Cyanide-containing wastewater refers to industrial wastewater containing CN groups. In the non-ferrous metal mineral extraction of gold silver and copper cyanide electroplating, chemical, coke, and other industries producing heat treatment process are discharged wastewater containing a large amount of cyanide, particularly mineral Xuanye large amounts of cyanide in the production process, wastewater CN - The high concentration of the product also contains a large amount of heavy metals, thiocyanate and other compounds, which are very serious to the external water environment. According to the literature, nearly 10 million tons of cyanide are discharged into water bodies every year. Cyanide is highly toxic substance, CN - will combine with the body ferricytochrome enzymes, generating cyanmethemoglobin loss of cytochrome oxidase and oxygen transfer function, in vivo causes tissue hypoxia and apnea. The lethal dose of cyanide varies from person to person, about 0.5-3.5mg/kg, and the lethal dose to other small animals (such as birds) and aquatic organisms is smaller, which seriously threatens the lives of humans, animals and aquatic organisms. Safety, destroying the ecological balance. The National Integrated Wastewater Discharge Standard GB 8978-1996 stipulates that the standard concentration of cyanide-containing wastewater in general enterprises is <0.5mg/L. Although companies actively use a variety of different methods to treat cyanide-containing wastewater, many industrial and mining companies still exceed the standard. Regardless of the technical staff, environmental managers, and entrepreneurs, they are striving to find new technologies and methods that are simple to operate, low in cost, and effective in processing. The author introduces the recent development of cyanide-containing wastewater treatment technology and the status quo of industrial and mining enterprises' application processes, and gives a brief review of the main treatment processes and technologies, hoping to inspire the innovation and improvement of cyanide-containing wastewater treatment technology.
I. Treatment methods and options for cyanide-containing wastewater
There are many domestic cyanide-containing wastewater treatment methods. In the early stage, there were alkali chloride method (liquid chlorine method, sodium hypochlorite method, bleaching powder method, chlorine dioxide method, etc.), acid chlorine method, inco-method method, acidification absorption-neutralization method, ozone method, Electrolysis method, ion exchange method, activated carbon catalytic oxidation method, biological method, pressurized hydrolysis method, and the like. Beginning in the 1990s, solvent extraction, hydrogen peroxide-copper catalytic oxidation, acidification precipitation-neutralization (two-step precipitation), etc., have begun to be applied in combination. In the early foreign countries, it was mainly the alkali chloride method and the inferior method. In the 1990s, biological oxidation, wet oxidation, and supercritical water oxidation began to appear. At present, there are many treatment methods for cyanide-containing wastewater at home and abroad, but which process is mainly determined by the mass concentration, nature of the cyanide-containing wastewater and the actual treatment effect.
The mass concentration of cyanide in wastewater can be roughly divided into high, medium and low. In general, the composition of complex high strength wastewater CN - in 800mg / L or more, there are a variety of cyanide concentration wastewater between (1 ~ x) × 10 3 mg / L, can be recovered and acidified to cyanide The residual liquid continues to be oxidized. The medium-mass concentration cyanide-containing wastewater is generally between 200 and 800 mg/L. The treatment process is selected according to the complexity of the wastewater components. The wastewater composition is simple and the cyanide recovery is economical. It is suitable for acidification first, and the residual liquid is used again. Secondary treatment; acidification recovery of non-economically beneficial wastewater can be directly destroyed by oxidation. Low-mass concentrations of cyanide-containing wastewater are commonly used for direct oxidative destruction. Cyanide gold dressing plant wastewater containing high concentrations of volatile acidified to - absorbent base cyanide recovery, concentration of pollutants to be reduced in the low levels, then the method or using a combination of oxidative damage treatment process to remove CN -.
In the actual production in China, high and medium concentration (close to 800mg / L) cyanide-containing wastewater is generally determined according to the complexity of the composition of the process; some simple wastewater, you can also recover cyanide, after the residue is recycled The oxidative destruction of CN - is directly carried out; the medium and low concentration wastewaters are all directly oxidized. In recent years, there have been many methods for recovering cyanide, such as acidification volatilization-alkali absorption method, extraction method, acid precipitation-neutralization method (two-step precipitation method), three-step precipitation method, and the like. The direct oxidation method is mainly a chlorination method, an inferior method, a hydrogen peroxide method, an ozone method, and the like. At present, factories and mines actually use a single treatment process, because it is difficult to meet national emission standards due to a single process, and most companies use a variety of combined processes. The main combination treatment process is the combination of acid recovery and direct oxidation technology, and the other combination is the combination of direct oxidation, natural purification and activated carbon adsorption process. Many new wastewater full cycle technology combination processes are also one of the main development trends.
Second, the main processing technology principle and application evaluation
(1) Emergency treatment methods for sudden pollution accidents
The easiest way is to rapidly convert the cyanide in the wastewater into a slightly toxic complex using an aqueous solution of ferrous sulfate. Some people call this method a chemical complex. The main chemical reactions are:
FeSO 4 ·7H 2 O→Fe 2 + +SO 4 2+ +7H 2 O
Fe 2 + +6CN - →Fe(CN) 6 4 -
2Fe 2 + +Fe(CN) 6 4 - →Fe 2 [Fe(CN) 6 ]
It is finally converted into a Prussian blue insoluble compound. The method is characterized by simple operation and low cost, but it does not meet national emission standards after wastewater treatment. In the 1970s, some domestic companies used this method, but they are not used now. From the point of view of environmental safety precautions, this method can be used as one of the methods for rapid remediation when cyanide generates sudden pollution accidents. The injection of ferrous sulfate solution into water can rapidly reduce the degree of damage caused by cyanide-containing pollutants in water. Reduce damage to the environment, especially to aquatic organisms. When the concentration of CN -in the wastewater is very low, the treatment effect of this method is not good.
(2) Oxidation method of medium and low mass concentration cyanide-containing wastewater
1. Alkaline chlorination
Alkaline chlorination is a method commonly used at home and abroad. The high-valent chlorine oxidant is added to the alkaline cyanide-containing wastewater. The commonly used oxidants are: ClO 2 , Cl 2 (both gas and liquid), bleaching powder, sodium hypochlorite, calcium hypochlorite, chlorite, and the like. In alkaline solution, typically generated OCl - valency or chlorine compound, the cyanide was first oxidized to cyanate, and further oxidized to carbon dioxide and nitrogen. The main chemical reactions are:
OCl - +CN - +H 2 O→CNCl+2OH -
CNCl+2OH - →CNO - +Cl - +H 2 O
2CNO - +3OCl - →CO 2 ↑+N 2 ↑+3Cl - +CO 3 2 -
The pH of the oxidation reaction is controlled at about 11, and the operation is simple. After adding the chlorine oxidant, it is only necessary to stir. If the composition of wastewater is complicated, the consumption of chlorine oxidant is high, generally 4 to 9 times of the theoretical value. When the purity of the agent is not high or the content of thiocyanate is high, the consumption of chlorine oxidant is larger; when it contains ferrocyanide complex, Oxidation to a ferricyanide complex becomes a soluble group, and the treated wastewater is difficult to meet national emission standards. The method is characterized by wide sources of drugs, low price, and low equipment investment, but the work environment is seriously polluted, and secondary cyanide chloride pollutants are generated, which is harmful to the operators, and the consumption of the chemicals is large, and the long-term use equipment is seriously corroded. .
2. Institutional law
The SO 2 -air method, known as the Inco method, was developed by Inco in 1982. It is mainly used to add a mixture of SO 2 and air to the treated waste liquid to control the pH under the conditions of 8 to 10, and in the second Under the catalysis of valence copper ions, the cyanide in wastewater is oxidized by the synergistic action of SO 2 and air. Process of the reaction, removing cyanide are three main ways volatilization, oxidation and adsorption precipitate, the precipitate is generated and milk of lime, the greater the amount of precipitation, and the adsorption amount of CN -. The method not only completely removes most of the cyanide from the lean liquid, but also eliminates the ferricyanide complex, but the method cannot recover the valuable component, is a consumable oxidation process, and the sulfur dioxide is also an atmospheric pollutant, which occurs. In the process of reaction, it is inevitable to escape and leak; after the water treatment, a large amount of solid waste containing cyanide is also generated, and there is a problem of blockage of the pipeline.
