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Traditional production methods of lead nitrate solution is reacted with lead nitrate and lead nitrate ingots, by salting out or evaporation method to obtain the product. In recent years, the price of lead ingots has increased, resulting in a significant increase in the cost of lead nitrate. In order to reduce costs, a method for producing lead nitrate directly using lead ore as a lead source has been studied. The test results show that under appropriate process conditions, the lead leaching rate of lead ore is more than 85%, the recovery rate is 80%, the product quality reaches the industrial first-class product standard, and the cost is reduced by about 20%. At the same time, the process has an enrichment effect on silver in the concentrate.
First, the test materials and basic principles
(1) Raw materials
The raw materials used in the test were refined lead ore and nitric acid.
Slag: lead ore fine powder produced in Liaoning Province, the x- ray diffraction analysis showed that the main composition galena, sphalerite is associated minerals, also contain small amounts of copper ore yellow, pyrite and traces of gray silver mine. Depending on the place of production, the main content of the product varies greatly. This test requires that the atomic ratio of lead and zinc in the ore powder is greater than 715. The main chemical composition is shown in Table 1, and the 2# mineral powder is not required.
Table 1 Chemical composition of concentrate
Nitric acid: GB337-84 second-class products
(2) Basic principles
After the mineral powder reacts with acid, the main reaction occurs as follows:
3PbS+8HNO 3 =3Pb(NO 3 ) 2 +2NO↑+3S↓+4H 2 O(1)
side effects:
3ZnS+8HNO 3 =3Zn(NO 3 ) 2 +2NO↑+3S↓+4H 2 O(2)
3CuS+8HNO 3 =3Cu(NO 3 ) 2 +2NO↑+3S↓+4H 2 O(3)
FeS+4HNO 3 =Fe(NO 3 ) 3 +NO↑+S↓+2H 2 O(4)
3Ag 2 S+8HNO 3 =6AgNO 3 +2NO↑+3S↓+4H 2 O(5)
It can be seen from the above reaction that as the lead in the ore is leached, a large amount of impurities also enter the solution in the form of nitrate. An appropriate amount of a precipitating agent is added to the acid hydrolyzate to precipitate and separate Cu 2 + , Fe 3 + , and Ag + ions.
Second, the process conditions and processes
(1) Process flow (see Figure 1)
Figure 1 Process for preparing lead nitrate
(2) Process conditions
1. Selection of acid hydrolysis process conditions
(1) Liquid-solid ratio: The reaction liquidity of the refined lead ore-nitrate-water system is good. The experiment shows that the liquid-solid ratio has no significant influence on the leaching rate. The choice of liquid-solid ratio mainly depends on the solubility of lead nitrate. A smaller liquid-solid ratio is selected to reduce the evaporation amount in the subsequent process, and the liquid-solid ratio is 2.1 to 2.3:1.
(2) The amount of acid used: The leaching rate of lead in the ore powder increases with the increase of the amount of acid added, but at the same time, the leaching rate of impurity ions also increases significantly. From the aspects of impurity elimination, acid consumption, etc., An acid coefficient of 1.1 is preferred. See Table 2.
Table 2 Effect of acid amount on acid hydrolysis rate
Note: acid addition coefficient = actual acid addition / theoretical acid addition (in Pb)
(3) Reaction temperature: due to the exothermic reaction of the acid hydrolysis reaction, the initial reaction system spontaneously heats up without external heating, and the temperature of the system is about 60 ° C after the acid addition is completed. The temperature is increased to make the reaction more rapid and complete. However, the decomposition of nitric acid and equipment corrosion should be considered. It is suitable to select 70 ° C ~ 75 ° C. See Table 3.
Table 3 Effect of reaction temperature on acid hydrolysis rate
(4) Reaction time: As the reaction time prolonged, the leaching rate of Pb increased, but after 40 minutes, the leaching rate did not change significantly after prolonging the time. The reaction time was insufficient, and the leachate was reddish brown, indicating that some of the nitric acid did not participate in the reaction and had been decomposed into nitrogen dioxide in the solution.
Table 4 Effect of reaction time on acid hydrolysis rate
Based on various factors, the following conditions were selected as the appropriate conditions for acid hydrolysis: acid addition factor 111, reaction temperature 70 ° C to 75 ° C, reaction time 40 min, liquid-solid ratio 211 to 2.3:1.
2. Purification of leachate
The composition of the leachate (g/L): Pb 230, Zn 2-27, Cu 0.9, Fe 1.5, Ag trace. The leachate is blue-green because it contains Cu 2 + and Fe 3 + ions. Under appropriate conditions, Fe 3 + , Cu 2 + and a trace amount of Ag+ may be precipitated by adding an appropriate amount of a precipitating agent, and removed by filtration to obtain a light green solution.
3. Control index of zinc content in mother liquor
Under the above acid hydrolysis conditions, the leaching rate of zinc in lead ore is about 50%. As the number of cycles increases, Zn 2 + gradually accumulates in the mother liquor. The solubility of Pb(NO 3 ) 2 and Zn(NO 3 ) 2 was found in Table 5.
