Sensor based electronic sorting proves itself yet again

We can expect electronic sorting to feature in next year's Comminution '25 conference, as X-Ray transmission sorting has become the process of choice for the pre-concentration of crushed ore prior to grinding.

Basic electronic sorting has been around for some time now, being first introduced in the late 1940s with fairly limited applications. Way back in 1979 it gets a mention in the 1st edition of Mineral Processing Technology with a diagram showing a typical sorter of the time, in which the ore was fed in a monolayer, as display of individual particles to the sorting device was essential. Things have progressed a great deal since then with  multi-layer beds and sensors to manage all kinds of ore properties.

1970s ore sorter

Originally their main use was for sorting diamond ores, making use of the fluorescence of diamonds under a beam of X-rays, and I remember my visit to the Premier Diamond Mine at Cullinan in South Africa in 1978, when a few months earlier the recently installed electronic sorter had picked up its first major find, the 353.9 carat Premier Rose. 

The Premier Mine was famous for the largest gem-diamond ever found, the 3106 carat Cullinan Diamond, prised out of the mine face in 1905. Last week there was news that Canada’s Lucara Diamond has recovered the second largest diamond ever found, at 2,492 carats, from its Karowe mine in Botswana. It is the largest diamond ever recovered by a mechanical process.

Lucara diamond

The diamond was detected and recovered by the company’s Mega Diamond Recovery (MDR) X-ray Transmission (XRT) technology, installed by TOMRA in 2017 to identify and preserve large, high-value stones. A computer processes the data gathered from the scan and creates a series of images that identifies individual stones by shape and density. If the density is close to that of a diamond, as the ore falls off the end of the belt, a jet of air blows the candidate into a collection bin.

According to the company, MDR XRT is particularly good for sorting out large, gem-quality diamonds and has already found some exceptional stones, including the 1,758-carat Sewelô diamond and the 1,109-carat Lesedi La Rona. It reinforces the unparalleled value XRT offers not only diamond mining companies but many other operations, making it arguably the most important mineral processing development in recent years.