Overview of Cyanide Cracking Process
Cyanide containing wastewater has a wide range of sources and is generated in the production processes of industries such as electroplating, mineral processing, and chemical engineering. The cyanide in these wastewater is a highly toxic substance that, if discharged directly without treatment, can cause irreversible damage to water bodies, soil, and the food chain. Cyanide entering water bodies can cause poisoning and death of aquatic organisms, disrupting the balance of aquatic ecology; Infiltration into the soil can affect soil fertility and microbial activity, posing a threat to crop growth. In addition, cyanide containing wastewater may also be transmitted through the food chain, ultimately threatening human health and safety.
The importance of cyanide removal technology is self-evident. It is a key means of treating cyanide containing wastewater, which can convert the cyanide in the wastewater into harmless or low toxic substances, ensure that the water quality meets national discharge standards, and thus protect the ecological environment and human health.
The development process of cyanide breaking technology is a continuous process of innovation and improvement. In the early days, people mainly used simple chemical precipitation methods to treat cyanide containing wastewater, but the treatment effect was limited. With the advancement of technology, various efficient cyanide removal processes such as chemical oxidation, biodegradation, and physical adsorption have gradually emerged, which have significantly improved treatment efficiency, cost, and environmental protection.
Common cyanide breaking process methods
Chemical oxidation method
alkaline chlorination process
The alkaline chlorination method is a commonly used cyanide breaking process, which uses chlorine gas or hypochlorite as a chlorinating agent to oxidize and decompose cyanide under alkaline conditions. The reaction process is divided into two stages. Firstly, cyanide is oxidized to cyanate, and the reaction is rapid in this stage; Then further oxidize the cyanate salt into carbon dioxide and nitrogen gas. The main chemical reaction formula is as follows:
Phase 1: CN−+ClO−+H2O=CNCl+2OH−CN^- + ClO^- + H_2O = CNCl + 2OH^-CN−+ClO−+H2O=CNCl+2OH−,CNCl+2OH−=CNO−+Cl−+H2OCNCl + 2OH^- = CNO^- + Cl^- + H_2OCNCl+2OH−=CNO−+Cl−+H2O；
Phase 2: 2CNO −+3ClO −=2CO2 ↑+N2 ↑+3ClO − 2CNO ^ -+3ClO ^ -=2CO2 ↑+N2 ↑+3Cl ^ -2CNO −+3ClO −=2CO2 ↑+N2 ↑+3ClO −.
The advantages of this method are mature process, simple operation, stable treatment effect, and the ability to effectively reduce the cyanide content in wastewater. The disadvantage is that it may produce chlorine containing by-products, which may cause secondary pollution to the environment, and the treatment cost is relatively high. It is suitable for treating low to medium concentration cyanide containing wastewater and is widely used in industries such as electroplating and chemical engineering.
Hydrogen peroxide method
The principle of the hydrogen peroxide method is that under the action of a catalyst, hydrogen peroxide decomposes to produce hydroxyl radicals with strong oxidizing properties, thereby oxidizing and decomposing cyanide. Common catalysts include iron salts, which can accelerate the decomposition of hydrogen peroxide and improve the efficiency of oxidation reactions. The reaction conditions generally require suitable pH values and temperature ranges, with pH values typically controlled between 9-11 and temperatures between 20-30 ℃. Compared with other chemical oxidation methods, hydrogen peroxide method has the advantages of mild reaction and no secondary pollution. The chlorinating agent used in the alkaline chlorination method may produce chlorine containing by-products, while the products of the hydrogen peroxide method are mainly water and oxygen, which are more environmentally friendly. However, the oxidation ability of this method is relatively weak, and its treatment effect on high concentration cyanide containing wastewater may not be as good as other methods.
Biodegradation method
Biodegradation is the use of microbial metabolism to break down cyanide into harmless substances. Under suitable environmental conditions, specific microorganisms can grow and reproduce using cyanide as a carbon and nitrogen source, converting cyanide into carbon dioxide, nitrogen, and water through a series of enzymatic reactions. This method is suitable for treating cyanide containing wastewater with low concentration and good biodegradability, such as wastewater from certain mineral processing plants and chemical enterprises. Its process characteristics are low processing cost and environmental friendliness, but the processing efficiency is relatively low and the reaction speed is slow. Factors such as wastewater quality, temperature, and pH value have a significant impact on biodegradation methods. If the wastewater contains a large amount of heavy metals or other toxic and harmful substances, it will inhibit the growth and metabolism of microorganisms; Low or high temperatures can affect the activity of microorganisms, and the generally suitable temperature range is 20-35 ℃; The pH value should be controlled between 6.5-8.5 to ensure the normal growth and metabolism of microorganisms.
