What is the comprehensive utilization of straw that is environmentally friendly and harmless?

1 characteristics and harmfulness of electroplating sludge most electroplating wastewater treatment methods will produce sludge, and chemical precipitation is the main source of sludge. Some methods, such as ion exchange method and activated carbon method, do not directly produce sludge, but in some auxiliary links of the method, such as the treatment of regenerated liquid, sludge will also be produced. Because chemical method is the main treatment method at home and abroad, the situation of electroplating sludge is very serious. According to different treatment methods of electroplating wastewater, electroplating sludge can be divided into mixed sludge and simple sludge. The former is sludge formed by mixed treatment of different kinds of electroplating wastewater; The latter is sludge formed by treating different kinds of electroplating wastewater separately, such as chromium-containing sludge, copper-containing sludge, nickel-containing sludge and zinc-containing sludge. But in fact, the wastewater from electroplating small enterprises is mostly treated mixed sludge. Therefore, at present, the treatment and resource utilization of electroplating sludge are also concentrated on mixed sludge. The sludge produced in electroplating wastewater treatment process contains harmful heavy metals, which are easy to accumulate, unstable and lose. If it is not handled properly, it will be piled up at will. The direct consequence is that these heavy metals such as copper, nickel, zinc and chromium in sludge will migrate along the path of sludge, soil, crops and human body under the action of rainwater leaching, which may cause secondary pollution of surface water, soil and groundwater, even endanger the biological chain and cause serious environmental damage. According to the characteristics and harmfulness of electroplating sludge, from the point of view of preventing environmental pollution and resource recovery, the following two treatment methods are mainly adopted. One is that the treated sludge will not cause secondary pollution and will be discarded for storage, that is, harmless disposal; Second, comprehensive recovery of heavy metal resources in sludge, that is, recycling. Harmless disposal of electroplating heavy metal sludge The harmless technology of sludge treatment and disposal is the premise of realizing sludge resource utilization. According to the Technical Policy for Prevention and Control of Hazardous Waste Pollution (Environment and Development [20065438+0] No.65438+099) issued by China in 200 1 and February 17, by 20 15, all urban hazardous wastes will be basically treated and disposed harmlessly. 2. 1 curing agent is an important technology in the treatment of hazardous solid waste and plays an important role in the regional centralized management system. Compared with other treatment methods, it has the advantages of easily available solidified materials, good treatment effect and low cost. Solidification process is a process that uses additives to change the engineering characteristics (such as permeability, compressibility and strength) of waste. In recent years, the United States, Japan and some European countries generally adopt solidification disposal technology for toxic solid waste, which is considered as the final disposal method to transform harmful substances into harmless substances. The curing materials used are cement, lime, glass and thermoplastic. Among them, cement solidification is the most commonly used solidification technology at home and abroad, and it is considered as a promising technology in the United States. It has been proved to be very effective in fixing some heavy metals. The National Environmental Protection Agency of the United States has also confirmed that it has a good effect on eliminating the sludge produced by some special factories. Jia et al. conducted a series of experimental studies on the solidification of electroplating sludge cement on the basis of summarizing ARoy et al. It is found that the strength (28d) of the sample obtained by adding No.425 cement to electroplating heavy metal sludge and curing the sample according to the ratio of concrete to sludge of 40: 1 or 50: 1 can reach the standard of No.275 cement. The cured body has good curing effect on zinc, copper, nickel and chromium ions. Through further research, it is found that the electroplating sludge is pre-solidified by ferrite, and then solidified with concrete at the ratio of 1: 30. By analyzing the samples and their leaching solution, it is found that this method has a good curing and stabilizing effect on zn, Ni, Cu and Cr, and the strength of the products can reach the standard of No.325 cement. Wu Shaolin et al. studied the leaching law of chromium in water with different dosage, ratio and pH value of additives, taking chromium electroplating sludge as the object, cement as the curing agent, thiourea and sodium silicate as additives. The experimental results show that the curing effect of cement is good, and the ratio of (cement): (chromium mud) is 1.5: 1.0. Adding additives such as thiourea and sodium silicate can reduce the leaching concentration of chromium, and the stabilization effect of thiourea is better than that of sodium silicate. There is a certain synergistic effect between them, and sodium silicate can significantly improve the strength of solidified blocks. Using HAS soil curing agent instead of cement to cure electroplating sludge can obtain slope protection bricks with good impermeability, impermeability and sufficient mechanical strength. This solidification process opens up a new way for the resource utilization of electroplating sludge. 