Practice of recycling wastewater from Hedong gold mine

I. Overview Zhaoyuan City, east gold ore processing plant was built in the spring of 1978, July 1980 and beginning of production, built at the beginning scale of 150t / d. In 1990, the concentrator expanded two 250t/d grinding and floating systems, and carried out corresponding transformation of the original crushing, screening and dewatering system. At the same time, the original 150t/d grinding and floating system was scrapped, and the production capacity of the concentrator was formed. 500t/d. In 1998, the overall technical transformation of mining and selecting production capacity expansion of 500t/d was carried out. At present, the actual processing capacity is 1000t/d. The beneficiation process uses a three-stage closed-circuit crushing mine, a closed-circuit grinding, and a single flotation process with one coarse and two fine sweeps. The water consumption per 1t of raw ore is 3.20m3, including 1.25m3/t for grinding, 0.25m3/t for flotation, 0.30m3/t for concentrate transportation, 0.15m3/t for dedusting of crushed ore, and 1.10m3/t for tailings. Ground washing, equipment maintenance, etc. 0.15m3/t. The water supply and water use process of the concentrator is shown in Figure 1.

Figure 1 Process of water supply and water use in the concentrator

Second, the problem of water use

The mining and production capacity of Hedong Gold Mine is 1000t/d, and the daily consumption of water is 3,200m3. The daily supply of wastewater is 500m3, and the new water needs 2700m3. The new water needs to be supplied from the Dujia water source located 15km away from the Hedong Gold Mine, and the second-level transportation is carried out. The new water cost is 2.6 yuan/m3. According to the statistics of water supply costs of Hedong Gold Mine in the past three years, the annual demand is more than 2.3 million yuan. Due to the drought and lack of rain in the Jiaodong Peninsula in recent years, the groundwater level has continued to decline, and the contradiction between ore dressing water and agricultural water has been intensified. It is often caused by severe drought, water supply and water supply and farmland irrigation. The supply of water directly affects the normal operation of the concentrator production. According to statistics, in 1998 and 1999 alone, the direct economic loss caused by water shortage parking reached 908,600 yuan. Since the ore dressing wastewater directly flows into the downstream reservoir of the tailings dam, and the wastewater contains a certain amount of mud sand, suspended solids and flotation reagents, the ore dressing wastewater is discharged in a large amount, which is not fully utilized and pollutes the environment. To this end, how to make full use of Hedong gold mine wastewater resources, implement sustainable development of mines, and reduce production costs has become an urgent problem to be solved in Hedong Gold Mine. In 2000, through the joint efforts of our mine researchers, through the collection and treatment of mineral processing wastewater samples, test analysis and practice, it is proved that the recycling of mineral processing wastewater is to save water, reduce the cost of mineral processing, and improve the economic, social and environmental benefits of mines. Effective Ways.

Third, the theoretical basis for the recycling of mineral processing wastewater

The nature of the beneficiation water is important when considering the recycling of water. This is mainly for flotation, flocculation and ore, but the nature of the water has important implications for re-election, flotation and ball milling, concentration and filtration. The nature of concentrate water and tailings water is different from fresh water. If the tailings water stays in the tailings pond for a sufficient period of time, the organic matter contained in the tailings water will usually decompose or adsorb, and most of the heavy metal cations will also precipitate. Of course, this depends to a large extent on the pH of the tailings water. However, continuous use of recycled water can make ionic polymerization difficult to balance and can cause problems for flotation. Qualitative and quantitative analysis of the organic components of tailings water and concentrate water using modern analytical techniques (GC-MS/HPLS-MS) to investigate the main organic species. Through analysis and investigation, it is found that these waters contain a certain amount of flotation reagents, and only about 35% of the flotation reagents added to the slurry react with minerals, while the remaining 65% are present in the water. The mine and tailings are discharged together. Although this part of the flotation agent has a certain loss during transportation and storage, the remaining part can continue to interact with minerals. In order to prove the possibility of recycling of ore dressing wastewater, the author conducted several tests. The test is to directly sample at the overflow of the classifier. After drying, dehydration, shrinking, and then adjusting the water with various pH values, the adjusted pulp concentration is 40%, and the sample fineness is -200 mesh. 50%, the gold content was 3.15g/t, and then the dosage test was carried out. The results are shown in Table 1. Table 1 Comparison of new water and wastewater beneficiation indicators

