Experimental studies on treatment and recycling of pickling sludge generated in stainless steel production

Sammanfattning: Pickling sludge generated in the stainless steel industries contains large amounts of calcium fluoride and water and relatively small amounts of metals. Therefore, such sludge is difficult to be directly recycled back to the EAF process and would be harmful to the environment if deposited as landfill for a long term. The main objective of the present thesis work is to find out proper ways to treat the pickling sludge and to recover useful metals from it. For this, characterisations, solid-state reduction and smelting reduction tests on the pickling sludge were carried out in the laboratory. Likewise, comparison studies on solid-state reduction of pure metal oxides with graphite and on pickling sludge with p-coke were conducted using TGA. In addition, the off-gas generated by smelting reduction of pickling sludge was monitored by measurements with a mass spectrometer. Through the present thesis study it can be concluded that it is possible to treat and recycle pickling sludge by using both solid-state reduction and smelting reduction methods. In order to completely separate the reduced metals from the sludge, the smelting reduction method would be preferred.