The sulfur dioxide-air oxidation process is simple, the equipment is not complicated, and the treatment effect is generally superior to the chlorine oxidation method (regardless of the toxicity of thiocyanide), the source of the medicament is relatively wide, the treatment cost is not high, and the investment is small. In 1984, Changchun Gold Research Institute began to study sulfur dioxide-air oxidation method, and completed industrial test in 1988; in 1991, applied in Shandong Zhaoyuan cyanide plant, the initial concentration of cyanide-containing wastewater was 380 ~ 400mg / L, removed The rate is above 99%, and the SCN - removal rate is between 46% and 86%, which has achieved certain effects. In foreign countries, cyanide gold extraction plants use this method to deal with cyanide-containing wastewater, such as Canada, the United States, Australia and other places have applications. The method also has other application processes, such as sodium sulfite method, sodium metabisulfite method and the like.
3. H 2 O 2 oxidation method
H 2 O 2 oxidizes cyanide at a pH of 9.5 to 11, at room temperature and with copper (Cu 2+ ) ions as a catalyst, and further hydrolyzes CNO - and CNO - depending on the pH. The main chemical reactions are:
CN - +H 2 O 2 →CNO - +H 2 O
CNO - +2H 2 O→NH 4 + +CO 3 2 -
Heavy metal ions form hydroxide precipitates, and ferricyanide ions are separated from other heavy metal ions to form ferricyanide complex salts. Copper, zinc and other metals in the form of metal cyanide complexes are formed once the cyanide is oxidized and removed. The hydroxide precipitates and excess hydrogen peroxide is rapidly decomposed into water and oxygen. The method is suitable for treating low-concentration cyanide-containing wastewater. H 2 O 2 oxidation method also directly purchases foreign catalysts for treatment, but the catalyst is more expensive, the source is insufficient, and the treatment cost is high; H 2 O 2 has certain dangers during transportation and use. The method of wastewater SCN - difficult to oxidize, the treated wastewater is still a certain toxicity. The technology was first used to treat cyanide-containing wastewater in 1974, after which Germany operated in a gold cyanide plant in Africa in 1984. In 1997, the gold deposit in Sanshan Island, Shandong Province was successfully used to treat the tailings of the acidification process. The mass concentration of cyanide was reduced from 5 to 50 mg/L to <0.5 mg/L.
4. Ozone oxidation method
Ozone has a very strong oxidizing ability, and the electrode potential is 2.07 mV, which is second only to fluorine and easily decomposes components that other oxidants cannot decompose. The chemical reaction mechanism of ozone oxidation treatment of cyanide is:
2CN - +2H + +H 2 O+3O 3 →2H 2 CO 3 +2O 2 +N 2
Ozone is first reacted with cyanide to form cyanate, which is hydrolyzed to produce nitrogen and carbonate. Ozonation treatment of cyanide in wastewater requires only ozone generating equipment, no need for chemical purchase and transportation, and the process is simple and convenient. After treatment, the total cyanide concentration of wastewater can reach the national sewage comprehensive discharge standard, and the treatment waste liquid does not Add other harmful substances, no secondary pollution, no further treatment is required. However, industrial applications have been limited due to the high cost of ozone generators and the difficulty in equipment maintenance. As long as the ozone generator can break through the bottleneck that produces ozone, the industrial application prospects are very broad. The ozone oxidation process consumes a large amount of electrical energy and is difficult to apply in the absence of electricity.
(3) Treatment method for high-quality concentration cyanide-containing wastewater
1. Acidification volatilization-alkali absorption method
Acidification volatiles - the alkali absorption method is a process, the traditional method of mass concentration of cyanide containing wastewater, domestic and early plant are the dressing method. The reaction mechanism of this method is:
Me+2CN - +H 2 SO 4 →MeSO 4 +2HCN↑ (Me is Na + , K + , C, etc.)
