Desorption of Cyanide and Copper from High Concentration Salts

The gold- containing waste liquid contains a large amount of cyanide. If these cyanide-containing waste water is not recycled and recycled, it will not only cause great harm to the environment, but also increase the cost of gold extraction. At the same time, due to the complexity of the gold ore composition, other metals react with cyanide into the waste liquid during the immersion process, so that the heavy metal content of the waste liquid is high.

Process technology for recovering cyanide and metal from waste liquids with ion exchange resins has been used for more than 50 years. As early as 1953, walker and Zabban studied the process technology for recovering metals and cyanide from electroplating waste. Shortly thereafter, ion exchange resins began to be used to treat spent liquid after gold extraction. Goldblatt has been studying the process of treating cyanide wastewater with ion exchange resins and proposed a recovery process using strong alkaline ion exchange resins. Later, Tallmadge reported a comparison of several resin handling properties. Since then, research reports on the treatment of cyanide-containing wastewater by ion exchange resins have gradually increased.

In 1985, Cy-tech Canada used ion exchange to treat cyanide-containing wastewater and reached industrial application levels. The cyano complex is adsorbed with an anion exchange resin, and the free cyanide is left in solution for recycling. A carbon leaching plant in Australia used a Vetrokele 912 (V912) adsorption resin produced by the French Institute of Geology to conduct a semi-industrial test on copper and sodium cyanide tailings with a concentration of 85 mg/L and 158 mg/L respectively; Romania Cyanide recovery test was carried out on a cyanide-containing wastewater from a cyanide plant using a strong alkali anion exchange resin. The results showed that cyanide in the waste liquid and metal cyanide complexes such as copper, iron and zinc were adsorbed. It can be recycled after washing. However, this method has not yet been applied on an industrial scale.

The author's research is on the recovery of heavy metals and the recycling of cyanide in gold-rich leaching solutions with high copper content (and a small amount of zinc and iron). Copper in solution mainly in the form of Cu (â… ) exists, since the Cu (â…¡) cyanide in the solution is unstable, decomposition of Cu (â… ) with CN - complexation:

Cu + +CN - =CuCN

CuCN+CN - ==Cu(CN) 2 -

Cu(CN) 2 - +CN - ==Cu(CN) 3 2-

Cu(CN) 3 2- +CN - ==Cu(CN) 4 3-

The reaction of Zn 2+ and Fe 2+ is relatively simple:

Zn 2+ +4CN - ==Zn(CN) 4 2-

Fe 2+ +6CN - ==Fe(CN) 6 4-

It can be seen from the reaction formula that the presence of metallic copper in the solution is complicated, and the existence state of the metal ion complex has a direct influence on the adsorption. Botz and Stevenson, knorre and Griffiths have studied the influence of the ion state in the adsorption process.

Many reports have proposed eluents for a wide variety of anion exchange resins, such as ammonium thiocyanate, thiourea, sodium hydroxide, sodium cyanide, and the like. Studies have shown that 2 mol/L NaNO 3 can effectively desorb the ferricyanide complex from the strongly basic ion exchange resin while desorbing some of the gold compounds. Recent studies have shown that high-concentration salt solutions can selectively desorb copper and ferricyanide complexes; the performance of ion-exchange resins in high-concentration salt solutions has attracted the interest of Australian gold mines and has been studied in detail because it has been reported The local surface water has a high salt concentration and can be supplied.

The author mainly studied the desorption of copper cyanide complex on ion exchange resin with NaCl solution. The desorbed concentrated solution is added to the acid solution to recover HCN and copper at a suitable temperature. Several salts were selected for desorption and the desorption effect was compared. It was found that NaCl had the best desorption effect. NaCl can effectively desorb the copper on the resin, but does not desorb zinc, and achieve the separation of copper and zinc. The NaCl desorbent will not release HCN gas during the desorption process, and will not bring new ions to the ion exchange resin. Impurity ions reduce the complexity of subsequent operations.

First, the test part

(1) Ion exchange resin

This test uses strong alkaline ion exchange resin 201 × 7 (strong base type I resin), with polystyrene framework and quaternary amine functional groups, the performance characteristics of ion exchange resin are shown in Table 1 and Table 2.

Table 1 Characteristics of ion exchange resin (1)

Functional group

Exchange capacity / (mmol·g -1 )

Particle size (0.3~1.2mm)

Moisture /%

Wet true density / (g·ml -1 )

-N + (CH 3 ) 3

≥3.0

≥95%

40~50

1.06~1.11


Table 2 Characteristics of ion exchange resin (2)

Wet density / (g·ml -1 )

Wear rate /%

Maximum temperature / °C

pH range

0.65~0.75

≥95

Hydrogen oxygen type ≤40 chlorine type ≤100

1~14


(2) Test solution

The test uses two solutions, one for the formulation of 0.7g / L NaCN solution, after addition of a cyanide waste one for the beneficiation of gold-containing plants, the components of the solution are shown in Table 2.

