Electroplating is an indispensable link in industrial development, but its environmental pollution cannot be ignored. Nowadays, a lot of research and experiments have been done at home and abroad on how to deal with electroplating sludge. Da Consulting brings you a review of current electroplating sludge treatment technology and an analysis of its future development prospects.
So far, the electroplating industry has been an indispensable process in industrial development. Now, in addition to developing technologies that can replace its functions, the focus is still on the prevention and control of electroplating pollution. The sludge produced during the electroplating production process contains a variety of sludges. The current treatment technology is not very mature, so the simple harmless treatment of electroplating sludge is still the mainstream of current treatment technology. But all in all, resource-based treatment of electroplating sludge technology will be a key research direction in dealing with heavy metal pollution.
1 Harmless treatment of electroplating sludge
1.1 Solidification/stabilization technology
Solidification/stabilization technology is one of the methods for the harmless treatment of electroplating sludge. an important technology. It mainly includes cement solidification, lime solidification, thermoplastic solidification, etc. The commonly used curing agents include cement, lime, asphalt, glass, HAS soil curing agent, etc., which are mixed with the sludge for solidification to seal the harmful metals in the sludge. In the solidified body, the purpose of eliminating pollution is achieved. Among them, cement solidification is the most commonly used technology, and it should also be a relatively mature treatment technology. Wang Jiyuan and others concluded through experiments that in the cement solidification process, appropriate additives should be added to adjust the cement: electroplating heavy metal sludge: river Sand: activated alumina: sodium silicate = 1:0.8:0.2:0.08:0.06, its compressive strength can be above 30MPa, and its curing effect is quite obvious. Based on the research on a single cement solidification/stabilization system, ARoy et al. further studied the method of solidifying heavy metals (containing chromium, nickel, tin, etc.) with a mixture of cement and fly ash, so as to achieve the goal of treating waste with waste. , the purpose of cost saving. Tu Jie and others used HAS soil curing agent instead of traditional curing substrate to solidify electroplating sludge at room temperature, and were able to obtain slope protection bricks with good resistance to leaching, corrosion resistance, permeability resistance, and sufficient mechanical strength. This curing The process has opened up a new way to utilize electroplating sludge resources. Zhong Yufeng and others used cement and fine sand as solidification substrates to treat electroplating sludge containing heavy metals such as Ni, Cr, and Cu. Through the leaching experiment of the solidified block, they found that cement solidified the electroplating sludge effectively, and appropriate chelating agents were added during the solidification process. KS-3 can improve the curing effect.
1.2 Thermochemical treatment technology
Thermochemical treatment technology (such as incineration, roasting, smelting, ion arc and microwave, etc.) is to decompose waste under high temperature conditions to make it The toxicity of certain highly toxic components is reduced, rapid and significant volume reduction is achieved, and the useful components of the waste are utilized. At present, the research on thermochemical treatment technology of electroplating sludge is more prominent in the research on the migration characteristics of heavy metals during the incineration process of electroplating sludge. The advantage is that it can greatly reduce the volume of electroplating sludge and reduce the cost of electroplating sludge. It is harmful to the environment. However, due to the high energy consumption of this method and certain requirements for incineration equipment and conditions, ordinary small electroplating manufacturers cannot afford the huge processing costs, and it is easy to cause secondary pollution to the environment during the incineration process. , so this processing method is relatively difficult to be promoted.
2 Electroplating sludge resource treatment
Electroplating sludge itself is also a resource, which contains a variety of metals essential for industry, such as chromium, nickel, zinc, etc., so It can recycle the heavy metals or directly use various heavy metals contained in the sludge as production resources. This can not only solve the pollution of heavy metals, but also achieve the recycling of non-renewable resources, and truly form a sustainable development model.
2.1 Chemical recovery of valuable metals
Chemical recovery of valuable metals only refers to the use of chemical separation and extraction methods to separate and recover heavy metals in electroplating sludge. These include acid leaching and ammonia leaching, chemical precipitation, ion exchange membrane method, etc.
2.1.1 Acid leaching method and ammonia leaching method
Acid leaching method is one of the most widely used leaching methods in hydrometallurgy. Commonly used leaching agents include hydrochloric acid, sulfuric acid, Nitric acid, aqua regia, etc.
Most of the metals in electroplating sludge exist in the form of hydroxides or oxides. The heavy metals in the sludge can be made to exist in the form of ions or complexes through acid leaching, and then mixed with ammonia solution or organic solution. The heavy metals in the leachate are separated and selectively recovered. The heavy metals recovered include high-grade metal elements or metal salts.
The ammonia leaching method usually uses ammonia liquid as the leaching agent, and adopts ammonia complex group leaching-ammonia evaporation-hydrolysis residue sulfuric acid leaching-solvent extraction-metal salt crystallization recovery process, starting from electroplating Most of the valuable metals are recovered from the sludge, among which the recovery rates of copper, zinc, nickel, chromium and iron are greater than 93%, 91%, 88%, 98% and 99% respectively.
When acid leaching or ammonia leaching is used to treat electroplating sludge, the total recovery rate of valuable metals and the ease of separation from other impurities are mainly affected by the leaching rate and leaching rate of valuable metals during the leaching process. Selective control of valuable metals and impurities in the liquid. The main feature of the acid leaching method is that it has a good leaching effect on valuable metals such as copper, zinc, and nickel, but has low selectivity for impurities, especially chromium, iron, and other impurities; while ammonia leaching has poor selectivity for impurities such as chromium and iron. The method has high selectivity for impurities such as chromium and iron, but has a low leaching rate for copper, zinc, nickel, etc.
