clean technology brochure

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Understanding Clean Technology


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Understanding Clean Technology

by Dr. Campbell PageTFL Ledertechnik AG

CH-4106 Basel

Version 2 , December 2004


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Contents:

1. Introduction 42. Leather production pathway 63. Solid wastes 7

3.1 Solid wastes in effluent 73.2 Suspended solids in effluent 7

4. Liquid wastes 84.1 Waste water treatment 84.2 Improvements possible using optimised processes 11

5. Contaminants in waste water 135.1 pH value 135.2 Oxygen demand 13

5.2.1 Chemical oxygen demand (COD) 145.2.2 Biochemical oxygen demand (BOD5) 14

5.3 Nitrogen 14

5.4 Sulphide (S2-) 155.5 Sulphates (SO4

2-) 155.6 Chlorides (Cl- ) 165.7 Oils and grease 165.8 Metals from the tannage 16

5.8.1 Chromium salts (chromium III, trivalent chrome) 175.8.2 Other metals 17

5.9 AOX chemicals and APEO surfactants 185.10 Toxicity of effluent components 18

6. Air wastes 197. Finished leather - unwanted contaminants 19

7.1 Formaldehyde in leather 207.2 Chromium (VI) in leather 227.3 Aromatic amines in leather 237.4 Heavy metals in leather 247.5 NMP-free polyurethane finishing products 247.6 EU Directive restricting NPE and NP products 25

8. Wet-white, wet-blue, vegetable extract? 269. Trends, future laws and restrictions 26


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1. Introduction

The raw hide or skin is a by-product of the meat industry and from this rawmaterial the leather tanning industry converts approximately 25% by weightinto leather. The production of leather from the raw hides and skins involves

an intensive use of water as well as many mechanical and chemicalprocessing steps. Consequently the tanning industry generates considerableamounts of solid, liquid and gaseous wastes. Well planned clean technologypractices through the use of minimising, re-cycling, and re-use of water andsolids following the best available technologies (BAT), can allow tanners tocomply with tough environmental pressures.

The modern leather industry has a responsibility to operate in a manner that iscompatible with the best ecological and environmental practices. Worldwidethere is a lot of emphasis on these aspects, which is requiring many tanneriesand supply industries to have a better understanding of the whole

environmental picture from the start to the end.

Consequently many new developments in the field of application processes,chemicals and dyes, as well as the process control and mechanicaldevelopments are concerned with clean technology. This means ecologicalfactors like reducing the load in the wastewater, exhaust emissions andlowering solid waste production have become the focus. Often it is asked ifthe new environment-friendly processes and products are also feasible for thetannery from the point of view of economy. There are many very positive andimpressive examples, which prove that economical and ecologicalconsiderations are not irreconcilable; to mention but a few:

safe and reliable hair-save processes;

ammonium-free deliming;

dust-free enzymes;

high-exhaust chrome tannage;

low salt liquid syntans and dyes;

solvent-free aqueous finishes.

Clean technology processes can have up-front additional costs but thesehave to be balanced against large savings from lower wastewater charges

and reduced sludge disposal costs. The regulations relating to ourenvironment will become stricter in the coming years and clean technologyhas to be understood and implemented.The idea of this brochure is to help the lay person understand the factorsinvolved and provide in a clear and uncomplicated way some of the optionsthat one has.


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Schematic overview of the clean technology inputs andoutputs for leather production

tannerywater, 25 - 50 m3

raw hide + chemicals(1000 kg)

solid wastes, 600 kg

finished leather, 250 kg

wastewater, 25 - 50 m

3


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2. Leather production pathway

Main chemical wastes Solid/air wastes

salt (manual removal) Raw hides

salt (TDS) Soaking

Green fleshing fleshings

sulphides, lime Unhairing, liming H2S

Lime fleshing trimmings and fleshings

ammonia N Deliming, bating

salt, chrome andvegetable tanning

agents

Pickling, tanning

Chrome splitting,shaving

shavings (chrome)trimmings (chrome)

vegetable extracts,chromium salts, salt(sulphate)

Retanning, dyeing,fatliquoring

Drying

Buffing, trimming leather trimmings, dust

liquid finishing residues,solvents

Finishing VOC

Leather


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3. Solid wastes

chrome shavings / gluestock and fleshings / fat

solids in effluent

sludge

The solid wastes like shavings, fleshing and trimming wastes and natural fatare normally reasonably efficiently removed in mechanical operations. Theycan be readily collected for further processing and a number of possible usesfor these wastes are available, such as converting to gelatine, etc.

