Different minerals have different requirements for the structure and performance of the collector. Sulfide ore has a certain natural hydrophobicity, and the collector used is generally a short carbon chain collector containing a sulfhydryl group; oxidized ore and salt minerals are relatively hydrophilic, and often require a strong collector of a long carbon chain; for such as molybdenite, stibnite, natural sulfur, graphite, coal and other natural clay hydrophobic mineral preferably buoyant, using only the hydrocarbon oil as collector flotation can be achieved. Therefore, collectors can be generally divided into three categories: sulfide ore collectors, oxide ore collectors, and hydrocarbon oil collectors. According to the type of the hydrophilic group, the collector can be divided into xanthate (xanthate), fatty acid, fatty amine, etc. According to the ion type, the collector can be further divided into a cationic collector, an anionic collector, Amphiphilic collectors, non-ionic polar collectors, and neutral oil collectors.

Schematic diagram of the action principle of collector and mineral

A xanthate

The structure and properties of xanthate

Since the discovery of xanthate collectors by Coral in 1925, xanthate has been the most widely used and most important class of sulfide ore collectors. The scientific name of xanthate collector is hydrocarbyl xanthate. In general, xanthate is a product of sodium xanthate, which is commonly known as sodium xanthate or xanthate. The xanthate used in industry is mainly various kinds of xanthate from ethyl to octyl, and xanthate containing more than 4 carbon atoms is also called advanced xanthate. In the synthesis of some advanced xanthate, potassium hydroxide is needed to improve the synthesis efficiency and improve the product traits. The product is potassium salt of xanthogen , which is called potassium xanthate. Yellow medicine is yellow in pure state, industrial products are generally light yellow to orange red powder, smelly, soluble in water, generally can be formulated into an aqueous solution with a mass concentration of 1% to 15%. The low-grade xanthate has no foaming property, and the surface activity of xanthate increases with the hydrocarbon chain. Xanthate is soluble in polar organic solvents such as alcohol and acetone, but insoluble in non-polar solvents such as ether and petroleum ether.

Xanthogen is usually a colorless or yellow oily liquid, an unstable weak acid with a pKa between 2 and 3. As a weak acid salt of xanthogen, xanthate will undergo ionization, hydrolysis, decomposition and other reactions in water, and the stability of its aqueous solution is affected by the pH value of the solution and oxidation. Xanthate is extremely unstable in acidic solution, will rapidly hydrolyze to produce xanthic acid and further decompose into alcohol and carbon disulfide; under alkaline conditions, xanthate is relatively stable, but too high alkali concentration will also cause decomposition of xanthate. The degradation performance of isobutyl xanthate at different pH values ​​is shown in Figure 2.

Degradation performance of isobutyl xanthate in aqueous solution

In the range of pH 7-12, xanthate is oxidized to dixanthin by oxygen or Fe3+ in aqueous solution. Yellow copper ore, galena, pyrite and other minerals sulfide oxidation xanthate has significant catalytic pyrite catalysis strongest. Shuanghuang is also a sulfide ore collector, and its selectivity is better than that of xanthate.

Since xanthate nature is not very stable, and therefore, should be placed when stored ventilated, cool, dry place, preventing contact with an oxidizing agent and a heavy metal compound and the like, to avoid drug decomposition failure.

b preparation method of xanthate

The principle of the synthesis of xanthate is relatively simple. The raw materials used are mainly alcohol, sodium hydroxide (or potassium hydroxide) and carbon disulfide. First, the alcohol reacts with sodium hydroxide to produce sodium alkoxide, and the sodium alkoxide is further reacted with carbon disulfide to form various xanthates. This method is also called the positive feeding method. In the 1970s, the former Shenyang Metallurgical Mineral Processing Chemical Factory invented the “reverse feeding method”, in which the alcohol and carbon disulfide were first added to the reactor (usually a kneading machine), and then slowly. Add sodium hydroxide or potassium hydroxide. The advantage of the anti-feeding method is that the reaction speed is fast, the conversion rate is high, and the product quality is good, so it is quickly promoted.

