Nano Zinc oxide is a new high functional artificial inorganic materials for the 21st century, due to its small particle size, large specific surface area, generally having a normal zinc oxide and activated zinc oxide can not be compared in terms of magnetic, optical, electrical and other sensitive Its special properties make it widely used in rubber, ceramics, household chemicals, coatings and magnetic materials. At present, there are many methods for preparing nano zinc oxide. There are mainly in-phase synthesis method, laser induced vapor deposition method, spray pyrolysis method, hydrothermal synthesis method, chemical precipitation method and the like. We use low-zinc mixed ore which is not commonly used in wet zinc smelting as raw material, and prepare nano-zinc oxide by the method of direct precipitation of leaching solution after purification. The industrial production line is established, the method is simple, the cost is low, the product performance is excellent, and the zinc resource is reasonable. Exploring a new path in the use and deep processing.
First, raw materials and production process
(1) Raw materials
The chemical composition of the raw materials is shown in Table 1. This material belongs to a mixed oxide of lead zinc ore, high low lead zinc, silicon, arsenic, cadmium high, not directly for the production of metallic zinc or lead smelting directly.
Table 1 Chemical composition of raw materials for production %
element | Zn | Pb | Cd | Fe | As | S | SiO 2 |
content | 18-20 | 41-42 | 3.2-3.4 | twenty three | 0.5 | 2.0 | 8-10 |
(2) Production process
The process flow determined by laboratory tests and used in production is shown in Figure 1.
Figure 1 Flow chart of production process of nanometer zinc oxide from mixed ore
(3) Major production equipment
1. Ball mill , Φ900×1800mm, 1 set;
2, reaction tank, V = 30m 3 , concrete casting lining porcelain plate, mechanical stirring (stirring speed n = 100 r / min), multiple;
3, ceramic acid-resistant pump, multiple, multiple models;
4. Box filter press: F=80m 2 , multiple sets;
5. One rotating flash dryer, CJG-XSZ125 type, one set of CJGR60 type bile hot air stove;
6. One flame-type roaster;
7, 2t/h horizontal quick-install boiler.
(4) Production scale
1200t/a nano zinc oxide and industrial basic zinc carbonate.
Second, the production process
(1) Process control in the production process
1. Grind the slurry to -100 mesh to the leaching tank, steam and slowly add industrial sulfuric acid, control the process temperature 40 ~ 50 ° C, pH 1.0 ~ 1.5, 1.5h after the use of zinc oxide paste neutralization solution To pH 4.5 ~ 5.0, pressure filtration.
2. The upper filter residue is subjected to two-stage acid leaching, and the industrial sulfuric acid is added, the temperature is raised to 75 ° C, the pH is maintained at 1.5 to 2.0, and the air is stirred for 2 hours, followed by pressure filtration. The obtained filter residue contains Pb-45%, which is a lead-extracting raw material. The secondary filtrate is returned to a section of acid leaching for slurrying. .
3. Pump a section of the immersion liquid into the purification tank, raise the temperature to 50 ° C, and stir. Was added potassium permanganate oxidation of 2-fold iron, manganese, arsenic, added in an amount theoretically calculated amount of addition. Control pH 5.2 ~ 5.4, until the solution appears reddish, and then stirred for more than 20 minutes, reddish, not pressure, that is, pressure filtration. The filter residue is sold as manganese powder.
4. Pump the iron removal liquid into the secondary purification tank, raise the temperature to 50 °C, and start the mixer. 2.5 times the theoretical calculation amount was added to the electric furnace zinc powder to replace the cadmium, time 30min, pressure filtration. The filter residue is sponge cadmium, containing Cd ~ 60%, the filtrate is refined zinc sulfate solution, the main component is Zn60 ~ 68 g / L impurities Cd, Cu, Mn, Fe, As are ≤ 1.0mg / L.
5. The refined zinc sulphate solution is pumped into a zinc tank, and an appropriate amount of a self-made L-type dispersant is added, and then ammonium bicarbonate is added in an amount of 2.4 times the zinc content of the solution, and the zinc is stirred and transformed. The temperature was maintained at 60 ° C, the end point was pH 6.8 to 7.0, and pressure filtration was carried out.
6. The zinc carbonate obtained by washing the zinc immersion with pure water is used until no white precipitate is detected by 0.1% BaCI 2 solution, and pressure filtration is carried out.
7. The washed filter cake is added to a rotary flasher for continuous drying, and the dried product has a water content of ≤2.5%. Previously, the basic-carbon zinc carbonate can also be directly packaged and sold as the market needs.
8. The dried precursors are placed in a flame-retarding furnace in batches and baked at 400-450 ° C for 120-150 min. It is baked and cooled to 40 ° C, which is a nano-active zinc oxide product, which is packaged and shipped.
