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Thousand Years of LOVE in Coal Preparation


Author Huang heng  

Archimedes, born in 287 B.C., and Roentgen, born in 1845, “fell in love” with each other because of coal preparation. HOT is the witness of the love of the millennium.

In the 1280s, Marco Polo came to China and saw that the Chinese used coal as fuel. At this time, the Chinese had mastered the preliminary coal washing technology.

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Iron smelting by burning coal in ancient Chian

Archimedes (287-212 BC), a great Greek philosopher and encyclopedic scientist, enjoys the reputation of "father of mechanics".Archimedes famously said, "Give me a lever and a place to stand, and I'll move the world."

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The Principle of Buoyancy 

It is said that King Hiero asked smith to make a crown of pure gold for him. However, after finishing the work, the king suspected that the gold crown made by the craftsman was not pure gold; the craftsman had stolen the gold. But he could not destroy the crown to prove that and the crown was as heavy as the pure gold handed over to the goldsmith. This question baffled the king and his ministers. At the suggestion of a minister, the king invited Archimedes to examine the crown.

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Archimedes thought long and hard but could not find a method for proving that the crown was not solid gold. Soon after, he filled a bathtub and noticed that water spilled over the edge as he got in and he realized that the water displaced by his body was equal to the weight of his body. Knowing that gold was heavier than other metals the crown maker could have substituted in, Archimedes had his method to determine that the crown was not pure gold. Forgetting that he was undressed, he went running naked down the streets from his home to the king shouting "Eureka!" (means “I have it”) 

After further experiments, he came to the palace. Archimedes put the crown and the same weight of pure gold in two pots full of water. Comparing the overflow of the two pots, he found that the basin with the crown overflowed more water than the other basin. This shows that the volume of the crown is larger than that of pure gold with the same weight, and the density is not the same, so it is proved that the crown is mixed with other metals.

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The significance of this experiment is far greater than finding out the truth. Archimedes discovered the law of buoyancy (Archimedes principle): the buoyancy obtained by an object in a liquid is equal to the weight of the liquid it discharges.

From the initial jigging coal preparation, the Archimedes principle has monopolized the core principle of coal preparation technology for hundreds of years.

Dense medium shallow slot separator is a coal preparation equipment that was regarded as paying tribute to Archimedes. Because it is really a huge "bathtub". Australian manufacturers call this device Dense Medium Bath, while Americans call this Dense Medium Vessel. It looks like below:

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“Bathtub” made by Techgart  

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William Conrad Roentgen is a famous German physicist. On November 8, 1895, Roentgen discovered X-rays, which paved the way for the creation of medical imaging technology. In 1901, he was awarded the first Nobel Prize in Physics.

This discovery not only had a major impact on medical diagnosis but also directly affected many major scientific discoveries in the 20th century. For example, Anthony Henry Becquerel won the Nobel Prize in Physics in 1903 with the Curies for discovering natural radioactivity.

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The first X-ray Image

Use of X-ray

Today, to commemorate the achievements of Roentgen, X-rays are called Roentgen rays in many countries, and the chemical element No. 111, Rg, is also named after Roentgen.

In the past two hundred years, X-rays have played a huge role in the fields of medicine, security inspection, non-destructive testing, and industrial flaw detection. With the advancement of technology, X-ray photography has experienced various stages of progress from the earliest photographic dry plate to the film/intensifying screen combination to the current digital X-ray image. From the late 1960s to the early 1970s, with the rapid development of computer and microelectronics technology, digital technology, computer network and communication technology sweeping the world have had a wide and profound impact on X-ray imaging equipment. 

The use of X-rays for mineral identification is not new (based on XRF).

In 1974, Jenkinson et al. proposed XRT-based technology for coal gangue separation. The use of this technology in coal preparation practice in the past 15 years. Several highly innovative beneficiation technology companies in Sweden, Germany, and South Africa launched XRT-based dry coal gangue separation technology at almost the same time (who knows what happened within these companies) and implemented it in 2004, which is the world's first XRT coal gangue dry separation system. After the technology was launched, it has been popularized globally. At the 2010 Global Coal Preparation Conference, Lütke von Ketelhodt published a paper "Dry Separation of Coal by Dual Energy X-ray Transmission". XRT technology began to attract the attention of the Chinese coal preparation industry. 

After 2016, XRT technology began to shine in the Chinese coal preparation market.

In fact, as early as the end of the last century (it sounds like a long time, in fact, just more than 20 years ago), there were articles on X-ray technology sorting in the domestic coal preparation field, which did not attract enough attention.

At present, the source of mainstream domestic manufacturing algorithms and technologies comes from a state key laboratory of Tsinghua University (for details, I will talk about it later, XRT, (x-ray-transmission)

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The core of XRT recognition is image recognition, which is a huge amount of basic work. The initial way is to use median filtering to preprocess the X-ray images of coal and gangue. The processed data uses the Robert operator to extract the target edge, and the edge is mapped back to the original image. Then the image is binarized by the Ostu method to calculate the height of coal and gangue; at the same time, the respective peak gray values and height are obtained through image segmentation and histogram analysis. Based on the relationship between gray level and height, the identification conditions and thresholds of coal and gangue are determined, so as to realize the identification of different sizes of coal and gangue. The current recognition technology based on convolutional neural networks has begun to become the mainstream, but it is still a huge amount of basic image processing work.

In this way, after crossing over 2132 years, Archimedes and Roentgen went hand in hand in the field of coal preparation and sang a thousand-year-old scientific love song.

Wait, the article is over? Isn’t there a gamma-ray sorting technology?

gamma rays? Please understand the radiation risks of natural rays, the difficulty of applying for the certificate, and the difficulty of renewing the certificate every year.

Companies that provide XRT technology for coal gangue separation in the coal preparation field:

  • Sweden-TOMRA
  • German-Steinert
  • Poland -COMEX (represented by KRS in Chinese market)

Chinese company:

If you wanna know more, pls contact:

Teresa Zheng, International Business Manager  


Tel/WA:+86 15281626323

Tiffany Chen, International Project Coordinator

Tel/WA: +86 182821-3350

Tari Wang, Mineral Process Engineer & Centrifuge Products Manager


Tel/WA:+86 1592734965

More details of XRT intelligent sorter, pls click my previous articles or the website: