Abstract : When cyanide copper plating wastewater breaks cyanogen, copper ion transforms into basic copper carbonate fine sediment particles. It needs to be added with a large amount of coagulant to adsorb, and then flocculant can be added to make it precipitated and separated. The processing cost is high. When cyanogen is broken, lime is used instead of caustic soda to adjust the pH. The carbon dioxide produced by breaking cyanide reacts with calcium oxide to form a large-particle precipitate of calcium carbonate. Basic copper carbonate and calcium carbonate are co-deposited, which solves the problem of sedimentation and separation. Lime is used to treat pyrophosphate copper plating wastewater. Calcium oxide reacts with pyrophosphate to form calcium pyrophosphate precipitate. At the same time, calcium oxide reacts with copper ions to form copper hydroxide, thereby realizing the recovery of copper. Treatment of coking copper electroplating wastewater with lime can achieve discharge standards. introduction The establishment of an environment-friendly and conservation-type electroplating model is the two major themes of the current sustainable development of the electroplating industry. With the shortage of non-ferrous metal resources in the world and the continuous increase in the cost of electroplated metal materials, the use of eco-friendly electroplating technology is the topic most concerned by the electroplating industry. China's privately-owned electroplating companies have a short development time, lack of funds in the early stage of development, and technical backwardness. Most small-scale electroplating factories still lack understanding of the recovery of metallic materials in electroplating wastewater, let alone research on recycling methods. For the cyanide copper plating and copper alloy electroplating wastewater, after the cyanogen is broken, the bivalent copper generated precipitate particles are small, precipitation and separation are difficult, and the separation cost is high. For this reason, a new recovery process was studied, lime was used to adjust the pH of the cyanogen-free pool and a coagulant aid, which solved the problem of high copper recovery costs. 1 Method principle 1.1 Treatment of cyanide copper plating and copper alloy waste water When the sodium cyanide is used to break the cyanogen, the pH of the cyanide-containing waste water needs to be adjusted to 11 to 12. The conventional process is to add sodium hydroxide. In the process of cyanogenation, cyanide is converted into carbon dioxide and nitrogen, and monovalent copper ions are oxidized to divalent copper ions to form fine particles of basic copper carbonate suspended in the waste water. If the natural sedimentation occurs, it will take more than one day to complete the process. Precipitation requires the addition of a large amount of a coagulant and the addition of a flocculant to completely separate the precipitate. Before the recovery of copper from copper cyanide copper and copper alloy wastewater was recovered, the cyanide-depleted wastewater was mixed into the comprehensive acid-containing wastewater. The acid-containing wastewater was treated with lime [1], and basic copper carbonate was adsorbed in the comprehensive wastewater. On the precipitate, the final precipitate is separated. In order to recover copper, the new cyanogen-breaking process is to add lime to adjust the pH when cyanogen is broken. The carbon dioxide generated by breaking cyanide reacts with calcium oxide to generate calcium carbonate, while basic copper carbonate and calcium carbonate are co-deposited to form large-particle precipitates. 1.2 Treatment of other copper-containing wastewater Divalent copper ions in bright copper plating wastewater react with lime to form copper hydroxide, which reacts with lime to form calcium sulfate and water. In pyrophosphate copper plating wastewater, pyrophosphate and copper ions exist in the form of complexes. When treated with lime, pyrophosphate reacts with calcium oxide to form calcium pyrophosphate precipitates, and copper ions react with calcium oxide to form hydroxides. copper. 2 recycling process 2.1 Composition of Wastewater Containing Copper Waste water containing copper includes cyanide copper plating, copper-zinc alloys, copper-tin alloys, acid bright copper plating, and pyrophosphate copper plating. Wastewater flows into cyanide copper plating, copper-zinc alloys, and copper-tin alloys. Cyanide-containing wastewater conditioning pool, acid bright copper plating and pyrophosphate copper plating wastewater flow into the copper-containing wastewater conditioning pool. The cyanide-plated copper and copper alloy wastewater contains complexing agents such as sodium cyanide, potassium sodium tartrate and ammonium thiocyanate, which react with copper ions to form copper complexes; pyrophosphate copper plating wastewater contains copper pyrophosphate Complexes. The cyanide copper and copper alloy waste water accounts for about 90% of the total copper-containing waste water, and the acid bright copper plating and pyrophosphate copper plating waste water accounts for about 10%. 