Flotation of Lead-Zinc Sulfide Ore

Posted on: Apr 28, 2022, · 8 min read.

Lead and zinc are one of the earliest metals extracted by humans from lead-zinc ore. They are widely used in the electrical industry, machinery industry, military industry, metallurgical industry, chemical industry, light industry and pharmaceutical industry and so on. In addition, lead metal also has many uses in the nuclear industry, petroleum industry and other sectors. In the lead-zinc ore, there are 11 kinds of lead industrial minerals and 6 kinds of zinc industrial minerals, among which galena and sphalerite are the most important.

Galena, sphalerite characteristics

The chemical formula of galena is PbS, the crystal structure is equiaxed, the sulfide ions are most closely packed in the cube, and the lead ions are filled in all the octahedral voids. The surface of fresh galena is hydrophobic, and the unoxidized galena is easy to float, and the floatability decreases after the surface is oxidized.

Xanthate or black medicine is a typical collector of galena. Xanthate has chemical adsorption on the surface of galena. Baiyao and ethyl sulfide are also commonly used collectors. Among them, butylammonium black medicine selectively captures galena. take effect.

Dichromate is an effective inhibitor of galena, but its inhibitory effect is decreased for galena activated by Cu2+. Galena that has been inhibited by dichromate is difficult to activate, and can only be activated after treatment with hydrochloric acid or with sodium chloride in an acidic medium. Cyanide cannot inhibit its flotation, sodium sulfide is very sensitive to the flotation of galena, and the presence of excess sulfide ions can inhibit the flotation of galena;

Sulfur dioxide, sulfurous acid and its salts, lime, zinc sulfate or other agents can inhibit the flotation of galena.

The chemical formula of sphalerite is ZnS, the crystal structure is equiaxed, and Zn ions are distributed at the corners of the unit cell and the center of all faces. S is located at the center of four of the eight small cubes into which the unit cell is divided. Potassium permanganate has a strong inhibitory effect on activated sphalerite when the concentration is 4 ～ 6×10\-5 mol/L, but makes it float well when the concentration is high. Its mechanism of action is: when the concentration of potassium permanganate is low, the metal hydroxyl compounds generated by the reaction with the zinc blende surface activation film and surface lattice ions play an inhibitory role and desorb xanthate; when the concentration is high, redox occurs on the mineral surface. The reaction produces a large amount of elemental sulfur.

Cyanide can strongly inhibit sphalerite, in addition, zinc sulfate and thiosulfate can inhibit the flotation of sphalerite.

Lead-zinc ore flotation

Lead-zinc ore is a polymetallic mineral rich in elemental lead and elemental zinc, mainly in the form of sulfide lead-zinc ore and oxide lead-zinc ore. Among them, lead-zinc sulfide ore belongs to easy-to-separate ore; lead-zinc oxide ore belongs to refractory ore. Due to the increasing demand for lead-zinc ore resources worldwide, both lead-zinc ores have mining value.

In the beneficiation process, the lead-zinc ore is mainly flotation, and the flotation methods of the sulfide lead-zinc ore and the oxide lead-zinc ore are different according to the selectivity of the ore. At present, most of the lead and zinc are obtained by sulfide separation, but with the development and utilization of resources, the resources of easily separated lead-zinc sulfide ore are gradually depleted, and the mining of lead-zinc oxide ore has gradually been paid more and more attention.

Compared with lead-zinc sulfide ore, lead-zinc oxide ore has more complex composition, more co-associated minerals, finer embedded particle size, easy to produce slime and contains a lot of soluble salts. Various reasons lead to the difficulty of flotation treatment of lead-zinc oxide ore. big.

This blog mainly introduces the flotation process of lead-zinc sulfide minerals

Flotation of lead-zinc sulfide ore

In the beneficiation process, the sulfide lead-zinc ore is mainly flotation. Among them, the proportion of zinc ore in most lead-zinc ore is higher than that of lead ore. Therefore, in the actual process, the method of "suppressing zinc and floating lead" is generally adopted. Main principles to deal with lead-zinc sulfide ore. The common flotation processes of lead-zinc sulfide ore are mainly: priority flotation, mixed flotation, equal flotation, fractional-speed branch flotation and separation potential flotation.

