London-listed miner and commodities trader Glencore International PLC (GLEN.LN) is seeking to build out its alumina marketing business, including pursuing contracts with new aluminum smelters starting production in the Middle East, it said Thursday.

The division is already showing growth from 2010 levels.

"We will continue to seek long-term purchase and supply contracts with existing counterparties, as well as targeting new business opportunities with smelters being opened in the Gulf and elsewhere," the company noted in its first half of 2011 earnings.

When Glencore announced its intention to float in London and Hong Kong earlier this year, its prospectus revealed that in 2010 the company marketed around 6.7 million metric tons of alumina, equivalent to 38% of the available alumina that can be marketed and 8% of world output.

It also marketed 3.9 million tons of aluminum, equivalent to 22% of the available aluminum that can be marketed and 9% of world output.

These combined volumes have increased substantially since then, although the company didn't provide a breakdown of whether the growth was in the alumina or metal side.

Marketed volumes for alumina and aluminum increased to 6.5 million tons in the first half compared to 5.6 million tons in the same period the year before, representing an increase of approximately 16%. The division generated revenue of $281 million in the first six months of the year, up 26% from the year-earlier period.

"Alumina arbitrage opportunities were broadly similar in the first half compared to the first half of 2010, apart from China, which swung from being a large importer to being more balanced," Glencore noted.

The average alumina spot price increased to around $400/ton in the first half from $330/ton in the year-earlier period, with average prices of around $405/ton in the second quarter. Glencore attributed this price rise to production problems in various facilities in Australia, start-up of new aluminum smelting capacity in the Gulf region and restarts of idled smelters in Europe and the U.S.

Alumina is the raw material used to make aluminum, which is consumed in the automotive, construction and aerospace sectors. Roughly two tons of alumina is used to make one ton of aluminum metal.