According to the existing practical experience, once the scale is generated at the portion where the scale is not desired, the following descaling method can be adopted.
First, the pile surface mine scale, generally use mechanical or artificial means, loosen 0.3 ~ 0.5m thick skin, use more foreign tiller with 0.5m long rake, some domestic mines such as Henan old Bay gold mine heap leaching field using The manual turning method makes the hard surface of the scale formed into debris to ensure uniform seepage of the immersion liquid.
Second, the nozzle fouling, the nozzle can be removed in the intermittent time of spraying, washed with dilute hydrochloric acid or nitric acid, after the exhaustion is exhausted, then wash off the residual acid with water, and put it on standby.
3. The blade of the pump and the inner wall of the pump are fouled. Only disassembled and descaled by chemical or mechanical means. In order to maintain production, a spare pump should be replaced at any time.
Fourth, the inner wall of the pipe is fouled. If it is a steel pipe, the problem is more troublesome. For example, a plastic pipe, especially a polyethylene pipe, can be tapped to allow the scale attached to the pipe wall to peel off automatically, and then rinsed with water. Experience has shown that PVC pipes are not as good as polyethylene pipes in this respect.
5. The fouling in the activated carbon bed is mostly prevented by fluidized adsorption and desorption to reduce scale. The scaled activated carbon is usually washed with dilute hydrochloric acid or nitric acid to remove calcium carbonate scale on the carbon.
6. When uranium ore heap leaching occurs, the hydrolysis and precipitation of metal ions often occur at the bottom of the heap. It should be based on prevention, strictly control the pH value of the medium, and closely observe the fluctuation of the dielectric potential. The potential in the leachate is gradually increased from low, or kept at a constant value. Once the potential of the leachate suddenly drops sharply, a large amount of hydrolysis and precipitation of metal ions must occur at the bottom of the heap. The degree of precipitation fouling is closely related to the decrease of the potential value, and the more the potential drops, the more serious the precipitation scale. Because the potential in the leachate characterizes the ratio of Fe 3 + ∕Fe 2 + in the solution. The decrease in potential indicates that the concentration of Fe 3 + in the solution is lowered, and the ratio of Fe 3 + ∕Fe 2 + is small. Fe 3 + at this time can not be reduced to Fe 2 +, but only a hydrolysis precipitation.
Whether the pH of the leachate can be used as a criterion for precipitation scale at the bottom of the heap is generally not acceptable. Because this hydrolysis occurs locally and slowly, rather than hydrolyzing in a certain section; in addition, the hydrolysis reaction of metal ions is as follows:
Fe 3 + +3H 2 O 
Fe(OH) 3 +3H +
Hydrolysis results in H + to compensate for the lack of acidity in the solution. Therefore, the pH value in the solution is not as clear as the potential in the solution, indicating the hydrolysis and precipitation process of Fe 3 + . Of course, when the catastrophic whole ore heap or heap has metal ions hydrolyzed, the pH value can also be used as a criterion.
Once the metal ion hydrolysis and precipitation occurs at the bottom of the heap, the spray intensity should be temporarily increased to increase the acidity to dissolve the descaling.
Seventh, since the anti-scaling agent can make the scale soft and loose, and can disperse the crystal nucleus of the scale within a certain period of time, it also has the performance of descaling. In fact, most of the methods used in heap leaching. U.S. Carlin gold, using phosphate solution (11%), only 14 days because dirt clogging causes the return to the original flow conduit within said to 14 days, with this method, detergent 50 ~75t. The Dulanski mine uses polyacrylate (3×10 -5 ), and the Zoeterman mine uses 0.5 × 10 -5 of malic anhydride to make the surface of the heap that has been scaled into a white hard shell, from February to March. After that, the original color of the ore is restored, and the seepage velocity of the ore heap is restored to the desired level.
The experience of most gold mine leaching sites in the United States has proven that long-term use of anti-fouling agents, and the addition of appropriate sites, the problem of fouling in heap leaching can be avoided.
Chen Mingyang done some other test for detergency test method is: beaker supersaturated Ca 2 + and CO 3 2 -, CaCO 3 to produce a heavy white precipitate was then allowed to stand for several days, the entire solution was decanted and the precipitate, so that The beaker is naturally dried. A thin, hard layer of white on the wall of the beaker and the bottom of the cup. No calcium added to the beaker of antifoulant solution, 15H stationary, the sample solution is measured Ca 2 + concentration. The results are shown in the table below.
Comparison of the anti-scaling effects of several anti-fouling agents
Test number | Time to form scale (d) | Anti-fouling agent | Dissolution time (h) | Calcium ion concentration in solution (mg∕L) | |
species | Concentration (×10 -6 ) | ||||
1 | 10 | FG601 | 10 | 15 | 53.12 |
2 | 10 | FG602 | 10 | 15 | 28.19 |
3 | 10 | FG603 | 10 | 15 | 56.22 |
4 | 10 | FG605 | 10 | 15 | 52.30 |
From the beginning, the industrial test showed white calcium carbonate scale in the pipeline, pump, resin layer in the adsorption tower, etc., after pickling, after 3 months, the injection well increased the injection pressure, and the pumping volume of the pumping well Still falling, indicating that sedimentation blockage occurred in the ore layer, resulting in reduced permeability of the ore layer. This situation is 20 months. The 601 anti-fouling agent was added on July 13, 1991, until August 25. There are two stages, from July 13 to 31, the amount of addition is 2 × 10 -6 , August 1 to 25, the amount of addition is 8 × 10 -6 . 1 and 2 are added before and after 601 antifoulant daily Ca 2 + CO 3 2 and treating the withdrawn liquid - an analysis result.
Fig.1 Change of CO 3 2 - concentration in leachate before and after adding anti-fouling agent
Before and after adding antifoulant FIG leachate Ca 2 + concentration change
It is seen from FIG. 1 and FIG. 2, after the addition of anti-fouling agent, extracting fluid and Ca 2 + CO 3 2 - concentration increased significantly, once the addition was stopped antifoulant, Ca 2 +, and CO 3 2 - concentration Reduced again.
It should also be noted that in the case of fouling, in order to descale, a high concentration of anti-fouling agent must be added, as in the aforementioned Carlin Gold Mine. However, due to the lack of experience of the experimenter, only the amount (2-8) × 10 -6 which is usually insufficient is added.
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