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TECHNOLOGY
Level of
scrap sorting
Description
1. Separation of incoming scrap into cast and wrought aluminium scrap
2. Scrap of wrought aluminium alloys within the same series
3.
Scrap of wrought aluminium alloys within the same series having the
same combination of alloying elements
4.
Scrap of wrought aluminium alloys within the same series consisting of
more than 2 compositionally similar/comparable alloys
5.
Scrap of wrought aluminium alloys consisting of 2 alloys within the
same series compositionally similar/comparable
6. Scrap streams of single wrought aluminium alloys
Table 3: Possible industrial levels practiced in wrought aluminium scrap sorting
and under which production scenarios should
the sorted streams used?
A possible way of providing the answers
to the above questions is by calculating the
appropriate composition of the pre-melt mixture
blended from various scrap streams of
different chemical composition, as presented
in Fig. 4.
The model enables: (i) computation of the
recycling-friendly compositions of (wrought)
aluminium alloys based on the known chemical
compositions and compositional tolerance
limits of scrap streams formulated by scrap
sorting in the scrap yard, or (ii) vice versa,
computation of the chemical composition and
compositional tolerance limits of scrap streams
starting from the known composition and tolerance
limits for alloying elements in the selected
aluminium alloy.
The same sorting levels should be applied
to clean and aluminium scrap contaminated
with organics or
other impurities.
Conclusions
The model presented
in this
work enables the
design of optimal
(standard
and non-standard
‘recyclingfriendly’)
compositions and properties of
wrought aluminium alloys with significantly
increased amounts of post-consumed scrap.
The following two routes were modelled in
detail: (i) the blending of standard and nonstandard
compositions of wrought aluminium
alloys starting from post-consumed aluminium
scrap sorted to various degrees simulated
by the model; and (ii) changing the initial
standard composition of wrought aluminium
alloys to non-standard ‘recycling friendly’
ones – with broader concentration tolerance
limits of alloying elements, without influencing
the selected alloy properties, specified in
advance.
The applied algorithms were found to be
very useful in the industrial design of both
procedures: (i) computation of the required
chemical composition of the scrap streams
obtained by sorting (or, in other words, the
post-consumed scrap sorting level), necessary
for achieving the standard wrought alloy composition;
and (ii) transformation of standard
to non-standard (recycling-friendly) compositions
with the key alloy properties (e. g. tensile
strength, elongation) remaining the same.
The most beneficial and particularly promising
approach might be the integral (or combined)
approach, assuring both possibilities:
(i) the standard chemical composition of the
alloy achieved by a sufficient level of post-consumed
scrap sorting predicted by the model,
and (ii) modelling the non-standard alloy
composition by less demanding (and more
cost-effective) sorting, but yet providing end
users with the desired alloy properties.
References
[1] ASM Specialty Handbook, Aluminium and Aluminium
Alloys, ed. J. R. Davis, ASM, Materials Park,
USA, 1998, 20.
[2] G. Gaustad, E. Olivetti, R. Kirchian, Resources,
Conservation and Recycling 58 (2012) 79
[3] A. Gesing, L. Berry, R. Dalton, R. Wolanski, TMS
2002, 3
[4] S. K. Das, Light Metals 2006, TMS 2006, 911
[5] J. T. Staley, R. E. Sanders, Jr., Handbook of Aluminium,
Vol. 2, ed. G. E. Totten, D. S. MacKenzie,
CRC, New York, USA 2003, 319
Author
Varuzan Kevorkijan, Independent Researcher, Betnavska
cesta 6, 2000 Maribor, Slovenia. Contact:
varuzan.kevorkijan@impol.si
Quick payback – ecological benefits – small investment
Dryplus process drastically reduces sludge volumes from anodising lines
The patented Dryplus process developed by
Modena-based Italtecno aims to significantly
increase the dry matter in the sludge from aluminium
anodising treatment lines. It enables
dry fractions to be obtained that are equivalent
to 40-50% of the total aluminium hydroxide
sludge instead of the usual 20-25% achieved
in traditional processes.
The environmental benefit of using Dryplus
technology is clearly evident: the sludge
volume is halved and considerably less truck
journeys are needed to transport the sludge.
This results in significant cost advantages
compared with traditional methods (see table).
The Dryplus process consists of a polypropylene
reactor with a volume of 10-15 m 3
that is suitable for use with alkaline solutions,
such as those from the concentrated rinse tank.
The alkalinity is neutralised in the reactor using
concentrates from the Freeal unit as well
as water from the acid rinse.
Aluminium hydroxide is precipitated out
with the help of a special flocculant from Italtecno,
leading to neutralisation of the concentrated
solutions under wellcontrolled
dynamic physical
conditions.
As a result of this treatment,
the aluminium hydroxide
precipitate has a higher sludge disposal
Estimated cost of
density than in the standard
Annual cost of
process: the dry fraction (40- sludge disposal
50%) is twice what can be
achieved with the conventional
processes used today.
Dryplus has been successfully
applied under actual industrial conditions.
Dryplus can be connected to any existing
waste water treatment plant, which will not
be adversely affected; instead it will be subjected
to less demanding conditions on a dayto-day
basis because the Dryplus technology
will handle the water with the highest impurity
content.
Parameter* Standard process Dryplus process
Dry fraction in sludge 20% 45%
Sludge production 1,300 tpy 578 tpy
80 €/t 80 €/t
104 46,222
Annual saving - 57,778
Based on treatment of water from an anodising line with 30,000 A
installed capacity
The savings in operating costs attributable to
Dryplus are significant and are summarised in
the table.
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