Currently, cyanidation is still the main method of extracting gold . With the continuous development of the gold industry, the emissions of cyanide-containing slurry in mines are also increasing. According to statistics, China's gold production enterprises emit 1.2×10 8 m ³ of cyanide-containing wastewater and 6.0×10 7 tons of cyanide-containing tailings. The tailings slurry contains a large amount of cyanide, and cyanide is highly toxic. Direct discharge or direct return to the mine filling is seriously polluting the surrounding environment, especially water resources, causing serious damage to humans, animals and plants and the entire ecosystem. It must be cyanated before discharge. There are many methods for treating cyanide-containing wastewater, such as ozone oxidation, alkaline chlorination, ion exchange adsorption, and biological methods. Most of the treatment of sewage from cyanide plant in gold mine adopts alkali chlorination method, which is mainly used for the whole mud cyanidation gold extraction process, but there are problems such as high treatment cost and easy secondary pollution to the environment. In this experiment, the cyanide-containing tailings slurry was used in the process of flowing to the tailings pond, and the cyanide was adsorbed by the 201×7 strong basic styrene anion exchange resin which was cheap and easy to obtain, so as to meet the discharge standard.

First, the test part

(1) Basic principle of 201×7 resin and cyanide

The 201×7 resin is formed by introducing a quaternary amine group [R-(CH ₃ ) ₃ OH] onto a polystyrene polymer skeleton having a degree of crosslinking of 7, and the quaternary amine group is a strongly basic group, and therefore, the resin Very strong alkaline. The 201×7 resin can be converted into a C1 ^- type to react with the cyanide slurry.

Cyanide gold extraction plant tailings slurry containing cyanide CN ^-, SCN ^-, and anions of various metal cyanide, such as _{^{Zn (CN) 4 2 -,}} Cu (CN) 4 2 -), Fe (CN) 6 4 ^- ), Pb(CN) ₄ ^{2 -} , Ni(CN) ₄ ^{2 -} , Au(CN) ₂ ^- , Ag(CN) ₂ ^-, etc., but free cyanide ions can only be adsorbed by the resin when converted into complex anions. The ion exchange method utilizes an ion exchange resin to adsorb cyanide in the form of an anion in the wastewater, that is, various cyanide complexes.

The reaction that occurs when the cyanide-containing tailings slurry flows through the ion exchange resin layer is as follows:

(2) Test methods

1. Pretreatment of ion exchange resin

Take an appropriate amount of resin in a beaker, add 4 times the amount of deionized water for 16h, rinse to clarification, then add 4 times the amount of 1mol / L sodium hydroxide solution, stir for 4h, then lye, and wash with deionized water to the middle Sex, add 4 times the amount of 1mol / L hydrochloric acid solution, stir for 4h, then pour out the acid, then wash with deionized water to neutral, the resin is converted to chlorine type, spare.

2, static adsorption

Take a certain amount of wet resin that has been converted into chlorine type in a beaker, add a certain amount of cyanide-containing tailings slurry, stir for a certain period of time, sample and analyze the mass concentration of cyanide in the adsorption solution, and calculate the adsorption amount (Q) and adsorption by the following formula. Rate (E):

Where: ρ. - initial mass concentration of cyanide in solution, mg / L; ρ - equilibrium mass concentration of cyanide in solution, mg / L; V - solution volume, mL; Vr - resin volume, mL.

Second, the results and discussion

(I) Determination of saturated adsorption capacity of ion exchange resin

Take 3.3 mL of 201×7 resin, add 100 mL of tailings slurry (cyanide mass concentration 765 mg/L), and separate the resin after a certain period of time to analyze the mass concentration of cyanide in the slurry. The results are shown in Table 1.

Table 1 Results of measurement of resin saturated adsorption capacity

It can be seen from Table 1 that the reaction was carried out for 60 min, and the ion exchange resin was adsorbed and saturated. It was calculated that the saturated adsorption capacity of the resin was about 21.41 mg/mL wet resin.

(2) Effect of adsorption time on cyanide adsorption

The 201×7 resin was mixed with the tailings slurry at a ratio of 1:30. The mass concentration of cyanide in the tailings slurry was 255.1 mg/L. After stirring for a certain period of time, the resin was separated and the mass concentration of cyanide in the slurry was sampled and analyzed. The adsorption rate is calculated according to the formula. The effect of adsorption time on cyanide adsorption rate is shown in Figure 1. It can be seen that with the extension of adsorption time, the adsorption rate of cyanide resin increases gradually; adsorption rate reaches 90.91% after adsorption for 10min, cyanide mass concentration in tailings slurry drops below 50mg/L; adsorption rate reaches 97.45 after adsorption for 20min %, the mass concentration of cyanide in the tailings slurry is reduced to below 20 mg/L; after that, the adsorption time is prolonged and the adsorption rate does not change much. Therefore, the resin adsorption time is preferably 30 minutes.

Figure 1 Effect of adsorption time on cyanide adsorption

(3) Effect of resin dosage on cyanide adsorption

Different amounts of 201×7 resin were mixed with the tailings slurry. The mass concentration of cyanide in the tailings slurry was 255.1 mg/L. After stirring for 10 minutes, the resin was separated and the mass concentration of cyanide in the slurry was analyzed. The adsorption rate was calculated according to the formula, and the effect of the amount of resin added on the adsorption rate of cyanide was investigated. The result is shown in Figure 2.

Figure 2 Effect of resin dosage on cyanide adsorption

It can be seen from Fig. 2 that as the amount of resin increases (the volume ratio of tailings slurry to resin decreases), the adsorption amount of cyanide by resin increases gradually; when the volume ratio of tailings slurry to resin is 20:1, the resin adsorption rate is 94.98%. When the volume ratio of tailings slurry to resin is 40:1, the adsorption rate of resin decreases to 81.81%; the volume ratio of tailings slurry to resin is less than or equal to 40:1, and the mass concentration of cyanide in the slurry after adsorption is less than 50mg/L. The larger the amount of resin added, the more reactive groups of the resin and the greater the amount of adsorption. Considering the cost, it is more appropriate to determine the volume ratio of the slurry to the resin by 40:1. However, it has also been observed that even if the amount of resin is large enough, the cyanide in the tailings slurry cannot be adsorbed 100%.

(4) Effect of slurry concentration on cyanide adsorption

201×7 resin was contacted with tailings slurry with different cyanide mass concentration. The volume ratio of tailings slurry to resin was 40:1. After stirring for 10 minutes, the resin was separated and the mass concentration of cyanide in the slurry was analyzed. The result is shown in Figure 3.

Figure 3 Effect of slurry concentration on cyanide adsorption

It can be seen from Fig. 3 that the lower the cyanide mass concentration, the better the adsorption effect. When the mass concentration of cyanide is below 255.1 mg/L, the adsorption rate reaches the maximum, and the mass concentration of cyanide in the slurry after adsorption falls below 50 mg/L, which meets the requirements. The process time of the cyanide-containing tailings slurry flowing to the tailings pond is very short, and the resin adsorption capacity is limited in a short time, which does not reach the saturated adsorption adsorption. Therefore, the method is not applicable to the high-quality concentration cyanide-containing tailings slurry.

Third, the conclusion

(I) The test results show that the 201×7 anion exchange resin has a good effect in treating low-concentration cyanide-containing tailings slurry in a short time, but it is not suitable for treating high-quality cyanide-containing tailings slurry.

(2) When the mass concentration of cyanide is 255.1mg/L, the volume ratio of tailings slurry to resin is 40:1, adsorption is about 10min, and the concentration of cyanide in the solution can reach 50mg/L or less, reaching the discharge standard.

(3) For low-concentration cyanide-containing tailings slurry, the cyanide in the 201×7 ion exchange resin can be adsorbed and discharged to the tailings pond.