Huang Kaiguo Wang Qiufeng

With the decreasing of mineral resources and the impact of waste residue on environmental pollution, the comprehensive utilization of renewable resources has become an urgent problem to be solved. In China, there are hundreds of thousands of tons of zinc leaching slag containing 300g/t of silver per year. A plant ^[1] treated a part of the slag by flotation, and recovered a part of the silver. However, due to its poor prescription, the butyl ammonium black medicine (BN) was used for flotation in the acidic zinc slag slurry. The recovery rate of silver is not high, only 60% to 65%. A unit ^[2] proposed a scheme for flotation of silver from acid zinc leaching slag with H ₂ SO ₄ llkg/t, Na ₂ S 1.8 kg/t, and BN 0.64 kg/t. Silver concentrate contains 3535.7 g/t of silver. The silver recovery rate is 60.05%. In view of the above problems, this paper has improved the flotation prescription and achieved obvious results.

First, the basis for improvement

It is well known that from the perspective of flotation, sulfide ore is easier to float than oxidized ore. For zinc dross, the silver oxide and the oxidized silver sulfide are not easily floated, resulting in a lower recovery rate of the entire silver. By reaction formula ^[3]

1/2Ag ₂ 0(aq)+1/2H ₂ 0+OH ^- =Ag (OH) ₂ ^-

It can be seen that Ag ₂ 0 can exist in the Ag (OH) ₂ ^- state, and after adding Na ₂ S, the precipitation flotation has similarity to the precipitation flotation of Ag ⁺ . Therefore, it is proposed to improve the recovery rate of silver in zinc dross from the results of the Ag ⁺ sulfide precipitation flotation test to improve the zinc dross flotation prescription.

(1) Ag ⁺ sulfide precipitation flotation

With AgNO ₃ solution 0.01mol / L, each sample 1mL, add 40mL flotation tank, the initial concentration of Ag ⁺ is 2.5 × 10 ^-4 mol / L, flotation of Ag ⁺ according to the flow shown in Figure 1.

The flotation results of Ag ⁺ sulfide precipitation (see Figure 2) show that the proper addition of Na ₂ S has the best effect on the flotation of Ag ⁺ . No or little effect is not good, excess is not needed; it also shows that the use of Ding xanthate (BX) as a collector is better than butyl ammonium black drug (BN).

(II) Effect of pH on Ag ⁺ precipitation flotation

Figure 3 shows the effect of pH on Ag ⁺ precipitation flotation. It is obvious that in acidic or strongly alkaline media, the flotation effect of Ag ⁺ is not good, the neutral medium works best, and further shows that BX is better than BN.

(2) Mixed use of collectors

Figure 4 shows the flotation results of BX and BN mixed in different proportions. It shows that the mixed ratio of the two is better than the single use, but m _HX :m _HN is preferably 6:4.

(4) Comparison of foaming agent RB and ether EA

RB is made from chemical by-products and is inexpensive. The results of the comparison with EA (see Figure 5) show that the amount of RB is 40% lower, the recovery rate of silver is higher than that of EA, and RB is superior to EA.

Second, improved new prescriptions and test results

Based on the above Ag ⁺ sulfide precipitation flotation test, the zinc leaching residue of a plant was subjected to flotation recovery of silver. The multi-element analysis of the sample and the phase analysis of silver were shown in Tables 1 and 2. It can be seen that there is a high content of silver in the zinc leaching residue. In addition to silver sulfide, silver is also silver oxide and other forms of silver. The addition of Na ₂ S allows the conversion of silver oxide and silver oxidized silver sulfide to silver sulfide.

Table 1 Multi-element analysis results of samples ω /%

Table 2 Results of phase analysis of silver in the sample

The design consists of Na ₂ S as a regulator, BX as a collector and auxiliary collector XY mixed, RB is a new prescription of foaming agent, and a closed-circuit test of rough selection, one selection and one sweep is carried out. The flow chart of the closed circuit test is shown in Figure 6. A silver concentrate with a silver content of 4369.73 g/t and a recovery rate of 79.44% was obtained (see Table 3), and the grade and recovery rate were significantly improved, and the silver in the zinc slag was successfully recovered.

Table 3 Closed circuit test results

The phase analysis results of silver concentrate are shown in Table 4. Compared with Table 2, it can be seen that silver oxide accounts for 8.45%, silver sulfide accounts for 79.59%, silver oxide has 1.96% silver oxide, and silver sulfide accounts for 1.96%. 94.21%, indicating that silver is basically recovered in the form of Ag ₂ S.

Table 4 Silver mineral phase analysis results

The new prescription used, adding Na ₂ S, on the one hand vulcanized the non-sulfurized silver in the zinc slag, is conducive to the recovery of silver; on the other hand, adjusting the pH of the slurry to a suitable pH of 6 to 6.5, avoiding in the acid zinc slag slurry Flotation corrosion of equipment. Adding the collector BX which is better than BN, and adding the auxiliary collector XY, strengthens the collection of silver in the zinc slag. Adding RB instead of diethyl ether, the amount is small, the foaming performance is strong and cheap.

Third, the conclusion

In this study, flotation tests based on Ag ⁺ sulfide precipitation, improve prescription from silver zinc slag flotation, to Na ₂ S as modifier, silver sulfide, zinc sulfide slag Africa, the floating mineral slurry to adjust the pH; with an auxiliary catch XY The agent is combined with BX to strengthen the collection of silver in the zinc slag; the butyl substituted by the RB with strong foaming performance, low price and low dosage is used to float from the zinc leaching residue containing 498.10g/t of silver. Silver, a silver concentrate having a silver content of 4369.73 g/t and a silver recovery of 79.44% was obtained. In order to float silver from the “disused” zinc leaching slag, it provides a new prescription, which is of great industrial value and economic significance for utilizing renewable resources, reducing environmental pollution and recovering precious silver metal.

references

1 Bai Xiumei. Flotation test in silver, lead and zinc with silver. Comprehensive utilization of minerals, 1982 (2): 15

2 Lu Wenfu. 3. Research on the comprehensive recovery of associated gold and silver in refractory ore. Jilin Metallurgy, 1990 (4): 10

3 Qiu Yongjia. University Chemistry Handbook. Jinan: Shandong Science Press, 1985. 277

RECOVERY OF SILVER FROM ZINC LEACH RESIDUES BY FLOTATION

Huang Kaiguo Wang Qiufeng

ABSTRACT

Up to now,the silver from zinc leach residues hasn't been recovered satisfactorily. In view of this situation,this paper has studied the effects of Na ₂ S,pH,collectors kinds and dosage on silver ion(Ag+)sulphide-precipitation. Based on this, the flotation prescription of silver from zinc leach residues has been improved. Using sodium sulphide(Na ₂ S),butylxanthate and subsidiary collector XY,RB as conditioner,combined collectors,forther,respectively,this study has recovered silver from zinc leach residues succesfully. The results indicate: using the improved flotation prescription, the concentrate containing silver 4369.73g/t, recovery 79.44% can be obtained from zinc leach residues containing silver 498.l0g/t. This study has offered basis and new drug rule for recovery of silver from zinc leach residues. It has an important economic value.

Key words zinc leach residues;silver;flotation

Originally published in the Journal of Central South University of Technology, December 1997, Vol. 28, No. 6 ☺

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