning light of "Recycle Now" will appear to remind the operator that the machine will enter a "sleep" state when it is not running. The whole recycling machine adopts closed loop and closed design, which can protect operators from chemicals. At present, the product has obtained safety marks such as UL, FCC, TUV and CE. Scientists have been studying ways to recover silver from the waste liquid from developing photos, but most of the recovery processes are inefficient and sometimes cause more pollution. Now the situation may change: a scientist at Oak Ridge National Laboratory has developed a process to recover 99.999% silver from photographic waste liquid. A key problem in most silver recovery processes is the formation of silver sulfate, which is a pollutant that is difficult to remove. The old procedure is to add a small amount of hypochlorous acid to a large amount of photographic waste liquid containing silver. The procedure of Oak Ridge National Laboratory is to pump the silver-containing waste liquid into the reaction tank.

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