2.2 Landfill From the economic, technical and waste status, landfill technology is more suitable for the harmless disposal of hazardous waste in China, but the domestic electroplating sludge landfill technology is still at a low level. Because most industrial hazardous wastes are simply stacked or buried, the damage to the environment is quite serious, especially the pollution of groundwater is very prominent. However, the technical obstacles are limited, and landfill is still necessary at present and in the near future. Special emphasis is placed on the safe landfill of hazardous waste, that is, pretreatment must be carried out before landfill to stabilize it so as to reduce the potential danger caused by toxicity or solubility. In recent years, the state has gradually improved the management and disposal of hazardous wastes such as electroplating sludge. 1995, the first hazardous waste landfill meeting international standards was built in Shenzhen, Guangdong Province. In 200 1 year, the state promulgated the Pollution Control Standard for Hazardous Waste Landfill (GB 18598-200 1), which laid a good foundation for truly realizing the harmless disposal of electroplating sludge. 2.3 Throwing into the sea is actually the transfer of pollutants. By choosing a disposal site with suitable distance and depth, electroplating sludge is dumped into the ocean. Throwing it into the sea used to be an important way of sludge disposal. For example, in 1899- 1965, the United States threw a variety of wastes, including electroplating heavy metal sludge, into the sea, and 25% ~ 45% of the solid wastes in European countries, Britain and Ireland were treated by throwing them into the sea. However, the sludge with obvious toxicity must be solidified before it can be put into the ocean. Whether it is directly thrown into the sea or solidified, the threat to the marine ecosystem and human health is inevitable, so the international convention has explicitly prohibited it, and it is not allowed to directly discharge pollutants into the sea after 1998. 2.4 Incineration Heat Treatment Sludge Incineration is to completely oxidize and decompose the organic matter in the sludge at high temperature, so as to minimize the toxicity of some highly toxic components in the sludge. Through incineration heat treatment, the volume of electroplating sludge can be greatly reduced and the harm to the environment can be reduced. In addition, the products of incineration are also valuable. For example, ashes can be used for brick making, paving or other purposes, and the heat generated by incineration can be used for power generation. Therefore, incineration heat treatment is a rapid and effective harmless technology for electroplating sludge. In recent years, some scholars have made extensive research on the resource utilization of incineration slag on the basis of incineration reduction. Liao Changhua and others took electroplating heavy metal sludge with low concentration of copper and nickel as the research object, and through incineration pretreatment at a suitable temperature, the heavy metal content in the sludge was improved, thus creating conditions for the final leaching of valuable metals to produce sponge copper and nickel sulfate products. However, due to high energy consumption and certain requirements for incineration equipment and conditions, it is difficult for ordinary small electroplating plants to bear huge treatment costs, so it is difficult to promote them in a large area. 3 Comprehensive Utilization of Electroplating Heavy Metal Sludge As an important heavy metal resource, electroplating sludge has always been the focus of research at home and abroad due to the depletion of resources and the aggravation of environmental pollution. In 1970s and 1980s, industrialized countries generally attached importance to developing new technologies for recovering heavy metals from electroplating sludge. During the "Seventh Five-Year Plan" and "Eighth Five-Year Plan" periods, China also set up a special research project on the recycling of electroplating sludge. As a cheap secondary resource, electroplating sludge can turn waste into treasure and bring considerable economic and environmental benefits as long as it is treated properly. With the rapid development of economy and society, the resource utilization of electroplating sludge will gradually become a promising green industry. 3. 1 recovery of heavy metals 3. 1 selective leaching of electroplating sludge by leaching-precipitation method to make the heavy metals in it agglomerate and dissolve, which is the key step to recover heavy metals and the key to determine the subsequent metal recovery rate. The leaching and dissolution of metals mainly include acid leaching and ammonia leaching. At present, ammonia leaching with relatively good selectivity is preferred in the world. Due to the separation and recovery of heavy metals in leaching solution by precipitation method, the process is simple and widely used. Researchers in Czech U proposed a multistage precipitation process for treating nickel-plated sludge, which was studied in the laboratory. This technology includes sludge acid leaching and various precipitation methods to purify sulfate leaching solution, so that impurities such as Fe, zn, cu, cr, Cd, A 1 stored in nickel-plated sludge are removed, and finally nickel in precipitation is separated from the purification solution in the form of hydroxide. The purity of the final nickel precipitate is enough to be directly reused in metallurgical industry. What about Mao and others? The technological route of sulfide precipitation separation and purification and copper recovery by sodium chlorate sulfuric acid system was studied. The total recovery rate of copper reached 94.5%. The preparation of nickel sulfate by room temperature leaching, iron filings replacement, multi-step precipitation purification and comprehensive utilization of electroplating sludge was studied, and sponge copper powder with a grade of over 90% and a recovery rate of 95% was obtained, and industrial pure nickel sulfate with a recovery rate of over 80% was also obtained. 