Physical adsorption method
The principle of physical adsorption method is to use the porous structure and surface activity of adsorption materials to adsorb cyanide in wastewater onto their surface. Activated carbon is a commonly used adsorbent material with characteristics such as large specific surface area and strong adsorption capacity. During the adsorption process, cyanide molecules are adsorbed into the pores of activated carbon through van der Waals forces, electrostatic attraction, and other mechanisms. In the cyanide cracking process, physical adsorption is usually used as a pre-treatment or deep treatment method. Pass cyanide containing wastewater through an adsorption column equipped with activated carbon to remove cyanide by adsorption. However, this method has certain limitations, as the adsorption capacity of activated carbon is limited and requires regular replacement or regeneration; The treatment effect of high concentration cyanide containing wastewater is poor, and if the activated carbon after adsorption is not treated properly, it may cause secondary pollution.
Advanced UV oxidation method
The principle of ultraviolet advanced oxidation method is to use the energy of ultraviolet light to excite oxidants to produce highly oxidative free radicals, such as hydroxyl radicals, thereby rapidly oxidizing and decomposing cyanide. This method has technical advantages such as strong oxidation ability, fast reaction speed, and non selectivity, and can effectively treat various difficult to degrade cyanide containing wastewater. The cyanide breaking equipment of Suzhou Yiqing Environmental Protection Technology Co., Ltd. adopts advanced ultraviolet oxidation technology and performs well in treating high concentration cyanide containing wastewater. This device uses a special ultraviolet light source and oxidant dosing system to quickly oxidize and decompose cyanide in wastewater, ensuring that the effluent quality meets discharge standards. Its unique design and advanced technology have improved the efficiency of oxidation reactions and reduced processing costs. Compared with traditional cyanide breaking processes, this equipment has the advantages of good treatment effect, small footprint, and high degree of automation, and is suitable for the treatment of high concentration cyanide containing wastewater in industries such as electroplating and mining.
Key points of cyanide cracking process control
Reaction condition control
ph control
Different cyanide breaking processes have varying pH requirements. The alkaline chlorination method needs to be carried out under alkaline conditions, and the pH value is usually controlled at 10-11. Within this range, the chlorinating agent can effectively oxidize cyanide. If the pH value is too low, toxic cyanide chloride gas will be produced, which will affect the treatment effect and safety; If the pH value is too high, it will reduce the reaction rate. The suitable pH value for the hydrogen peroxide method is 9-11, which is conducive to the decomposition of hydrogen peroxide to produce hydroxyl radicals and improve oxidation efficiency. The biodegradation method requires a pH value of 6.5-8.5 to maintain microbial activity. Adjusting the pH value can be achieved by adding acid or alkali, such as sulfuric acid, sodium hydroxide, etc., and the dosage needs to be accurately calculated based on the initial pH value of the wastewater and process requirements.
temperature control
The temperature has a significant impact on the cyanide breaking reaction. Generally speaking, an increase in temperature can accelerate the reaction rate, but excessively high temperatures may lead to the decomposition of oxidants or microbial inactivation. The suitable temperature range for alkaline chlorination method is 20-30 ℃. If the temperature is too low, the reaction rate will slow down, and if it is too high, chlorine gas will escape, reducing the treatment effect. The hydrogen peroxide method has a better reaction effect at 20-30 ℃. The suitable temperature for biodegradation is 20-35 ℃. If the temperature is too low, microbial metabolism will be slow, while if it is too high, it will damage the cellular structure of microorganisms. The temperature can be adjusted through heating or cooling equipment, such as steam heating, cold water cooling, etc.
Control of oxidant dosage
The determination of the dosage of oxidants requires comprehensive consideration of the cyanide concentration, treatment process, and treatment objectives of the wastewater. For the alkaline chlorination method, the theoretical dosage can be calculated according to the chemical reaction formula based on the cyanide content in the wastewater, and an appropriate excess can be added on this basis, generally by 10% -20%. The dosage of hydrogen peroxide method needs to be determined through experiments based on the properties and treatment requirements of the wastewater. Insufficient dosage can lead to incomplete cyanide treatment, affecting the effluent quality; Excessive dosage can increase processing costs and may also result in secondary pollution. Therefore, it is necessary to strictly control the amount of oxidant added, and precise addition can be achieved through equipment such as metering pumps.
Equipment operation control
Mixing system control
The stirring system plays a crucial role in the cyanide cracking reaction. It can fully mix wastewater with oxidants, improve reaction speed and treatment efficiency. The stirring speed should be adjusted according to the reaction process and equipment type, generally controlled at 100-300 r/min. The stirring time should be determined according to the progress of the reaction to ensure that the reaction proceeds fully. At the same time, it is necessary to regularly maintain and manage the mixing system, check the operation status of the mixer, replace worn parts in a timely manner, and ensure the normal operation of the mixing system.
PH monitoring and control system control
The pH monitoring and regulation system monitors the pH value of wastewater in real time through pH sensors, and automatically adjusts the amount of acid or alkali added according to the set value. The accuracy and stability of the system directly affect the effectiveness of the cyanide breaking reaction. To ensure the accuracy of the system, it is necessary to calibrate the pH sensor regularly; To ensure stability, it is necessary to check whether the circuit and pipeline connections of the system are normal. If abnormal situations occur, such as excessive pH fluctuations, sensors and dosing equipment should be checked in a timely manner to troubleshoot.
