Freebee FY-5 Salt Flux
Salt flux is used when recycling aluminium. This is an introduction to
salt flux composition, usage and ratios. Rotary furnace fluxes and
techniques will be explained, and you will get to know more about
environmental impact, recovery efficiency and the many benefits of
using Freebee FY-5 Salt Flux
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20
Advantages that works for you
Freebee FY-5 Salt Flux is of very high purity and offers several advantages
in aluminium recovery
Freebee FY-5 Salt Flux is of very high purity and it
offers several advantages over the standard salt fluxes
presently used in the majority of reclamation plants.
Freebee FY-5 Salt Flux benefits
1.
2.
3.
4.
Lower flux consumption.
Higher metal recoveries.
Lower energy costs.
A reduction of black dross generated;
therefore less disposal costs.
5. The high purity of Freebee FY-5
reduces the possibility of contaminating
the metal with unwanted elements.
6. Safety - mixing under strict control
ensures the absence of oxidising
agents.
USAGE
Salt flux is used for recovering aluminium from high
surface area or dirty aluminium scrap and dross.
The furnaces used may be reverberatory with side well
or fixed and tilting rotary salt bath furnaces, each of
these furnaces is trying to accomplish the same thing;
that is to melt scrap with minimal losses arising from the
oxidation of the aluminium.
Freebee FY-5 Salt Flux
SALT FLUX RATIOS
Usually a mixture of Sodium Chloride (NaCl) and
Potassium Chloride (KCl) is used to make a salt flux. It
may be seen from the phase diagram that at a weight
ratio of 42% NaCl and 58% KCl the binary mixture
gives a minimum eutectic melting point of 658°C.
Pure NaCl melts at 800.4°C and pure KCl at 790°C.
(Pure aluminium melts at 660°C and its alloys will melt
at lower temperatures).
The benefits of using a mixture close to the eutectic
melting point is that less heat energy would be required
to melt it and so less oxidation of the aluminium would
occur.
However, salt flux mixtures with larger proportions of
NaCl are frequently used because NaCl is cheaper to
buy than KCl. These mixtures will melt at higher
temperatures but the decrease in metal recovery and
increased energy cost due to the higher melting point of
the flux is balanced against the less expensive salt flux.
Using a salt flux in these furnaces provides several
beneficial actions:
1. It protects the aluminium from further oxidation
during melting.
2. It strips the dirt and oxides away from the
surface of the molten aluminium.
3. It suspends the dirt and oxide materials
thereby preventing them from contaminating
the aluminium metal.
Eutectic melting point
Ratio NaCl /KCL
0/100
70/30
50/50
40/60
100/0
Melt Temp Aluminum
1430ºF/777ºC
1287ºF/697ºC
1220ºF/660ºC
1229ºF/665ºC
1480ºF/804ºC
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20
COMPOSITION
Freebee´s FY-5 Salt Flux offers distinct advantages
over other commercially available salt fluxes. These
advantages are due to its composition and very high
purity.
Freebee FY-5 Salt Flux composition
47.5% NaCl
47.5% KCl
5% Synthetic cryolite
THE CRYOLITE EFFECT
A binary mixture of molten NaCl and KCl will protect
aluminium from oxidation and will suspend oxide films
and other particulate but it is not effective in disrupting
the oxide film surrounding the aluminium droplet.
The addition of small amounts of cryolite (3-5%) has the
effect of stripping off the oxide skin surrounding the
aluminium droplets and allows them to coalesce to form
larger droplets that can escape from the liquid salt flux
into the main pool of metal. This increases metal
recovery as it reduces the amount of aluminium
droplets becoming trapped in the spent salt cake.
It is also claimed that when pieces of aluminium scrap
such as shredded cans are melted in a salt flux
containing cryolite, they melt and change shape to a
nearly spherical drop due to the least interfacial area.
Without cryolite the shape remains far from spherical,
thus there is more surface area for oxidation to occur.
Also additions of small quantities of cryolite will depress
the melting point of the salt flux mixture, which will
inhibit still further the possibility of oxidation of the
aluminium and also reduce energy costs.
ROTARY FURNACE FLUXES
The fluxes now used in rotary furnace operation
worldwide have been developed in laboratory and field
use over several years. It is understood that the most
effective salt mixtures are those that melt rapidly at the
lowest melting temperature.
Various combinations of metallic salts have been tested
and reported in technical papers and although some
disagreement is normal in laboratory findings and
conclusions, it is agreed that a flux that melts at the
lowest possible temperature below the melting point of
aluminum is important.
The flux mixture must have the ability to dissolve and
absorb aluminum oxide, dirt and other impurities while
reducing the surface tension of liquid aluminum
globules. Coalescence of the globules is promoted by
the reduction of the surface tension; therefore rapid
fluidity of the aluminum is achieved. Fluxes must not
contaminate the metal nor be volatile or harmful to
employees.
Several mixtures of chemical salts achieve the desired
results, however cost is a major factor due to the
quantities used in a production furnace. Therefore
various blends of sodium chloride (NaCl), potassium
chloride (KCl), aluminum fluoride (ALF3), cryolite
(Na3ALF6), and flour-spar (CaF2) are routinely used in
rotary furnaces.
The grain size of the salts should be the same to
promote homogenous blending but should not be so
fine that it is dusty. Proper sizing is 2-3 mm to minimize
dusting and properly mix with the charge material.
FLUX USAGE TECHNIQUES
The tilting rotary furnace utilizes a dry flux method.
Fixed axis furnaces use a wet method that uses a flux
ratio 0.9 to 1.20. The dry method uses a flux ratio of
0.35 to 0.5. Ratios are calculated on the non-metallic
portion of the charge material. With a 50% dross charge
weighing 10 ton the wet method would require 5 ton of
flux while the dry method would require approximately
2.5 ton. Therefore, with the dry flux method, furnace
capacity is increased, energy saving is realized, and
salt slag disposal is substantially reduced.
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20
The introduction of melting fluxes into the furnace
differs with the type material, amount of contamination,
and metallic percentage in the material. The furnace
condition is also important to the process and the
furnace walls must be kept clean or flux will stick and
build out reducing the capacity of the drum and
adversely affect furnace and energy performance.
Best results with clean high recovery material is
achieved when the flux is charged and melted before
scrap charging whereas flux can be charged with dross
at the same time the dross is charged. With certain
types of contaminated scraps it is often desirable to
charge the flux in stages to curtail burning of
hydrocarbons and other contamination.
Flux must be stored in a dry, clean area. Accurate
weighing of flux is essential to furnace control, optimum
recovery and cost saving. In-sufficient amount of flux
will result in thermitting of the furnace resulting in lost
recovery. Too much flux also results in lost recovery
due to metal becoming trapped in the salt slag.
Flux can often be used more than once with clean
materials. Properly designed salt slag pans are
essential to optimum recovery by capturing any metal
removed with the slag.
Environmental Impact
The use of a salt flux, however, generates spent flux
(black dross), which has high disposal costs. The
amount of black dross produced depends upon type of
furnace and the percentage of aluminium present in the
scrap being melted. E.g. a tilting rotary salt furnace can
use half the amount of flux needed in a fixed rotary salt
furnace, also the more non metallics present in the
scrap the more flux is required.
Impurities
The impurities that are found in commercially available
industrial salts have a pronounced effect on the
efficiency of the scrap re-melting process.
Insoluble materials
These are any materials that do not dissolve into the
molten salt flux, and usually the same materials do not
dissolve in water. Examples are aluminium oxide, iron
oxide, silica and dirt. These materials are detrimental
because they inhibit metal droplet coalescence and
they use up some of the salt flux capacity to hold
oxides.
Calcium Sulphate
Calcium Sulphate (CaSO4) occurs naturally as Gypsum
and is frequently found in the NaCl salt deposits. The
CaSO4 reacts with the molten aluminium and any
magnesium present so that the metals are no longer
available for metal recovery. The reaction may best be
explained by the following reactions.
· 8Al + 3CaSO4 = 4Al2O3 + 3CaS
· 10/ 2/3 Al + 4CaSO4 = CaS + 4 1/3Al2O3 + Al2S3 +
Ca0
· 8Mg + 2CaSO4 = 6MgO + MgS + CaOMgO
For the first two equations it can be calculated that
1 kg of CaSO4 in the salt flux would consume 0.53
kg of aluminium.
