China targets low grade boron

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Published: Thursday, 28 April 2011

To meet rising domestic demand China’s borates industry must start to develop its low grade boron resources as high grade reserves become depleted. Yu Yongfu assesses processing techniques to improve grade and recovery.


Railing salt mined from the Chaka salt lake of
Qinghai province, China; also an important boron
minerals resource but development is restricted
by poor transport and poor mining conditions.
Panoramio

Boron minerals are mainly used to produce borax, boric acid, various boron compounds and elemental boron.

These derivatives are important chemical raw materials used in a range of sectors such as metallurgy, construction materials, chemicals, nuclear technology, medicine, and agriculture.

Even though China is comparatively rich in boron resources (see panel), boron mineral products are far from meeting the demands of domestic markets.

In 2007, China’s boron mineral production capacity was 145,000 tonnes and borax production capacity was 400,000 tonnes. However, imported boron products amounted to 648,700 tonnes.

The key issue that needs addressing is the fact that China’s richest boron mineral resource is becoming exhausted, and is now in a stage of dilution.

The primary boron mineral exploited today in China is ascharite, from which is produced boric acid and borax.

Indeed, over 95% of raw material used by the Chinese boron industry is ascharite, although, incredibly, the mineral only accounts for 6.64% of China’s total boron reserves.

Paigeite accounts for 58.54% of total reserves, but its exploitation is challenged by complicated structure and outdated processing techniques.

The salt lake deposits mainly distributed in the Qinghai Tibet Plateau account for 33.13% of total reserves, but development here is restricted by poor transport and poor mining conditions.

The majority of the low grade boron minerals, such as ludwigite, owing to their low boron content and high impurities, have not yet been exploited.

Therefore the primary aim for sustainable development of China’s boron industry, and in order to meet domestic demand, is to research and implement the processing of alternative and low grade boron mineral resources.

Boron production

China’s boron mineral production capacity is 487,000 tpa (at standard 12% B2O3 grade). There are eight main boron producing areas in China, and six of these are in Liaoning, accounting for 90% of China’s total boron production.

In Liaoning, boron mineralisation is mainly distributed in the districts of Fengcheng, Kuandian, and Dashiqiao.

The largest deposits are the Fengcheng Wengquanguo deposit, Kuandian Huayuangou deposit, Kuandian Errengou deposit, Kuandian Luanjiago deposit, Kuandian Wudaoling deposit, and the Yinkou Houxianyu deposit.

The massive paigeite deposit of Wengquanguo, Liaoning hosts a demonstrated reserve of 21.85m. tonnes B2O3 and accounts for 58% of China’s total boron reserves.

The deposit contains on average 7.5% B2O3 and 30% Fe. It has a planned mine life of 50-100 years, but has not been fully exploited owing to its complicated structure.

Qinghai province is the second largest boron mineral resource province in China with five large boron mineral deposits: the large Chaidan, small Chaidan, Yiliping, Xitaijinaier, and Chaerhan salt lakes, and the medium sized Dongtaijinaier lake.

Since the 1950s, the ulexite and pinnoite mineralisation on the surface of the Chaidan lakes has been thoroughly exploited, while the mass of diluted minerals at the lakes’ bottom have not been fully exploited.

By the end of the 1980s, surface mining conducted at Temilike, Qinghai, extracted about 1,000 tonnes of ulexite, and mining recovery was about 70% and separation recovery 60-80%. However, in general, boron mineral development in Qinghai remains small scale.

In Tibet, although the boron resource is very rich, and surface mining is amenable, poor transport conditions mean that only the high grade, 20% B2O3, material is taken and the remainder of the resource wasted.

Overall, only a small proportion of China’s boron reserves are exploited, and the high grade boron reserves are becoming depleted.

The majority of the remaining boron resources are characterised by low grade, development difficulties, and complex processing.

