Rusal Aughinish on the Shannon Estuary, the largest alumina refinery in Europe, returned to profit last year to record pre-tax profits of $15.59m (€12.15m).

The chief factor behind Ireland’s largest manufacturing site returning to profit arose an exceptional gain of $25.39m from the closing down of its defined benefit pension scheme.

Revenues at Limerick Alumina Refining Ltd and subsidiaries increased by 4%, from $586m to $607.88m, in the 12 months to the end of December 2013.

The pre-tax profit includes a non-cash depreciation cost of $28.9m. The firm also recorded an actuarial loss of $4m on its defined pension scheme.

Separate figures provided to the Environmental Protection Agency confirm the refinery produced over 1.9m tonnes of alumina hydrate last year, a 1% increase on 2012.

The plant extracts alumina from bauxite, with around 70% of bauxite processed at the refinery coming from Guinea in Africa and the remainder from Brazil. The finished product, alumina, is exported for further processing through smelting to aluminium metal.

The pre-tax profit last year follows a pre-tax loss in 2012 of $10.4m — a positive swing of $25.9m.

According to the directors’ report, “during the year, due to a shortfall in the minimum funding requirements of the defined benefit pension scheme, the group entered into discussions with the defined benefit pension trustees regarding the closure of the scheme”.

“An agreement was entered into on October 2, 2013, to cease contributions to the scheme and to transfer employees’ entitlements in the defined benefit scheme to a defined contribution scheme. As a result, a curtailment gain of $25.39m has been recognised.”

In a post-balance sheet event, the accounts state that the group entered into an agreement with Glencore to provide it with alumina from 2014-16. Part payment was received in advance, and the share and assets have been pledged as “security for the advance”.

At the end of December, the group had accumulated profits of $215m — the Aughinish Alumina refinery is valued at $1.2bn by its Russian parent, United Company Rusal.

The company is controlled by Russian oligarch Oleg Deripaska having been purchased from Glencore in 2007.

The numbers employed at Aughinish remained static at 450, though staff costs increased by 15%, from $45.5m to $52.2m.

Shareholder funds stood at $281.42m that included the $215.5m in accumulated profits, with $54m in share capital and other reserves totalling $11.8m.

The filings show that remuneration to directors last year decreased from $670,000 to $654,000.