WHITE PAPER
RUST REMOVAL
METHODS
A review of the practical
considerations associated
with different rust removal
technologies
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Brentford, Middlesex TW8 9ES UK
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Rust removal methods
CONTENTS
Summary ........................................................................................................................................... 2
Rust Removal Overview .................................................................................................................. 3
Chemical Rust Removal ................................................................................................................. 3
Table 1. Advantages and Disadvantages of Acid Rust Removal .................................... 3
Table 2. Advantages and Disadvantages of Alkali Rust Removal .................................. 4
Physical Methods of Rust Removal ............................................................................................... 4
Table 3. Advantages and Disadvantages of Blast Rust Removal ................................... 5
Aqueous Technology Rust Removal ............................................................................................. 5
Table 4. Advantages & Disadvantages of Aqueous Rust Removal ................................ 6
Practical Applications of aqueous Chemistry............................................................................. 6
Latest Developments in Aqueous Rust Removal ....................................................................... 7
Table 5. Advantages & Disadvantages of Ultrasonic Rust Removal .............................. 8
conclusions ....................................................................................................................................... 8
Contact Us ......................................................................................................................................... 8
SUMMARY
Rust can be removed from affected parts utilising
an aqueous chelating 1 solution which is not classed
as hazardous, in stark contrast to conventional
chemical and physical rust removal methods, all of
which create serious health and safety risks. The
slow reaction rate of chelating rust removal
chemistry can be overcome by harnessing the
power of ultrasonic technology commonly found in
cleaning operations. Suitable specialist equipment
is readily available in a package with ready to use de-rusting solution in a fully serviced
product, the use of which negates the need to subcontract rust removal operations to 3rd
party suppliers. This approach affords the best opportunity to achieve productivity gains
in a busy industrial environment.
1
Chelation is the formation of a bond non-metallic ions and metal ions to form a molecule.
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Rust removal methods
RUST REMOVAL OVERVIEW
The formation of rust is an extremely complex subject, however it is relentless in its goal
and the damage it can cause is recognised by all. Industry spends billions trying to
prevent its formation and in its safe removal.
This paper looks briefly at the advantages and disadvantages of conventional chemical
and physical methods of rust removal and discusses practical ways to utilise modern
chelating technology which has none of the serious health and safety risks of the
conventional methods.
CHEMICAL RUST REMOVAL
Mineral acids, such as hydrochloric acid, sulphuric acid
and phosphoric acid, are used in industry to remove rust
from iron and steel parts, typically as part of a surface
finishing process, for example hot dip galvanising. Organic
acids, such as tannic acid, can be used, usually in small
scale operations due to cost considerations. They are also
used in proprietary automotive rust treatment products.
Table 1. Advantages and Disadvantages of Acid Rust Removal
Advantages
 Relative low cost
commodity chemicals
 Operate at ambient
temperature
 Fast acting
 Suitable for surface rust
only
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Disadvantages
× Short bath life
× Extremely hazardous chemicals
× Flammable hydrogen gas required
× Attacks base metal also
× Indiscriminate – attacks associated fittings & fixtures
× Leaves active surface prone to flash rusting
× Acidic environment also attacks the fabric of the
building in which it is used
× Waste treatment or removal is expensive
× Control & Extraction of acidic vapours very difficult
× Corrosive environment generates high facilities
maintenance costs
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Rust removal methods
Due to the numerous disadvantages of acid, not least the health and safety concerns, it
is rarely used except where it's low chemical cost and fast acting nature are needed to
sustain the demands of the business.
Hot alkali solutions such as caustic soda (sodium hydroxide) and caustic potash
(potassium hydroxide) will remove rust from iron and steel, and when combined with
sequestering agents to hold the dissolved iron in solution, they can be very effective,
particularly at near boiling temperatures. However since hot alkali is very corrosive,
dissolving soft metals such as aluminium, its use is restricted to iron and steel parts only.
It is commonly used in automotive restoration on body panels and cast iron engine parts
where its ability to remove oil and grease as well as paint residues is beneficial. Typically
this service is offered by specialist 3rd party contractors rather than in house operators.
Table 2. Advantages and Disadvantages of Alkali Rust Removal
Advantages
 Relative low cost commodity
chemicals
 Fairly quick acting
 Does not attack iron or steel base
metal
 Does not leave a highly active
surface
 Can also remove paint and grease
removal too
 Suitable for deep rust removal
Disadvantages
× High temperature operation
× High energy costs
× Extremely dangerous chemicals
× Extremely dangerous high temperature
operation
× Attacks most other metals and organics
× Humidity destroys the building
× Can produce evolved gasses
× Waste treatment or removal is expensive
× Control & extraction of alkaline vapours
very difficult
× Humid environment requires high
maintenance costs
PHYSICAL METHODS OF RUST REMOVAL
Risk assessments and consequential precautions for
chemical rust removal are daunting; it is no surprise
that physical methods, (abrading the surface to
remove rust) seem a favourable alternative. In the
domestic workshop, or low volume environments a
simple wire brush or sander is common. In larger
industry blasting is more typical; historically sand
blasting was used but nowadays there are numerous
specialist blast media to choose from.
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Rust removal methods
Whichever media is used high energy input is required and localised heating results as a
by-product of the friction generated which can irrevocably alter the surface of the part
being treated. Machined parts may lose their tolerances and soft metals or additional
fittings could be destroyed completely. The complete stripping down of parts before
blasting is necessary to preserve these items. Even so the smallest contamination with
blast media can lead to a catastrophic failure of the component in use (i.e a bearing).
New blast media have been devised to overcome some of these risks 2 , i.e. dry ice
disappears totally after use and soda blasting is soft enough to use on aluminium and is
water soluble so it can be completely rinsed free after treatment. These are expensive
options found almost exclusively in high technology industries.
Table 3. Advantages and Disadvantages of Blast Rust Removal
Advantages
 Involves no chemicals
 Removes paint residues too
 Simple manual options for
small volumes
 Not prone to post treatment
“flash rusting”
Disadvantages
× High energy running costs (compressed air)
× High consumable costs
× High labour costs
× Very labour & resource intensive
× Can be extremely noisy
× Inevitable dusty environment
× Can damage base part or surface
× High capital investment
× Can be difficult to automate
× Specialist mediums very expensive
× Different mediums required for different jobs
× Extraction of abrasive dust very difficult
× Abrasive nature leads to high equipment
AQUEOUS TECHNOLOGY RUST REMOVAL
In 1985 a British Patent appeared 3 for a chemical rust removal process which was
aqueous based with a completely neutral pH. It utilises iron's multivalent nature and its
ability to form stable complexes with specific tailored chelating molecules. Put simply,
the solution converts the red rust to a completely different form of iron compound which
is lifted from the surface of the part and into the aqueous solution. In doing so it does not
attack the base metal, and as a neutral aqueous solution it does not attack any other
For a fuller discussion of blast media Abrasive Cleaning and its Application, vol 83, Breziaova and
Dagmar, Trans Tec Publishing, 2015
3
BP 2,157,322A Diversey Ltd. October 1985
2
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Rust removal methods
surfaces or materials either. Subsequent developments have identified alternative
conditions to refine the process. 4 5
From these first inventions the technology has been refined into a practical process that
has a neutral pH and is not classed as hazardous. Various products are on the market 6
which, at a stroke remove all of the hazards from chemical and physical methods of rust
removal listed above. Although it has been in use by industry over the last 15 years, there
is still great potential for this technology.
Table 4. Advantages & Disadvantages of Aqueous Rust Removal
Advantages
 Completely neutral pH
Not classed as hazardous
 Does not attack the base metal
 Aqueous based technology completely
safe on almost all surfaces
 Specifically attacks rust – nothing else
 Operates at ambient temperatures
 Very simple immersion process
 Does not leave a chemically active surface
 Not prone to post treatment “flash rusting”
 Will leave paint and even stickers intact
 Very low energy costs improves
environmental credentials
 Very low maintenance costs as a result
Disadvantages
× Fairly slow acting
× Reaction time reduces as iron
content increases
× Deactivated by absorption of
oxygen (air)
× Rarely suitable for spray
application
× Degreasing preliminary step
necessary
× Guard against rust/remove/rust
etch cycle
PRACTICAL APPLICATIONS OF AQUEOUS
CHEMISTRY
Aqueous technology works only by immersion, it cannot be sprayed or brushed onto
rusty areas. This is because the solution is “deactivated” by absorption of oxygen from
the atmosphere and simply does not work. In fact an oxygenated solution may even
promote surface rusting when sprayed onto unprotected iron or steel, in much the same
way as spraying salty water.