3. 1.2 leaching-solvent extraction method The solvent extraction method of electroplating sludge is to add an organic solvent that is complementary and compatible with water or an organic solvent containing an extractant into the leaching solution, and make part of heavy metal substances in the sludge enter the organic phase through the mass transfer process, so as to achieve the purpose of separation and concentration, also known as liquid-liquid extraction method. In 1970s, Swedish National Technology Development Committee supported Chalmers University to develop AM-MAR "leaching-solvent extraction" process to recover heavy metals such as copper, zinc and nickel from electroplating sludge, which gradually formed an industrial scale. In China, Zhu et al. have carried out a series of experimental studies on recovering valuable metals from electroplating sludge with solvent extraction technology as the main body. Firstly, valuable metals were recovered from electroplating sludge by ammonia complexation, group leaching, ammonia evaporation, sulfuric acid hydrolysis, solvent extraction and metal salt crystallization, and various high-purity metal salt products containing copper, zinc, nickel and chromium were obtained. Later, the four-stage countercurrent extraction process of N, kerosene and HsO was adopted, which can make the extraction rate of copper reach 99%, while the loss of nickel and zinc stored in * * * is almost zero. In this process, copper is recovered in the form of copper salt CuSO 5h: O or electrolytic high-purity copper. Preliminary economic analysis shows that its output value offsets the daily operating expenses and has high economic benefits. The whole process is simple and recyclable, and basically does not produce secondary pollution. Later, after improving the process, the team also studied sulfuric acid leaching -P ~ kerosene-sulfuric acid system to extract and separate iron-sodium soap -P:. Chromium and aluminum were extracted by kerosene-sulfuric acid system and separated by aluminum-stripping process, and metals were recovered from ammonia leaching residue of electroplating sludge. Through the optimization experiment, the optimum process parameters of the whole process were determined. The results show that chromium, aluminum and iron in iron-chromium slag can be recovered as high-purity salts and can be used as chemical reagents, and the recovery rate is above 95%. J.E.Silva of Portugal and others studied the process of extracting crystalline zinc and nickel from electroplating sludge containing heavy metals such as copper, chromium, zinc and nickel by sulfuric acid leaching-copper removal by replacement-chromium removal by precipitation -D2EHPA and Cyancx272. The results show that the extraction rate of zinc by D2EHPA is higher than that by Cyancx272, and all zinc existing in organic phase can be recovered. High purity nickel sulfate product can be obtained after crystallization. In the removal stage of copper and chromium, the recovery rate of copper reaches 90%, and the generated Cr-CaCO precipitates, which makes it possible to manufacture silicate materials. 3. 1.3 electrolytic method According to the basic principle of electrolysis in physical chemistry, some domestic smelters have electrolyzed sludge mainly containing Fe(OH) and Cr(OH), and the method of Wuhan smelter is worth learning. They added a certain amount of water and sulfuric acid to the sludge, boiled it for 30 minutes, moved the filtered filtrate to a freezing tank, and then added 1 ~ 2.5 times the theoretical amount of ammonium sulfate to convert the generated chromium sulfate and ferric sulfate into ferric sulfate, which was separated at a low temperature (75℃) according to the solubility difference between chromium and iron. Finally, more than 90% chromium can be recovered. 3. 1.4 hydrogen reduction separation method hydrogen reduction separation of metal substances is a relatively mature technology. Since 1950s, copper, nickel and cobalt have been produced by hydrogen reduction in industry, and remarkable economic and social benefits have been achieved. Zhang Guandong and others? . The valuable metals such as copper, nickel and zinc in the ammonia leaching products of electroplating sludge were comprehensively recovered by wet hydrogen reduction method, and copper powder and nickel powder were successfully separated. The experimental results show that the separation effect of copper and nickel is good in weakly acidic ammonium sulfate solution. The purity of the two metal powders can reach 99.5%, which meets the product requirements of 3 copper powder and 3 nickel powder. The recovery rate of copper is 99% and that of nickel is over 98%. On this basis, the zinc in the reduction tail liquid was recovered. This method has the advantages of simple process, low investment and high product purity, and is worthy of further improvement and popularization in industrial production. 3. 1.5 calcination acid dissolution method JitkaJandova et al. (Through experimental research, it is found that it is a simple and feasible method to dissolve copper-containing electroplating sludge in acid, calcine it, then dissolve it in acid, and finally recover it in the form of copper salt. In the process of high-temperature calcination, most impurities, such as iron, zinc, aluminum, nickel and silicon, are converted into slowly dissolved oxides, so that copper can be separated in the subsequent process and finally recovered in the form of Cu (SO) H: 0. The method is simple in process, does not need to add other reagents, and has strong economy and simplicity. However, there are many impurities in the recovered copper salt, and the process needs to be further optimized. 