Leaching procedure and work system

The heap must be washed before it is sprayed. Its purpose is to wash away the impurities mixed in the pile-up process, especially to remove some harmful impurities, to create conditions for spray leaching. The gold heap leaching, required alkaline water (milk of lime or caustic soda to the washing water adjusted to pH 12 or more), dried heap, the heap has been to wash the pH of the effluent water stabilizes at 9.0 or more, to allow a Sodium cyanide is dissolved to spray leaching. Otherwise, not only the consumption of sodium cyanide is large, but also the cyanide formation of hydrogen cyanide may endanger the health of the operator. The same is true for uranium ore heap leaching. Washing the fine mud with washing water and dissolving a part of water-soluble impurities is beneficial to leaching.

The heap washing process of Shuangwang Gold Mine is taken as an example to illustrate the washing process and its importance. Shuangwang gold ore is gold albite and breccia based oxide ores, the gold is a natural gold, gold-bearing minerals as pyrite and minor amounts of limonite ore, collected from the test surface mine ore. According to the geological report, the rock is mainly albite, and it is concluded that the ore is alkaline. On the spot, 10,000 tons of heap leaching, but encountered a lot of trouble. On the first day, the mine was washed with water for 10 hours, and the effluent from the ore heap (the moisture content of the heap was determined to be 8% on this day). After 6 hours of washing, the effluent water changed from turbid to clear, indicating that the pile had been washed out. Fine mud and debris mixed in. Thereafter, the heap was washed with alkaline water having a pH of 12, and it was estimated that the pH of the heap reached 9 or more after 2 days of washing, but the pH of the effluent from the heap was still 6.5 after 5 days of continuous washing. At this time, the effluent water of the washing ore heap is clear and transparent, and a large amount of white precipitate is generated by adding caustic soda; a small amount of clear and transparent water is heated and boiled, and a large amount of white precipitate also appears. The resulting precipitate was filtered, hydrochloric acid was added dropwise, and the precipitate was dissolved immediately. The test confirmed that the ore is not alkaline, but acidic. After the alkaline water passes through the ore heap, the alkali is neutralized, so the water flowing out is also acidic, which contains a large amount of HCO ₃ ^- and soluble calcium. Adding caustic soda to it, the following reactions occur:

HCO ₃ ^- +OH ^- CO ₃ ² ^- +H ₂ O

Ca ² ⁺ +CO ₃ ² ^- CaCO ₃ â†“

When heated and boiled, the reaction is as follows:

Ca(HCO ₃ ) ₂ CaCO ₃ â†“+CO ₂ â†‘+H ₂ O

After finding the cause, the heap was washed with a 2 mol/L alkaline solution, and by the ninth day, the pH reached 8.4. At this time, the effluent water analysis was carried out to confirm that the calcium content was small. Since the ore contained humic acid, the effluent water changed from clear to light yellow, showing a large amount of foam, and the pH value rose very slowly. Until the twelfth day, the pH of the effluent from the heap reached 9. Mine stack after such washing, the elimination of the heap of material and the alkali consumption Ca ² ^+, and sodium hydroxide is used in leaching for the protection of a base, thus fouling does not occur, and low consumption of cyanide.

The heap washing must be patient and not impatient. In dry and water-deficient areas, insufficient water wash is often a problem, but in any case, the heap must be washed before the spray leaching.

Heap leaching in Maquan gold mine in Gansu, the first one has a longer washing time and lasts for 40 days. The reason is that the washing liquid is too alkaline.

The effluent from the washing ore heap in the gold ore heap leaching should not be recycled until the pH value is less than 8.4. Otherwise, the alkali or lime consumption is too large, and the surface of the nozzle, pipe fittings and heap will be scaled. After the effluent pH reaches 8.4, it can be recycled. The more thorough the heap washing, the better the subsequent leaching.

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