20 centuries ago, the metal part of the world zinc smelting ore from oxidation, when the United States, Belgium, France and other countries are usually Smelter Zinc oxide ores with high-grade ore. For zinc oxide ore, it mainly refers to zinc silicate Zn 2 Si0 4 and heteropolar Zn 4 (Si 2 0 7 )(OH) 2 ·H 2 0. These ores are often accompanied by smithsonite ZnC0 3 . The dimer can be further reacted with silicic acid H 4 SiO 4 to form a polysilicate or a branched polysilicic acid such as a trimer or a tetramer. The polysilicic acid is repolymerized to form a colloidal SiO 2 particle, i.e., a SiO 2 sol. It can be seen that the most important influence on the polymerization rate of silicic acid is the pH value, and the effect of pH value is as follows: The professional equipment applied for automatic assembling of the automotive Starter, and integrated with functions of robot feeder, electrical performance tester as well as visual system. Possible for you to adjust parameters for data analysis and quality control. JINLAN provides you complete solutions for start production, including assembly solutions of drive shaft, ORC drive gear and electromagnetic switch as well as the tests related. Starter General Assembly Line,Starter Assembly Line,Vehicle Starter Assembling,Automatic Starter Assembling Line Wujiang Jinlan Machinery Manufacture Co.,Ltd , https://www.jinlan-technology.com
The biggest difficulty in the wet treatment of zinc oxide ore is the formation of colloidal SiO 2 which is difficult to filter upon leaching. For decades, people have done a lot of work around obtaining pulp that is easy to filter, and thus have made breakthroughs in the harm of silicon in the slurry. Some acid leaching technologies for treating zinc silicate have been used for industrial production.
Behavior and control of Si0 2 during leaching
Both zinc silicate and heteropolar ore are easily dissolved by dilute sulfuric acid. When zinc is dissolved, SiO 2 also enters the solution, and the reaction is
Zn 2 Si0 4 +2H 2 S0 4 → 2ZnS0 4 +Si(OH) 4 (or H 4 Si0 4 )
Zn 4 (Si 2 0 7 )(OH) 2 ·H 2 0+4H 2 S0 4 → 4ZnS0 4 +2Si(OH) 4 +2H 2 0
The silicic acid entering the solution is very unstable, and polymerization occurs between the molecules to form polysilicic acid, which is polymerized into a silica sol by silicic acid, which is then gelled to form a hydrogel. The polymerization process firstly polymerizes a monomolecular silicic acid into a bimolecular polymer, a trimolecular polymer, and finally forms a multimolecular polymer to become a stable colloidal solution. If the concentration of SiO 2 in the solution is sufficiently large, it will automatically enter the gelation process and become a hydrogel during the placement process. The content of the solution in the hydrogel is usually above 95%, and the fluidity is lost in a semi-solid state, which brings difficulty in liquid-solid separation.
Silicic acid is charged. It is generally believed that the isoelectric point of ortho silicic acid is near pH=2, and when the pH is higher than the isoelectric point, the ortho silicic acid can be dissociated as follows.
H 4 Si0 4 â†â†’ -H 3 Si0 4 - +H +
When the pH is lower than the isoelectric point, H 4 Si0 4 can be combined with H + in the solution.
H 4 Si0 4 + H + â†â†’ H 5 Si0 4 +
For the polymerization process of silicic acid, Professor Dai Anbang has done a lot of research and proposed two mechanisms of silicic acid polymerization in different pH ranges. They think that there are two kinds of negative ions H 2 Si0 4 2 - and H 3 Si0 4 in the solution. - Both of them gradually bind to H + in the solution as the concentration of the added acid increases. [next] 
In the acidic solution with pH<2, the coordination number of the silicate is 6, and the silicic acid molecule and the positively charged silicate ion H 5 Si0 4 + undergo a hydroxy combination reaction to form a disilicate. It is polymerized from disilicate, trisilicate, polysilicic acid to form a silica sol or a silica gel.
A Factors affecting silica sol and gelation Factors affecting silica sol and gelation are as follows:
(1) Concentration Under certain conditions of temperature and pH, the concentration of SiO 2 in the silica sol solution is faster, and the concentration is small, the gelation is slow. It is generally considered that the concentration is less than 1% and it is not easy to gel.
(2) The effect of temperature and temperature on gelation is related to the pH value of silica gel solution. In the acidic solution, the gelation rate increases, and in alkaline solution, the opposite is true. The gelation rate of the elevated temperature decreases.
(3) The electrolyte leaching solution contains a large amount of electrolyte, which is unfavorable to the stability of the sol, and the gelation rate is increased.
(4) pH value has the greatest influence on the gelation rate of silica sol. When the solution is close to neutral, the gelation rate is the highest; in acidic or alkaline solution, the gelation rate is small.
In an alkaline medium, SiO 2 is mainly present in the aforementioned orthosilicate ions (A) and (B), and both of them are negatively charged, and aggregation is less likely to occur. When the solution is acidic, a part of ortho silicic acid (C) will be formed. At this time, the silicic acid in the solution mainly exists in two forms (B) and (C), and the polymerization reaction is easy to occur, so the gelation rate is the largest. As the pH becomes lower and lower, the concentration of ortho silicic acid (C) becomes smaller and smaller, and the polymerization rate becomes smaller. Therefore there should be a minimum point on the gel curve.
Her (Her) believes that the relationship between gel time and pH is the gelation time as the ordinate and the pH value on the abscissa. The N-shaped curve is obtained. The lowest pH is 5.5 and the highest pH is equal to 2. . The N-shaped curve obtained by Professor Dai Anbang from theory and experiment is shown in the figure below. The lowest point of the curve is pH=7~8, and the highest point is pH=1.5~2.0. [next]
(1) The silicic acid is the most stable near the isoelectric point of silicic acid at pH=2, and the polymerization rate is the smallest;
(2) When pH>2 and pH<1, the rate of silicic acid polymerization increases, and the polymerization rate increases as the pH value increases or decreases until a bulky, loose network structure hydrogel is formed. According to the characteristics of silicic acid, one can try to make it form an easy-to-filter form before gelation, without polymerizing into a gel, which creates favorable conditions for the solid separation of the slurry.
B Ways to prevent silicic acid hazards during leaching of zinc oxide ore The ways to prevent the damage of silicic acid are as follows:
(1) Try not to produce colloidal SiO 2 in the leaching of zinc oxide ore, even if it is produced, it should be minimized.
(2) Zinc oxide leaching does not control the dissolution of SiO 2 , but tries to control the polymerization of silicic acid in the slurry to remove the silicic acid before gelation to improve the solid separation performance of the slurry.
Zinc oxide ore acid leaching process A Vieille-Montagne process The procedure is: first grind the mineral material to 80 μm , add it to the neutral solution of zinc sulfate, and heat it to 70~90 with constant stirring. °C, then slowly (not less than 3h) add human waste liquid containing 100~200g/L of free acid, so that the acidity of the solution is gradually increased, until the pH value reaches 1.5 or so, and the solution contains acid 1.5~15g/L. Leach the end point. Stirring at a temperature of 70 to 90 ° C for 2 to 4 hours allows almost all of the dissolved silicon to be precipitated as insoluble crystalline silicon. At the end of the operation, the slurry contains a zinc sulfate solution, suspended crystalline SiO 2 and a residue. At 70-90 ° C and stirring, the polymerization rate of silicic acid is very high, so that the concentration of colloidal SiO 2 in the solution is lower than the required silicon content in the solution when the leaching reaches the end point, and the concentration of Si0 2 is from 0.487. ~0.762g/L is reduced to 0.147~0.291g/L at the end of stirring. The filtration performance of the slurry is better. After concentration, the filtration rate can reach 125 ~ 652kg / (m 2 · h) dry residue. Since the pulp has a high acid content (1.5~15g/LH 2 SO 4 ), it is necessary to neutralize the acid before it is sent to the purification process. This process can be carried out after filtration or before filtration. [next]
Thailand used the Laoshan method to establish a Tak Zinc Smelter zinc smelter with a Belgian joint venture. The design capacity is 6 x 104t/a electric zinc. It was put into operation in November 1984 and reached production in 1985. The raw material of the plant is from the northwestern part of Thailand, with an average zinc content of 20% to 25%. The main zinc-containing minerals in the ore are: 60% heterogeneous ore, 30% zinc ore, and 10% hydrozinite. . The main production process of the plant is: the ore is transported from the yard to the ore workshop, and the grinding is performed by ball mill and hydrocyclone closed-circuit for wet grinding. The grain size requirement is -80 μm . The finely ground slurry is pumped to the leaching workshop for leaching. Continuous operation was carried out with 5 leaching tanks and 3 neutralization tanks. The leaching tank was lifted by mechanical agitation air, and the leaching time was 8~12 hours, and it was filtered by a horizontal vacuum belt filter.
B Neutralization Condensation Method and EZ Process China Kunming Metallurgical Research Institute developed neutralization coacervation method and the downstream continuous leaching method (EZ method) created by Australian Electric Zinc Co., Ltd., which are further neutralized after oxidized ore acid leaching. The method of cohesion. The EZ method was suspended after an industrial test of 5 t/d. After the 2t/d expansion test, the Kunming Institute of Metallurgy's neutralization coagulation method has built a number of small wet zinc smelting plants with an electric zinc of 200~2000t/a. The treated oxidized ore components generally contain Zn. About 30%.
The neutralization coacervation process consists of two stages of leaching and silicic acid condensation. The agglomerating section mainly processes the SiO 2 dissolved in the slurry, and neutralizes and adds Fe 3+ , A1 3+ coagulant to make the colloidal Si0 2 high. The pH, high Zn 2+ concentration and sufficient counterion Fe 3+ , A1 3+ coagulant are polymerized into relatively close-packed particles, which are easy to filter.