Non-metallic mineral acid, alkali, salt purification methods, equipment and influencing factors

The chemical purification of minerals is the use of chemical differences between different minerals. Chemical or chemical methods combined with physical methods to achieve separation or purification of minerals, mainly used in some high purity requirements, and mechanical and physical beneficiation methods Purification of high value-added minerals that are difficult to achieve purity requirements, such as high purity quartz , kaolin , bentonite , diatomaceous earth, and the like.

Non-metallic acids, bases, salts of mineral processing, mainly under the corresponding acid, an alkali agent effect, the soluble mineral component (useful minerals or mineral impurities) leaching, so that the insoluble mineral components (useful minerals or mineral impurities The process of separation. The leaching process is accomplished by a chemical reaction. The corresponding acids, bases, salts and pharmaceuticals should be used for different useful minerals and impurity minerals.

Table 1 Application range of common acid, alkali and salt treatment methods

1. Non-metallic mineral acid leaching

Acidic leaching commonly used sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, hydrofluoric acid as a leaching agent, of which sulfuric acid is used most.

(1) sulfuric acid leaching

Concentrated sulfuric acid (H2SO4) is a strong oxidant that oxidizes almost all metals when heated. Hydrogen is not released, since oxidation occurs by means of undissociated sulfuric acid molecules, which oxidize most of the sulfides to sulfates.

Concentrated sulfuric acid has a strong water absorption effect, and the clay mineral treated therewith can be used as a water-absorbing desiccant. Many organic substances, especially carbohydrates, once carbonized by contact with concentrated sulfuric acid. Concentrated sulfuric acid treated clay minerals are generally carried out under normal pressure and heated at 100-105 °C.

High purity active silica was prepared by treating diatomaceous earth with sulfuric acid leaching.

(2) Hydrofluoric acid treatment

Hydrofluoric acid was a colorless liquid boiling at 19.4 °C. Vapor has a irritating odor, is extremely toxic, and is more expensive. It can be dissociated into ions in water.

Hydrofluoric acid is characterized by its ability to dissolve SiO2 and silicate to form gaseous SiF4, so it is commonly used to prepare high purity SiO2 or remove mineral SiO2 impurities.

When leaching metal impurities in silica (SiO2), for some finely packed impurity minerals, a small amount of HF (low concentration) is used to help partially dissolve SiO2, so that the impurity metal ions are more easily leached by other agents, such as 0.02. %-0.1% dilute hydrofluoric acid and sodium dithionite (0.02%-0.2%), the treatment of quartz at room temperature can reduce its Fe2O3 content from 0.15% to 0.028%.

Ultra-pure SiO2 is prepared by HF treatment of silica (quartz). The process is as follows: high-grade quartz sand (SiO2 greater than 99.9%) is leached by concentrated HF treatment, SiO2 is dissolved and silicon tetrafluoride gas is generated, and silicon tetrafluoride gas is collected. It reacts with water (deionized water) and deposits pure SiO2, which can reach 99.999%, and the original impurities remain in the solution.

(3) Hydrochloric acid treatment

Hydrochloric acid can react with various metal compounds to form soluble metal chlorides, which have stronger reaction ability than dilute sulfuric acid and can leach some oxoacid salts which cannot be leached by sulfuric acid. Like sulfuric acid, it is widely used in the mineral processing industry. The disadvantage is that the equipment has high corrosion protection requirements.

The iron removal and purification of quartz sand is usually carried out by using hydrochloric acid method or hydrochloric acid in combination with other acids. The solution is treated with 18% hydrochloric acid solution, 5% by weight, heated to 50-80 ° C, and the action time is 2-3 h. The iron (Fe2O3) content was reduced to 0.015%.

Add hydrochloric acid (concentration of 1%-10%) solution and fluorosilicic acid (concentration of 1%-10%) to the slurry containing 20%-80% of quartz sand solids (or after washing with water and hydrochloric acid) And treated with fluorosilicic acid), treated at a temperature between 75 ° C and the boiling point of the solution for 2-3 h, and filtered to remove acid, which can reduce the Fe 2 O 3 content in the quartz sand from 0.059% to 0.0005%-0.0002%.

2. Alkali treatment and salt treatment of minerals

(1) sodium hydroxide

This is currently the most widely used and mature method in China. It is mainly used for the leaching of alkali metals and alkaline earth metal minerals such as silicates and carbonates, such as the purification of graphite and fine-grained diamond concentrates.