Table 2 Static test and analytical determination method

Total cyanide mass concentration / (mg·L -1 )

CN-mass concentration / (mg·L -1 )

Cu mass concentration / (mg · L -1 )

Zn mass concentration / (mg · L -1 )

Fe mass concentration / (mg · L -1 )

pH

2051.8

723.5

1280

125

70

10


Pretreatment of ion exchange resin: The ion exchange resin is treated by a static method, and the ion exchange resin is first rinsed with deionized water until the water is clarified. Add the fully swollen ion exchange resin to 4 times the amount of 1mol/L HCl, soak for 8h, then pour out the acid solution, wash it with deionized water until neutral; then add 4 times the amount of 4% NaOH for 8h, then pour out the lye, use Ion water wash to neutral. Finally, the ion exchange resin is converted to an OH - type ion exchange resin.

The procedure of this test was to stir the solution at room temperature with a magnetic stirrer and a power agitator. Analyze the mass concentration changes of total cyanide, Cu and Zn in the solution and resin exchange process. Different amounts of ion exchange resin and different mass concentrations of NaCl solution were desorbed, and the mass concentration of total cyanide, Cu and Zn in the desorbed solution was determined. The desorbed ion exchange resin was soaked in a NaCl solution and then reconstituted with NaOH.

Determination of total cyanide analysis using GB 7486-84: phosphoric acid and EDTA was added to the solution in a distillation apparatus, the temperature control may be separated by a cryogenic distillation furnace cyanide, absorption with NaOH distilled HCN, and then the amount of silver Method Titration analysis.

Determination of Copper Analysis: Due to the high copper content in solution, so the use of iodine Method; solution taking into account the interference of iron and other impurities, the acid is first added to remove volatile impurities was evaporated, aqueous ammonia and ammonium bifluoride hidden iron, then treated with iodine Volumetric titration.

The analysis of zinc was carried out by atomic absorption method.

(3) Dynamic test

The dynamic test was carried out in 3 glass columns connected in series. The ion exchange resin is placed in an exchange column, and the air bubbles are removed, and the solution is transported to the ion exchange column by a constant current pump, and a certain flow rate is controlled, and the adsorption solution is about 60 times the bed volume; after the adsorption, distilled water is used. The ion exchange resin was washed for 1 h, during which time there was a loss of cyanide. When desorbing, a countercurrent desorption is used, and the volume is 10 times the volume of the bed. The mass concentration of cyanide and metal in the solution is determined during the adsorption and desorption processes. The inner diameter of the ion exchange column was 2.0 cm, the column height was 16.2 cm, and the three columns were charged with 135 ml of an ion exchange resin. Operating conditions are shown in Table 3.

Table 3 Dynamic test operating conditions

Bed diameter / cm

Bed height / cm

Ion exchange resin volume / ml

Adsorption speed / (ml·min -1 )

Countercurrent elution time / min

Desorption rate / (ml·min -1 )

2051.8

723.5

1280

125

70

10


Second, the results and discussion

(1) Selection of desorbent

Based on the affinity of the ion exchange resin for different ions, five solutions were selected for comparison. 5 ml of the ion exchange resin after adsorption was taken and desorbed by the same concentration of KCl, NaNO 3 , MgCl 2 , NaCl and a mixture of NaCl and NaOH for 2 h, and the mass concentration of total cyanide in the desorbed solution was analyzed and analyzed. The results are shown in Fig. 1. It can be seen from the test results that among the selected desorbents, the desorption effect of the NaCl solution is the best, which is related to the affinity of Cl - and the radius of Na + . According to the test results, NaCl was selected as the desorbent.

(2) Effect of solution mass concentration on desorption rate

8 parts of the ion exchange resin after adsorption were taken, 3 ml each; and 150 ml of a NaCl solution having a mass concentration of 40, 60, 80, 100, 120, 140, 160, 180 g/L was prepared. The mass concentration of total cyanide, Cu and Zn in the solution was determined by magnetic stirring for 2 h. The test results are shown in Fig. 2.

It can be seen from the test results that the desorption liquid has a mass concentration of 160 g/L, and the desorption effect of total cyanide and copper is the best. To a certain extent, the higher the mass concentration of the desorbent is, the easier it is to exchange with the ion exchange resin, but the desorption effect is not ideal when the solution mass concentration is too high, resulting in cost increase and high salinity affecting subsequent operations. This trend can be seen in 2. Therefore, comprehensive consideration, the subsequent test selected the desorption liquid mass concentration of 100g / L. High concentrations of NaCl can desorb copper, zinc was however no significant effect, because the affinity of zinc and a strong ion exchange resin, Cl - which can not be desorbed from the ion exchange resin reactive groups.

(3) Effect of temperature on desorption rate

Take 3 ml of the adsorbed ion exchange resin, prepare 150 ml of 100 g/L NaCl solution, and desorb at 25 ° C, 30 ° C, 35 ° C, 40 ° C, 45 ° C for 2 h. The test results are shown in Figure 3.

The OH - type ion exchange resin has poor temperature resistance, and the maximum temperature is 50 ° C, so the test temperature is up to 45 ° C. It can be seen from Fig. 3 that as the temperature increases, the desorption rate of copper and cyanide increases, and as the temperature increases, the ion exchange rate increases significantly, so heating facilitates desorption.