Oxidation reduction potential (ORP) control
The oxidation-reduction potential (ORP) reflects the oxidation-reduction state of wastewater and is of great significance in cyanide cracking processes. The ORP control range varies for different processes. The ORP for alkaline chlorination method is generally controlled at 600-700 mV, while for hydrogen peroxide method it is controlled at 400-500 mV. By monitoring the ORP value, the progress of the reaction can be determined and the endpoint of the reaction can be controlled. When the ORP value reaches the set range, it indicates that the reaction is basically complete and the addition of oxidant can be stopped. ORP sensors can be used for real-time monitoring, and the amount of oxidant added can be adjusted through an automatic control system to achieve precise control of the reaction.
Case Study and Effect Evaluation of Cyanide Breaking Technology
Actual case analysis and analysis
In the electroplating industry, a certain enterprise uses alkaline chlorination method to treat cyanide containing wastewater. The treatment process is as follows: first collect the wastewater into a regulating tank, adjust the pH value to 10-11, and then add sodium hypochlorite for oxidation reaction, with a reaction time of about 1-2 hours. In terms of operating parameters, the amount of sodium hypochlorite added is determined based on the concentration of cyanide in the wastewater, with a general excess of 10% -20%. After treatment, the cyanide concentration in the wastewater decreased from the initial 50mg/L to below 0.5mg/L, with a cyanide breakthrough rate of up to 99%, and the effluent quality met the national discharge standards. The investment in this process equipment is relatively low, and the operating cost is mainly due to the cost of chemicals, resulting in significant economic benefits.
In the mining industry, cyanide containing wastewater from a certain beneficiation plant is treated using ultraviolet advanced oxidation method. The wastewater is first pretreated to remove large particle impurities, and then enters the advanced ultraviolet oxidation equipment for oxidation reaction under the action of ultraviolet light and oxidant, with a reaction time of about 30-60 minutes. In terms of operating parameters, the amount of oxidant added is determined based on the wastewater quality and treatment requirements. After treatment, the cyanide concentration in high concentration cyanide containing wastewater decreased from 200mg/L to below 1mg/L, and the treatment effect was good. Although the equipment investment is relatively high, the processing efficiency is high, the footprint is small, and the long-term economic benefits are considerable.
Performance indicators and methods
The main indicators for evaluating the effectiveness of cyanide breaking technology include cyanide breaking rate and effluent quality. Cyanide breakage rate refers to the proportion of reduction in cyanide concentration in wastewater before and after treatment. The calculation formula is: Cyanide breakage rate=(cyanide concentration before treatment - cyanide concentration after treatment)/cyanide concentration before treatment x 100%. The effluent quality mainly focuses on whether the content of pollutants such as cyanide and heavy metals meets national or local discharge standards.
The evaluation method mainly adopts chemical analysis methods such as titration and spectrophotometry, and regularly tests the wastewater before and after treatment. The evaluation criteria are based on relevant environmental regulations and industry standards. According to the evaluation results, if the cyanide breakthrough rate does not meet expectations or the effluent quality does not meet standards, process optimization and adjustment can be carried out by adjusting reaction conditions (such as pH value, temperature, oxidant dosage, etc.), optimizing process parameters, or replacing treatment processes to improve the cyanide breakthrough effect and effluent quality.
Development Trends and Prospects of Cyanide Cracking Technology
Technological innovation direction
The future technological innovation direction of cyanide breaking process will focus on the research and development of new oxidants, integration and automation of processes. In the research and development of new oxidants, scientists are committed to finding more efficient and environmentally friendly alternatives to reduce the secondary pollution caused by traditional oxidants. For example, some new compounds with strong oxidizing properties and harmless reaction products are being studied and tested. The integration of processes is the organic combination of multiple cyanide breaking processes, leveraging their respective advantages to improve treatment efficiency and effectiveness. For example, integrating chemical oxidation with biodegradation, first reducing cyanide concentration through chemical oxidation, and then further purifying water quality through biodegradation. In terms of automation, advanced sensors and control systems are utilized to achieve real-time monitoring and precise control of cyanide cracking reactions, reducing human interference and improving the stability and reliability of the processing. These innovations will drive the development of cyanide breaking processes towards higher efficiency, environmental friendliness, and intelligence.
Requirements for Environmental Protection and Sustainable Development
The cyanide breaking process is of great significance in environmental protection and sustainable development. With increasingly strict environmental standards, the cyanide cracking process must be continuously improved to meet the requirements. On the one hand, it is necessary to reduce pollutant emissions during the treatment process and avoid secondary pollution. For example, using cleaner oxidants and processes to reduce the production of chlorine containing by-products. On the other hand, attention should be paid to the recycling and reuse of resources. Cyanide containing wastewater may contain valuable metal elements, which can be recovered and reused through cyanide removal processes to achieve maximum resource utilization. In addition, the application of environmentally friendly processes such as biodegradation will be further promoted to reduce the impact on the environment. The cyanide breaking process not only meets environmental requirements but also achieves effective utilization of resources, contributing to sustainable development.
