Study on the extraction of cadmium and cotton from copper and cadmium

There is no separate deposit cadmium, lead and zinc ore often symbiotic, cadmium from 0.01% to 0.07%, while most of the zinc concentrate into the dressing. About 95% of the cadmium is recovered from the zinc smelting process. The raw materials for smelting mainly include copper cadmium slag in the wet cleaning process, zinc-depleted cadmium-rich blue powder, copper-lead-zinc smelting soot, and leaching of the zinc-white factory. Slag, etc., in which the content of cadmium fluctuates greatly. At present, the comprehensive recovery rate of cadmium in China's zinc smelting process is about 80%, and the average cadmium content in zinc concentrate is about 0.1% to 0.2%. The cadmium grade is low, and the enrichment and extraction is difficult. The cadmium grade in a company's zinc concentrate is only about 0.15%. In the traditional wet zinc smelting-leaching-purification-electrowinning process, a considerable part of cadmium is dispersed, resulting in reduced recovery and environmental pollution. At present, the company sells sponge cadmium as a product, and the produced sponge cadmium contains only 50% to 60% of cadmium, which cannot meet the requirements of vacuum refining for cadmium. Therefore, this paper is aimed at the current cadmium production status of the company. The extraction process of cadmium cotton was optimized.

First, experimental materials and reagents

The test raw materials are copper cadmium slag obtained by purifying the liquid in the immersion liquid of Chihong Company. The copper cadmium slag is vacuum dried at 80 ° C for 36 hours, the weight is constant, the water content is 19.82%, and the dried samples are sent to analyze the main elements such as Zn, Cu and Cd. The result was (%): Zn 23.16, Cu 7.76, Cd 17.95, Co 0.02, Fe 0.19, Sb 0.074. EDS analysis showed starting material, 98% of the copper present in the elemental metallic form, there is gathered around zinc sulfate, metallic zinc, without high enriched alone, most of cadmium in the form of cadmium metal, with a small amount of sulfuric ACID cadmium.

The replacement zinc powder is blown zinc powder, no agglomeration, no impurities, total zinc >98%, active zinc component >92%, zinc powder particle size -0.251~+0.147mm; other reagents have 98% concentrated sulfuric acid, analytical purity Zinc oxide, manganese dioxide and lime; main equipment: 500mL burning, LabTech EH35A plus automatic temperature control heater, IKARW20digital digital mixer, thermometer, analytical balance, vacuum pump, vacuum drying oven, triangle funnel, Lange BT100-1J Constant flow pump, PHS-3D pH meter and 6503 high temperature composite electrode.

Second, the test principle process

The experimental principle flow is shown in Figure 1. The process produces high-purity cadmium by smelting and vacuum refining of the produced cadmium. Through the combination of fire method and wet method, cadmium is replaced by rectification instead of electrolytic refining cadmium, and the existing process is modified to prepare high-grade cadmium cotton. The cadmium grade is increased from the current 50% to 60% to over 80%. After continuous smelting, the continuous rectification can be carried out, the intermittent smelting process and electrowinning can be eliminated, the continuous operation of refined cadmium production can be realized, the working environment of workers can be optimized, the automation level can be improved, the cadmium environmental pollution can be reduced, and the cadmium extraction closed loop can be realized. zero emission.

Figure 1 Principle process

Third, the results and discussion

(1) Copper cadmium slag leaching

1, the impact of the endpoint pH

Leaching experimental conditions: liquid-solid ratio 6:1, time 6h, temperature 80-85 ° C, initial acid concentration 10 ~ 15g / L, process control solution pH = 1.5 ~ 1.8, after 5.5h, adjust the pulp end pH, filter, The leaching residue is washed with an acid having a pH of 4.5 to 5.0. The results are shown in Table 1.

Table 1 Effect of endpoint pH

Table 1 shows that when pH=5.22, the leaching rate of cadmium is 98.31%, and the solution contains 25.25 g/L of Cd; when the pH of the end point is 5.74, the zinc content of slag is increased to 7.64%. When the zinc content of the leaching residue is high, it will not be utilized. After the subsequent copper slag fire treatment, while the pH is increased, the hydrolysis tendency of zinc is increased, so the pH of the leaching end point should not exceed 5.4.

2, the impact of leaching time

Leaching experimental conditions: liquid-solid ratio 6:1, temperature 80-85 ° C, initial acid concentration 10-15 g / L, process control solution pH = 1.5 ~ 1.8, 0.5 h before each end of leaching, adjust the pH of the solution to 2.0 ~ 2.5, stirring for 0.5 h, the leaching residue was washed with an acid having a pH of 4.5 to 5.0. The experimental results are shown in Table 2.

Table 2 Effect of leaching time

The results show that with the prolongation of time, the zinc content of the slag is gradually reduced, but the experimental results of several groups are not changed greatly, the leaching rate of cadmium is more than 99%, the cadmium contains less than 0.65%, and the slag contains more than 33.5% of copper. For 2h, the experimental results have reached the requirements of leaching. The reason is that the experiment is carried out with 500 mL of burning, and the experimental temperature is stable and the stirring is sufficient. However, the production should be controlled for 4 to 6 hours to complete the reaction. The zinc content of the four experimental data listed in Table 2 is relatively low. This is because the end point pH is low, the end point pH is 4.0 to 4.5, but the copper content is slightly higher, and the composition of the solution is shown in Table 3.

