Abstract: This paper takes the heap leaching of low-grade oxidized gold ore as an example to introduce the general process of heap leaching, analyzes the environmental pollution and ecological damage caused by heap leaching, and proposes corresponding pollution prevention measures.
First, the application prospects of heap leaching technology
Among the gold resources in China, the amount of low-grade oxidized ore (the ore gold grade 1-3g/t) occupies a certain proportion. It is economically uneconomical to use this conventional cyanide gold extraction process, and the heap leaching process is adopted. There are still economic benefits. The heap leaching gold extraction process is simple, the operation is easy, the investment is small, and the benefit is good. Therefore, the heap leaching gold extraction process is widely used.
Second, the introduction of heap leaching gold selection process
Since oxidized ore is generally buried shallow, the mining method is generally open-pit mining. The ore is broken below 50 mm, and is 25 mm or less for hard ore, and then piled up on a heap-preserving pile that has been treated with anti-seepage treatment at a stacking angle of 30-45 degrees. Before the unsprayed stone sulfur + alkali catalytic mixture, the heap is alkali leached with sodium hydroxide aqueous solution to make the pH of the leachate reach 11-12, preventing the decomposition of the stone sulfur + base catalytic mixture. The general treatment time is 1 -3 days.
After the ore heap is treated with alkali, the mixture is sprayed and leached with a mixture of stone sulfur + alkali catalytic mixture and sodium hydroxide (a ratio of about 1:10), and the concentration of the stone sulfur + base catalytic mixture is about 0.06%. Leachate spray degree: 0.05-0.15 liters / ton of mine · minutes, spray height is generally maintained at about 10 cm, spray for one hour, stop for two hours, spray time is about 7-9 days. The noble liquid formed by spraying is adsorbed by activated carbon to form gold-bearing carbon, and the poor liquid is recycled, and the gold-loaded carbon is refined by electrolysis or pyrometallurgy to extract the finished gold.
3. Main environmental pollution and ecological impact of heap leaching projects
1. Ecological and environmental impacts. The ecological impact of the heap leaching project is mainly caused by open mining, stripping and heap leaching, destroying and occupying land, destroying the original natural ecosystem and affecting the regional landscape. Sensitive areas may also have an impact on regional biodiversity.
2. Water environment impact. The main water pollution sources of wastewater from heap leaching operations generally include mine pit wastewater, rock drilling wastewater, lean liquid, working yard rainwater, heap leaching waste leaching water, and heap leaching field percolating water. Under normal circumstances, mine pit water, rock drilling wastewater, and rainwater pollutants in the operating field are low, which has little impact on the environment. The impact of this type of project on the water environment is mainly reflected in the basic recycling of wastewater. The impact of the water environment is mainly the leakage of the heap leaching field and the discharge of the heap leaching accident, such as the leaching of the anti-seepage layer of the heap leaching field, or the flooding leading to the heap leaching field. The spray overflows or crosses the stack.
3. Atmospheric environmental impact. The atmospheric pollutants in the heap leaching project mainly include the generation of dust during the mining, transportation and pile-up process and the hydrogen chloride produced during the heap leaching process. Therefore, heap leaching has less impact on the surrounding atmospheric environment.
4. Environmental protection measures for heap leaching projects
1. Selection of heap leaching site: The heap leaching site requires uniform site quality, and should avoid faults, fault fracture zones, karst zones, and natural landslides or debris flow affected areas; the site should have sufficient bearing strength and certain terrain slope, On the natural foundation layer with good anti-seepage performance, the distance between the ground surface of the foundation layer and the groundwater level shall not be less than 1.5m; the site shall conform to the overall planning of the local urban and rural construction and avoid the environmentally sensitive area.
2. Anti-seepage of the heap leaching site: The anti-seepage project of the heap leaching site is both a production requirement and a need for pollution prevention. Generally adopt three-layer anti-seepage structure: the first layer: the granular stone foundation (filling asphalt concrete) with appropriate slope can play the role of stabilizing the foundation. Generally, the fine soil with a thickness of about 20cm is laid on the foundation, and then compacted. The second layer: the mulch with the clear sand in the middle of the pavement: firstly lay three layers of colored strips on top of the fine soil layer, then lay a 0.2mm thick plastic sheet, and then lay a layer of colored strips on the plastic sheet. Cloth, and then paved with 20cm thick fine sand; the third layer: padded anti-seepage film protective layer: the top is laid about 1m thick ore. At the same time, drainage facilities such as drainage ditch, diversion trough and overflow channel should also be treated with anti-seepage treatment.
3. Diversion canal: In order to prevent rainwater runoff from entering the heap leaching field, a diversion channel is arranged around the heap leaching field to intercept the rainwater and divert it to the downstream of the heap leaching field.
4. Flood control pool: According to the maximum rainfall and heap leaching area in the area where the heap leaching site is located, calculate the maximum rainfall collection amount of the heap leaching site, build a flood control pool accordingly, and adopt appropriate anti-seepage measures for the flood control pond.
The environmentally friendly gold extraction agent developed and produced by the company has the following characteristics:
1 Safe and non-toxic, the environmental protection costs of the gold mining plant can be minimized.
2 leaching speed is fast. Generally, the leaching rate of 90% or more can be achieved within 6-8 hours. Therefore, the production efficiency is high, and the leaching operation is convenient, and can be completed at room temperature and in a medium having a pH of 3 to 11.
3 high leaching rate. Hunan Ling Mountain tailings (including Au2.7g / t) and ore (including Au7g / t), cold house paint Taoyuan gold (including Au8g / t), Beijing Wanzhuang gold silver ore (including Au20g / t, with Ag180g / t) The leaching tests carried out by the sulfuric acid slag (including Au0.9g/t) and Zhaoyuan flotation concentrate (including Au70g/t) of Zhongyuan Gold Smelter all illustrate this point.
4 is less sensitive to associated metals. Therefore, the leaching production is less affected by the nature of the ore and the leachate can be recycled.
5 good chemical stability, low drug consumption.
6 The raw materials for the production of pharmaceuticals are sufficient and the price is stable.
The 7 series of immersion gold new drugs are available in a wide range of products, and the best medicinal agents can be selected according to the ore characteristics.
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