High-arsenic zinc oxide comprehensive recovery technology

I. Introduction

The blast furnace slag of the two systems of Shaoguan Smelter is about 10,000 tons of zinc oxide recovered by smouldering Shanghai. The main chemical composition is shown in Table 1.

Table 1 Chemical composition of zinc oxide

There is also a small amount of C, S, Cl, F, etc., indicate that crystalline phases: Zn, Pb, As is present in a form of an oxide, salt forms most of the presence of germanium Ge, Ag and Pb were contained in.

At present, most of the sub-zinc oxide returns to the sintering ingredients, and this treatment has three shortcomings.

(A) Since the zinc oxide times the total amount of arsenic-containing nearly 1000 t, the whole plant Shaoguan smelter arsenic enrichment of about 50% into secondary zinc oxide, arsenic point of convergence is the factory, while the year of lead in zinc concentrate The arsenic with people is about 500-800 t, if not treated in time. Arsenic will continue to enrich the cycle in the system, causing tremendous pressure on the environment.

(B) the continuous enrichment of arsenic, the arsenic content in various materials will be increasingly high, and high arsenic materials have a negative impact can not be ignored for the main process plant -ISF furnace, while giving valuable scattered metals germanium, indium Recycling brings difficulties.

(3) When the secondary zinc oxide is returned to the sintering batch, the dust is large and the arsenic content is high, which causes the operating environment to be bad. At the same time, excessive addition of zinc oxide causes the strength and the blocking rate of the sintered block to decrease, which affects the quality and yield of the sintered block. .

Therefore, finding a suitable method for treating sub-zinc oxide, comprehensively recovering valuable metals such as lead, zinc, antimony and arsenic, and producing products that are popular in the market, can turn waste into treasure and obtain considerable economic benefits.

Second, the test principle and process

When zinc oxide is added with sulfuric acid and a small amount of water, zinc and lead rapidly form sulfates, and the main reaction modes are:

ZnO+H ₂ SO ₄ =ZnSO ₄ +H ₂ O (1)

PbO + H ₂ SO ₄ = PbSO ₄ +H ₂ O (2)

ZnGeO ₃ +H ₂ SO ₄ = ZnSO ₄ + GeO ₂ +H ₂ O (3)

As ₂ O ₃十3H ₂ O=2H ₃ AsO ₃ (4)

When burned at 350-550 ° C, H ₃ ASO ₃ is re-decomposed, and H ₂ O and As ₂ O _{3 are} volatilized:

2H ₃ AsO ₃ =AS ₂ O ₃ +3H ₂ O (5)

Zinc sulfate can be decomposed at temperatures above 600 ° C. The melting point of lead sulfate is 1170 ° C and begins to decompose above 950 ° C. Both products remain in the calcine at this temperature and are not volatilized; There is a small amount of carbon in zinc oxide, and GeO ₂ may be partially reduced to GeO. In addition, due to the presence of Cl and F in the sub-zinc oxide, GeCl ₄ may be formed, and GeF ₄ may be partially volatilized; while Cl and F mainly form HCI. HF evaporates.

When the calcined water is immersed, zinc sulfate is dissolved in water, and strontium is also dissolved in 30%, and lead silver is enriched in the slag for further recovery. The main process flow chart is shown in Figure 1.

Figure 1 Principle of comprehensive recovery of zinc oxide by sulfuric acid roasting

Third, the test part

(1) Direct acid leaching

Directly leaching the secondary zinc oxide with sulfuric acid: 1/s = 5:1, temperature 70-90 ° C, time 1.5 h, final acid 10-20 g / L, 96% leaching of Zn when leaching, As, Ge Leaching 94%, 70%, F, Cl leaching more than 90%, while Pb, Ag silver is left in the slag, the chemical composition of the leachate (g / L); Zn90 ~ 100, As8 ~ 20, Ge 0.1 ~ 0.2, F0 .1～0.2, Cl0.1～0.2, the content of As, F and Cl in the acid leaching solution is high, it is very difficult to directly purify it into electrolyte.

(2) sulfuric acid roasting

The secondary zinc oxide is directly acid-leached and the acid consumption is 110% to 120% of sulfuric acid and a small amount of water is mixed, and then the mixture is placed in a graphite crucible for calcination. The parameters of different calcination temperature, sulfuric acid amount, roasting time and the like were investigated.

1. Effect of different amounts of sulfuric acid on the volatilization rate of materials

Each 200 g zinc oxide plus 90 mL, 100 mL, 110 mL, 120 mL, 130 mL sulfuric acid was calcined at 400 ° C for 7 h, the metal volatilization rate is shown in Figure 2. F, Cl volatilizes more thoroughly in this acidity range.