IV. Wastewater Circulation Return Scheme (I) Concentrate Water Circulation In order to reduce the consumption of fresh water, a local water circulation scheme is adopted. The gold concentrate is pumped into the thickener, and the overflow water in the thickener is directly returned to the classifier for recycling, which replaces the supplementary water and flotation operation of the grinding and grading operation and the defoaming water of a rough selection operation. Reduce the consumption of flotation chemicals. For different ores, the ability to use this process requires confirmation of the continuous flotation of the ore. (II) Tailings water circulation 1. Determine the size of the sedimentation tank. See Table 2 for the composition of the particles in the tailings slurry of Hedong Gold Mine. Table 2 Particle composition in tailings slurry

As can be seen from the results in Table 2, the ultrafine particle suspension containing 5 μm or less is contained in the tailings slurry, and is an insoluble inorganic substance. In order to illustrate the problem, the author regards tailings slurry as a dispersion system, and water is a dispersing agent. The precipitation law of mineral particles in an aqueous medium, ie the sedimentation velocity, can be obtained according to Stokes' law:

Where: w-particle sedimentation velocity (m/s); γ1-particle density (kg/m3); γ2-media density (kg/m3); R-particle radius (m); μ-media viscosity (kg·s /m2); g-gravity acceleration (m/s2). It can be seen from Stokes' law that the sedimentation velocity of mineral particles in an aqueous medium under gravity is proportional to the square of the particle radius R. Therefore, the particle size of minerals is an important factor affecting the sedimentation rate. At present, the results of the influence of general mineral particle size on sedimentation velocity are shown in Table 3. Table 3 Effect of mineral particle size on sedimentation velocity

From the results in Table 3, the area of ​​the sedimentation tank required for the sedimentation of tailings particles can be calculated by the following formula:

Where: A-precipitation tank area (m2); Q-total overflow flow rate (m3/h); u-minimum particle sedimentation velocity (m/h); k-correction coefficient, generally k=1.05-1.2. After sedimentation through the sedimentation tank, the height difference between the sedimentation tank and the high level pool of the concentrator is used to make the tailings clarified water flow to the high level pool of the concentrator for recycling. 2. After the area of ​​the return water sedimentation tank is determined, the water in the sedimentation tank adopts the concrete well--pipe drainage method. The drainage well has an inner diameter of 210m, a height of 710m, and a drainage pipe inner diameter of 110m. In order to prevent uneven subsidence, the drainage well and drain pipe foundation should be placed on the old soil layer or rock foundation with uniform geological changes. Drains are strictly prohibited from being placed on the fill (where the soil or stone is filled). The construction of the drainage pipe in the sedimentation tank is carried out on site, that is, the concrete pipe is placed in the dug trench, the gap is filled with concrete, the slope is i=0.0332, and after brushing the cold substrate on the outer wall of the drainage pipe, three layers of asphalt horseshoe grease are brushed. Then backfill 1m thick clay , and the backfill on both sides of the drain should be filled and compacted. Outside the sedimentation tank, two iron pipes with a diameter of 203 mm flow from the high-level pool of the concentrator, one of which is reserved. According to statistics, after tailings wastewater is precipitated in the sedimentation tank, 90% is recycled and 10% is discharged into the reservoir for agricultural irrigation. The current water supply process of the selected mine is shown in Figure 2.

Figure 2 Selected plant water supply process

V. Economic Benefits, Social Benefits and Environmental Benefits 1. At present, only the underground water supply and ore dressing wastewater recycling can meet the production needs of the Hedong Gold Mine Concentrator. Stopping the water from the Dujia water source can save 2.3 million yuan per year. 2. The recycling of wastewater reduces the consumption of flotation reagents. According to statistics, the annual savings of 52,800 yuan. 3. The recycling of wastewater has no effect on the grade of gold concentrate, and the recovery rate of flotation has increased by 0.4% compared with the past, and the annual economic benefit can be increased by 273,600 yuan. 4. Waste water recycling, which eliminates the polluted environment, ensures normal production, significantly reduces the cost of mineral processing, and realizes the unification of economic, social and environmental benefits.

VI. Conclusion 1. The recycling of concentrate water and tailings water can effectively utilize the effective flotation reagents and reduce the amount of flotation reagents. 2. Concentrate water and tailings water have no effect on the grade of gold concentrate. 3. The use of beneficiation wastewater instead of clean water can effectively reduce the amount of clean water. 4. When circulating water is used for flotation, if the various process indicators are significantly reduced, firstly, the method of adjusting the agent should be used to change the situation, such as reducing the amount of foaming agent, increasing or decreasing the amount of yellow drug and adjusting the medium. . When this is still not effective, the amount of circulating water for flotation is reduced.

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