Countermeasures for treatment and pollution prevention of cyanide-containing wastewater from heap leaching
In recent years. Our gold business has made great progress, various types of gold deposits, with the advancement of science and technology. It has been developed and utilized by the industry, and the “heap leaching gold selection†process in low-grade oxidized ore has been mastered and utilized by some enterprises. Good economic benefits have been achieved in production practice. With the development of the depth and breadth of production, the number of gold selection plants is increasing. A large amount of highly volatile sodium cyanide drugs are used in the production process, and the treatment of cyanide-containing wastewater produced is also becoming more and more important. 1. Cyanide properties and hazards Cyanide can be divided into two types. One is complex cyanide, and the cyanide ion and metal ion of the complex cyanide molecule are firmly bonded by coordination. For example, Cu(CN) 4 -2 in Fe(CN) -3 ; K 2 Cu(CN) 4 ] in [K 3 Fe(CN) 6 ] is not easily dissolved, and their chemical properties and toxicity are different. Another simple cyanide is mainly alkali metal salts such as KCN, NaCN, etc., which have high solubility and strong toxicity. It is easy to produce highly toxic gases under acidic conditions. The use of “heap leaching gold†is a highly toxic drug of sodium cyanide. The wastewater contains cyanide. If it flows into the river, it will cause water pollution, such as being absorbed by humans, animals and skin. Cyanide enters the stomach and can be immediately hydrolyzed into hydrogen cyanide into the blood under the action of gastric acid. Fe 3+ of cytochrome oxidase binds to cyanide in the blood to form cyanide high- iron cytochrome oxidase. Loss of ability to transfer electrons by Fe 3+ causes interruption of the respiratory chain. The cells suffocate and die. Cyanide is a highly toxic substance, and HCN 270ppm in the air can kill people. The cyanide content of water is converted into cyanide ion (CN - ) concentration of 0.01 mg/L, which is harmful to fish, and 0.3 mg/L has an effect on aquatic organisms. It can not purify the water body. When the concentration is above 0.1mg/L, it will be harmful to the growth of rice. Heap leaching gold is a high concentration of cyanide-containing wastewater produced during production and after treatment of waste ore. If not handled in time. Will affect the surrounding water system. It threatens the normal production and life of humans and animals, so it is necessary to treat the cyanide-containing wastewater to meet the national emission standards. Does not cause environmental pollution. Second, heap leaching gold, the choice of treatment methods for cyanide-containing wastewater There are many methods for treating cyanide-containing wastewater, such as: 1. alkaline chlorination method; 2. sodium hypochlorite addition method; 3. liquid chlorine addition method. Due to the sodium hypochlorite addition method and the liquid chlorine addition method, the input cost is high. The management is difficult. For the characteristics of the heap leaching process, the alkaline chlorination method is suitable, simple and reliable. The laboratory treatment results of cyanide-containing wastewater are shown in Table 1. Cyanide waste water was added bleach (containing 20.76% chlorine) with lime to adjust PH removed stirred CN -. Table 1 Bleaching powder kg/m 3 Stirring time (hours) Adding amount kg/m 3 CN - mg/L before treatment CN - mg/L after treatment Except CN - rate (%) PH 2 1 2 152.01 0.318 99.79 10.5 4 1 2 152.01 0.167 99.89 10.5 (1) Heap leaching gold selection production process After the leaching process, the oxidized ore is excavated, and two sections of open-circuit coarse crushing are carried out to obtain a lump ore having a particle size of less than 25 mm. Directly carrying out the open-air heap leaching of the yard, spraying with cyanide solution, the leached precious liquid enters the sedimentation tank for clarification, and the clarified liquid is adsorbed by the adsorption tank or the adsorption tank to obtain the gold-carbon product. see picture 1 figure 1 (2) Optimize the process flow and improve the cycle utilization rate The process design should maximize the use efficiency of sodium cyanide (NaCN) solution and the recycling rate of lean liquid. The treated wastewater is also recycled as much as possible to minimize the consumption of NaCN and the amount of CN - produced and discharged, and strive to achieve non-emission. (3) Alkaline chlorination treatment of cyanide-containing wastewater The wastewater generated by the heap leaching gold selection process is mainly cyanide-containing wastewater and can be treated by alkaline chlorination. Alkaline chlorination treatment of cyanide-containing wastewater is technically mature and widely used. According to the results of the wastewater treatment test provided by the Jilin Province Metallurgical Research Institute, the CN - concentration of the cyanide-containing ore water can be reduced to less than 0.36 mg/L after oxidation treatment with bleaching powder. In order to obtain this treatment effect in production, it must be realized through certain engineering facilities, in addition to being properly managed. 1, the basic principle CN oxide is less toxic - - that the reaction is CN: alkaline cyanide oxidation treatment of wastewater containing cyanide can be divided into two phases: the first phase CN - +ClO - +H 2 0=CNCl+2OH - CNCl+2OH - =CNO - +CN - +H 2 O Among them, the highly toxic CNCI is easily liberated under acidic conditions. The CNCI can be converted to ClO - in a few minutes only under alkaline conditions of pH > 10 with sufficient oxidant present. When PH < 10, the reaction is very slow; when PH < 8.5, there is a danger of releasing CNCI. Second stage: further oxidation of ClO - to CO 2 and N 2 . 