US 4,810,405 Dearborn, March 1989
US 20,060,094,637 A1 Henkel 2005
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Safetykleen Europe Ltd. wwwsafetykleen.eu
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Rust removal methods
In the immersion process this absorption of oxygen
from the atmosphere occurs at the liquid/air interface.
Therefore the whole part must be fully immersed
below the level of the liquid, and agitation of any kind
should be minimised. Otherwise a mechanism of
rusting / rust removal / new rusting may develop which
when repeated will eventually etch into the part.
Process tanks must be made of stainless steel or
plastic; the only other requirement is a means of loading and emptying the parts from the
solution. This may make use of simple baskets or lifting apparatus for heavier parts.
Immersion without agitation can lead to extended rust removal times. Indeed overnight
immersion is recommended and even though this can be efficient in terms of productivity
(particularly as the risk assessment allows this to be carried out safely on site), it can be
limiting in a production environment.
Reaction times can be accelerated by operating at increased temperature, however the
bath life is compromised severely due to absorption of oxygen from the atmosphere
exaggerated by convection currents in the solution. Agitation of a cold solution by
conventional pumps or blades will prevent the solution working at all.
LATEST DEVELOPMENTS IN AQUEOUS RUST
REMOVAL
The use of ultrasonic agitation appears not to
increase surface absorption of oxygen markedly
and yet greatly improves the rate of reaction and
hence rust removal times. This is the latest
evolution of the neutral aqueous de-ruster
technology. It is a very practical option particularly
as the use of ultrasonic equipment has become
more affordable in recent years. Harnessing
ultrasonic power leads to de-rusting action which is
seen instantly on immersion of the component. Process times can be reduced to
minutes, however it should be noted this is variable dependent on the component being
processed. The slow reaction rate is no longer a limiting factor when considering aqueous
rust removal technology over more conventional methods.
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Rust removal methods
Table 5. Advantages & Disadvantages of Ultrasonic Rust Removal
Advantages
 Instant Action
 De-gas function creates ideal
operating conditions
 Completely neutral pH
 Not classed as hazardous
 Does not attack the base
metal
 Aqueous based technology
completely safe on almost all
surfaces
 Specifically removes rust –
nothing else
 Operates even at ambient
temperatures
 Operator free process
Does not leave a chemically
active surface prone to post
treatment “flash rusting”
 Will leave paint and even
stickers intact
Disadvantages
× Reaction time reduces
as iron content
increases
× Deactivated by
absorption of oxygen
(air)
× Degreasing preliminary
step necessary
CONCLUSIONS
The use of aqueous technology typically leads risk assessments to conclude that there is
no longer any reason to contract out rust removal processes given the non-hazardous
nature of the chemical and the low labour requirement of the process.
It is the nature of rust that its severity and frequency varies. Being able to respond in
house greatly improves productivity and can reduce process costs and indirect costs in
relation to transport, administration and the logistics of managing & coordinating 3rd
party contractors.
The simplicity of operation and equipment required lends itself to cell production
environments. Rust removal stations may be positioned for maximum productivity and
with relatively compact machine designs they can easily be located within work cells.
It can be beneficial to contract the supply and maintenance of de-rusting processes to a
service provider; thus allowing fresh solutions to be provided and waste fluids to be
removed in compliance with local legislation. In some cases the equipment may be
provided and maintained as part of this service.
CONTACT US
For more information on our services and solutions please feel free to visit
www.safetykleen.eu, call +44 (0)1909 519300 or email [email protected]
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held responsible for the accuracy of the information herein or for any consequence arising from it. Clients are encouraged to seek
Safetykleen’s current advice on their specific needs before acting upon any of the content.
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