(2) Several key production processes
1. Control of leaching process conditions
The raw material has a high silicon to zinc ratio (SiO 2 /Zn of 0.4 to 0.5 / L), and the combined state of silicon (MeO · SiO 2 ) accounts for a considerable proportion. This portion of silicon enters the solution upon leaching to form Si(OH) 4 monosilicate, which undergoes polymerization to form colloidal particles of 0.001 um to 0.1 um. The formation of a large amount of colloidal silica makes the liquid-solid separation difficult and the leaching process cannot be performed. How to avoid or reduce the formation of colloidal silica is the primary problem that must be solved in the leaching process.
It is known that silicic acid is stably present in a single molecule form under the conditions of a solution pH of 1.0 to 2.0. When the pH of the solution is less than 1.0 or greater than 2.0, the silicic acid will polymerize to form silica gel particles; and at a temperature of 65-75 ° C, pH 5.2-5.4, the monomeric silicic acid in the solution is amorphous. The SiO 2 morphology precipitates, thereby greatly improving the slurry filtration performance.
The production process adopts the reverse immersion method, that is, the mineral powder is slurried with the secondary leaching solution (pH 2.0-3.0), and then the industrial sulfuric acid is continuously added slowly, and the sulfuric acid speed is controlled to make the pH value of the solution quickly break through the dangerous zone of the silica gel polymerization. pH 2 to 4. That is, the pH value of the solution is strictly stabilized in the range of 1.5 to 2.0, and the zinc in the ore is leached as much as possible by stirring the reaction for 1.5 to 2.0 hr; then the temperature of the solution is controlled at 65-70 ° C, and the neutralizing agent is added to bring the pH of the solution to 4.0 quickly. ~4.5. When a large amount of granular SiO 2 appeared in the filtrate, the timing was started, and further stirring was carried out for 1.0 to 1.5 hr of silicon, and pressure filtration (pressure filtration rate of 0.4 to 0.6 m 3 /m 2 ·h) was carried out. The residue is washed (secondary leaching) to recover the soluble zinc in the slag, and the washing liquid is returned to the leaching and rinsing.
2. Oxidation neutralization of leachate to remove iron and manganese
The main components of the leachate are (g/L): Zn 58-70, Cd 6.0-8.0, Fe 0.9-1.3, Mn 0.15-0.20, and As0.20-0.30, which must be cleaned and removed. In the production, strong oxidant potassium permanganate is used to oxidize Fe and Mn into high-valent oxides, which are removed by hydrolysis into the precipitate, and the arsenic in the solution is also removed by adsorption. A new acid is produced during the oxidation reaction, so it is necessary to neutralize the acid with a neutralizing agent (zinc oxide paste) to maintain the pH of 5.2 to 5.4 to ensure complete elimination. The main reaction of the process is as follows:
6FeSO 4 + 2KMnO 4 + 5ZnO + 11H 2 O = 2MnO
(OH) 2 ↓+6Fe(OH) 3 ↓+K 2 SO 4 +5ZnSO 4
3MnSO 4 + 2KMnO 4 + 2ZnO + 5H 2 O = 5MnO
(OH) 2 ↓+K 2 SO 4 +3ZnSO 4
The amount of potassium permanganate added is an appropriate excess of the theoretical amount of the reaction of (Fe + Mn + As), and the end point of the reaction is based on a reddish color (a slight excess of potassium permanganate).
3. Transformation of zinc
When the zinc sulfate is converted into the precursor basic zinc carbonate, the commonly used transitioning precipitant is sodium carbonate, and agricultural ammonium hydrogencarbonate is used to reduce the cost. The reactions that occur at this time are as follows:
3ZnSO 4 +6NH 4 HCO 3 =ZnCO 3 ·2Zn(OH) 2 ·H 2 O↓+5CO 2 ↑+3(NH 4 ) 2 SO 4
In order to ensure the nanostructure of the precipitated particles and reduce the adhesion of the grains, a self-made L-type dispersant was experimentally studied and added when the zinc was converted.
Both the test and the production showed that the required amount of ammonium bicarbonate and dispersant were quickly added at a temperature of 40 to 50 ° C, and the mixture was further stirred for 1 hr, and the precipitate was aged to obtain a crystal precipitate of desired quality. And facilitate the next process of washing and filtration.
4, the use of rotary flash machine
Before the washing is qualified, the basic zinc carbonate is dehydrated and dried by a rotary flash furnace heated by a biliary hot blast stove. The drying process is quick and continuous, the dried product is not agglomerated, the grains are not agglomerated, and the water is not condensed. Controllable.
Third, the production results
(1) Main production technical indicators
The direct zinc recovery rate is 80%; the total zinc recovery rate is 82%; the total lead recovery rate is 99%.
(2) The main unit consumption of nano zinc oxide finished products
Raw ore (Zn19%) ~ 5.0t, zinc powder 140 ~ 150kg, sulfuric acid 3.2t, ammonium bicarbonate 2.0t, potassium permanganate 55 ~ 60kg, bovine gum 5 kg, L-type dispersant.
(3) Quality of by-products
Lead sulphate slag: containing Pb 45%, Zn 3%, S 9%; cadmium slag: containing cd ~ 60%, sponge-like; manganese slag: containing MnO 2 ≥ 68%.