Rotary Tilting Furnace
A skin of oxides and sulphides is formed around the
droplets of molten aluminium, which ends up
suspended in the molten salt and contributes to extra
dross formation.
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20
Moisture
Water in the salt flux is detrimental for two reasons.
Firstly you do not want to pay for water and secondly
the presence of water during melting can lead to
enhanced oxide formation and so reduce metal
recovery.
Hazards
In addition to the impurities mentioned above there may
also be the risk of the salt flux being contaminated with
powerful oxidising agents that are of similar appearance
to the salt flux in both colour and texture and yet are
extremely hazardous.
sodium sulphate; this also is a powerful oxidising agent.
Sodium sulphate is widely used in the manufacture of a
variety of products including glass and detergents.
An explosion, which occurred in a rotary furnace, has
been attributed to contamination of the salt flux with
sodium sulphate. Preliminary investigations at a U.K.
University using small laboratory experiments support
this.
Turning the downsides up!
When these oxidising agents and molten aluminium
come into contact there is a rapid and high release of
energy in the form of heat, from the reaction:
Despite the environmental side effects of
recycling aluminium, we must bear in mind, that
aluminium has a very high recovery rate.
2AL + 3/2O2 = Al2O3
Therefore the reclamation plants are doing a
very important job when it comes to preserving
nature.
By using the Freebee FY-5 Salt Flux in a rotary
tilting furnace, the salt cake for landfill will
decrease remarkably.
This together with the huge energy savings turn
out to be essential to our environment.
The many benefits of using the Freebee FY-5
Salt Flux when recovering aluminium from
different type of alumimium scrap are worth
considering.
Used Beverage Cans
Fertilisers such as ammonium nitrate are common
substances and are powerful oxidising agents. There
have been occasions when small quantities of these
substances have been accidentally charged into
aluminium melting furnaces with disastrous
consequences. One kilogram of ammonium nitrate
reacting completely with molten aluminium releases the
equivalent energy of 4 kilograms of TNT.
Optimize your business savings and more
importantly contribute to improve sustainability
and nature.
Another common substance that we believe is used in
China to promote a thermite reaction in furnace skim is
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20
RECOVERY EFFICIENCY
The recovery efficiencies listed below are based on
actual experience. These efficiencies are to be viewed
as guidelines as to what might be expected from the
furnace. It should be noted that actual recoveries are
dependent on many factors and may vary from those
given below.
Average Recoveries and Flux Usage for Typical Materials in rotary furnaces
Material type
Low Copper Sheet-Unpainted – New
Low Copper Sheet – Painted - New
Low Copper Sheet-Unpainted – Old
Low Copper Sheet – Painted - Old
New Cast
Old Cast
Shredded Cast
Swarf-Dry
Swarf-5%0il
Swarf-10% Oil
Closure Bale Scrap
Class 1 Can Body-Clean
Class 2 Can Scrap Lid Laquered
Class 3 Can Scrap-Body-decorated
Class 4 Can Scrap Lid Laquered plus compound
UBC Delacquered
UBC Un-Delacquered
Foil Bare-Mixed Gauge-New Production
Foil Decorated-Mixed Gauge
New Production Painted Extrusions
Litho Print Sheet-New coated without paper
Litho Print sheet-New coated with paper
Old Sheet
Fragmented Automobile Scrap
Greasy Flashings
Dross 40% Metallic
Dross 50% Metallic
Dross 60% Metallic
Dross 70% Metallic
Dross 80% Metallic
Recovery
Efficiency %
95
90
90
85
95
85
90
96
89
80
85
96
89
89
87
89
85
93
85
91
95
83
85
85
75
88
89
90
92
93
Target Flux
Addition %
3
6
3
6
3
10
6
5
8
10
8
8
5
7
6
8
10
5
10
5
4
8
10
8
10
20
18
15
12
10
Contact us today
Our team of experts is looking forward to provide
you with further specifications and pricing.
January 2015. The information in this
folder is subject to change.
Freebee A/S ◦ Bønderskov 4 ◦ DK-5540 Ullerslev ◦ Denmark ◦ www.freebee.dk ◦ [email protected] ◦ Tel: +45 81 10 41 20