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New technologies in diamond-bearing ore beneficiation

25 february 2019

The development of new technologies in diamond-bearing ore beneficiation is required to increase the stone recovery level and prevent their damage in crushing as well as to reduce the capital and operational expenses of diamond miners.

In recent years, the technology of diamond-bearing ore beneficiation by the Norwegian TOMRA company is increasingly popular and it is based on the use of the X-ray absorption method to detect diamonds. The company produces X-ray (transmission) separators - COM Tertiary XRT - that gradually replace dense medium separation (DMS) plants and X-ray luminescent separators. The COM Tertiary XRT separators use electric X-ray tubes and DUOLINE highly-sensitive innovation touch-sensitive X-ray chambers enabling the use of two independent sensor lines of varying spectral sensitivity. The data transmitted by this chamber is processed by a patented TOMRA Sorting high-speed processor that is able to identify the material atom density irrespective of its thickness. Thus, this technology allows the detection of all diamond types, including the stones with a shell, low luminescent ones and Type II diamonds (having practically no impurities). Besides, the particle size range of the diamonds extracted increases – from 25-30 mm to 60 mm and higher. All this results in a high-quality concentrate requiring no additional processing before manual sorting, which reduces the operational expenses markedly. Moreover, the TOMRA separators feature low power and water consumption.

Canadian Lucara Diamond Corp. was one of the first companies to introduce the TOMRA equipment into its technological cycle. In early 2015, Lucara installed six new separators, 150 tph, at the Karowe diamond mine in Botswana, and the success was not long in coming – in November, the company recovered its 1,109 carat rough diamond, the second largest rough diamond ever recovered (after Cullinan). After Lucara Diamond, other diamond miners like the Australia-based Lucapa Diamond Company Ltd and Merlin Diamonds Limited started using the TOMRA separators. The Russian diamond miners followed suit – in late 2017, the TOMRA separator was installed by AK ALROSA (PAO) at its factory No.14 of the Aikhal Mining and Processing Plant in the Republic of Sakha (Yakutia) to carry out technological testing, and in October 2018, AGD Diamonds (AO) that operates the Grib diamond pipe in the Arkhangelsk Region purchased this equipment and started its commercial use.

The X-ray absorption method was incorporated by other technological enterprises. For example, DebTech (De Beers’ subsidiary) developed a sorting XRT Coarse Concentrator Plus (CC+) facility, and in late 2018, it introduced it at one of the world’s largest diamond mines – Jwaneng in Botswana.

Simultaneously with TOMRA, the Bourevestnik innovation centre (ALROSA’s subsidiary) worked on the development of X-ray separators. By 2014, the сentre developed RGS-1M and RGS-2 X-ray separators that were also introduced at the ALROSA’s enterprises.

To solve the problem of low luminescent diamond extraction, the Russian Irgiredmet research institute developed the method of triboelectric separation based on the electric charges generated during friction. The laboratory and industrial tests of the triboelectric separator showed that its use in the dry conditioning of a diamond concentrate was promising. The Ukrainian ‘Prodekologiya’ research and production firm manufactures the triboelectric separators (Type EBS-T), however, they found wider use in another sphere - in recycling of polymers, e-wastes and cables.

Severalmaz (PAO) (ALROSA Group’s subsidiary) carried out tests of the pilot plant at the Lomonosov Mining & Processing Division (MPD) in the Arkhangelsk Region; the pilot plant is based on the fast-neutron method and was developed by Diamant (OOO) against the order of ALROSA. The plant enables the detection of a diamond in the kimberlite ore without damaging it. The tests allowed determine the optimal plant capacity, 102 kg per hour, and the diamond recovery was 97%. The future Diamant plans included the development of the commercial separator based on the fast-neutron method with the capacity of 30 tons per hour.

The UK-based diamond miner, Gem Diamonds, also concerned about damaging the diamonds during their recovery from the ore has developed and tested their technique of non-mechanical crushing based on the electric power. In 2019, the company scheduled to test this technique using the tailings from the beneficiation plants at the Letseng mine in Botswana.

Among the new developments in the primary beneficiation of the diamond-bearing ores, special mention should go to the Sepair dry (pneumatic) beneficiation plant developed by the Novosibirsk-based Gormashexport company. ALROSA tested the plant in 2011 using poor cut-off grade ores at the Sytykanskaya pipe in the Republic of Sakha (Yakutia). One of the main advantages of this technology is the possibility to work at extremely low temperatures (down to minus 50oC), which is especially important in the severe climate of Yakutia.

Module beneficiation plants are used to process primary deposit ores as well as placer ones, including the ores in detailed exploration. In Russia, these plants are manufactured by Technologies, Equipment and Integration, a research and development company based in St. Petersburg.

The module equipment consists of primary jaw crushers, scrubbers, dense medium separation plants and X-ray units. The units can be used separately or as part of the beneficiation plants. For example, a beneficiation plant OK-Komplekt-4 consisting of three module units: a unit for beneficiation of bulk kimberlite samples, for beneficiation of kern kimberlite, bulk and small–size alluvial samples, and units for conditioning of concentrates, has a capacity of 4 tons per hour. The main advantages of the module beneficiation plants include: the possibility of transportation the equipment by usual freight vehicles; the possibility of installing them on the unequipped sites near mine workings, and low power consumption.

The similar module systems are manufactured abroad by the CDE Global company, Ireland, that offers ‘turn-key’ projects in compliance with the requirements of mining and exploration companies.

On the whole, the technology development level for the beneficiation of diamond-bearing ores in Russia and abroad is approximately the same. That said, the main driver of the technological progress in the ore processing and diamond extraction in the country is, undoubtedly, ALROSA, the leader of the national diamond mining industry.

Anastasiya Smolnikova, Chief Specialist, Solid Minerals Section at All-Russia Research Institute of Mineral Raw Materials