3.1 Solid wastes in effluent

Gross solids are those larger than an effluent sampling devices can handle,hence they are not measured. The waste components that give rise to thisproblem are:

trimmings and gross shavings;

fleshing residues;

solid hair debris;

large pieces of leather cuttings;

other solid contaminants like paper/plastic bags.

They can be removed by means of coarse bar screens set in the wastewaterflow. If not removed these materials can block the pipes causing severeproblems.

3.2 Suspended solids in effluent

Main source:Most of the suspended solids are protein residues from the beamhouseoperations - mainly from the liming process. However, large quantities arealso produced owing to non-exhausted vegetable tannins, another sourcebeing poor uptake during retanning.

Problems:If the wastewater is to be treated on-site, the main problems that arise are due

to the large volume of sludge that forms as the solids settle. Sludge oftencontains up to 97% water, giving rise to very large quantities of 'light' sludge.Even viscous sludge has a water content of around 93%, and can easily blocksludge pumps and pipes. All this sludge has to be removed, transported, de-watered, dried and disposed of.


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Analysis:The suspended solids component of an effluent is defined as the quantity ofinsoluble matter contained in the wastewater and can be determined byfiltration or by centrifugation.The majority of these solids settle within 5 to 10 minutes, although some fine

solids require more than an hour to settle. Semi-colloidal solids are very finesolids that will not settle even after a considerable period of time. They can,however, be filtered from solutions. Together with the more readily settleablesolids, they thus comprise the suspended solids of an effluent that can bemeasured.

4. Liquid wastes

Sources of liquid wastes

4.1 Waste water treatment

The major part of the waste in a tannery is diluted in the effluent. This sewagewater cannot be discharged into surface waters or even communalwastewater without intensive treatment in purification plants.Legal limits are given as concentrations of the relevant pollutant in thewastewater, usually in milligrams/litre (mg/l), sometimes as parts per million(ppm). Peaks of concentrations of certain toxic pollutants above these limitsmust be avoided to protect the environment. Most of the communal fees arecalculated according to the sum parameter; where the total amount of adischarged pollutant per day or per month is determined. However, thedisposal charges can also include penalty fees if the peak limits areexceeded. Typically holding tanks are used to even out fluctuations over a

24h period.

Beamhouse81%

Wet-end

19%


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tannery effluent

unhairing liming

pickling / tanning

sulphide

oxidation

chromeprecipitation

balancingtank

(24h)primary

settling tank

(4h)

flocculation

sludge

Primary treatment of waste water

As a simple overview the process is as follows:

Primary treatment (precipitation and flocculation treatments):

- removed 50 90% total suspended solids40 70% CODapprox. 60% BOD

- not removed inorganic salts

Many tanneries undertake this primary treatment process either on-site or in acollective water treatment facility. Through flocculation and precipitation itremoves most of the suspended organic matter and anionic organic productslike syntans, fatliquors and dyes. Prior to this the concentrated sulphide wastestream is separated and converted by aeration to sulphates, as well thechromium waste stream can be separated and in modern treatment plants thechromium salts can be relatively easily precipitated and recycled.


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Secondary (biological) treatment of waste water

A simple overview the secondary or biological process that follows the primarytreatment is as follows:

Secondary treatment (biological treatment):

removed 80% total suspended solids70% COD99% BOD

not removed inorganic salts

The standard aerobic biological treatment plant will readily degrade the typicaleffluents of leather processing. Once the bacteria in the active sludge havedigested the organic components they will settle out and be removed as

sludge. To avoid depleting the bacteria in the active sludge it is important thatsome 40% of the liquid flow-through is returned to the digestion tank.The nitrogenous compounds can be broken down by combining intensiveaerobic and anoxic biological treatments. The oxygen demand is very high,thus leading to correspondingly high operational and energy costs, (40% ofthe oxygen demand).

An efficiently run secondary treatment plant can meet relatively stringent limitsfor COD and BOD and allow discharge to surface water. Tanners are oftenreluctant to re-use water as they are not certain what contaminants remain init. However, this water, which will contain residual salts, can be considered for

re-use, for example in the pickle float.

40 % return

treated waste

biolo ical di estion

settlin tank

slud e

water

secondar


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0

100

200

300

400

Beamhouse Wet-End

kg/tonrawh

ides

Standard

Optimised

4.2 Improvements possible using optimised processes

As has been indicated it is difficult to remove inorganic salts from waste waterby waste water treatment plants. So logically it is best to try and minimise theamount used in producing leather. A number of reduced salt processes have

been developed and the results of one study using an optimised (low-salt)procedure are presented. If we take a specific parameter such as totaldissolved salt (TDS), which is a considerable problem in locations where thewater supplies are limited and are not close to the sea, there can besignificant reductions in the amount of TDS in the waste water. Naturally themajor effect of implementing an optimised process is to be had in theBeamhouse.

