Recovery of metal from slag/mixed metal generated in ferroalloy plants—a case study

Abstract

Most ferroalloy plants lose considerable amounts of metal in their slag and metal–slag mix. A potential source of income for alloy smelters is the massive reserves of metal contained in their slag dumps. Depending on the smelting process and the age of the slag dump, the metal contents vary between 3% and 15%. One important means of reducing costs has been the widespread introduction of metal-from-slag recovery techniques in vogue since mid-1990s. Recovery of metal from mixed metal and slag through mechanized means is widely practiced and assumes immense importance from the metal recovery and environment point of view. A metal-from-slag plant allows producers to cope with fluctuating ferroalloy markets. During times of low prices, a producer can shut down furnaces and rely on the low-cost metal-from-slag product to remain viable. When demand is high, the plant is a low-cost means to boost production. Simple physical (gravity) separation methods like jigging and tabling are in vogue for the recovery of metal. Virtually all charge chrome plants now use the crushing/jigging process to recover chrome alloy from both stockpiled and currently produced slag. Studies were carried out at R&D, Tata Steel to develop a flow sheet for the recovery of metal from metal–slag mix generated in its charge chrome (ferrochrome with 50–60% chromium) plant, Bamnipal. The studies showed that in the case of the charge chrome plant, crushing of mixed metal and slag to below 10 mm followed by jigging of the −10+1 mm material and tabling of the −1 mm material would help recover 10 tpd of metal from the 18 tpd of mixed metal. Based on the studies, a plant is now operational at the Ferro-Alloy Plant (FAP), Bamnipal which recovers ferrochrome metal from mixed metal and slag.