Valuable waste

Recovery of chromite values from ferrochrome industry flue dust

a) Remnants of ferrochrome metal trapped within the slag
b) Remnants of ferrochrome metal along with the flue dust
c) Remnants of ferrochrome metal trapped within the silicates
d) Remnants of ferrochrome metal along the outlines of the chromite grains
C = chromite and FC = ferrochrome metal

XRD pattern of the flue dust sample showing the iron carbide, chromite and quartz phases in the sample

Schematic representation of the mineral separator operation

$a) +500 μm sieve fraction sample showing presence of fused carbon particles (black), metallic particles (shining) and silicates (light/white coloured) (20 x)b) +210 μm sieve fraction sample showing presence of different types of globules with or without metallic particles (30 x)c) +210 μm sieve fraction sample showing presence of broken hollow globules (top), porous globules (bottom right extreme), solid globules and fractured globules (30 x)d) Some of the silicate globules are entrapped within the fused carbon mass in the +210 μm sieve fraction (30 x)$ Mikroaufnahmen mit dem Stereomikroskop • Stereomicroscope photomicrographs

a) +500 μm sieve fraction sample showing presence of fused carbon particles (black), metallic particles (shining) and silicates (light/white coloured) (20 x)
b) +210 μm sieve fraction sample showing presence of different types of globules with or without metallic particles (30 x)
c) +210 μm sieve fraction sample showing presence of broken hollow globules (top), porous globules (bottom right extreme), solid globules and fractured globules (30 x)
d) Some of the silicate globules are entrapped within the fused carbon mass in the +210 μm sieve fraction (30 x)

Mikroaufnahmen mit dem Stereomikroskop • Stereomicroscope photomicrographs

Summary: Ferrochrome industry waste, such as flue dust, contains chromite minerals that are considered to be hazardous materials if left untreated, stockpiled or landfilled. Recovery of chromite values, by physical beneficiation techniques, can be applied to support recycling, the remaining waste being transformed into non-toxic materials for safe disposal. It is beneficial both with regard to saving raw material resources as well as reducing chromium pollution. To understand the nature of this waste and to develop a process for recovery of the chromium values, studies were conducted, with closer examination of the methods and equipment used, e.g. optical microscopy, XRD, Mozley mineral separator and magnetic separation.

1 Introduction

Waste is a source of secondary raw materials, but at the same time can negatively impact the natural environment and public health. The flue dust generated from the ferrochrome industry is one such waste containing chromite minerals. The toxic nature of trivalent and hexavalent chromium makes the flue dust from the ferrochrome industry hazardous. About 400-500 kg residue is generated per tonne of ferrochrome metal produced – this residue includes slag, flue dust and sludge [6]. Flue dust generation is increasing enormously as the production of ferrochrome increases, creating the...