Change in TDS parameter when using a low-salt optimised process

The individual components in the effluents were also measured in order tohave a better overall idea of how the effluent parameters have changed. Asexpected the salts like sulphate and chloride are noticeably reduced.


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0

50

100

150

200

250300

350

400

COD BOD chloride sulfide sulfate TDS

kg/tonraw

hides

Standard beamhouse

Optimised beamhouse

0

5

10

15

20

25

30

35

COD BOD chloride sulphate TDS

kg/tonrawh

ides

Standard wet-end

Optimised wet-end

Waste water analysis in the whole Beamhouse process

Waste water analysis in the whole Wet-End process


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5. Contaminants in waste water

The effect on the environment of excessive pollutant levels commonly foundin untreated tannery effluents can be severe. So it is important that wastewater parameters can be measured and monitored.

The individual components that are typically measured in effluents and theirimpact are described below in a simplified manner for guidance. The mainproblems presented by those components are summarised together with anoutline of quantitative analytical methods.

5.1 pH value

Main source:Most discharged floats.

Problem:

Acceptable limits for the discharge of wastewaters to both surface waters andsewers vary, ranging between from pH 5.5 to 10.0. If the surface water pHshifts too far away from the pH range of 6.5 - 7.5, sensitive fish and plant lifeare susceptible to loss.Municipal and common treatment plants prefer discharges to be slightlyalkaline as it reduces the corrosive effect on concrete and helps compensatefor the domestic wastewater that tends to be slightly acid. When biologicalprocesses are included as part of the treatment, the pH is lowered to moreneutral conditions by the carbon dioxide so evolved.

Analysis:pH-meter; titration with acid / alkali.

5.2 Oxygen demand

Main source:Surfactants, all non-exhausted organic auxiliaries, hide substance from theliming process, ammonium and sulphide.

Problem:All these components in effluents are broken down by bacterial action into

more simple components. Oxygen is required for both the survival of thesebacteria (aerobic bacteria) and the breakdown of the components. Dependingon their composition, this breakdown can be quite rapid or may take a verylong time.

If effluent with a high oxygen demand is discharged directly into surfacewater, the sensitive balance maintained in the water becomes overloaded.Oxygen is stripped from the water causing oxygen dependent plants, bacteria,and fish to die. The outcome is an environment populated by non-oxygendependent (anaerobic) bacteria leading to toxic water conditions.A healthy river can tolerate substances with low levels of oxygen demand.

The load created by tanneries can be excessive, so the effluent requirestreatment prior to discharge.


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Analysis:This can be achieved in two different ways:

5.2.1 Chemical oxygen demand (COD)

This method measures the oxygen required to oxidise the effluent samplecompletely. It gives a value for all the contaminants, which means thematerials that would normally be digested in the BOD5 analysis (within 5days), the longer term biodegradable products, as well as the chemicals thatremain unaffected by bacterial activity.The method is fast and very aggressive. A suitable volume of effluent is boiledwith an oxidiser (potassium dichromate) and sulphuric acid. As the effluentcomponents oxidise, they use oxygen from the potassium dichromate. Theamount used is determined by titration.

5.2.2 Biochemical oxygen demand (BOD5)

This method is more complex. Essentially, the effluent sample is diluted inwater, the pH is adjusted and it is seeded with bacteria (often settled sewageeffluent). The samples are then incubated in the dark for five days at 20C.Bacteria use the oxygen dissolved in the water while the organic matter in thesample is broken down. The oxygen remaining is determined and the BOD5can be calculated by comparison to the oxygen in the effluent-free sample.The results of the BOD5 are always lower than those obtained using the CODanalysis. As a rule of thumb, the ratio between COD: BOD is 2.5:1, althoughin untreated effluent samples variations can be found as great as 2:1 and 3:1.This depends on the chemicals used in the different leather making processes

and their rate of biodegradability.

5.3 Nitrogen

Main source:The most common sources are ammonia (from deliming materials) and thenitrogen contained in proteinaceous materials (from liming/unhairingoperations).

Problem:Nitrogen is a key nutrition factor for plants. High levels released bysubstances containing nitrogen over-stimulate growth. Water-based plantsand algae grow too rapidly, thereby waterways become clogged and flows areimpaired.The nitrogen released through protein breakdown and the deliming process isin the form of ammonia. Large volumes of oxygen are needed so bacteria canconvert it into water and nitrogen gas. If oxygen demand is greater than thelevel supplied naturally by the water stream, toxic anaerobic conditions canrapidly develop.Both processes lead to an eutrophication of the surface water.