Table 5 Solubility of Pb(NO 3 ) 2 and Zn(NO 3 ) 2 (g/100gH 2 O)
It can be seen from Table 5 that the solubility of Zn(NO 3 ) 2 and Pb(NO 3 ) 2 increases with increasing temperature, and the solubility of Zn(NO 3 ) 2 is much greater than the solubility of Pb(NO 3 ) 2 . . When Pb(NO 3 ) 2 was crystallized at room temperature, the content of zinc in the mother liquor for 12 cycles was 42 g/L, which was still much smaller than the saturation concentration of Zn(NO 3 ) 2 . Tests have shown that a standard Pb(NO 3 ) 2 product is fully available.
The crystallization mother liquor contains Pb from about 140g/L to 150g/L. When the zinc content in the mother liquor is above 45g/L, the molar ratio of Pb to Zn is about 1:1. In order to ensure product quality and prevent crystallization of Zn 2 + Purity, control the Zn 2 + content in the mother liquor below 45g / L.
(3) Process
According to the above process conditions, the mother liquor (or clear water) is placed in the acid hydrolysis tank, and stirring is started, and the ore powder and nitric acid are respectively added. After the addition is completed, the mixture is heated and reacted at 70 ° C to 75 ° C for 40 minutes. Add an appropriate amount of precipitant to remove impurity ions, and filter while hot.
Under this condition, the leaching rate of lead can reach more than 85%. The filtrate was placed in an evaporator, concentrated nitric acid was added, the pH was adjusted to less than 2, and when it was evaporated to 103.5 ° C, the heating was stopped, and the mixture was naturally cooled to room temperature and centrifuged. The mother liquor returns to the ingredients, and after several cycles, it is treated and discharged.
The wet crystals were dried at 120 °C. The yield of lead can reach more than 80%.
Third, product quality and technical economic comparison
The method is produced on an industrial device with an annual output of 1000t of lead nitrate. The main content of lead nitrate is over 99%, and the impurity content index is in accordance with QJ/EHG02101-90 standard. See Table 6.
Table 6 Product quality indicators (enterprise standard)
The main raw material consumption (t/t) of the two processes is shown in Table 7.
Table 7 Unit consumption of main raw materials in two processes (t/t)
The raw material cost of lead nitrate products accounts for about 75% of the production cost. The cost difference between the products obtained from the two processes is mainly determined by the consumption and price of raw lead ore powder or lead ingot and nitric acid. The raw material fee for the lead ore method is Y 1 , and the raw material fee for the lead ingot method is Y 2 , then the main raw material costs for the two processes are calculated as follows:
Y 1 = 0.802 × mineral powder price + 0.82 × nitric acid price + other auxiliary materials fee
Y 2 = 0.65 × lead ingot price + 0.51 × nitric acid price
Four or three waste treatment
Production produce an exhaust gas NO x, residue (containing Pb 2 +) and a small amount of washing waste water plant, further, requiring regular treatment of the mother liquor after several cycles.
The treatment of the exhaust gas is still treated according to the original process, absorbed by the lye (or lime milk), and the by-product sodium nitrite can be recovered at the same time.
The slag rate of this process was 40%, and the Pb 2 + was blocked by treatment with Na 2 S and lime milk, and discarded. If the original ore grade is higher, the silver grade of the slag is doubled and can be supplied to the smelter as a silver mine, thereby further reducing the cost of lead nitrate in the main product.
The number of cycles of mother liquor and the distribution of lead: The number of cycles of mother liquor depends on the grade of the ore and the content of zinc, which depends on the ratio of lead to zinc. The larger the lead-zinc ratio, the more the number of cycles.
When the zinc content in the mother liquor reaches above 45g/L, the mother liquor is no longer returned to the ingredients. After treatment with lime and Na 2 S, the waste residue is filtered out and the waste water is discharged. The distribution of lead in this test is shown in Table 8. After 12 cycles, the zinc content in the mother liquor was 42 g/L, and the ingredients were no longer returned. The lead discharged accounted for 2.2% of the total input lead, and the discharged HNO 3 accounted for 1.65% of the total input. It can be seen that the mother liquor discharge and post-treatment have less impact on cost accounting.
Table 8 Distribution of lead (in Pb/g)
V. Results and discussion
1, with a fine powder instead of a metal lead galena ingot production lead nitrate is feasible, product quality and stability. In the case of a large difference between the price of mineral powder and lead ingot, this process has high economic benefits.
2. This method can be used for production on the original process production line with little investment.
3. This process enriches the silver in lead ore.
4. During the acid hydrolysis process, due to the influence of the mineral flotation agent, a large amount of gas generated by the reaction accumulates in the upper layer of the slurry, which affects the feeding speed and reduces the utilization rate of the equipment.
references
1. Tianjin Chemical Industry Research Institute, etc. Handbook of Inorganic Salt Industry. Chemical Industry Press, 1995.
2, Beijing Normal University, etc. Inorganic Chemistry. People's Education Press. 982.
3. Editor-in-Chief of Wuhan University. Analytical Chemistry. Higher Education Press.990.
4. Department of Nonferrous Metals Smelting, Zhongnan Institute of Mining and Metallurgy, Nonferrous Metallurgy, Metallurgical Industry Press, 959.
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