The main method of industrial preparation of xanthate is direct synthesis using a kneader. The kneader production method has the characteristics of simple process, high efficiency, low cost, no waste water discharge in the production process, and is the main process of the production of xanthate in China. The alcohol, sodium hydroxide and carbon disulfide are basically compounded according to the ratio (molar ratio) of the theoretical substance of 1: 1: general reaction temperature is preferably 10-20 ° C, and the temperature is raised to 30 when the reaction is near completion. ~40 ° C, the outside of the kneader is cooled with ice brine at -25 ~ -15 °C. The temperature must be strictly controlled during the synthesis of xanthate, otherwise it will not only seriously affect the quality of the product but may also cause danger.

At present, the xanthate products produced by China's ore dressing pharmacy are mainly ethyl xanthate, butyl xanthate and isobutyl xanthate, and also produce isopropyl xanthate, (iso)pentyl xanthate and hexyl xanthate. Wait. Zhongxingji xanthate is difficult to synthesize by kneading machine, and the products are mostly sticky. For the synthesis of advanced xanthate with 6 carbon atoms or more, it is easy to obtain a product with better properties by using potassium hydroxide instead of sodium hydroxide.

The xanthate synthesized by the kneading machine method generally contains water, the product has poor stability, can not be stored for too long, and has a shelf life of 3 months, which is suitable for use in the nearest sale. After the yellow drug is dried, a high-quality xanthate can be obtained, and in the production, the granular xanthate is generally obtained by granulation and drying.

It is difficult to achieve closed production by the kneading machine method, and a small amount of carbon disulfide volatilization loss occurs in the production process. In order to solve this problem, a solvent-based synthesis of xanthate has been used, and the method also employs a "reverse addition method" in which the solvent is usually an alcohol of one of the reactants. The solvent process can achieve semi-closed production and semi-automatic control, generally by vacuum evaporation to achieve solvent recovery and at the same time to obtain high quality powdered xanthate. The disadvantage of this method is that the solvent recovery process consumes more energy and increases production costs.

c Xanthate flotation performance

Is the most commonly used xanthate flotation collectors, not only has a good effect on the collector nonferrous metal sulfide ores, oxide ores and for many heavy metals such as white lead, malachite, lead sulfate, silver ore, also has angular catch Ability to collect. In fact, xanthate is used in almost all areas of metal sulfide ore flotation, and it is a sulfide mineral collector with broad spectrum characteristics. As far as the relationship between the molecular structure of the xanthate collector and the flotation performance is concerned, as the carbon chain in the xanthate molecule grows, its ability to capture increases. Although methylphylone has the lowest cost, its ability to capture is too weak, and there is almost no application value in the flotation. Ethyl xanthate and butyl xanthate are the most widely used two kinds of xanthate. They not only have strong harvesting ability and selectivity, but also have a wide range of synthetic raw materials such as ethanol and butanol, and low cost. Five high-grade xanthate drugs such as amyl xanthate, hexyl xanthate and sylvestre xanthate have strong harvesting power and are suitable for flotation of difficult ore dressing, which has a good effect on improving metal recovery rate. The same carbon number of xanthate isomers, such as n-butyl xanthate, isobutyl xanthate and sec-butyl xanthate, have the same flotation performance.

In terms of the relationship between mineral floatability and xanthate collectors, the floatability of minerals generally depends on the solubility of the metal ions of the mineral and the salts of xanthogenate. The greater the solubility, the worse the floatability. For example, the order of solubility of copper, lead, and zinc xanthogenate in water is: Zn2+>Pb2+>Cu+. Therefore, with xanthate as the collector, the floatability of the porphyrite and galena is better than that of flash. Zinc mine. Bornite and galena can be floated using ethyl xanthate, while sphalerite requires high-grade xanthate to float.

In the metal sulfide ore flotation, xanthate is usually formulated into a solution having a mass concentration of 10%, and the amount is generally 50 to 100 g/t, and the flotation pH is generally 8 to 11. The consumption of xanthate depends mainly on three factors: one is the adsorption of hydrophobic layer on the surface of floating minerals, the second is chemical reaction with metal ions in the slurry, and the third is the adsorption of gangue minerals, especially slime, on xanthate. Therefore, for ores with high oxidation rate, high impurity metal ions in the slurry and large sludge content, the dosage of xanthate should be significantly increased, sometimes reaching 200~300g/t. In the flotation of oxidized ore, the amount of xanthate can be as high as 1 kg/t or more.

