The same element in mineral raw materials tends to be produced in different mineral forms. For example, the forms of iron in quartz are magnetite, hematite, and limonite. These different minerals containing the same elements have very different properties, and the methods and processes for beneficiation and purification are also very different.
Therefore, the occurrence of useful and harmful elements in the ore is an important basis for the preparation of the beneficiation purification plan and the prediction of the separation index.
The analysis of the occurrence state of an element mainly solves two problems: one is the existence form of the element in the ore or the product; the other is the phase composition of the element and its distribution in different mineral phases.
First, the form of the element
The occurrence of useful and harmful elements in ore can be divided into three main forms:
1 independent mineral;
2 types of the same image;
3 adsorption form.
For quartz raw materials such as ordinary vein quartz , quartzite and quartz sandstone , the main source of impurities is various independent minerals in the ore. Such impurities can be purified by conventional techniques to remove most of them, but the inclusions and isomorphisms are similar. Although the content of impurities in quartz is low, it is very difficult to remove due to its special occurrence state, which is the bottleneck for the purification of most quartz raw materials.
The analysis of the occurrence of elements generally uses chemical phase analysis, optical microscopy, electron microscopy, and electron probe analysis.
(1) Independent minerals
The elements are present in the ore as separate minerals, including elemental minerals, compounds and colloidal minerals. In ore, the same element may exist in the form of a mineral or in several different mineral forms.
(1) The same kind of elements are self-assembled into natural element minerals, called elemental minerals . Common elemental minerals such as natural gold , natural silver , natural copper , natural sputum, etc.
(2) Two or more elements are combined with each other to form a compound in the ore, which is the main form of occurrence of the element. For example, iron and oxygen constitute magnetite and hematite; lead and sulfur constitute galena; copper, iron and sulfur constitute chalcopyrite.
(3) The mineral formed by colloidal deposition is called colloidal mineral , and a part of iron, manganese , phosphorus and other ores are enriched by colloid precipitation. When the colloidal solution produces a precipitate, certain beneficial and harmful components are also mixed in to form colloidal minerals such as limonite, hard manganese ore.
(2) The same type of image
In the process of mineral crystallization, a certain particle (atomic, ion or molecule) in its structural unit can be replaced by other particles of similar nature without destroying its crystal structure, called the isomorphism.
As in the quartz lattice, Si 4+ is often replaced by A1 3+ , Fe 3+ , B 3+ , Ti 4+ , Ge 4+ and P 5+ .
Fig.1 Schematic diagram of the structure of trace elements in the quartz crystal lattice
These rare elements are generally not recoverable by mechanical sorting and usually require recovery by pyrometallurgy or hydrometallurgy.
It should be noted that some minerals in the form of separate minerals can sometimes be present in another mineral in the form of tiny droplets or leaf-like inclusions of 1-2 μm. When minerals are present in such a finely dispersed state (<10 μm), mechanical beneficiation cannot be separated.
Therefore, the minerals present in the form of such fine inclusions are generally classified as dispersed, and their selectivity is similar to that of the isomorphic state.
(3) Adsorption form
The form in which certain elements are attracted to other ore-charged substances in an ionic state and present in ores or weathering crusts is called an adsorbed form.
Some elements in the ore-producing ore often exist in this state. For example, rare earth elements adsorbed by clay minerals in granite weathering crusts , such as ionic rare earth minerals discovered in recent years in China.
If useful elements exist in this form, it is powerless to use general chemical phase analysis and rock ore identification methods.
The state of occurrence of elements is different, and the processing method and difficulty level are different. When the elements in the ore are in the form of independent minerals, they are generally recovered by mechanical beneficiation.
Useful elements in the form of isomorphisms, fine inclusions and adsorbed forms are not recoverable by mechanical beneficiation methods and usually require pyrometallurgy or hydrometallurgical recovery.
Second, the basic method of element storage state analysis
Due to the diversity of elements in the ore, the methods and procedures of the survey vary with the characteristics of the ore and the requirements of the mission. It is often necessary to supplement each other with several methods in order to arrive at a reliable conclusion.
Elemental state analysis is usually carried out on the basis of chemical analysis and mineral composition analysis. The purpose is to determine the form of the elements (independent minerals, isomorphisms, adsorption forms) and the different forms of the elements. The size of the scale.