HCN+NaOH→NaCN+H 2 O
The process and technical parameters of the method are: the pH is controlled between 2 and 3, the boiling point of HCN is 25.6 ° C, and the non-volatile strong acid - H 2 SO 4 is mixed with the wastewater, and the temperature is increased by 30 ° C to 40 ° C. The air is extracted by compressed air or stripped with the remaining hot steam of the boiler; HCN is extremely volatile, and the evaporated HCN is absorbed by the NaOH solution; after absorption, the sodium cyanide solution can be reused. The absorption rate of cyanide is generally between 85% and 95%. When the process conditions are controlled, the mass concentration of residual liquid cyanide can reach 3~5mg/L, the general mass concentration is 10~20mg/L; the control condition is not good, and the mass concentration of residual liquid cyanide is 30~50mg/L. The effects of electroplating cyanide-containing wastewater are mainly heavy metal ions, while the factors affecting cyanide-containing wastewater in gold mines are complex. In addition to heavy metals Fe, Cu, Zn, Ag, Au, some acidic anions also react. For example: Many plant cyanide cyanide waste water containing a large amount of SCN -, a precipitation reaction, to produce a white of CuSCN; Fe content is high, precipitation of iron salts is also generated.
The method is characterized in that the cyanide can be recovered to the maximum extent, the resources are recycled, the effective utilization rate of cyanide is maximized, and the economic benefit is remarkable; the disadvantage is that the one-time investment is too large, some small and medium-sized enterprises are difficult to bear, the operation operation is complicated, and after the treatment The cyanide-containing residual liquid does not meet national emission standards. For example, some large-scale gold mining plants in Shandong Province use two acidifications twice to achieve national emission standards, and further treatment of residual liquids is needed. Therefore, the acidification volatilization-alkali absorption method is suitable for sewage containing a high concentration of cyanide, and is preferably combined with other processes. The acidification volatilization-alkali absorption method has a better treatment effect, high resource utilization rate, and large economic benefits, but the investment is large, the operation cost is high, and the technical maintenance is complicated.
2, two-step precipitation and impurity closed loop full cycle process (two-step precipitation method)
The two-step precipitation method was developed by Changchun Gold Research Institute when it treated wastewater from a cyanide plant in Shandong. The method is mainly aimed at the high-efficiency closed-circuit full-circulation method developed by the domestic small and medium-sized gold concentrator with high-quality SCN - sewage, and realizes the “zero emission†of sewage. The basic reaction principle is:
2Cu + +2SCN - →Cu 2 (SCN) 2 ↓ (white)
Ca 2+ +SO 4 2 - →CaSO 4 ↓ (white)
Pb 2+ +SO 4 2 - →PbSO 4 ↓ (white)
H + +CN - →HCN
Static precipitation, most of the HCN is in solution, only a small amount of HCN gas volatilizes, but is still controlled in a closed container. In the solution, the removal rate of harmful heavy metals is between 80% and 95%.
The acidified lean liquid after precipitation contains a large amount of sulfate ions, and is directly added to the calcium oxide (slurry) to neutralize, and the pH is controlled between 10 and 12, and a large amount of white precipitate is produced.
After neutralization, a large amount of cyanide reconverted to CN -, while removing a large amount of SO 4 2 -. After solid-liquid separation, the solution can be directly returned to the production process for circulation after adding sodium cyanide. According to the price calculation at the end of the 1990s, the cost of poor liquid per treatment of 1m high quality (above 2000mg/L) was 9.26 yuan, the recovery of valuable resources was 37 yuan, and the profit was 27.74 yuan. The economic benefit was very significant.
The disadvantage of this method is that the first step must be completely precipitated, and the clarification time is long. Otherwise, when the alkali is added, the cuprous thiocyanate has a remelting phenomenon, which affects the treatment effect. The technical problem is that unprecipitated CaSO 4 can cause valve clogging. Therefore, the process requires an increase in the time of the second step of precipitation. If the process deals with the problem of secondary precipitation of CaSO 4 , it will have broad application prospects.