2.1.2 Ion exchange membrane method
Because ion exchange membranes have selective transmission of ions, ion exchange membranes are used in many industrial separation methods in metallurgical solution separation processes. important application value. The ion exchange membrane method is to place the liquid membrane in the sludge leachate. The mobile carrier selectively complexes metal ions outside the membrane, and then diffuses into the membrane and contacts the membrane for complexation. Finally, the metal ions enter the membrane. Repeating this method repeatedly will eventually enrich the metal ions in the membrane, purify the wastewater, and allow the metal ions to be reused.
2.2 Biological treatment technology
Biological treatment technology mainly uses microorganisms to reduce and metabolize some heavy metals in sludge. However, this technology is still in the exploratory stage, and a systematic treatment plan has not yet been formed. It has only been proved through some individual experiments that microorganisms can perform reductive metabolism of certain heavy metals. However, the mechanism of reductive metabolism of heavy metals by microorganisms has not yet been fully understood. For example, SSilverMarques et al. performed reductive metabolism of Cr3+ using Pseudomonas spp. Bewtra's experiments showed that bacteria can effectively convert metal ions in electroplating sludge into water-insoluble sulfides. Wu Qianjing and others studied a new process for microbial treatment of electroplating wastewater and sludge. The process has a purification rate of Cr(VI), Cr3+, Ni2+, Cu2+ plasma of more than 99.9%, and a metal recovery rate of 85%.
2.3 Making various industrial materials
After treatment, electroplating wastewater can be made into different industrial materials due to different compositions and contents. For example, the residual product of electroplating sludge containing chromium can be made into magnetic materials by the ferrite process. In China, chromium-containing sludge has been successfully used to make MX-400 medium-wave antenna magnet rod, a manganese-zinc ferrite, and , this process has the advantages of simplicity, high yield, no secondary pollution, and low treatment cost; industrial catalysts can be made from chromium-containing sludge using the electrolysis method and the iron filings and iron powder method. Some scientific research units use this sludge to make It has become a medium-temperature shift catalyst for ammonia synthesis, such as C4-2, C6 and B104, a medium-temperature shift iron-chromium series catalyst.
2.4 Making Fertilizer
To make fertilizer from electroplating sludge, it is fermented by microorganisms under artificial control and under certain conditions such as moisture and ventilation, and then the fermentation products are combined with chemical fertilizers. The process of forming compound fertilizer. Research shows that when chromium-containing sludge is treated from electroplating waste chromium liquid, its physical and chemical properties are significantly changed, the content is significantly reduced, and the harm to plants is significantly reduced. Then, the treated chromium-containing sludge is mixed with Chemical fertilizers are formulated into compound fertilizers, which have obvious effects on the good growth of plants. Therefore, turning electroplating sludge into fertilizer not only solves the problem of sludge pollution but also improves agricultural production, achieving dual benefits.
3 Material treatment of electroplating sludge
The material treatment of electroplating sludge is the process of producing building materials or other materials from sludge as raw material or auxiliary materials. Electroplating sludge The material technology mainly includes: firing bricks and tiles, producing modified plastic products, etc.
3.1 Fired Bricks
Fired bricks can absorb a large amount of electroplating sludge and can maintain the electroplating sludge disposal and utilization method.
Experiments show that when electroplating sludge and clay are made into red bricks and green bricks in a certain proportion for testing and quality inspection, the leaching concentration of metals can meet the water quality standards of drinking water sources and the hygiene standards of drinking water. Therefore, fired bricks and tiles The method is also reasonable.
3.2 Production of modified plastic products
The production of modified plastic products is a new technology jointly developed by many scientific research units in Shanghai. Basically, the method of plastic solidification is to use electroplating sludge as filler, mix it with waste plastic at an appropriate temperature, and go through processes such as pressing and molding to make modified plastic products. Moreover, the leaching test of the product Also in line with national standards, electroplating sludge and waste plastics are combined to produce modified plastic products. In addition to solving the problem of safe disposal of waste plastics, it also makes full use of waste resources and realizes waste resource treatment, which has good social and environmental benefits.
4 Prospect Analysis and Outlook
The composition and properties of electroplating sludge are very complex, and its effective treatment has always been the focus and difficulty of research. However, among all the current treatment and utilization methods of electroplating sludge at home and abroad, although solidification/stabilization technology and material chemistry technology are relatively mature, the attitude towards the recycling of heavy metals is that they basically do not recycle, so the economic benefits are extremely low and the comprehensive benefits are very low. Generally, it is only suitable for local use. Although thermochemical technology can significantly reduce the volume of electroplating sludge and reduce its harm to the environment, it also has its own shortcomings. For example, it is easy to cause secondary pollution to the environment during the incineration process, and requires additional assistance during incineration. Fuel, investment and operating costs are high, and it is difficult to be widely promoted, so further improvements are needed. The resource treatment of electroplating sludge, especially the recovery technology of valuable metals, has been studied very early. It is relatively mature, has a high recovery rate of heavy metals, and has good economic and environmental benefits. It is currently the best treatment and utilization technology. Microbial treatment technology has the advantages of being cheap, efficient, without secondary pollution, and having a wide range of sources of adsorbent materials. It has the greatest development potential. However, it still needs to reduce the toxic effects of high levels of heavy metals in electroplating sludge on microorganisms, and how to cultivate highly adaptable, treatment-resistant microorganisms. Developing bacterial strains with high waste efficiency and understanding the mechanism of how microorganisms process heavy metals are still challenges. The resource utilization of electroplating sludge meets the requirements of sustainable development in today's society. It can not only effectively eliminate the hazards of electroplating sludge, but also bring considerable economic and environmental benefits. It has become the focus of the development of electroplating sludge treatment technology, including the use of chemical methods. Recycling useful metal elements is the main content of future research, and applying biotechnology to electroplating sludge treatment is a new development direction.
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