(1) Chemical phase analysis
For elements that exist in different types of independent minerals, chemical phase analysis is generally used to determine the amount and proportion of elements in different minerals.
(II) Mineral micro-area analysis
In order to further ascertain the type of elemental mineral or carrier mineral (the element is present in the mineral with minor or minor components), mineral micro-analysis is usually carried out by means of optical microscopy, electron microscopy, electron probe, ion probe, etc. .
Optical microscopy uses the difference in optical properties of different mineral phases under the microscope to identify and analyze minerals. It is used to analyze the types and relative contents of minerals in ore samples, determine the types of independent minerals and possible carrier minerals, and analyze the elements. The state of occurrence.
Microscopic analysis methods such as electron microscopy, electron probe, and ion probe are effective methods for the identification and analysis of fine trace minerals, especially the ability to determine the microdomain of a mineral phase by energy spectrum analysis, spectral analysis or mass spectrometry. The chemical composition, or the X-ray scanning of the elemental features, is used to analyze the presence of the element in the mineral.
Qta- quartz, Ms- white mica, Tur- tourmaline
Figure 2 Photograph of a quartz sandstone in Jiangyou
Therefore, these analytical methods have become the main methods for studying the state of elemental existence, and can be used for the determination of chemical composition of independent minerals, the determination of isomorphic components, and the determination of the chemical composition of mineral inner rings and fine inclusions.
For example, using the X-ray surface scanning method of the electronic probe element feature, it is possible to accurately determine whether the element exists in the form of an independent mineral or in the form of a homogeneous image or a fine inclusion.
If an element is significantly enriched in a mineral phase, the characteristic X-ray surface scan image is a bright homogeneous spot, indicating that the element exists as a separate mineral;
If an element has a low content and a uniform distribution in a certain mineral phase, the characteristic X-ray surface scan image is a uniform star-shaped fine bright spot, indicating that the element exists in the form of a homogeneous image;
If the trace elements are unevenly distributed on the surface of the mineral, and the characteristic X-ray surface scan image is a small uneven spot with uneven distribution, it indicates that the element exists in the form of fine inclusions.
(3) Electrodialysis
Electrodialysis is an effective method to study the state of adsorption of elements in the form of adsorption. Electrodialysis is based on the action of an external DC high-voltage electric field to desorb ions in the adsorbed state of the mineral and migrate to the opposite polarity electrode. The ratio of the amount that migrates from minerals to water and the total amount of that element in the mineral is called the dialysis rate of that element.
Obviously, the dialysis rate of the element in the adsorption state is much larger than the dialysis rate in other states, and the occurrence state of the element can be determined according to the magnitude of the dialysis rate.
The order of the dialysis rates of the different states of the elements is: adsorption state > independent mineral state > isomorphism.
(4) Analysis of chemical composition of single mineral
The chemical composition analysis of a single mineral is usually a chemical analysis of a single mineral separated and extracted. However, when mineral separation and extraction are difficult, the composition of the mineral micro-area can also be analyzed by means of an electron probe or an ion probe.
The chemical composition analysis of a single mineral can accurately grasp the content of various components in the mineral, and plays an important role in judging the occurrence state of the element.
Usually, the major elements are mainly in the form of independent minerals, while the trace elements are mainly in the form of isomorphic or microinclusions.
Third, the elemental calculation of the elements
The elemental composition refers to the content and proportion of useful elements in the ore in various minerals, and can also be understood as the proportion and dispersion of useful elements in independent minerals (from the viewpoint of mineral processing, where useful elements are used mechanically The ratio of the fine inclusions, the isomorphisms, or the adsorption forms that are difficult to sort can be said to be in a dispersed state.
According to the calculation of the elemental allocation:
It is possible to understand the concentration of elements (independent minerals that can be sorted mechanically) and the dispersion (in the state of dispersed minerals);
It can predict the maximum recovery rate of beneficiation, the highest index (grade) of concentrate, the reasonable loss grade of tailings and the possibility of removing harmful impurities;
It can provide important information for beneficiation purification.
The allocation calculation of the elements is based on the basic state of the element's occurrence. In order to perform the calculation of the elements, it is necessary to obtain the following parameter data:
1 the percentage of minerals in the ore;
2 the content of the element in different minerals;
3 The content (grade) of the element in the ore.
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