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Analysis:Ammonia is released from the wastewater by boiling it with sodium hydroxide,and subsequently trapping it in a boric acid solution. The level of ammoniareleased is determined by titration and its value calculated as ammoniacalnitrogen.

The other method, the Total Kjeldahl Nitrogen (TKN) method, analyses all thenitrogenous matter including proteins. This is broken down first by boiling thesample with sulphuric acid to form ammonium compounds. These are thenanalysed according to the method above.

5.4 Sulphide (S2-)

Main source:Sodium sulphide, sodium hydrosulphide and the breakdown of hair in theunhairing process.

Problems:The problem here arises when the pH of the effluent drops below 9.5, verytoxic hydrogen sulphide gas, H2S, evolves from the effluent: Characterised bya smell of rotten eggs. Even a low concentration causes headaches, nausea,and eye irritation. At higher levels it is lethal.Hydrogen sulphide is readily soluble in water and causes rapid corrosion ofmetal pipes, fittings and building materials. If discharged to surface water,even low concentrations can be a toxicological hazard.

Analysis:The most accurate methods rely on the acidification of effluent to generatehydrogen sulphide. It is trapped and converted into zinc sulphide. The amountof sulphide is determined by titration.

5.5 Sulphates (SO42-)

Main source:Sulphuric acid, chromium sulphate tanning and retanning agents and sodiumsulphate, used as a standardising salt in many powdered products like batingenzymes, synthetic retanning agents and dyes.An additional source is created by oxidation of sulphide from in the effluent

treatment process.

Problem:Problems arise with soluble sulphates for two main reasons:1. Sulphates cannot be removed completely from a solution by chemicalmeans. Under certain biological conditions, it is possible to remove thesulphate from a solution and bind the sulphur into micro-organisms.Generally, however, the sulphate either remains as sulphate or is brokendown by anaerobic bacteria to produce malodorous hydrogen sulphide. Ifeffluents remain static this bacterial conversion process occurs very rapidly ineffluent treatment plants, sewage systems and watercourses. This results in

the corrosion of metal parts and concrete.2. The total concentration of salts (TDS) in the surface water is increased.


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Analysis:Adding barium chloride solution to a sample of filtered effluent.

5.6 Chlorides (Cl- )

Main source:Common salt (sodium chloride) used in hide and skin preservation or thepickling process.

Problem:Chlorides are highly soluble and stable, and cannot be removed by effluenttreatment and nature. They remain as a problem in surface waters sincechlorides inhibit the growth of plants, bacteria and fish. If the effluent water isused for irrigation purposes, surface salinity increases through evaporation.High salt contents are only acceptable if the effluents are discharged intotidal/marine environments.

Analysis:Titrating of effluent with a silver nitrate solution.

5.7 Oils and grease

Main source:Natural oils and grease released from the skin structure, non-exhaustedfatliquors.

Problem:Grease and fatty particles tend to float and agglomerate, they bind to othermaterials causing potential blockage problems especially in effluent treatmentsystems. Grease or thin layers of oil on the water surface can reduce theoxygen transfer from the atmosphere. If these fatty substances are inemulsions, they can create a very high oxygen demand on account of theirslow bio-degradability.

Analysis:Extraction of the effluent sample with a suitable solvent and evaporation of theorganic phase. The residual grease can be weighed and calculated.

5.8 Metals from the tannage

Metal compounds are not biodegradable. They can thus be regarded as long-term environmental features. Heavy metals are the subjects of close attentionsince they can also have accumulative properties.


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5.8.1 Chromium salts (chromium III, trivalent chrome)

Main source:Non-exhausted floats from the tanning and retanning.

Problem:Chrome tanning is carried out in form of greenish chromium (III) sulphatesalts. (It should be clearly differentiated from the highly toxic and oxidisingchromium (VI) chromate salts, which are not used for tanning.)

Excess chromium sulphate from the tanning process float is typicallydischarged to a separate tank, where it can be easily precipitated underalkaline conditions and collected by filtration for re-use. This procedure is acommon practice worldwide and efficiently removes most of the solublechromium salts from the effluent.

A small amount of the chromium salts can also be washed out from theleather during retanning, dyeing and acidification processes, so together withproteins it finishes up in the sludge. Depending on the amount of chromiumthe sludge it may be required to be disposed of separately as a hazardouswaste.

Analysis:Oxidation of the sample by nitric acid to form the soluble chromate. Severalanalytical techniques are possible, for example, atomic absorption; titration asbarium chromate or colorimetric measurement at 670 nm.

5.8.2 Other metals

Main source:Non-exhausted floats from chrome-free aluminium or zirconium based tanningand retanning processes.

Problem:Depending on the chemical species, these metals have differing toxicity that isalso affected by the presence of other organic matter, complexing agents andthe pH of the water. Aluminium, in particular, appears to inhibit the growth ofgreen algae and crustaceans are sensitive to it in low concentrations.

Analysis:Complexometric titration methods using chelating ligands like EDTA andspecific indicators.


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5.9 AOX chemicals and APEO surfactants

Main source:Degreasing of small skins and finishing operations.

Problems:Organic halogen containing chemicals (AOX) and alkyl phenol ethoxylatedsurfactants (APEO), e.g. nonylphenyl ethoxylate (NPE), can be difficult tobreak down. Thus they can remain in the eco-system for extended periods oftime and can accumulate in the food chain.These substances with low bio-degradability in effluents discharged to surfacewaters can contribute significantly to the COD/BOD load.

Analysis:Highly specialised methods often based on HPLC (high performance liquidchromatography) or GC (gas chromatography).

5.10 Toxicity of effluent components

Main source:Non-exhausted bactericides and fungicides, tanning agents.

Problems:Biocides by their very nature are toxic or they would not function. They areused to protect the partially processed hides from bacterial and fungaldamage. Often processes using these substances cannot be avoided. If theyare insufficiently exhausted during the process or spilled by accident, they endup in the wastewater and can cause problems in the sewage plant and insurface waters.

Analysis:A measure of toxicity of a chemical in water can be expressed as LD50,representing the dose, which will kill 50 per cent of a sample species. Notevery species reacts to the same degree to a given exposure, and the type ofresponse to an equal dose of a chemical may differ widely. When values aregiven, the species under test should be stated and the time period taken forevaluation should normally be either 24 hours, 96 hours or 14 days.

Highly specialised analytical methods often based on HPLC (highperformance liquid chromatography) or GC (gas chromatography).


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6. Air wastes

In the water treatment processes like tanning and post-tanning it is unlikelyany significant air emissions will be released if good operating procedures arefollowed. With sulphides from the liming / unhairing process as long as the pH

is kept above 8.5 then the formation of H2S gas is avoided.

In the finishing process the introduction of water-based technologies hasreduced the amount of VOC emissions to the air. The exhaust air emissionsfrom spray finish applications are typically passed through a wet scrubbingprocedure to keep this from becoming a problem.

7. Finished leather - unwanted contaminants

What the consumer buys is the end product, finished leather. With a growingdemand for more information about consumer products and their preparation

it is logical that the end article leather is also subject to an array of commentsabout its ecological and toxicological properties. The media is quick tohighlight comments like some 20% of leather consists of chemicals andtherefore it could be harmful, without considering the real truth of thecomment in more depth. The overwhelming majority of products found inleather are harmless and offer no danger to users of the natural product,leather.

The development of analytical methods to determine very low levels ofcontaminants in consumer products like textiles has also been applied toleather. So now a list of unwanted substances found at trace levels have beendeveloped and are widely circulated. A full risk analysis to determine the realtoxic limits has in most cases not been undertaken.

Analyses for trace levels of the following substances are now common:

formaldehyde

chromium (VI)

certain organic amines derived from azo dyes

organotin compounds

nickel, cadmium, lead and other heavy metals

pentachlorophenol and chlorinated phenols

Additionally tests for NPE, extractable chromium (III), extractable organicsubstances, biocides, organohalogen compounds are requested by someecological labels.

This list can look very daunting at first when you are asked to ensure none ofthem are your leather. In most cases they have been taken from lists for otherpurposes and products, therefore some of the listed contaminants are notfound in leather.

We cover some of the more important ones here in some detail to give a goodbackground to the problem and the methods used for testing them.


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7.1 Formaldehyde in leather

IntroductionFormaldehyde is widely used in the manufacture of chemicals. In the case ofleather chemicals it is used to join together molecules to form larger molecular

structures, the so-called condensation products.Once this chemical reaction has occurred the formaldehyde is no longeravailable and cannot be detected. The only free-formaldehyde that isdetectable originates from the small excesses used in manufacture that havenot reacted completely. Some of this formaldehyde is released (also calledreversibly bound) by water extraction, as well some formaldehyde is enclosedin the matrix of the leather and can be emitted in gas form as freeformaldehyde.

In our environment the main sources of formaldehyde are from incompletecombustion processes. So it can be found outside in the streets from motor

exhaust fumes and inside probably from cigarette smoke, which can containlevels of 100 ppm. Trace levels of formaldehyde are commonly found asemissions from some building materials, but also in many natural products, forexample, fruit like apples can contain 10 20 ppm. Additionally up to 2000ppm in cosmetic items and 1000 ppm in toothpaste is allowed in the EU.

Under mild alkaline conditions formaldehyde reacts readily with protein andcollagen and this has been used in the past for formaldehyde tannages ofleather.

In combined tannery effluents formaldehyde can normally not be detected

even in trace levels. It rapidly reacts with other compounds of the effluent andis readily degradable in wastewater treatment plants.

Test MethodsThere are several methods for quantitative analysis of formaldehyde in leatherand care must be taken in determining which method is being used, whatlimits are required and in interpreting the results. The 2 main methods usedare as follows:

1) Free formaldehyde and releasable formaldehyde by waterextraction method (Test Methods: CEN ISO/TS 17226, IUC 19, DIN

53315)This is the traditional method of analysis, extracting the leather at 40C for 1hin a deionised water solution containing a small amount of wetting agent. Theextracted solution is analysed either by liquid chromatography (preferredmethod) or colourimetrically for formaldehyde (or more correctly aldehyde)content. Since the analytical conditions for preparing these samples for the 2procedures are not the same they will give different results.


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Additionally the colourimetric method is subject to interference from extracteddyes and additionally measures all aldehyde substances, so it is not specificfor formaldehyde. BLC has reported that using this colourimetric method,some 80% of results obtained from coloured leathers must be consideredincorrect.

2) Free-formaldehyde by gas phase method(Test Methods: VDA 275, PV 3925 - VW/Audi, EN 717-3)

A gas phase method was originally developed for building materials and isnow used especially by the automotive industry. This method determines justthe free-formaldehyde content in leather. A leather sample is suspended overa deionised water solution in a closed bottle. This container is heated at 60Cfor 3 hours and after cooling for 1 hour the amount of formaldehydetransferred via the gas phase into the water solution is measuredcolourimetrically.The leather sample is not in direct contact with the water, so the method is

only measuring the formaldehyde that can be released into the air by warmingthe sample.

Limits allowedIn Europe there are currently no legal limits for formaldehyde in leather.

In leather the limit values normally requested are set by commercialcompanies promoting their ecological label, for example Oeko-Tex and SG.For shoes an additional ecological label covering the whole life cycle of theshoe is available from the EU.

Typically requested eco-label limits for free-formaldehyde in leather usingthe traditional water extraction method are:

for leather with indirect skin contact, such as shoes, limits of 150 or300 ppm, are required depending on the ecological label;

for leather items with direct skin contact a level of 75 ppm is required;

for childrens shoes the level is lower at 50 ppm.

The automotive industry normally recommends the gas phase method ofanalysis, but note carefully, the limits for this different method are much lower,

typically 10 ppm.

What differences are there between the water extraction and gas phasemethods?It is not possible to compare results between the two methods. The traditionalwater extraction method will typically give considerably higher resultscompared with the gas phase method; some comparisons indicate that values5 to 10 times higher could be expected. The water extraction is measuringboth types of formaldehyde, namely the free-formaldehyde as well as thereleasable formaldehyde.It should be noted that changes in the extraction temperature and times could

have a considerable influence on the result, so these parameters in the testmethod must be followed closely.


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What level of formaldehyde in leather is achievable?Modern chemical products and application processes enable a limit of300ppm (water extraction method) to be complied with. With appropriateselection of products the lower levels can also be complied with.

Where does the formaldehyde in leather come from?The most common and therefore the most critical sources are formaldehyde-releasing products such as:

organic tanning agents;

resin-type retanning agents;

fixing agents used at the end of the drum application process.

There are several other possible sources, such as, syntans, fatliquors andretanning/dyeing auxiliaries, but generally they only become a problem if oneuses high amounts or has to reach very low limits.

How can you avoid having formaldehyde in leather?Select only those products that are either formaldehyde-free or have lowformaldehyde content. Basically in the normal tannery situation this meansavoid using those few products such as resin-based retanning agents, fixingagents and organic tanning agents which could release high levels offormaldehyde.It is very difficult to try reducing the formaldehyde level during or after leatherproduction. For example, processes that include the use of products to reactwith formaldehyde can reduce the level of formaldehyde in leather but can not

eliminate it.

7.2 Chromium (VI) in leather

IntroductionChromium can exist in several oxidation states. For leather tanning the mostimportant chemical used is basic chromium sulphate, it has the oxidation statechromium (III). This oxidation state is a natural trace mineral that we need inour bodies for our everyday life.Chromium (III) can be oxidised in some special situations to the much moretoxic form, namely chromium (VI). It should be clearly stated that this Cr (VI)

oxidation state does not tan leather and does not form organic complexes,e.g. organic chromium complex dyes cannot be chromium (VI) based.

Test MethodThe standard method for chromium (VI) in leather is:

1) Cr (VI) in leather(Test Methods, CEN/TS 14495, IUC 18, DIN 53314)

The traditional method of analysis is to shake the leather in a deaerated pH 8buffer solution at room temperature for 3h. The solution is analysedcolourimetrically for chromium (VI) content. The analytical conditions require it

to be made under an inert atmosphere to avoid the oxidation of the Cr (III)during the analytical procedure.


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The colourimetric method can be subject to interference from organicsubstances such as extracted dyes and possibly vegetable tanning agents.Therefore it is important that these components are removed by using smallchromatographic cartridge clean-up procedures before adding thediphenylcarbizide colour-developing agent.

a) Limits allowedIn Europe since Cr (VI) is listed as a carcinogen the legal limit is quite simple:it must not be detectable. Hence the actual limit is de facto the detection limitfor the analytical procedures. The DIN 53314 method stated 3 ppm as thedetection limit but inter lab trials showed wide variations in results whenmaking analyses on leather samples. Subsequently it was shown the DINmethod is unsuitable for many coloured leathers as any extracted dye causedan interference to the analytical result. Therefore the DIN method is onlysuitable for analysing for Cr(VI) in undyed leathers. The new CEN/TS 14495method has a clean-up procedure to remove the extracted dye. So this

method and various other eco-labels have recognised the complex matrix thatleather is in terms of analysis and they set 10 ppm as a level, which can bedetected with reliability over a wide range of leather samples.

Where does the chromium (VI) come from?The main sources of Cr (VI) are likely to be from the oxidation of trace levelsof Cr (III) through fatliquors, moisture, heat and light.

How can you avoid having chromium (VI) in leather?Select products that allow reductive conditions during the retanning,fatliquoring and dyeing process. Avoid the use of unsaturated fats in situationswhere oxidation could occur. Avoid storing for extended periods chrometanned leathers in moist and warm situations.

7.3 Aromatic amines in leather

IntroductionIn 1994 the Health Ministry in Germany introduced a regulation, which forbidscertain aromatic amines that can result from azo dye cleavage in thoseconsumer goods with skin contact. The regulation allowed a period of timebefore it came into affect. The amines forbidden were those on the German

MAK list of chemicals known to cause cancer or suspected to cause cancer.Since at that time no official analytical procedures existed for these amines, aperiod of uncertainty existed.

Over the following few years, analytical methods were established withreasonable detection limits to minimise the chances of false positives andsome other European countries introduced similar regulations. In order tomake a uniform regulation in the EU, it made a directive in 2002 that was verysimilar to the German regulation and the list of forbidden aromatic amines wasincreased to 22. At this time all except one of the 22 amines can be analysedusing standard sophisticated HPLC analytical techniques, although the

interpretation of the results needs to be made with care, as there is still thepossibility of false positive results.


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Test MethodThe standard method for forbidden amines in leather is:

1) Dyed leather- test for aromatic amines from the break down of azodyes (Test Methods, CEN/TS 17234, IUC 20, DIN 53316.)

The leather is digested at pH 6 and 70C in the presence of a reducing agent,which splits the azo bonds in the azo dyes. The aromatic amines formed areextracted and analysed by HPLC.The method sets 30 ppm per amine as the minimum detection level. Resultsabove this level would indicate it is possible an azo dye has been used whichcan split to release the forbidden amine.

Where do the amines come from?Aromatic amines are an essential raw material for making azo dyes, withoutthese amines it is not possible to make azo dyes. Today the dye suppliers donot use any of the small number of forbidden amines in the manufacture of

azo dyes.

How can you avoid having forbidden amines from azo dyes?Purchase the dyes from reliable suppliers who are prepared to back up theirservice with a guarantee of compliance with the regulations when leathersamples are analysed.

7.4 Heavy metals in leather

Many eco-labels require the absence of heavy metals such as nickel, tin,mercury. These are not present in the normal preparation of leather and havecome from other industries, e.g. allergic reactions to nickel in jewellery.

Traces of organotin compounds like tributyl tin (TBT) were found in sometextile garments and received a lot of media attention. Since then the eco-labels have required that there should be no detectable amounts of TBT in theconsumer article. To our knowledge there has been no problem with TBT inleather products.

7.5 NMP-free polyurethane finishing products

In 2001 the solvent N-methyl-pyrrolidone (NMP) was included in theCalifornian Proposition 65, the common name for a Californian regulation,which lists chemicals that could cause health risks to the citizens or affect itswater sources. Consumer articles containing any Proposition 65 listedsubstances must contain a warning label when sold in California. If nominimum safe limit has been set then any detectable amount must belabelled.The solvent NMP is used in many polyurethane dispersions for improving theflow and film formation during finishing. Automotive leathers in particular aredependent on polyurethane finishes so there has been a need to developalternative finishing formulations.


