A common method for removing the impurity from mineral powders--PUDA mineral powder packing machine

Whiteness is one of the important optical properties of minerals and one of the important indexes affecting the application of mineral powders.

There are many factors affecting mineral whiteness, such as carbon organic matter and impurity of iron and titanium minerals, valence state of impurity elements in minerals, crystal chemical environment, particle size of minerals, etc.

Among them, carbon organic matter in minerals, impurity containing iron and titanium minerals, valence of impurity elements and other impurities have a negative effect on mineral whiteness and whitening effect. Therefore, removing or reducing their content or influence is conducive to improving the true whiteness or whitening effect of minerals.

At present, the common methods of impurity whitening of minerals mainly include physical method and chemical method, such as mechanical crushing method, heavy separation method, magnetic separation method, flotation method, calcining method, acid leaching method, oxidation method and so on.

Mechanical crushing

Mechanical comminution is a method of pulverizing lumpy minerals into powder by a series of processes.

Common process means include extrusion, impact, friction and shear four ways and their random combination.

Because the impurity Fe and Ti in nonmetallic minerals are very fine in particle size, the impurity monomer can be better stripped and whiten by crushing the mineral.

For the mechanical crushing method, pollution is a very important problem. In the process of grinding materials, the inner wall of the mill and grinding medium are also worn.

Gravity separation method

Reseparation means that the primary ore is washed and broken first, and then impurities such as silicon dioxide are removed by means of jigging and shaking table according to the difference of mineral density.

For example, the density and particle size difference between kaolin and angulite can be used to remove the light organic matter and the high-density impurities containing elements such as iron, titanium and manganese, such as Fe2O3, so as to achieve the purpose of purifying kaolin and reduce or remove the negative influence of impurities on its whiteness.

Magnetic separation method

Magnetic separation is a method of separating minerals in a magnetic field according to their magnetic differences.

Because the magnetic properties of iron minerals are different from those of silica-alumina minerals, magnetic separation can separate the iron impurities in slurry from clay minerals, reduce the iron content of clay minerals and increase the whiteness of clay minerals.

Flotation process

Flotation method USES different physical and chemical properties of mineral surface and the difference of mineral floatability to separate impurities. The commonly used methods are adsorption flotation and double liquid layer flotation.

The adsorption flotation process whitens impurities from clay minerals by using target chemicals.

Calcination method

Calcination is particularly effective at absorbing heat to decompose or produce volatile products such as minerals containing carbon impurities, which can be converted into carbon dioxide for removal.

For example, carbon impurities can be removed by roasting kaolin, magnetic impurities can be removed by magnetization roasting and magnetic separation, and some metal impurities can be removed by chlorination roasting.

Acid leaching

The acid leaching method is mainly to convert the insoluble impurity mineral in the pulp into the ionic state, and then wash it away.

The acid leaching method mainly USES strong and concentrated acid to remove impurities such as Ti and Cr.

The influence factors of acid treatment effect include acid type, acid concentration, acid leaching temperature and acid leaching time, etc.

The inorganic acid bleaching process USES hydrochloric acid or sulfuric acid as the leaching agent to remove iron and whiten at a certain temperature.

Organic acid bleaching is a process in which organic acids such as grape acid, citric acid and oxalic acid are used as leaching agents to whiten clay minerals.

Alkali treatment method

Alkali treatment means to use alkaline solution such as sodium carbonate or sodium hydroxide to convert insoluble valuable metals into soluble salts, and then wash and remove them.

For example, Liu Chuang et al. used NaOH alkali solution to remove Al, Fe and other impurities in quartz sand, so that the quartz sand can meet the requirements of quartz tube for electric light source.

Salt treatment

In the salt treatment method, ammonium chloride or sodium chloride is mainly used. The impurity removal mechanism is that chlorine salt releases Cl2 at high temperature and reacts with the impurities Fe2O3 and TiO2 in the mineral to form gaseous FeCl3 and TiCl4, so as to effectively remove the impurities of iron and titanium in the mineral.

Reduction method

Reduction method is to convert high-priced metal ions into low-priced ions that can be easily removed by reducing agents. Common reducing agents include sodium disulfite, so2 urea, sulfite and so on.

The most commonly used reducing agent is Na2S2O4(safety powder).

oxidation

Oxidation method is aimed at minerals containing pyrite or organic matter. It USES strong oxidants, such as sodium hypochlorite, hydrogen peroxide, potassium permanganate, chlorine gas and ozone, etc. to oxidize them into soluble ionic compounds, so as to achieve the separation effect of minerals and impurities.

The most commonly used oxidant in industry is sodium hypochlorite.

Chemical encapsulation

Chemical encapsulation is the coating of other substances on the outside of the particle, which encapsulates the raw material and improves its performance.

There are two kinds of wrapping methods, one is mechanical coating and the other is chemical precipitation.

Although mechanical coating is simple to operate, due to physical adsorption, the binding force is very weak, and the coating layer is easy to fall off, resulting in the unstable performance of the whole product.

In contrast, chemical precipitation is formed by chemical reactions that form strong chemical bonds, which bind tightly together and make it difficult for the shell to fall off.

Microbial hybridization

The method of microbial impurity removal is to remove the impurity heavy metal by using the biodegradability of microorganism.

At present, there are mainly two microbial treatment technologies: biological oxidation leaching and biological reduction leaching.

Microbial oxidation leaching is a process in which microbial iron oxide mineral impurities are used and then the impurities are removed by rinsing and filtration. It is considered to be an innovative, environmentally friendly and efficient method of iron removal.

Most of the microbial reduction leaching methods use Fe3+ in the form of insoluble oxides in the environment with pH 7. The organic matter is used as the electron donor for the microorganism, and the only electron acceptor is Fe3+. When the oxidized organic matter continues to provide the energy needed for microbial culture, the iron reduction reaction will continue.

Summary

On the whole, physical process is simple, low cost, but low iron removal efficiency, whitening effect is limited, and the product is difficult to meet the requirements of industrial standards.

There are many kinds of chemical iron removal and whitening methods with good effect, but they also have the problems of high cost and environmental pollution. In practical operation, different chemical methods are often combined to learn from each other to achieve the best iron removal effect.

PUDA mineral powder packing machine: