Workers attempting to get close to the regional government offices in southern Namur threw bricks at police, who responded with tear gas and water cannon.
Police said two policemen had to be hospitalized with the others treated locally, all for minor injuries. It was unclear how many protesters were injured.
ArcelorMittal, the world's largest steel company, blamed a slump in demand and structural overcapacity in Europe for last week's decision to close the plants. It says it will continue to operate five steel production lines, which employ 800 people.
The protesters want the regional government to intervene.
"Enough of promises, we want results. We want them (the Walloon region) to take over our plant," ArcelorMittal worker Marc Detrier said of the Walloon regional government.
"I want to tell the workers that I understand their revolt and worry when faced with the future," Di Rupo said.
However it is unlikely that Di Rupo would consider nationalizing the steel plant; opting instead for helping out areas hit by industrial decline by investing in rebuilding the area and new technology.
In the past, he said, "we were able to help certain industries by investing in innovative products."
ArcelorMittal was involved in a similar controversy in France late last year when it revealed plans to close two blast furnaces at its plant in Florange, northern France.
In the end, following talks between Mittal and President Francois Hollande, a deal was agreed where slightly fewer jobs were cut and more was invested in the plant.