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7.6 EU Directive restricting the use of nonylphenol ethoxylate(NPE) and nonylphenol (NP) products

BackgroundAn EU risk assessment was made under the Existing Substances Regulation

93/793/EEC because of the large quantity of nonylphenol (NP) manufacturedand used, as well as its toxicity to aquatic organisms and concerns about itsbiodegradability. The nonylphenol ethoxylated (NPE) products were alsoassessed as they are the main pathway of nonylphenol into the environment.

For NP the risk assessment showed that the main concern is the high aquatictoxicity and that it did not break down readily in ecosystems. No adversehuman exposure risks during use were identified.

The environmental risk assessment indicated the need to reduce the risksassociated with the production, formulation into products and end-uses ofNPE and NP. It is estimated that the proposed restrictions will decrease

emissions to the aquatic environment by about 80%.

EU DirectiveThe EU passed in July 2003 the directive 2003/53/EC, which will restrict themarketing and use in Europe of products and product formulations thatcontain more than 0.1% of NPE or NP. This applies to many industriesincluding the textile and leather industries, except in the case of closedapplication systems where no release into waste waters occurs.

The EU European countries have until January 2005 to implement in theirown country the necessary legislation to make this EU directive into law.

So in summary, the sale and use of products containing more than 0.1%NPE or NP will not be allowed in Europe from Jan. 2005.

It should be clearly understood that in this EU Directive there is no restrictionon the import of goods like leather, which have been treated with NPEproducts outside of Europe.

The above explains the official chemical regulations in EU, some leatherspecifiers and users have interpreted the Directive differently by forbidding theuse of NPE during leather processing. They check their leather deliveries fromall over the world by analysing the leather for residues of the NPE surfactants.

This has resulted in an EU restriction on the use of NPE surfactants nowbeing implemented in many parts of the world.


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8. Wet-white, wet-blue, vegetable extract?

Several ecological balance studies have been undertaken comparing thevarious methods of preparing leather and their uses. The oldest tanningprocess using vegetable extracts to tan leathers has traditionally been looked

at as the natural leather. Chrome tanned (wet blue) leather has for over ahundred years proved its suitability and superiority as a material for themanufacture of shoes, garments and upholstery leather. Wet blue tannedleathers have come under criticism because of the difficulties that manypeople have understanding chromium. In the last years a rapidly growingmarket has developed for automotive leather based on wet white, that isaldehyde tanned, free-of-chrome leather. For the automotive industry thereare advantages in the dry heat stability of wet white leather compared withchrome tanned leather. Additionally the absence of chromium(III) salts in theshavings, waste water and end leather article has resulted in comments thatwet white processes are ecologically better.

Interestingly the ecological balance studies showed that when all aspects areevaluated there was little between the leather processes. For example, thenatural vegetable tanning processes had disadvantages with high wastewaterCOD loading, as to a lesser extent does the wet white. Wet blue leathersneeded less chemicals and often showed superior performance properties.

Overall the results indicated that when using best available technologies thereis little difference in the life cycle ecological balances between the methods ofpreparing leather. It depends on the leather article desired by the customerand the weighting given to each aspect.

9. Trends, future laws and restrictions

The Waste Management, Sustainable Development and Environmental unitswithin the EU are quite active in leading with new environmental regulations,which over time other countries often implement. A number of projects anddirectives are currently being worked on, such as:

IPPC, Intergrated Pollution Prevention and Control, setting emissionlimits EU wide according to the implementation of best availabletechnologies;

Directives on restrictions on marketing and use of dangeroussubstances and preparations

o (nonylphenol ethoxylate)o (azo colorants)o (organostannic compounds)o (short chain chlorinated paraffins);


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Environmental agreements within EU countries simplification andimprovement of regulations

Directive on Dangerous Substances for transporting DangerousGoods including waste materials

Directive on Sewerage Sludge restrictions on heavy metals forsludge applied to agricultural land

Directive on Landfill reduce landfilling of biodegradable waste

Project RESTORM, Radically Environmentally Sustainable TanneryOperation by Resource Management, to assist the tanning industrychange to production methods to ensure a sustainable manufacturingindustry for the future.

Our environment and eco-system is something we all have a responsibility toprotect. So we must expect that further restrictions will be implemented toavoid polluting, as well as ecological and toxicological harm. By using the bestavailable technologies and optimised systems the leather industry can meetthese challenges.

The request for information about consumer products is a growing demandand this will certainly lead to more laws and restrictions. Leather as a naturalbased product can abide with all reasonable requests.

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