The Monckton site near Barnsley has struggled to secure enough long-term contracts amid “unprecedented turmoil” in European coke markets.
Owner Hargreaves Services confirmed the closure plan after announcing in October that it would consult the 130-strong workforce about plans to close the plant.
It said there had been no significant improvement in market conditions or customer demand since the initial announcement.
The company pledged to look for alternative employment opportunities for staff, both within the wider company and externally.
The plant, which supplies coke destined for use in glass, detergents and steel manufacturing, has been hit because Chinese coke suppliers are able to undercut international prices.
It had been expected to make a profit of £2m in the current financial year to May, but the company said the outlook beyond this year was ‘’very poor’’ given current market prices.
Hargreaves employs 2,700 people in operations ranging from the importing of coal and coke to bulk haulage.
Last year it closed the Maltby coal mine, near Rotherham, although it still has nine surface mines, including seven in Scotland.
It said that surface mining operations were performing well but warned that 2016 forward coal prices have fallen by a further £4 per tonne in the last three months.
Monckton produced 200,000 tonnes of coke per year.
The coke was produced by baking coal in high-temperature ovens without any air for 20 hours.
During the baking process, by-products such as benzole and tar were removed, leaving coke with a high carbon content.