In converting cast iron into wrought iron in a reverberatory (puddling) furnace, the furnace is lined with

Haematite lining oxidises carbon, sulphur, phosphorus and silicon in the molten cast iron, for example $\mathrm{Fe}{}_2\mathrm{O}{}_3+3\mathrm{C}\to 2\mathrm{Fe}+3\mathrm{CO}$. A silica or graphite lining would not supply oxygen, and limestone is the basic lining of other steel-making furnaces.