Established bauxite

Materials World magazine
,
28 Nov 2018

Michael Schwartz reviews bauxite production globally and focuses on a key producer.

Some 90% of all bauxite mined is processed to produce alumina, and about 90% of alumina is smelted to make aluminium. This is the time-honoured formula for bauxite processing that, for reasons of sheer volume, focuses on the USA. Indeed, it is the US Geological Survey (USGS) that provides invaluable information on current trends. In 2017, for example, saw 4.2Mt consumed in the USA, almost all imported, the value of this quantity being estimated at US$130m.

Country by country, USA bauxite imports came from Jamaica (46%), Brazil (30%) and Guinea (21%). Alumina imports witnessed Australia’s pre-eminence (39%) followed by Surinam (24%) and Brazil (20%). For alumina, Jamaica generated just 5%.

Bauxite resources are estimated to be 55–75 billion tonnes, within Africa (32%), Oceania (23%), South America and the Caribbean (21%), Asia (18%) and elsewhere (6%). Domestic bauxite resources cannot meet long-term USA demand, but the USA and most other major aluminium-producing countries have essentially inexhaustible, but sub-economic, resources of aluminium lying within materials other than bauxite.

Lee Bray, mineral commodity specialist with the USGS, told Materials World, ‘Most bauxite deposits are found at or near the surface. Bauxite forms as a result of chemical weathering of minerals that contain aluminium. Slightly acidic water produced by the reaction of carbon dioxide with rainwater breaks down bonds in the minerals and leaches silicon dioxide, potassium, calcium and other elements away. This leaves behind aluminium hydroxide and iron oxide as well as trace amounts of titanium dioxide and some other elements.’

Precisely because this process happens at the surface, bauxite deposits are generally mined as surface operations, with deposits sometimes extending several miles in all directions. The deposits themselves can range from just a few metres thick to tens of metres thick. Bray explained that underground processes applied to less than 10% of all bauxite mined and occurred where deposits have been covered by sedimentary rocks or lava flows after the bauxite formed. In addition, as the mining of surface deposits is generally cheaper than mining underground, deeply buried deposits are not attractive to most mining companies.

Bauxite is the only raw material used in the production of alumina on a commercial scale in the USA. However, although currently not economically competitive with bauxite, vast resources of clay are technically feasible sources of alumina. These potential alumina sources include alunite, anorthosite, coal wastes and oil shales. Silicon carbide and alumina-zirconia can substitute for bauxite-based abrasives but cost more.

The Bayer process

After bauxite is mined, the aluminium oxide, or alumina, is extracted from it so that the final aluminium product may in turn be produced. The Bayer process, discovered in 1887, is the primary process by which alumina is extracted from bauxite. To produce pure aluminium, alumina is smelted using the Hall–Héroult electrolytic process for what is called primary production.

Three USA-based Bayer refineries produced 4Mt of the total noted. In turn, 60% of the alumina generated went to primary aluminium smelters, the rest to non-metallurgical products such as chemicals, ceramics and refractories.

If not aluminium?

Where the aluminium oxide content of the bauxite has not been diverted to aluminium, the remaining products are deployed to several other processes, notably abrasives, cement, chemicals and refractories. Aluminium oxide, while typically referred to as alumina, may also be called aloxide, aloxite or alundum, depending on the industry and the use determined for the metal.

These alternative uses can include the production of spark plug insulators and metallic paint. There are more specialised uses. As a fuel component for solid rocket boosters, on superconducting devices such as quantum interference devices and electron transistors and even as a dosimeter for radiation protection.

‘Some bauxite still has a high level of silica that inhibits the reagents used to extract aluminium hydroxide. This bauxite is used for other uses such as abrasives, in certain types of cement, as a slag adjuster in the steel industry, or to produce aluminium sulphate,’ said Bray. ‘Some bauxite has extremely low levels of iron and silica so is suitable for use as a refractory material. These uses account for the 10% of bauxite that does not go into alumina production.’

Indonesia’s change of policy

In June 2018 the government of Indonesia permitted exports of bauxite for the first time since January 2014. Export permits were then issued for five years to companies constructing refineries in Indonesia – two have been completed, with another to be completed in 2019.

‘The easing of the export ban by Indonesia has resulted in more bauxite available to certain consumers, mainly in China,’ commented Bray. ‘This has had a minimal impact on the overall supply and pricing. I never characterise a policy decision or price change as good or bad. A consumer is happy with increased availability and decreased price and a producer is less happy when the price decreases. Therefore, I stay neutral on what is good or bad.’