2CN0 - +40H - +3CL 2 →2CO 2 +N 2 +6CL - +2H 2 0 At this stage, the pH is generally controlled to be 8-9. 2, the process. The effect of alkaline chlorination treatment depends largely on whether the process design is reasonable. According to the process flow of Figure 2, the cyanide-containing wastewater is processed according to the heap leaching process. In the process flow of Figure 2, the adjustment tank is used to adjust the water quantity and water quality, and the residence time is 1 to 2 hours. There should be a stirring device to prevent the precipitation of the waste water; the first oxidation pool mainly completes the first stage oxidation, and the residence time is more than 10 minutes. When the pH value is greater than 1O, stirring and mixing equipment should be provided; the second oxidation tank mainly completes the second stage oxidation, and the residence time is more than 30 minutes, and stirring and mixing equipment should be provided. The redox electrode is used to control the dosage of the bleaching powder, and the pH electrode is used to control the acid or alkali dosage. It is worth noting that many alkaline chlorination treatment equipments do not perform well, mainly due to improper control of pH, oxidant dosage, mixing strength and residence time of wastewater in the reactor. Example: The treatment of cyanide-containing wastewater by alkaline chlorination in a gold mine in southern Anhui is very effective. The following examples are shown in Table 2, Tables 3 and 4: Table 2 Sampling date CN - mg/L before treatment CN - mg/L after treatment Removal rate (%) 2002.5.25 135.12 0.142 99.89 2002.2.25 137.15 0.153 99.88 date year 2002 Sample point monitoring result item The wastewater is discharged into the upper 100 m slope before the creek Wastewater discharged into the front section of the creek (watering reservoir) Wastewater discharged into the 50m section downstream of Xiaoxikou Wastewater discharged into the middle and lower reaches of Xiaoxikou The creek enters the 50-meter section of the Baiyang River 5.25 PH 7.47 7.02 6.84 7.67 7.01 5.25 Chemical oxygen demand (CODer) 13 16 15 13 15 5.25 Total oxide 0.0025 0.0025 0.0025 0.0025 0.0025 5.25 Chromium (hexavalent) 0.005 0.005 0.005 0.005 0.005 5.25 Total copper 0.005 0.005 0.005 0.005 0.005 5.25 Total arsen 0.025 0.025 0.025 0.025 0.025 5.25 Total cadm 0.005 0.005 0.005 0.005 0.005 5.25 Total lead 0.005 0.005 0.005 0.005 0.005 date year 2002 Xiaoxi enters the 50-meter slope of the lower reaches of the Baiyang River The creek enters the 1000m section of the lower reaches of the Baiyang River The creek enters the 5000m section of the lower reaches of the Baiyang River Xiaoxi enters the 10000-meter section of the lower reaches of the Baiyang River Surface water environmental quality standard GB3838-2002 class III (mg/L) 5.25 7.91 7.41 7.55 8.00 6.5-8.5 5.25 15 13 12 12 ≤15 5.25 0.0025 0.0025 0.0025 0.0025 ≤0.05 (fishing 0.005) 5.25 0.005 0.005 0.005 0.005 ≤0.05 5.25 0.005 0.005 0.005 0.005 ≤1.0 (fishing 0.01) 5.25 0.025 0.025 0.025 0.025 ≤0.05 5.25 0.005 0.005 0.005 0.005 ≤0.005 5.25 0.005 0.005 0.005 0.005 ≤0.005 (1) Prevent accident discharge In production, there may be a large amount of cyanide-containing wastewater overflowing or leaking due to production accidents, equipment failures, maintenance and unbalanced wastewater processes. For this, the design should consider preventive measures. Set up enough wastewater storage tanks. (2) Minimize unorganized emissions All tanks of process equipment, storage tanks and storage tanks, etc., should be designed with effective anti-leakage measures to avoid leakage of cyanide-containing solution. Where it is easy to leak cyanide-containing wastewater, anti-leakage measures should be considered in the design. The ground is smooth and flat, and a storage tank for recycling waste water and solution is provided. V. Strengthening wastewater discharge management (1) Waste water in tailings stacking and discharging open channels. The concentration of cyanide is relatively high, and there are some fluctuations with the change of rainfall and the operation status of the wastewater treatment facility. Different measures for prevention and control of 42 pollution should be taken in the rainy or non-raining weather. (2) Repair the drainage ditch around the ore dressing site, and divert the external water into the beneficiation site. (3) Establish a sound monitoring system, and conduct sampling analysis and emergency analysis on the whole process every day. (4) The treated wastewater must meet the national emission standards before it can be discharged. The product structure is firm, the size is accurate,and can be customized for various vehicle models,which can be designed, developed and manufactured independently according to customer requirements, the customer unanimously gives the high praise, Customized Automobile Spare Part Product,Metal Sheet Stamping,Car Completed Sunroof Frame,Steel Metal Stamping Sheet NINGBO YINZHOU HONGBO AUTOPARTS CO., LTD., , https://www.honghuaqiye.com
Third, heap leaching gold containing cyanide wastewater treatment 
Table 3 Summary table of monitoring results of surrounding surface water (1)
Table 4 Summary table of monitoring results of surrounding surface water (2)
4. Precautions for treatment of cyanide-containing wastewater from heap leaching
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