Table 3 Filtrate at different leaching times

(2) Two-stage countercurrent leaching of leaching slag

In order to control the dispersion of cadmium as much as possible, improve the recovery of zinc and the grade of copper slag, a section of leaching slag (a piece of enlarged experimental slag, containing 6.2.20% of Zn, 24.27% of Cu, 0.49% of Cd, and 51.4% of water) was carried out. Countercurrent leaching. Two-stage leaching experimental conditions: liquid-solid ratio 5:1, temperature 75-80 ° C, pH control 2.0=2.5, time 3 h.

The results show that the second stage leaching slag contains Cu 29.86%, Cd 0.26%, and the filtrate contains Zn 3.9g/L. The filtrate is returned to the copper cadmium slag for a leaching process, and the filter slag is sent to the copper smelter for the copper method.

(III) Selective enrichment of sponge cadmium

Sponge cadmium was produced by amplifying the experimental filtrate with a zinc powder replacement. Before the replacement, the solution contained Cd 24.50g/L. Considering the total volume of the liquid before replacement, the experiment was carried out in 500mL of burning. The volume of the experimental solution was 300mL, the temperature was 50-55°C, the reaction time was 45-60min, and the amount of zinc powder was in solution. 80% of the theoretical amount of cadmium, zinc powder added time 10min. Sponge cadmium filtration washing, vacuum drying. The experimental data is shown in Table 4.

Table 4 Results of a zinc powder replacement test

Table 4 shows that when the zinc content of the liquid before displacement is 30-40g/L, the cadmium content of the primary replacement sponge cadmium can reach more than 85%, the zinc content of the sponge cadmium is less than 2.5%, but the zinc content of the liquid before the replacement is 80-130g/ At L, the cadmium content of the primary replacement sponge cadmium product was reduced to 78.42%, and the zinc content was increased to 3.25%.

After the replacement, the solution still has 3~5g/L cadmium, and the residual cadmium is replaced by zinc powder. The cadmium slag is returned to a section of copper cadmium slag, and the filtrate is returned to the zinc smelting neutral leaching after removing the cobalt .

(4) Sponge cadmium liquid leaching

Because the liquid before the replacement is high in zinc but low in cadmium, the ratio of zinc to cadmium is (4-5):1, so the sponge cadmium obtained by one replacement is not only high in zinc, but also has low cadmium grade and some other impurities. Can not meet the requirements of the crude cadmium refining process (cadmium grade is greater than 80%, Zn is less than 4%), and it is not easy to pressurize the cluster, so the sponge cadmium needs to be leached and removed.

Due to the small amount of sponge cadmium produced by the laboratory, the raw materials used in the sponge cadmium leaching experiment were provided by Chihong. The sponge cadmium component was (%): Cd 53.53, Zn 10.46, Cu 0.14, Fe 0.091.

Experimental conditions and operation of cadmium leaching solution of sponge cadmium: The sponge cadmium after natural oxidation in the open air is leached with high acid, the initial concentration of sulfuric acid is 400-500g/L, the liquid-solid ratio is 1:1, the temperature is 90-95°C, and the experiment uses mechanical stirring. And pass the appropriate amount of air, react for more than 3h, according to the amount of residual acid and Cu, add fresh sponge cadmium to reduce acid and remove copper, then dilute to liquid to solid ratio of 3:1 (ratio with raw materials), and adjust the acidity with lime slurry to About 4.0, add potassium permanganate to remove iron , add iron milk after adding iron to adjust the acidity to 5.0 ~ 5.2, filter, filter residue back to copper cadmium leaching, the filtrate is used for the next step of zinc powder secondary replacement. Analytical determination of filter residue containing Cd 2.94%, Zn 2.48%, solution containing Zn 25g / L, Cd 176g / L.

(5) Study on extraction of crude cadmium

The liquid leaching solution was replaced by zinc powder for the second generation of cadmium. The experimental conditions were as follows: Cd 176g/L and Zn 25g/L before the replacement. Considering the total volume of the liquid before replacement, the experiment was carried out in 500mL. The volume of the solution is 300 mL, the temperature is 50-55 ° C, the reaction time is 0.5-1.0 h, the amount of zinc powder is 1.1%-1.2% of the theoretical amount of cadmium in the solution, and the zinc powder is slowly added, and the addition time is 10 min. Cadmium cotton is naturally filtered and vacuum dried. The product contains 95.12% cadmium and 2.17% Zn.

The secondary replacement cadmium has a higher purity, the cadmium cotton contains more than 80% cadmium, and the zinc content is less than 4%, which can meet the requirements of the next step of cadmium cotton refining and vacuum refining.

Fourth, the conclusion

The selective leaching of copper cadmium slag, the selective enrichment of sponge cadmium and the optimization conditions of cadmium cotton extraction process were determined. After the process optimization, the cadmium cotton contains more than 80% cadmium and less than 4% zinc, which can meet the requirements of the subsequent cadmium vacuum refining.

HPMC

Hydroxypropyl methyl cellulose is a kind of non-ionic cellulose ether which is made from natural macromolecular material cellulose through a series of chemical processing. They are a white powder that swells into a clear or slightly turbid colloidal solution in cold water. It has the characteristics of thickening, adhesion, dispersion, emulsification, film forming, suspension, adsorption, gel, surface activity, water retention and colloid protection. Hydroxypropyl methyl cellulose and methyl cellulose can be used in building materials, coating industry, synthetic Resin, ceramic industry, medicine, textile, agriculture, daily chemical and other industries.
Chemical equation:
Hydroxypropylmethylcellulose (HPMC) [C6H7O2 (OH) 3-m-n (OCH3) m (OCH2CH (OH) CH3) n] x
Application field:
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