(4) Chemical quality of industrial basic zinc carbonate (see Table 2)
Table 2 Chemical quality comparison table of industrial basic zinc carbonate products
Indicator project | HG/T2523-93 standard | This product |
| Superior product | First grade | Qualified product |
Main content (in terms of Zn) (on a dry basis) mass fraction /% | ≥ | 57.5 | 57.0 | 56.5 | 58.4 |
Loss of mass loss | | 25.0~28.0 | 25.0~30.0 | 25.0~32.0 | 27.5 |
Heavy metal (in Pb) mass fraction /% | ≤ | 0.04 | 0.05 | 0.05 | 0.0005 |
Moisture /% | ≤ | 2.5 | 3.5 | 5.0 | 2.10 |
Sulfate (SO 4 meter) mass fraction /% | ≤ | 0.60 | 0.80 | - | 0.50 |
Fineness (through 75μm screen) mass fraction /% | ≥ | 95.0 | 94.0 | 93.0 | 99.5 |
Cadmium (Cd) mass fraction /% | ≤ | 0.10 | - | - | 0.0003 |
(5) Quality of nano zinc oxide materialization of main products
Table 3 shows the comparison of the physical and chemical indicators of the finished product nano zinc oxide with the national standard and the German Bayer product standard.
Table 3 Comparison table of physical and chemical indicators of nano zinc oxide products
index | This product | GB/T19589-2004 standard | German Bayer Standard |
Class 1 | Class 2 | Category 3 |
ZnO% | 96.6~96.8 | ≥99.0 | ≥97.0 | ≥95.0 | 93~96 |
Electron microscopy average particle size / nm | 30 | ≤100 | ≤100 | ≤100 | 50 |
Specific surface area / (m2 · g -1 ) | 25 | ≥15 | ≥15 | ≥35 | 45 |
Reunion index | - | ≤100 | ≤100 | ≤100 | - |
Pb/% | 0.0006 | ≤0.001 | ≤0.001 | ≤0.03 | ≤0.04 |
Mn/% | 0.0006 | ≤0.001 | ≤0.01 | ≤0.005 | ≤0.002 |
Cu/% | 0.0003 | ≤0.0005 | ≥0.0005 | ≥0.003 | ≤0.001 |
Cd/% | 0.00015 | ≤0.0015 | ≤0.005 | - | - |
Hg/% | - | ≤0.0001 | - | - | - |
As/% | 0.0002 | ≤0.0003 | - | - | - |
105 ° C volatiles /% | 0.6 | ≤0.5 | ≤0.5 | ≤0.7 | - |
Water soluble substance /% | 0.7 | ≤0.1 | ≤0.1 | ≤0.7 | 1.0 |
HCI insolubles /% | 0.015 | ≤0.2 | ≤0.02 | ≤0.05 | - |
Burning vector /% | 2.8 | - | ≤2 | ≤4 | 3 to 6 |
Note: GB/T19589-2004 is the first national standard for nano zinc oxide issued in China.
Figure 2 shows a 100,000-fold magnification of a transmission mirror (TME) of a nano-zinc oxide finished product. It can be seen from the figure that the shape of the new nano-zinc oxide finished product is mainly spherical, and the particle size is 10 nm to 100 nm. According to BET (specific surface area), the average particle diameter is 30 nm.
Figure 2: Transmission mirror of nano zinc oxide finished product
It can be seen from Table 3 and Figure 2 that the newly produced nano zinc oxide finished products have much lower content of impurities than the national standard l standard, and the physical quality is between 2 and 3 categories. German Bayer products.
Fourth, the application effect of nano zinc oxide finished products on rubber products
The nano-zinc oxide products produced by the company were sent to the Yunnan Provincial Rubber Product Quality Supervision and Inspection Station, and added into the tobacco sheet rubber to make rubber products. The hardness, tensile strength and elongation of the A-type were carried out. Determination test of rate, breaking permanent deformation, 300% modulus and other items. The test results (Table 4) show that the physical and mechanical properties of the three parts of the nano zinc oxide used in this project are similar to those of the commercially available indirect zinc oxide. Prove that this product can be used in rubber products to reduce the amount of money, so as to achieve the purpose of saving.
Table 4 Physical index determination test of rubber products with different types of zinc oxide added
Test items | test result |
Add 3 samples of this product | Commercially available indirect zinc oxide sample of 5 parts |
Tensile strength / MPa | 19.4 | 19.9 |
Elongation at break/% | 620 | 610 |
300% fixed tensile stress / MPa | 3.0 | 3.4 |
Tear off permanent deformation /% | 23.2 | 24.8 |
Hardness (Shore type) / degree | 54 | 54 |
The finished product industrial basic zinc carbonate and nano zinc oxide are sold to rubber products factories, shoe factories, ceramic factories, feed processing plants and other enterprises in Guangxi, Fujian, Guangdong and other provinces, which are very popular.
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