(4) Effect of desorbent volume on desorption rate

As the volume of the desorbent changes, the desorption rate shows some fluctuations, as shown in Figure 4. In contrast, the fluctuation of cyanide is greater, which is related to the presence of free cyanide in the solution; the free cyanide in the solution is determined by analysis, and it is found that the content of free cyanide is higher when the volume of the desorbed solution becomes larger. Decreased, which led to a decrease in the total cyanide desorption rate. It can also be seen from Fig. 4 that when the solution volume is 150 ml, copper and total cyanide have the best desorption point at the same time. Therefore, the desorption solution of 5 times the volume of the ion exchange resin is used as the optimum volume.

(5) Comparison of desorption effects between self-formed test solution and cyanide-containing waste liquid

In order to further study the behavior of free cyanide and complex cyanide in NaCl desorption solution, the effect of self-prepared sodium cyanide test solution and ion exchange resin adsorbed by cyanide-containing waste liquid was compared. Take 2 parts of the adsorbed 201×7 ion exchange resin, one part is to adsorb cyanide-containing waste liquid, and the other part is adsorbed self-prepared sodium cyanide test solution, each part is 5ml; respectively, 100g/L NaCl solution is added, Stirring at a constant rate was determined by sampling analysis at 2, 5, 10, 15, 25, 45, 60, 120, and 140 min, respectively. The test results are shown in Figure 5.

It can be seen from Fig. 5 that the desorption rate of the cyanide-containing waste liquid is obviously inferior to that of the self-prepared test solution, which is consistent with the experimental results of the adsorption theory and the effect of the volume on the total cyanide desorption rate. CN - has less affinity with ion exchange resins than metal complex cyanide, and its desorption is relatively easy and fast. Most of the cyanide-containing waste liquid is complex cyanide ion, and the desorption rate of the ion exchange resin adsorbing the cyanide-containing waste liquid reaches 30% in a short time. At this time, the mass concentration of free cyanide in the solution is determined and analyzed, and the free is proved. The desorption rate of cyanide is indeed very consistent with the self-formulated test solution. After 20 min, the desorption rate of the ion exchange resin slowly rises, at this time the desorption of complex cyanide ions, because their ionic radius and spatial structure pose certain obstacles to the ion exchange process.

(6) Dynamic test

The constant flow pump control speed is 25r/min, and the flow rate is 25ml/min. When the volume of the solution flowing through the resin layer was about 10 L, the ion exchange resin reached saturation. The mass concentration of total cyanide and copper ions in the effluent was measured at different time points, and the breakthrough point of the ion exchange resin was determined as the mass concentration of the effluent was 5% of the mass concentration of the original liquid ( According to the measured data, the breakthrough point of total cyanide is 800ml, the breakthrough point of copper is 3000ml, the breakthrough point of total cyanide is more than that of copper, and the saturation point of total cyanide is also Before copper. According to the material balance, the mass concentration of total cyanide and copper in the solution before and after the adsorption was determined by analysis. The saturation exchange capacity of the ion exchange resin to the total cyanide was 35.7 mg/ml wet resin , and the copper was 33.4 mg/ml wet resin . The test results are shown in Figures 6 and 7.

The molar ratios of cyanide and copper in the solution were calculated separately, 3.9 before adsorption, 6.3 after adsorption, and cyan and copper ratio of 2.5 on the ion exchange resin. The ion exchange resin was simultaneously loaded with a complex of zinc and iron by the mass concentration of zinc and iron, indicating that the copper on the ion exchange resin is mainly in the form of Cu(CN) 2 - because of Cu ( CN) 4 3- requires 3 exchange groups for exchange and 4th CN - unstable, Cu(CN) 3 2- requires 2 exchange groups, while Cu(CN) 2 - only requires one exchange group the affinity group and a linear structure, and an ion exchange resin strongest, most easy exchange, the structure of the copper cyanide complex being changed exchange process. A similar situation has occurred with silver and iron, which has also been described in the relevant literature.

After a sufficient amount of eluent, the total cyanide and copper supported on the ion exchange resin were substantially rinsed, and the mass concentration of zinc in the solution was analyzed, and the highest value was 9 mg/L, and the average mass concentration was 3.29 mg/L. This phenomenon allows the NaCl solution to effectively separate copper and zinc. Since the total content of zinc in the solution is not high, when zinc is accumulated to a certain extent, zinc is eluted by pickling.

It can be seen from the elution curve that the mass concentration of total cyanide reaches 4g/L, the mass concentration of copper reaches about 3g/L, and the leaching rate reaches over 90%.

Third, the conclusion

The results of this study show that the high-concentration NaCl solution is used as a cyanide desorbent to realize the cyanide-free desorption process of the ion exchange resin, which reduces the operational risk in the desorption test and also makes the regeneration of the ion exchange resin simple. Since NaCl can't desorb zinc, it just achieves the separation of copper and zinc. This is because Zn(CN) 4 2- and resin have high affinity, Cl - in high concentration salt solution is not analyzed and environmentally friendly. The zinc cyanide complex competes for the active site on the resin.

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