2.2 Copper Complex Oxidation Process Before the copper is recovered, the copper complex in the electroplating wastewater is first destroyed and the Cu+ ions are oxidized to Cu2+ ions. In this paper, the sodium hypochlorite solution and the hydrogen peroxide combination method are used to destroy the complexes such as cyanide and potassium sodium tartrate[2]. Three cyanide-breaking pools are provided. The cyanogen-containing waste water and the copper-bearing waste water are pumped into the first-stage cyanogen-free cyanide pool, respectively. Lime milk is added to the tank to adjust pH=11-12, and the pH control system is used to adjust the addition of lime milk. The amount of sodium hypochlorite solution is added to the pool to destroy the cyanide. In the second-stage cyanogenation reactor, the addition of hydrogen peroxide continues to break the cyanogen and oxidize potassium sodium tartrate. Due to the slower reaction rate, a third level of cyanogen-free cyanide pool was added. According to the chemical analysis data and experience in the third-level cyanogenation pool, Check the removal of complexing agents such as cyanide and potassium sodium tartrate. With the completion of the oxidation reaction, Cu+ in the wastewater is completely converted to Cu2+, and basic copper carbonate and copper hydroxide precipitates are formed. In the above process, after the pyrophosphate copper plating wastewater reacts with lime, the complex formed between copper and pyrophosphate is destroyed to generate copper hydroxide. Analytical data shows that the use of this process to treat cyanide and copper complexes can allow wastewater to discharge to standard. In the treatment of cyanogen- and copper-containing waste water, adding lime to adjust pH and precipitate copper ions reduces processing costs. At the same time, lime serves as a coagulant aid and completely precipitates pyrophosphate. In the above process, the copper ions in the electroplating waste water are converted into a precipitate of basic copper carbonate. If the amount of lime added is large, the copper ions can also be converted into copper hydroxide precipitates. Because lime needs to be precipitated with pyrophosphate in pyrophosphate copper plating wastewater, the amount of lime added can not be too small, the cost of using lime is very low, and lime can be added excessively in the process. The cyanide- and copper-bearing wastewater is treated in a tertiary cyanide-destroying pool and then flows into the flocculation pool. Sodium metabisulfite is used to reduce excess hydrogen peroxide in the flocculation pool, and polyacrylamide flocculant is added to make the precipitate particles grow. If no sodium metabisulphite is added in the flocculation tank, the residual hydrogen peroxide will decompose to generate oxygen. This gas will be adsorbed on the surface of the precipitate particles, so that the precipitate will float, and the amount of sodium metabisulfite added will not float to the sediment. Quasi-appropriate excess. After the waste water passes through the flocculation tank, it flows into the inclined tube sedimentation tank. The sediment is separated from the water and enters the precipitation thickening tank. Then it is filtered by the filter press, the filter cake is recovered, and the filtrate flows back to the conditioning tank. After the copper-containing filter cake is recovered, it is purchased by a professional company and sent to a professional manufacturer for the production of copper sulfate. It can also produce electrolytic copper. 3 Benefits Our company's four electroplating workshops produce copper-containing waste water. Analysis and monitoring data show that the average concentration of copper in cyanide copper plating wastewater is 345mg/L, that is, 0.345kg of copper per ton of waste water, monthly cyanide copper plating wastewater The total amount is about 4,600 tons, including 1,587 kg of copper, plus copper in other copper-containing waste water, and about 1,700 kg of copper can be recovered each month. The company's monthly sales of copper-containing sludge account for RMB 30,000 to 40,000 yuan. After the company recovered the copper in the electroplating wastewater, it avoided the inefficient consumption of copper metal, which reduced the cost of electroplating, reduced the secondary pollution of the electroplating sludge to the environment, and achieved good economic and social benefits. Electroplating is a heavy pollution industry. Under the current situation that China's electroplating wastewater treatment processes and technologies are relatively backward, we actively study the recovery methods for non-ferrous metals in electroplating wastewater, and establish a conservation and environmental protection electroplating mode to maintain the sustainable development of the electroplating industry. It is of great significance.
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