3. Solvent extraction method
The solvent extraction method is a process for treating high-quality cyanide-depleted liquids researched and developed by Tsinghua University in a gold smelter in Shandong Province in the late 1990s. The extraction process principle [14] is to extract the harmful elements such as Cu, Zn, which are the main heavy metals in the poor liquid by using organic amine extractant. The extracted lean liquid still has a large amount of CN - , which is directly returned to the production process for recycling; The organic phase is back-extracted using a NaOH solution to regenerate the organic amine extractant, and the extractant is recycled. The aqueous solution after alkali treatment contains only a small amount of elements such as copper and zinc, does not affect the leaching of gold and silver, and returns to the gold leaching production process to recycle the extractant and cyanide to achieve a lean liquid circulation.
The high-copper and high-zinc partial waste liquid after the process is concentrated is 1/6 of the original lean liquid volume, and is also treated by acidification. The amount of accumulation is not small, and the subsequent treatment of gold is cumbersome. The extractant is expensive and expensive compared to inorganic reagents such as acids, bases, and salts used in other processes.
4, natural purification method
The cyanide-containing wastewater is contained in a container or an industrial pool or a mine tailings pond. Under the conditions of temperature and pressure in the natural environment, the mass concentration of cyanide gradually decreases with time. This method is called natural purification. It includes the volatilization of cyanide, self-decomposition, oxidation, photochemical degradation, biodegradation, precipitation adsorption, etc. It is the result of a complex combination of physical chemistry, photochemistry and biochemistry. Therefore, the natural purification method does not require the use of mechanical equipment, and does not require the addition of any chemicals to achieve the purpose of removing cyanide.
The natural purification method has the advantages of low investment and low production cost. Mining companies at home and abroad adopt this method, which is mainly used for supplementary treatment of low-quality concentration cyanide-containing wastewater. The natural purification method requires sufficient purification time and sufficient oxygen exchange area, as well as unobstructed gas diffusion conditions and a good underground anti-seepage layer, which needs to be kept away from birds and biological drinking water, and the application conditions are very demanding.
This method is often used in the gold production industry for pre-treatment and subsequent treatment, but water pollution accidents and poisoning events often occur due to the lack of application conditions.
5. Biological treatment
Biological treatment methods are mainly two methods of microbial treatment and plant treatment. The biotechnology reported in the literature is mainly microbial treatment technology. Commonly used microbial treatment methods mainly include activated sludge method and biofilm method. At present, biofilms are mainly designed into biofilters by means of membranes or in the form of fillers, or tower-type biofilters are used to treat cyanide-containing wastewater. It is also used to treat low-quality tailings wastewater with aquatic plants. For example, a gold mine in Guangdong has used aquatic plants to degrade trace cyanide in tailings water. A gold mine in the Heilongjiang River Basin has also used plant degradation to discharge low-concentration concentrations of wastewater. Cyanide.
In recent years, biological treatment of cyanide-containing wastewater has gradually become the main direction of research at home and abroad. Although cyanide is a highly toxic substance, some microorganisms can obtain carbon and nitrogen nutrients from cyanide, and some microorganisms even use cyanide as a carbon source and nitrogen source to convert cyanide into carbon dioxide during its metabolism. , ammonia or formic acid, formamide, etc., so that the cyanide-containing wastewater is biodegradable. The biological method can overcome the disadvantages such as incomplete removal of the metal cyanide complex, but this method has problems such as low treatment concentration and low load bearing.
Biological treatment is also one of the more promising methods. The key to its technology is to cultivate the dominant strains or new processes that can directly treat medium-quality sewage.
6, membrane method
The membrane method is mainly a liquid membrane method, a gas membrane method and a membrane separation technique.
The principle of liquid membrane separation for the recovery of cyanide is mainly based on the water-in-oil type system. The solvent constitutes a matrix of the film, and the hydrophilic group and the hydrophobic group of the surfactant are aligned to stabilize the film type, and the emulsion is dispersed in the third phase to form a liquid film. After acidification of wastewater containing cyanide, HCN by the oil phase (oil or coal surfactant) film, generates NaCN into the aqueous NaOH phase reaction. The oil phase is separated and HCN is recovered, and NaCN is recovered after demulsification. The liquid film method was used in Shandong Cangshang Gold Mine in Shandong Province to treat cyanide-containing wastewater in 1994, and then researchers have successively recovered cyanide by liquid membrane method.