Examples include: paigeite at Fengcheng, Wengquanguo, Liaoning, magnesium-calcium borate sediments in the Tibet salt lake, the low grade boron at the bottom of Qinghai large Chaidan Lake, and the low grade ascharite in the north-east.

The boron chemical industry of China will be confronted with a severe shortage of raw materials unless there are breakthroughs on separation technology and new boron mineral resource exploitation.

Progress on separation

Much of the work to date on studying the development of Chinese boron has focused on the endogenic deposits of Liaoning and Jilin, and especially the paigeite at Fengcheng, Wengquangou, Liaoning.

Routine separation

This process utilises gravity separation, magnetic separation, and flotation according to the nature of the minerals.

In 2006, the Changsha Research Institute of Mining & Metallurgy carried out separation technology research and development on the paigeite at Fengcheng, Wengquangou, Liaoning.

Tests were conducted on two mineral samples of Yejiagou section ascharite magnetite type, and Wengquangou section ludwigite magnetite.

The mineral composition was found to be relatively complicated. The usable mineral is mainly magnetite, and then ludwigite and ascharite, and limonite is distributed in fragments. The metal sulphide is mainly pyrrhotite and the gangue mineral is mainly serpentine.

During research, dry pre-separation continuous grinding, magnetic separation, and flotation separation was adopted where the iron and boron were separated by high efficiency magnetic separation technology.

A boron concentrate of 14.37% B2O3 was achieved, with a recovery of 35.03%, and a gross boron recovery of 65.74%.

The recovery process is being used in the design of a 2.2m. tpa paigeite plant at Fengcheng Wengquangou by Liaoning Capital Steel Paigeite Co.

The process flow sheet used by the Liaoning Geologic Experiment Research Institute recovers boron minerals by flotation from gravity separated tailings, takes sulphuric acid as the modifier, soluble glass as the inhibitor, and oxidised paraffin soap as the collector to obtain a boron concentrate of >18% B2O3.

Zhengzhou Mineral Multipurpose Utilization Research Institute of the Ministry of Geology and Mineral Resources has adopted the use of spirals and a table concentrator for recovery of ulichile in its gravity and magnetic separation process.

At the Hunan Changning boron mine, a relatively rare large deposit in south China, calcination is employed which enhances the boron concentrate from 6.5% to 13% with recovery at about 82%. However, the method has been difficult to implement at industrial production levels.

Work on the deposit by the Changsha Research Institute revealed that the boron minerals are mainly holtonite and ascharite, and then ludwigite.

Processing tests showed that a flotation separation magnetic separation combined flow sheet realised a concentrate of 12.13 B2O3, and a recovery of 77.55%. A single flotation separation flow sheet yielded 12.13% B2O3, with a 76.78% recovery.

The results demonstrated that the methods were structurally simple and feasible for industrial production.

Wet separation

The wet separation process mainly deals with boron bearing iron concentrates obtained by magnetic separation. Boron is extracted by acid leaching, boric acid is extracted from lixivium, and then the leaching slag is magnetically separated to obtain the iron concentrate, separating boron from the iron.

Zhengzhou Mineral Multipurpose Utilization Research Institute has carried out such processing and concluded that the technique was characterised by high acid consumption, high production costs, difficult processing of effluent treatment, and hard to solve environmental protection issues.

Pyrogenic separation process

The pyrogenic separation method is characterised by primary iron making and secondary boron extraction, and can be divided into the furnace method and the solid phase reduction fusion separation method.

Northeastern University has put forward its “Furnace Method” to develop paigeite: the boron bearing iron concentrate is first obtained by separation, and then an iron and boron separation test is conducted in a 13m3 furnace, with a processing capacity of 8,000 tpa, producing borax, boric acid, boron bearing pig iron, and magnesium sulphate monohydrate.

Solid phase reduction fusion reduces the 80-90% iron oxide in the raw paigeite or paigeite processed by discarding tailings into metallic iron by non-caking coking coal under 1,110ºC.