(2) Sodium carbonate and sodium sulfide treatment

Sodium carbonate solution has weaker decomposition ability to mineral raw materials, but has higher selectivity and less corrosiveness to equipment. Therefore, mineral raw materials with high carbonate content are still an effective metal ion leaching agent. Commonly used for cation exchange of clay minerals.

Sodium carbonate can also be used in combination with sodium hydroxide to remove metal oxides. For example, in the removal of iron from silica sand, 40%-50% NaOH is added to sodium carbonate, and heated at 100-110 °C for 4-5 hours. After washing and dehydration, the Fe2O3 content is reduced from o.7% to 0.015%-0.025%. .

(3) Sodium chloride, ammonium chloride

Sodium chloride and ammonium chloride can be used as a leaching agent to remove metal impurities from minerals. For example, when silica sand is removed from the silica sand by adding 0.1%-5% ammonium chloride, the temperature at which the ammonium chloride is decomposed is heated. When NaCl is added, the quartz sand is immersed in the solution, and then the sand is satin-fired in a high-temperature furnace, so that the iron in the sand escapes in the form of FeCl3, and the temperature is 650 ° C, and the Fe2O3 content can be reduced from 0.04% to 0.02. %.

3. Main factors affecting the purification effect of acid and alkali

The whole leaching process mainly includes two major steps of diffusion and adsorption-chemical reaction, so the factors affecting the mineral acid-base leaching are:

(1) Raw ore properties (mineral composition, permeability, porosity);

(2) Operating factors (mineral particle size, leaching reagent concentration, leaching time, and agitation during leaching).

The particle size of the mineral raw material has a great influence on the solid-liquid phase interface and the slurry viscosity. Increased fineness increases leaching speed over a range of particle sizes. However, too fine will increase the viscosity of the slurry, and the diffusion resistance will increase to reduce the leaching speed.

The concentration of the leaching reagent is one of the main factors affecting the leaching speed. The higher the concentration of the leaching reagent, the greater the leaching speed.

Stirring during leaching accelerates the completion of the entire leaching reaction with high leaching speed and leaching rate. Under normal circumstances, the stirring speed is increased appropriately, the leaching effect is also good, and the stirring speed is too high, which causes the "synchronous" movement of the ore particles with the solution. At this time, the stirring loses its role of reducing the thickness of the diffusion layer and increases the energy consumption.

4. Mineral leaching process equipment

(1) Percolation leaching tank

Depending on the amount of processing, the housing of the slot can be made of different materials. If the treatment volume is small, carbon steel tank or barrel can be used; when the treatment amount is large, brick, stone and cement are used, and the inner liner is lined with a certain thickness of anti-corrosion layer, and can not leak.

To facilitate the flow of the leachate, the bottom is slightly inclined toward the outlet of the leachate. After plugging the outlet, the ore (less than 10 mm) is evenly filled into the tank by hand or mechanically, and the prepared leaching agent is added, and the solution is immersed for several hours or more before being discharged.

Multiple percolation tanks can be operated simultaneously in production.

(2) Atmospheric pressure stirring leaching equipment (mechanical stirring leaching tank)

The mechanical agitation leaching tank can be divided into two types: single propeller and multi-blade agitation. The mechanical agitator can adopt different shapes, including paddle type, propeller type, anchor type and turbine type.

The material of the agitator should be determined according to the leaching medium. When the acid is immersed, the tank body can be made of carbon steel, lining rubber, acid-resistant brick or PTFE plastic; or stainless steel tank, enamel tank, etc. For alkaline leaching, a common carbon steel tank can be used.

The agitating paddle is generally carbon steel lining, lining glass reinforced plastic or made of stainless steel. The tank body is cylindrical, the groove is a circular or flat bottom, and there is a circulation cylinder in the center. The stirring paddle is mounted in the lower part of the circulation cylinder.

Electric heating, jacket heating or direct steam heating can be used to control the temperature of the leaching process. When the steam is directly heated, the condensation of the steam changes the concentration of the slurry and the concentration of the reagent. The volume of the agitation tank depends on the scale of production, and the mechanical agitation tank is generally used to produce smaller scale factories and mines.

(3) Pressure stirring leaching equipment (whistle air stirring pressure tank)

The slurry enters from the lower end of the kettle, mixes with the compressed air, and enters the kettle through the whirlpool from the nozzle. It rises in the turbulent state and then discharges through the discharge pipe. The heating or cooling of the slurry in the kettle generally adopts a jacket indirect heat transfer mode. The kettle is equipped with an accident discharge tube. After the leaching of the slurry in the autoclave, the pressure must be reduced to normal pressure before being sent to the next operation.