Common collectors for lead-zinc ore

1. Xanthate such drugs include xanthate, xanthate, etc.
2. Sulfur and nitrogen, such as ethyl sulfide, have stronger collecting ability than xanthate. It has strong ability to collect lead ore and chalcopyrite, weaker ability to collect pyrite, good selectivity, faster flotation speed, and less use than xanthate. It has a stronger collection ratio for the coarse-grained sulfide ore. When it is used for the separation of copper-lead-sulfur ratio ore, it can obtain a better separation effect than xanthate.
3. Black medicine

Black medicine is an effective collector of sulfide ore, and its collecting ability is weaker than that of xanthate, and the solubility product of dihydrocarbyl dithiophosphate of the same metal ion is larger than that of xanthate of the corresponding ion. Black medicine has foaming properties.

Black medicine commonly used in industry are: No. 25 black medicine, butylammonium black medicine, amine black medicine, and naphthenic black medicine. Among them, butylammonium black medicine (dibutylammonium dithiophosphate) is a white powder, which is easily soluble in water, turns black after deliquescence, and has certain foaming properties. It is suitable for the flotation of copper, lead, zinc, nickel and other sulfide minerals. . The weak alkaline pulp has a weak ability to collect pyrite and pyrrhotite, and a relatively strong ability to collect lead ore.

Lead and zinc flotation regulator

Adjusters can be divided into: inhibitors, activators, medium pH adjusters, sludge dispersants, coagulants and coagulants according to their functions in the flotation process.

Modulators include various inorganic compounds (eg, salts, bases, and acids), organic compounds. The same agent often plays different roles under different flotation conditions.

1. Inhibitors
2. Lime (CaO) has strong water absorption, and reacts with water to form slaked lime Ca(OH)2. It is insoluble in water and is a strong alkali. The reaction when added to the flotation pulp is as follows:

CaO+H2O=Ca(OH)2

Ca(OH)2\=CaOH++OH\-

CaOH+=Ca2++0H\-

Lime is often used to increase the pH of pulp and inhibit iron sulfide minerals. In copper sulfide, lead and zinc ores, there are often associated iron sulfide ore (pyrite, pyrrhotite and marcasite, pyrite (such as arsenopyrite), in order to better flotation of copper, lead, zinc Minerals, often add lime to inhibit iron sulfide minerals.

Lime galena, especially galena with a slightly oxidized surface, has an inhibitory effect. Therefore, when flotation of galena from polymetallic sulfide ores, sodium carbonate is often used to adjust the pH of the pulp. If the pH of the slurry must be adjusted with lime due to the high pyrite content, the amount of lime should be controlled.

Lime has an influence on the foaming ability of the foaming agent. For example, the foaming ability of pine oil type dressing agent increases with the increase of pH, and the foaming ability of phenolic foaming agent increases with the increase of pH. and decrease.

Lime itself is a coagulant, which can coagulate the fine particles in the ore pulp. Therefore, when the lime is the most appropriate, the flotation foam can maintain a certain viscosity; when the amount is too large, it will promote the coagulation of fine ore particles, which will cause the foam to stick and expand, which will affect the normal progress of the flotation process.

2. Cyanide (NaCN, KCN) Cyanide is an effective inhibitor in the separation of lead and zinc. Cyanide is mainly sodium cyanide and potassium cyanide, but also calcium cyanide.

Cyanide is a salt formed by strong base and weak acid, which is hydrolyzed in pulp to generate HCN and CN-

KCN=K++CN\-

CN+H2O=HCN++OH\-

It can be seen from the above equilibrium formula that in the alkaline pulp, the CN- concentration is increased, which is beneficial to the inhibition. If the pH is lowered, the formation of HCN (hydrocyanic acid) reduces the inhibitory effect. Therefore, with cyanide, the alkalinity of the pulp must be maintained.

Cyanide is a highly toxic agent, and research into cyanide-free or less-cyanide inhibitors has been ongoing for many years.

3. Zinc sulfate

The pure product of zinc sulfate is white crystal, which is easily soluble in water. It is an inhibitor of sphalerite. Usually, it has inhibitory effect in alkaline pulp. The higher the pH of the pulp, the more obvious the inhibitory effect. Zinc sulfate produces the following reactions in water:

ZnSO4\=Zn2++SO42-

Zn2++2H2O=Zn(OH)2+2H+

Zn(OH)2 is an amphoteric compound, soluble in acid to form a salt

Zn(OH)2+H2SO4\=ZnSO4+2H2O

Zn(OH)2+NaOH=NaHZnO2+H2O

Zn(OH)2+2NaOH=Na2ZnO2+2H2O

When zinc sulfate is used alone, the co-suppression effect is poor, and it is usually used in combination with cyanide, sodium sulfide, sulfite or thiosulfate, sodium carbonate, etc.

The combined use of zinc sulfate and cyanide can enhance the inhibition of sphalerite. The commonly used ratio is: cyanide: zinc sulfate = 1:2-5. At this time, CN- and Zn2+ form colloidal Zn(CN)2 precipitation.

4. Sulfurous acid, sulfite, SO2 gas, etc.

Such agents as sulfurous acid, sulfite, and sulfur dioxide gas include sulfur dioxide (SO2), sulfurous acid (H2SO3), sodium sulfite, and sodium thiosulfate.

Sulfur dioxide dissolves in water to form sulfurous acid:

SO2+H2O=H2SO3

The solubility of sulfur dioxide in water decreases with the increase of temperature. At 18 °C, it is absorbed by water, and the concentration of sulfurous acid is 1.2%; when the temperature rises to 30 °C, the concentration of sulfurous acid is 0.6%. Sulfurous acid and its salts have strong reducing properties, so they are unstable. Sulfurous acid can form acid salts, bisulfites or normal salts (sulfites) with many metal ions. Except for the normal alkali metal sulfites, which are easily soluble in water, normal salts of other metals are slightly soluble in water.

Sulfurous acid dissociates in two steps in water, and the concentration of H2SO3, HSO3- and SO32- in the solution depends on the pH value of the solution. When using sulfite flotation, the pH of the paddle is usually controlled within the range of 5-7. At this time, the inhibitory effect is mainly HSO3-. Sulfur dioxide and sulfurous acid (salt) are mainly used to inhibit pyrite and sphalerite. Use weak acid ore pulp (pH=5-7) caused by lime dissolved with sulfur dioxide, or use sulfur dioxide in combination with zinc sulfate, ferrous sulfate, iron sulfate, etc. as inhibitors.

At this time, galena, pyrite and sphalerite are inhibited, and the inhibited sphalerite can be activated with a small amount of copper sulfate. Sodium thiosulfate, sodium metabisulfite can also be used instead of sulfite) to inhibit sphalerite and pyrite.

For sphalerite, which is strongly activated by copper ions, only sulfite has a poor inhibitory effect. At this time, if zinc sulfate, sodium sulfide or cyanide are added at the same time, the inhibitory effect can be enhanced. Sulfite is prone to oxidative failure in pulp, so its inhibitory effect has time. In order to make the process stable, the method of adding in stages is usually adopted.

5. Foaming agent

The foaming agent should be a heteropolar organic substance, the polar group is hydrophilic, and the non-polar group is aeroophilic, so that the molecules of the foaming agent are aligned at the interface of air and water, and most of the foaming agents are surface-active substances. , which can strongly reduce the surface tension of water. The surface activity of the same series of organic surfactants increases according to the "one-third" rule, which is the so-called "Tefonbe rule". The foaming agent should have proper solubility. The solubility of the foaming agent has a great influence on the foaming performance and the characteristics of forming bubbles. If the solubility is high, the consumption of the drug will be large, or a large amount of foam will occur rapidly, but it cannot be durable. When the solubility is too low, the ice will not dissolve in time. With the loss of foam, or the foaming speed is slow, the duration is long, and it is difficult to control.