The reduced mineral generates the magnetic product with metallic iron and B2O3 slag after magnetic separation, and then the boron bearing pig iron or boron free semi steel or high activity boron rich slag are obtained through fusion and separation by electric furnace.

Recovery of B2O3 and iron is over 95%, and the boron rich slag contains >20% B2O3 and can be used for producing boric acid and borax.

Conclusions

With the objective to alleviate the shortage of Chinese boron minerals by targeting low grade domestic resources and developing suitable processing methods to improve boron concentrate grades and recovery, the industry is focusing on four main areas of research.

New research on separation

Compared with wet and pryogenic separation processes, the routine separation process is characterised by technical applicability, low production costs, and easy industrial application. Research on new separation processes for boron is planned to be enhanced.

New equipment

Since the majority of boron mineralisation coexists with iron mineralisation, and that both are distributed in fine grains, certain high efficiency fine grinding, and separation equipment for iron separation can be applied for boron and iron separation.

Flotation separation agents

The majority of boron minerals are distributed as fine grains and coexist with many gangue minerals, thus separation is difficult. Flotation separation is an efficient method for separation of boron minerals and gangue minerals and for improvement of boron concentrate grades.

Combined separation-smelting

Domestic boron mineralisation is complicated in structure and coexists with many other valuable elements making separation a challenge. With research on a combined process of separation and smelting, elements can be recovered, thus realising the economic value of the mineral resource to its fullest extent.

Source: adapted from “Development and technical progress on separation of China’s boron mineral resource” by Prof. Yu Yongfu, presented at Forum on Development of Boron Industry, 28 September 2010, Shenyang, China. Yu is a member of the China Academy of Engineering and is supervisor of doctoral postgraduates of Ore Processing Engineering discipline at Wuhan University of Technology. He was also senior engineer, Changsha Mining & Metallurgical Research Institute.



China’s boron resources

China’s boron resources, which host a demonstrated reserve of just over 49m. tonnes, are mainly concentrated in two regions: in the north-east, in Liaoning and Jilin provinces; and in the south-west in Qinghai province and Tibet autonomous region (see chart).

Three main metallogenic belts host boron minerals: the Liaoning East Jilin South Sedimentary Metamorphic Boron Mineral Metallogenic Belt; the Qinghai-Tibet Plateau Salt Lake Boron Mineral Metallogenic Belt; and the Jiangsu Liuheyeshan Guangxi Mount Zhongshan Huangbao Skarn Boron Metallogenic Belt.

Chinese boron deposits are divided into two types: continental salt lakes and skarn deposits, with each further divided into exogenic and endogenic deposits.


World boron reserves (total 210m. tonnes B2O3 content)

Source: USGS


Exogenetic deposit types:

Ascharite type: eg. Zhuanmiaogou and Houxianyu, Liaoning.
Ascharite magnetite serpentinite type: eg. Fengcheng, Liaoning; Xiaodonggou, Jilin.
Ascharite magnetite type: eg. Wenguangou, Liaoning.

At Wengquangou, Fengcheng, Liaoning there is a large boron reserve of 21.85m. tonnes.

Besides the dominant boron mineral occurrences within the main regions (see map), Tibet also has boron bearing lake mud and lake water.

The majority of boron mineral reserves in China are characterised by low grade, with ³12% B2O3 accounting for 90.74%, and ³20% B2O3 only 8.54%.

Over 95% of raw material used by the boron industry is ascharite, although, incredibly, the mineral only accounts for 6.64% of China’s total boron reserves.

Paigeite accounts for 58.54% of total reserves, but its exploitation is challenged by complicated structure and outdated processing techniques.

The salt lake deposits mainly distributed in the Qinghai Tibet Plateau account for 33.13% of total reserves, but development here is restricted by poor transport and poor mining conditions.

Chinese boron resource rich regions showing dominant mineral occurrences