3.2 ferrite comprehensive utilization technology ferrite technology is developed according to the principle of ferrite production. It is an affirmative method for many scholars to apply ferrite comprehensive utilization technology to treat electroplating heavy metal sludge and make suitable industrial products. Because electroplating sludge is the product of ferrous flocculation of electroplating wastewater, electroplating sludge generally contains a lot of iron ions, especially in electroplating sludge containing cr, which can be converted into composite ferrite by appropriate inorganic synthesis technology. Metal ions such as iron ions in electroplating sludge are bound to the lattice site of Fe3O4 with inverse spinel face-centered cubic structure, and its crystal structure is stable, thus achieving the purpose of eliminating secondary pollution. Ferritization can be divided into dry process and wet process. Jia of Shanghai Jiaotong University used electroplating sludge produced by Shanghai Electric Machine Factory and Shanghai Water Pump Factory as raw materials to synthesize iron black products by wet method, and developed C43-3 1 black alkyd paint, Y53-4-2 iron black oily antirust paint and other products with iron black pigment as raw materials. Then, on the original basis, a new dry reduction drying process was developed after ferrite was synthesized by electroplating sludge wet method, and a patent was applied. This process can synthesize magnetic flaw detection powder with excellent performance, which has the advantages of simple process, high yield, no secondary pollution and low treatment cost. 3.3 Composting Fertilizer The main method to control heavy metal pollution of sludge at home and abroad is to use sludge compost. Composting is a process of transforming organic matter into fertilizer through microbial fermentation under certain moisture, C/N and ventilation conditions. Many microorganisms in nature have the ability to oxidize and decompose organic matter. Practice has proved that microorganisms can be used to biodegrade organic matter under certain humidity and pH conditions to form humus-like substances, which can be used as fertilizers and improve soil. According to the different requirements of microorganisms for 0, it can be divided into aerobic composting and anaerobic composting. Composting can increase the temperature, speed up its decomposition and kill pathogenic bacteria. The research of electroplating sludge compost is still in the exploratory stage. Zhou et al. used the chromium-containing sludge in electroplating waste chromium solution for composting. After 24 days, the chromium (VI) content in 1g sludge decreased from 4.060mg to 0.028mg, which solidified most heavy metals and greatly reduced the toxicity. The composted sludge was applied to flower pot experiment, which showed good growth response, avoided the human food chain and opened up a new way for the treatment and resource utilization of chromium-containing sludge. Researchers at Shanghai Jiaotong University. . Ferrite synthesized from electroplating sludge was magnetized to make magnetic fertilizer, which was applied in the field. The results show that the application of this magnetic fertilizer can obviously increase the yield of chicken feathers, onions and other crops and shorten the growth cycle. However, the content of heavy metals in electroplating sludge in China is generally high and its composition is complex. There are still difficulties and risks in using composted sludge in agriculture, and the composting cycle is long and the procedure is complex, which also limits the research of electroplating sludge composting. 3.4 Production of Modified Plastic Products Using electroplating sludge and waste plastics to jointly produce modified plastic products is a new technology that is original in China and jointly developed by many scientific research units in Shanghai. Its basic principle is to adopt the method of plastic solidification, take electroplating sludge as filler, mix it with waste plastic at a proper temperature, and make modified plastic products by pressing or injection molding. After electroplating sludge was dried at 400-600℃ in special TGZS300 high-humidity material dryer, the heavy metals were basically stable, and the leaching test met the national standards. The research shows that unmodified electroplating sludge and plastic are physically mixed and belong to package curing. However, after being modified by surfactant (such as sodium oleate), X-ray powder diffraction pattern analysis shows that it has obvious chemical effect, improves the hydrophobicity of sludge, and the contact angle reaches 100. Therefore, it can be inferred that it has good compatibility with plastics, and even filling will improve the mechanical properties. The plastic products (including modified and dried electroplating sludge) produced by this process show that the leaching rate of heavy metals and the mechanical strength of plastic products can reach the specified indexes. Using electroplating sludge and waste plastics to produce modified plastic products not only solves the safe disposal of waste materials, but also makes full use of waste resources. It is an important way to turn waste into treasure, comprehensively utilize and realize waste resource utilization, and has good social and environmental benefits. Conclusion Electroplating industry is one of the three major polluting industries in the world today. Facing the increasingly fragile global ecological environment and increasingly scarce resources, it is of great significance to actively carry out the harmless disposal and comprehensive utilization of electroplating sludge, and it is also an inevitable choice to realize social sustainable development.