Milling Bigadiç borates

Published: Monday, 27 April 2009

In August 2007, a vertical roller mill of type LM 19.20 for colemanite grinding was installed at Eti Maden Isletmeleri’s Bigadiç boron works in Turkey. Dr. Regina Krammer of Loesche reports on its progress

 Loesche’s vertical mill installation has allowed Eti Maden to expand its Bigadiç borates plant by 325,000 tpa. Courtesy Loesche
The modern mining industry in Turkey started with the foundation of the Turkish republic in 1923. Around half of all existing natural minerals can be found in Turkey, of which approximately 60 minerals are economically utilised.

Turkey is one of the leading producers of barytes, boron minerals, celestite, chromite, feldspar, limestone, magnesite, marble, perlite, and pumice. In excess of 150m. tonnes of industrial minerals were produced, accounting for 2.14% of the worldwide trading.

The private sector dominates Turkey’s industrial mineral and metal sectors. Enterprises include exploration and production companies owned by domestic and foreign stockholders, mining and manufacturing subsidiaries of large Turkish conglomerates, and medium-sized family-owned mining companies.

Turkey is the largest producer of boron in the world. Domestic boron reserves contain about 850m. tonnes of borates, which means nearly 63% of all worldwide boron deposits are located in Turkey.

It is estimated that global boron consumption reached 3.7m. tonnes in 2007. Of this amount, the glass sector (glass fibre, glass wool, and borosilicate glasses) consumes the most. The second largest consuming sector is the frit-glaze ceramic sector, which has also increased significantly over the last few years (until recently) due to global economic growth.

Borates find use in several different sectors, however the principal markets are: glass glazes, frits, enamels, flame retardants, insulation, agriculture, detergents and soaps, and flame retardants.

Colemanite, like other borate minerals, is complex and found in playa lakes and other evaporite environments. It is a secondary mineral that is formed by alteration of borax and ulexite. Colemanite is transparent to translucent and forms small but richly faceted crystals of milky white or yellowish colour.

Colemanite grinding at Bigadiç II

The new Loesche mill LM 19.20 was installed at the Bigadiç boron works in Balikesir, Turkey in August 2007. The plant, owned by Eti Maden Isletmeleri, started its production activities in 1976 and since has expanded operations to three open pit mines from which 800,000 tpa of ulexite and colemanite ores are produced.

The raw ore is enriched to produce 650,000 tpa colemanite and ulexite concentrates and milled into 90,000 tpa ground products.

In 2004, the company began the expansion of its 650,000 tpa Bigadiç boron plant with the construction of a third concentrator that would add 325,000 tpa to the Bigadiç plant.

Milling Bigadiç borates

For Bigadiç’s production and throughput requirements, the Loesche mill LM 19.20 was chosen.

The vertical roller mills possess the following design features: a flat grinding table, individually mounted rollers, a hydro-pneumatic spring system, and either two, three, four or six rollers of conical shape. LM 19.20 has a grinding table diameter of 1.9 metres and two grinding rollers.

The grinding principle of a vertical roller mill can be described as follows: the feed material is introduced onto the rotating grinding table, is crushed by the rollers and ground through the action of the forces emanating from the hydraulic roller spring assembly. The grinding material is spun outwards by the rotation of the grinding table.

The upwardly-directed hot gas current captures the material in the vicinity of the louvre ring that surrounds the grinding table and conveys it to the classifier.

Coarse material is rejected by the classifier (according to the grit size) and falls onto the grinding table again in the internal grit recirculation system for renewed grinding. On request, this grit can also be removed directly from the grinding process to use it as pre-material in other processes and products. The final ground product passes through the classifier and exits the Loesche mill with the process gas flow.

No false air intake into the mill occurs due to the complete covering of the rollers, which also means no dust outlet occurs. An autogenously hard-facing within the mill provides from wear.

The erection of the LM 19.20 started in September 2006 and the grinding plant was put successfully in operation in August 2007. The achieved operational data of the plant can be seen in the operational data table.

Operational data of verticle grinder LM 19.20

Guaranteed Achieved
Throughput (tph) 25 29.23
(% passing 75_m sieve) 87 ± 5 90.73
(% passing 45_m sieve) 75 ± 5 75.83

Compact VRM introduction

Loesche used the experience acquired in Bigadiç to respectively develop new concepts for the industrial minerals sector. To tackle ecological and environmental challenges, the company has developed compact vertical roller mills: LM 15.2 (table diameter 1.5 metres) and LM 12.2 (table diameter 1.2 metres).

With these mills several materials such as lime, quicklime, dolomite, talc, bentonite, barite and other minerals can be ground.

The design features of these mills (see LM 15.2 3-D schematic) has some design features which impart the following advantages: a simplified design and therefore very robust; can be preassembled in the workshop with the mill classifier erected onsite site in less than one week (average time 8-9 weeks); and, a telescopic pedestal arrangement enables an easier transport on regular flatbed trucks.

In addition the compact modular system for the grinding plant allows minimum space requirements and the mill enables the control of particle fineness and size distribution.

The mill is also maintenance friendly and shows a high flexibility with respect to product changes. In terms of financial investment, the operational costs are very low; and the lowest possible investments costs can be guaranteed for a standard grinding plant.

Not only in the cement or slag grinding industry, but also in the industrial minerals sector, vertical roller mills show high energy efficiency and flexibility in respect of different materials to be ground.

 General flowsheet of the colemanite grinding plant in Bigadiç with the Loesche mill type LM 19.20 D in green. Courtesy Loesche

Contributors: Dr. Regina Krammer, deputy head of training center, and Thomas Leppak, head of customer support, Loesche GmbH, Germany, and Bekir Aslan of Eti Maden Sletmeleri Genel Müdürlüsü, Turkey.