In recent years, with the increasing demand for mineral resources, such as lean, fine and miscellaneous, and the demand for resource utilization, the research on long-chain high-grade xanthate has received much attention, not only the yellow medicines such as amyl xanthate and hexyl xanthate. Products in China's non-ferrous metal mines have become more and more popular, and some higher-carbon long-chain xanthate such as C8 ~ C10, C10 ~ C12 xanthate have also appeared. It is worth noting that in the application of long-chain yellow yam, mixed xanthate products occupy an important position, including mixed pentyl and butyl xanthate, hexyl and butyl mixed xanthate and so on. Similar to the butyl and ethyl mixed xanthate, the long carbon chain mixed xanthate can play a synergistic effect of different carbon chain xanthate collectors to a certain extent, and is also more conducive to reducing its sales price and improving market competitiveness. .

B xanthate collector

Xanthate is a derivative of xanthate, which is mainly synthesized by the reaction of xanthate with chlorinated hydrocarbons, or by the reaction of xanthate with a compound such as acrylonitrile. Such agents developed in China include alkyl succinic acid acrylate, alkyl xanthate nitrile ethyl ester and alkyl xanthate formate, etc., and are a class of excellent sulfide ore flotation collectors.

a alkyl xylate acrylate

The alkyl xanthate propylene grease is prepared by reacting xanthate with 3-chloropropene at a temperature not exceeding 35 °C.

When ethyl xanthate is used, the product is propylene xanthogenate, when propyl xanthate is used, the product is propyl xanthogen acrylate, and so on. Commercially available propylene terephthalate is ethyl xylenate acrylate (domestic grade 0S-23), n-butyl xanthogen acrylate (domestic grade 0S-43 or 43 xantylene ester), isoamyl jaundice Acrylic acid acrylate (Aero 3302, S-3302 or AF-3302).

The alkyl propyl xanthate is mostly a yellow oily liquid, and its trapping ability is enhanced as the alkyl carbon chain grows. The most characteristic of the propylene terephthalate collector is its selectivity. Its ability to capture pyrite is even weaker than that of black medicine. Even if the pyrite is activated by copper ions, as long as there is a small amount of sodium cyanide. That is, a strong inhibitory effect can occur. The medicament is suitable for flotation of copper-molybdenum sulfide ore, not only can improve the recovery rate of copper and molybdenum, but also can greatly reduce the dosage of the xanthate collector and reduce the cost of the medicament.

b alkyl xanthate nitrile ethyl ester

The alkyl xanthate propionitrile ester can be synthesized by reacting xanthate with acrylonitrile or β-halopropionitrile.

When the xanthate used is ethylxanthate, the product is ethyl xanthate nitrile ethyl ester, abbreviated as 23 yellow nitrite or OSN-23; when the xanthate used is n-butyl xanthate, the product is n-butyl yellow Acetic acid nitrile ethyl ester, referred to as 43 yellow nitrile ester or OSN-43.

The ethyl nitrile ethyl xanthate is an orange-yellow oily liquid, and the n-butyl xanthate nitrile ethyl ester is a pale yellow oily liquid, both of which are selective collectors for copper sulfide ore flotation, which can be used at lower pH. Flotation of copper sulfide ore under the value. In some cases, combined with xanthate collectors, the sorting effect can be improved.

c alkyl xanthate formate

Alkyl xanthate formate is also an important xanthogenate which is synthesized by the reaction of xanthate with chloroformate.

The chloroformate used generally includes methyl chloroformate, ethyl chloroformate and butyl chloroformate. The production of this kind of medicament in China mainly uses ethyl chloroformate as raw material, and the corresponding collector products include ethyl xanthate ethyl formate, isopropyl xanthogen ethyl formate and isobutyl xanthate ethyl formate. Wait. The product is generally a yellow oily liquid, which is characterized in that it is easily dispersed in the pulp, has a high efficacy, and is used in a small amount, and is a selective collector for high-sulfur copper ore flotation, at a pH of 5.0 to 8.5. At the same time, the copper sulfide ore can be floated well.

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