Pre-selection and waste disposal technology is an indispensable part of modern mining. It aims to remove a large amount of useless materials and increase the proportion of useful minerals by pre-sorting ore, thereby reducing the processing volume of subsequent processes, reducing production costs and improving economic benefits. According to different mineral characteristics, pre-selection and waste disposal technology is mainly divided into several methods such as manual picking and waste disposal, photoelectric sorting and waste disposal, gravity separation and waste disposal technology and magnetic separation. These technologies and their equipment will be introduced in detail below.

1. Manual picking and waste disposal

Manual picking and waste disposal is the earliest pre-selection and waste disposal method used. It was once widely used in the pre-disposal of coal mines, gold mines, tin mines and other minerals in my country. Manual picking has the limitations of low sorting efficiency, high labor costs and high labor intensity of workers. With the development and progress of pre-selection equipment, manual picking is gradually withdrawing from the stage of history and being replaced by intelligent photoelectric mineral processing technology.

2. Photoelectric sorting and waste disposal

Photoelectric sorting and waste disposal technology is widely used in pre-waste disposal, and is suitable for pre-selection and disposal of various ores such as lead-zinc ore, tungsten ore, limonite, copper oxide ore, molybdenum ore, spodumene, antimony ore, coal gangue, fluorite, talc, wollastonite, calcite, barite, silicon slag, phosphate ore, magnesite, etc. Photoelectric sorting technology is mainly divided into photoelectric color sorting, visible light intelligent sorting technology and X-ray intelligent sorting technology.

2.1 Photoelectric color sorting technology: The color sorter mainly uses the different frequencies or wavelengths of light waves reflected by materials of different colors to separate useful minerals from waste rocks. This technology is widely used in the sorting of calcite, quartz, calcium carbonate, potassium feldspar, fluorite, dolomite, barite, electrolytic aluminum, etc. The color sorter has a high sorting accuracy and is especially suitable for processing ores with obvious surface characteristics.

2.2 Visible light(optical) intelligent sorting technology: Visible light(optical) intelligent sorting technology mainly uses the surface feature differences of the ore to be sorted for identification and sorting. It can mainly identify multiple colors, textures, gloss, shapes, luster, spots and other features, and perform composite sorting to separate useful minerals from waste minerals. Visible light intelligent sorting technology is particularly suitable for all kinds of ores with complex surface features and difficult sorting.

2.3 X-ray intelligent sorting technology: X-ray intelligent sorting machine is the most commonly used equipment, suitable for all kinds of metal mines and coal gangue and other ores, and its feed particle size range is generally 10-300mm. The sorting principle of X-ray intelligent sorting machine is to detect the density and composition of the ore through X-ray penetration technology, so as to achieve the sorting of the ore.

3. Gravity separation and discarding technology

Gravity separation is suitable for sorting ores with large differences in particle size and density. Heavy medium pre-selection and discarding technology and jigging pre-selection and discarding technology are the most widely used methods of gravity separation and pre-disposal technology. Its advantages are low production cost, large material processing volume and low environmental pollution.

Heavy medium pre-selection: Heavy medium beneficiation is usually used for pre-disposal of ores with coarse-grained or aggregated distribution, as well as pre-disposal of ores that are easily separated by monomers during the crushing process. Heavy medium cyclone is a common heavy medium pre-disposal equipment in industry. Its separation is based on the Archimedean principle. It uses heavy medium with a density between the target mineral and the gangue mineral to make low-density particles float and high-density particles sink, thereby achieving the separation process.

Jigging pre-selection: Jigging is an effective method for treating coarse and medium ores. Its working principle is to separate materials in vertical alternating media according to density differences. Jigging pre-selection and disposal method is widely used in the pretreatment of coal mines, tin-copper mines, tungsten mines and other minerals.

4. Magnetic separation

Magnetic pre-disposal technology is often used to treat iron ores such as magnetite and hematite. There are two common magnetic pre-disposal processes, namely coarse dry magnetic pre-disposal and pre-grinding wet pre-disposal. The earliest magnetic separation pre-waste was to use permanent magnetic (electromagnetic) magnetic drums to pre-select and discard coarse-grained strong magnetic iron ore. Later, for ores with higher dissociation after fine crushing, special drum magnetic separators were used. In order to solve the pre-selection and discarding of weak magnetic coarse particles, permanent magnetic drum strong magnetic separators appeared.

With the development and utilization of mineral resources, the types of ores have increased, the beneficiation process has become more complicated, and the requirements for beneficiation equipment have become higher and higher. The pre-selection and discarding technology conforms to the concept of "early discarding when possible, more crushing and less grinding", and has the advantages of reducing the subsequent operation processing volume, improving the selection grade, and reducing enterprise costs. With the advancement of beneficiation technology and the development of beneficiation equipment, the particle size range of pre-selection and discarding will become wider and wider, and the types of minerals will become more and more.

In the future, intelligent photoelectric beneficiation equipment will play a greater role in the field of complex polymetallic ores, difficult beneficiation, and low-grade ores. The demand for large processing capacity, high discarding rate and high sorting accuracy, and high adaptability of different types of ores will become the research and development direction of intelligent photoelectric beneficiation equipment.