The gaseous membrane method is relatively rare. This method is in the laboratory test of recycling and closed loop of electroplating cyanide-containing wastewater.
At present, microfiltration, ultrafiltration and nanofiltration, reverse osmosis and other technologies are based on membrane separation technology. The membrane separation principle is based on the hollow fiber membrane recovery of cyanide. When separating, the acid-containing cyanide-containing wastewater flows on one side of the membrane, and the cyanide-based lye is flowed on the other side; the chemical potential difference of HCN diffusion exists on both sides of the membrane. The HCN in the wastewater is diffused into the alkali absorption liquid through the membrane micropores by the chemical potential difference, and NaOH reacts with HCN to form NaCN. Membrane separation technology is widely used in industrial water treatment, urban domestic sewage deep treatment and industrial production; in the field of cyanide-containing wastewater treatment, membrane separation technology and other technologies have combined market potential; the disadvantage is large investment, high power consumption and cost High, equipment is not perfect, membrane pollution is difficult to solve.
7. Wet air oxidation method and supercritical water oxidation method
Both the wet air oxidation method and the supercritical water oxidation method use oxygen as an oxidant to treat high-quality cyanide-containing wastewater at high temperature and high pressure. There are already sewage treatment plants in foreign countries, and only five manufacturers in the United States use wet air oxidation to treat acrylonitrile wastewater. The domestic research started late. Some people studied the wet air oxidation method and selected five main factors such as temperature and pressure for orthogonal experiment. The results show that temperature is the main influencing factor, followed by reaction time and pH value.
Supercritical water oxidation is an emerging technology for treating cyanide-containing wastewater. This technique was first proposed by Modell and has outstanding advantages in terms of contaminants that cannot be completely removed or difficult to completely oxidize by conventional methods. The method has high removal rate of toxic substances (more than 99.99%), simple reactor structure, small volume, wide application range, no further treatment of product cleaning, and self-heating without external heating. However, under high temperature and high pressure conditions, the material requirements of the equipment are strict. In China, basic research has mainly emerged in the late 1990s, and many studies have been reported.
Due to the shortcomings of supercritical water oxidation technology, such as catalyst problems and high temperature, high pressure corrosion resistance and inorganic salt precipitation problems, such methods are demanding on equipment, large one-time investment, high power consumption, but the advantage is oxidation Thorough, no secondary pollution, can meet national emission standards, is environmentally friendly, and is an ideal target for processing technology. At present, the method has not been promoted because the technical problems have not been solved; after the key technical problems are solved, there will be huge application prospects.
8, ion exchange method
The ion exchange method is a method in which ions are exchanged by using an ion exchanger and a solution. A variety of metal cyanide complexes in cyanide wastewater have a strong affinity for anion exchange resins, so anion exchange resins are generally used for the recovery of cyanide and valuable metals in wastewater. The advantage of this method is that the purified water has good and stable water quality and can be recycled. Ion exchange resins have a small particle size and limited mechanical strength. It is necessary to research and develop high-capacity and high-strength ideal resins, as well as equipment that is specifically and efficiently integrated. The ion exchange process is complicated, the operation is difficult, the processing cost is high, and the economic benefit is small. Due to the different selectivity of different ion exchange resins for different ions, it is difficult to achieve complete treatment for more complex multi-ion systems. In the existing ion exchange resin method, after the cyanide-containing tail liquid is adsorbed, the residual cyanide mass concentration is too high, and other methods are needed for secondary treatment to achieve the efflux standard. The ion exchange resin is frequently regenerated, the process operation is complicated, the maintenance is difficult, and the workload is large.
9. High pressure hydrolysis and electrochemical methods
High-pressure hydrolysis at high temperatures, high pressure, CN - the reaction with water to form non-toxic ammonia and carbonates, transition metal salts can play a role in the catalytic reaction. The method is safe and effective, has wide treatment concentration range, good effect, no secondary pollution, simple operation and stable operation. However, this method requires high temperature and high pressure special equipment, and the operation and operation cost is high, which affects application promotion. Canada established a heating and pressurized hydrolysis industrialization device in the early 1980s, and is now optimizing the reactor structure and operation. In actual operation, the reaction temperature is generally controlled in the range of 170 ° C to 180 ° C, the pressure is controlled at about 0.9 MPa, and the pH of the reaction is controlled at about 10.5. There are few studies on the pressurized hydrolysis of cyanide-containing wastewater in China, and there are few reports. The kinetics of cyanide hydrolysis reaction under atmospheric pressure reflux conditions has been studied. Some conditions have been carried out on the cyanide removal rate of cyanide-containing wastewater and the influencing factors such as pressure, temperature and solution pH.
Common electrochemical methods are electrodialysis and electrolysis. Electrolysis is a relatively mature water treatment technology. In the early days, due to power and cost, the development has been slow, and it is mostly used to treat electroplating wastewater containing cyanide and chromium . In recent years, with the development of the power industry, the electrolysis method has increasingly become a hot spot in water treatment technology. Some people have summarized the advantages of electrolytic water treatment technology: in the electrolysis process, cyanide in wastewater can be degraded into carbon dioxide and simple inorganic compounds, with little or no secondary pollution; energy efficiency is higher, because the electrochemical process is generally at room temperature. It can be carried out under normal pressure; it can be treated by a single method or combined with other treatment methods. As a pretreatment method, the electrolysis equipment and the operation method are generally simple. The shortcomings of the electrolysis method are large power consumption, long processing time, special electrolysis equipment, high operation and operation cost, and are not suitable for the treatment of low-quality cyanide-containing wastewater, and are often used for the treatment of high-quality cyanide-containing wastewater. This method is often limited in the treatment of cyanide-containing wastewater from gold mines, which often destroys cyanide and cannot be reused.
Third, the conclusion
At present, China has reached the world's advanced level in the field of cyanide-containing wastewater treatment technology and process methods. In particular, the oxidative destruction technology of cyanide-containing wastewater and the cyanide full-cycle recycling technology have been relatively mature in industrial production, but various processes. They are still not perfect and need further improvement. The cyanide-containing wastewater comes from all walks of life. The quality concentration, nature and composition of wastewater vary, and there are differences in methods and process selection. From the development of technical methods and trend analysis of process applications, there are the following characteristics:
(1) For medium and high-quality cyanide-containing wastewater and simple cyanide wastewater, the cyanide recovery process, such as acid recovery, extraction, two-step precipitation, etc., will be preferred, and the residual liquid will continue to be oxidized to meet national emission standards. In the application of this combined process, the solid waste generated in the process is treated or sold as a by-product.
(2) Medium and low mass concentration of cyanide-containing wastewater, the process method has a wide selection range, and the one-step treatment method can select wet oxidation method, supercritical water oxidation method, etc. The common combination process is oxidation destruction method + activated carbon adsorption method. In the case of clearer wastewater, less suspended solids and salt, consider using pressurized hydrolysis, ion exchange, membrane separation, etc., and the treated water should be recycled back to the production process as much as possible to reduce wastewater discharge. .
(3) For wastewater containing cyanide concentration below 10 mg/L, a combined process of biological treatment and natural purification may be employed. The wastewater treated by this method must be strictly monitored at the total discharge port and discharged to the external water environment of the plant after reaching the national sewage discharge standard.
In summary, the treatment of cyanide-containing wastewater should proceed from the principles of cleaner production and sustainable development, recover cyanide and precious metals as much as possible, and recycle water, reduce emissions, or eliminate toxic pollutants. Therefore, it is urgent to improve and perfect the existing treatment process, strengthen the research of new processes and new methods, and truly achieve the full cycle of cyanide-containing wastewater to achieve zero discharge of sewage.Household Gloves Formers apply to produce household gloves.
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