In contrast, Malaysia still bans bauxite mining although allowing exports of stockpiled bauxite. This ban was imposed in January 2016 because of concerns about pollution from mines and uncovered stockpiles at ports.

Guinea Alumina Corporation

Materials World approached alumina operator Guinea Alumina Corporation (GAC), which is a wholly owned subsidiary of Emirates Global Aluminium (EGA) and is currently developing a bauxite mine and associated export facilities in the Republic of Guinea. GAC was founded in 2001 as Global Alumina with the aim of constructing and operating an alumina refinery in the Republic of Guinea. Emirates Global Aluminium acquired full ownership of GAC in May 2013.

GAC’s mining concession has an initial term of 25 years, commencing from its promulgation by the Decree of the President of Guinea in 2005, renewing automatically for a further 25 years, and thereafter ten years on a conditional basis. The current bauxite mine being developed by GAC, along with associated export facilities, lies in the Boké region of northwestern Guinea, close to existing mines that are operated by other companies. GAC’s present operation comprises the first phase of its investment in Guinea.

At present, the drive is towards stable operations. Once these have been achieved, anticipated production is 12Mt/y of bauxite, exclusively for export. Peter Darling, GAC’s communications manager, clarifies, ‘Bauxite typically runs from about 32–60% aluminium. Some goes to refineries in the United Arab Emirates, but the lion’s share goes to China.’

In terrestrial terms, GAC’s project is focused on low hills whose plateaux host the bauxite deposits. GAC is currently at the stage of building the supporting infrastructure, in preparation for a traditional open-pit drill-and-blast operation. The resulting broken material will be loaded directly onto trucks and taken for crushing.

‘It’s surface mining, approximately 1m top soil, 1m of iron-rich capping and between 15m and 45m of bauxite – typically about 25m thick, with the bottom horizon being a second iron-rich zone. Reactive silica, which is important at the refining stage – taking bauxite to alumina – is typically between 1% and 2.5%,’ said Darling.

Moving the mineral by rail and sea

GAC’s concession is close to an existing railway line operated by Compering des Bauxites de Guinée and used by other companies
mining nearby to transport bauxite ore to the port at Kamsar some 75km to the southwest.

A spur now under construction will connect with this railway line. GAC is also building rail loops and facilities both for train loading at its concession and for unloading at its port facilities at Kamsar. Capacity upgrading is also being undertaken along with the other companies involved.

In maritime terms, GAC is constructing a 1.5km jetty with a conveyor belt to move bauxite ore from shore to barge. The bauxite ore will be trans-shipped from these barges to larger ocean-going vessels using EGA’s trans-shipment facilities at anchorage points offshore.

Kamsar is located at the mouth of a river, the Rio Nunez. GAC is widening and deepening the navigation channel from its jetty to the open sea. During construction, it lands materials and equipment at a container terminal built by GAC at Kamsar port, opened in 2016. Once construction of the mine and associated facilities is complete, it will be made available for commercial use by other companies
and organisations.

Corporate social responsibility

GAC will progressively rehabilitate mined areas as it finishes the mining of each plateau. As Peter Darling explained to Materials World, ‘Environmentally it’s highly scrutinised and involves forest, fauna, chimpanzees and natural environmental stewardship.’

Local sourcing is also crucial. Since 2016 more than 56% of the total number of supply contracts GAC has awarded has been won by Guinean companies. The total value of these contracts is over US$37m. However, all too often the goods and services GAC requires are not available in Guinea. To address this social challenge GAC has trained, at the Boké Vocational Training Centre, almost 1,000 young people in skills that directly support construction and mining, maintenance, welding and electrical services.

Bauxite prices

Bray summarised some highly varied price developments in the bauxite sector. The average price Free Alongside Ship (FAS) for USA imports for consumption of metallurgical-grade alumina during the first eight months of 2017 was US$456/t, 34% higher than that of the same period in 2016, while it ranged between US$395/t and US$576/t.

World alumina production through October 2017 increased by 13% compared with that of the same period in 2016. For the first nine months of 2017, the estimated average price (FAS) for USA imports for consumption of crude-dry bauxite was US$29/t, slightly higher than that of the same period in 2016.

Successful operations in several varied countries testify to the stability and financial viability of bauxite.