Figure 2 Effect of different amounts of sulfuric acid on the volatilization rate of metals

It can be seen from Fig. 2 that in this acidity range, lead and zinc are all in the calcine, and arsenic strontium increases with the increase of the amount of acid added, and 110-120 mL of sulfuric acid is added (that is, the acid consumption of direct acid leaching is 110%). ～120%), the effect is better, and the volatility of arsenic is above 90%.

2. Effect of different calcination temperatures on metal volatilization rate

Each 200 g zinc oxide plus 120 mL sulfuric acid and a small amount of water were mixed and burned at 300 ° C, 350 ° C, 400 ° C, 500 ° C for 7 h. F and Cl volatilize completely in the lower temperature range, while arsenic volatilizes above 90% above 350 °C, and the volatilization of bismuth is about 40%, while lead and zinc are hardly volatilized. The volatilization temperature is preferably 400 to 500 ° C. See Figure 3.

Figure 3 Effect of different calcination temperatures on metal volatilization rate

3. Effect of calcination time on metal volatilization rate

200 g of zinc oxide and 115 mL of sulfuric acid (98%) and a small amount of water were calcined at 400-500 °C for 3 h, 4 h, 5 h, 6 h, 7 h. F and C1 were almost completely evaporated at 3 h, and the metal volatilization curve changed. Figure 4.

Figure 4 Effect of different calcination time on metal volatilization rate

It is known from Fig. 4 that zinc and lead have no volatilization at all, and arsenic and antimony increase the volatilization rate with time. The arsenic volatilization rate reached more than 90% at around 5h, and the calcination time was better at 5h.

Based on the above conditions, the optimum conditions for the calcination of sulfuric acid are as follows: adding 1.1 to 1.2 times of sulfuric acid by weight of the sub-zinc oxide, and calcining at 400 to 500 ° C for 5 hours, the desired calcination result can be obtained.

(3) The calcined acid is diffused by adding the water to the calcined water, the condition I/s=5:1, the temperature is 70 ° C, the time is 1.5 h, the leaching end point is pH=3, the amount of leaching slag is 30% of the secondary zinc oxide, the leachate and the slag The chemical composition is shown in Table 2.

Table 2 Chemical composition of calcined water immersion liquid and slag

It is known from Table 2 that the As in the leachate is below 0.3g/L, and F and Cl have met the electrolysis requirements. As long as the acid leaching solution is slightly treated, a qualified pre-electrolytic solution can be obtained, and the slag is rich in lead-containing 50. More than % lead concentrate containing less than 0.4% arsenic may be returned to the sintering batch or otherwise treated.

Fourth, industrial trials

The industrial test processed a total of 9.2 t zinc oxide, yielding 17.36 t of calcine and 0.75 t of soot. The test uses a rotary kiln for arsenic removal, fluorine and chlorine. The kiln has a length of 12 m and a slope of 1.2 m in diameter ^. . The test conditions were as follows: zinc oxide: sulfuric acid = 1:0.91, calcination time of 5 h, calcination temperature of 450-550 ° C, feed 500 kg / h. Since the amount of sulfuric acid added is almost the amount of reaction with the secondary zinc oxide, there is almost no smoke in the chimney. The technical index is: the arsenic removal rate is 85%-95%, and the removal rate of F and Cl is more than 95%, while the volatility of Ge is better than the small test, less than 30%, while Pb, Zn and Ag are almost non-volatile. The arsenic in the calcined sand is less than 0.5%, and the average value of the chemical components of the secondary zinc oxide, the calcine and the soot in the expansion test is shown in Table 3.

Table 3 Chemical composition of secondary zinc oxide, calcine and soot in industrial test face (%)

As can be seen from Table 3, the industrial test is basically in agreement with the small test.

V. Conclusion

(1) The treatment of sub-zinc oxide by "sulfuric acid roasting-water immersion" has a simple process, high direct yield of lead and zinc, low cost and low consumption of reagents. On the basis of small-scale tests, industrial tests have proved that the process can better remove arsenic, fluorine and chlorine from zinc oxide.

(2) The calcination conditions are: temperature 400-500 ° C, the acid addition amount is 110%-120% of the weight of the sub-zinc oxide, the roasting time is 5 h, and the roasting water immersion condition is: 1/s=5:1, The time is 1.5 h, the temperature is 60-80 ° C, the direct yield of lead is more than 99%, the direct yield of zinc is 98%, the removal rate of arsenic is 90%, and the direct yield of hydrazine is 60%. 98% of zinc, about 60% of strontium, and about 0.5% of arsenic in the raw material enter the leaching solution, while lead and silver are all left in the slag, and the leaching slag contains more than 50% of lead and less than 0.4% of arsenic.

(3) One shortcoming of the process is that it is dispersed in the process, which increases the recovery cost of the plutonium and reduces the recovery rate of plutonium.

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