Production of iron chloride from stainless steel swarf via hydrometallurgy
Typ
Examensarbete för masterexamen
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2020
Författare
Ottink, Thomas
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Stainless steel swarf is a hazardous waste which is largely deposited in landfills.
Recycling of valuable metals from this swarf has been difficult due to its high content
of hazardous metalworking fluids. This thesis presents a hydrometallurgic approach
for the production of iron chlorides from stainless steel swarf. Iron chlorides are
a valuable product and can be used as a flocculant in wastewater treatment. A
swarf sample from the production of ball bearings containing 69% iron (Fe) was
leached with hydrochloric acid (HCl) at static pH levels. Design of experiments and
regression modelling was used to determine the effects of temperature, pH and solid
to liquid (S:L) ratio on the leachability of Fe, Cr, Mn, Ni and Mo. Temperature
and pH greatly influenced the leachability of Ni and leaching rates of Fe and Mn.
Extraction of these metals was generally favored at higher temperatures and acid
concentrations. Operating at a high pH was crucial for preventing dissolution of
both Cr and Mo. Higher temperatures were also found to inhibit leaching of Cr.
While the leachability of most metals was unaffected by S:L ratio, Ni was leached
to a lesser extent at high S:L ratios. A very high purity of Fe was achieved when
leaching at 60oC, pH 4 and S:L=1:20. After leaching for 4 h at these conditions, a
final solution containing 21800 mg/l Fe, 150 mg/l Mn, 12 mg/l Ni and no Cr or Mo
was obtained. Moreover, only 1% of the cutting fluid was transferred to the aqueous
phase. Over 96% of Fe was extracted as FeCl2 and the remaining fraction as FeCl3.
These findings show that metal recovery from stainless steel swarf is possible with
minimal extraction of oil based cutting fluids.
Beskrivning
Ämne/nyckelord
Hydrometallurgy , Selective leaching , Stainless steel swarf , Cutting Fluid , Hydrochloric acid , Ferrous chloride , Ferric chloride