UNIONE NAZIONALE INDUSTRIA CONCIARIA - Euroleather

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Italian tanning production has now adopted industrialcharacteristics, although maintaining a number of traditionalaspects of handicraft processing which ensure theproduct’s high quality: more and more efficient tanningmaterials and machines, automation of complete operationalsequences, rationalisation of the production processand environmental protection, represent an integral partof the activities of every tannery.An approach referred to as the ‘black box’ can be adoptedin order to identify the environmental aspects of a tannery’sprocesses, in the same way as the other industrialproduction processes. In particular, tannery productioncan be considered to be a process to transform raw materialsand energy into finished products.This transformation is achieved with the input of water,energy and chemical products. The environmental interactionsassociated with the process are mainly representedby water discharges, waste materials and atmosphericemissions. Therefore, the consumption of resourcesor emission is considered to represent an environmentalaspect and as such is managed in the tannery.The tannery’s production cycle comprises a series ofchemical and mechanical treatments which enable decayingorganic matter (raw hides and skins) to be transformedinto a high value added product for footwear, furnishing,clothing and leather goods.A description of the various phases which comprise thetannery operations is provided below, with informationconcerning the main related environmental aspects andregarding the principal actions adopted to prevent and tomitigate them.curingThe raw hides and skins which arrive in the tanneryhave been subjected to a curing process to slow downtheir possible decomposition, maintaining the hides/skinsin the best condition up to the production operations. Thefollowing methods are used most frequently:® chilling: the hides/skins are preserved at temperatureswhich prevent the activities of bacteria, also withthe help of suitable products. This method is only validfor short periods and entails the constant use of means oftransport and refrigerated warehousing;® salting: after flaying, the hides/skins are saturatedwith salt (sodium chloride, NaCl) that prevents the developmentof bacteria and therefore the decompositionreactions;® drying: the hides/skins are dried so that the humiditycontent is fairly low to prevent the bacteria from living andto prevent decaying enzyme reactions.A curing process performed incorrectly can cause freeammonia to develop and bad odours, which do not representa hazard to human health and to the eco-system ingeneral, as such, but influence the quality of life of the inhabitantsliving in the surrounding areas. To avoid the formationof ammonia and unpleasant odours, the raw hides/skins are not exposed to weathering, which speeds up thedecaying processes, but are stored in the tannery, insidecold rooms at temperatures slightly above a 0°C.beamhouse operationsThe beamhouse operations are performed to removefrom the hides/skins all the components which are no longeruseful to the production process (for example: preservationsalt, hair, portions of subcutaneous tissue), to relaxthe collagen structure and favour the penetration of thevarious tanning agents. The first beamhouse operations(soaking, liming/unhairing) are performed in the drums;these are large cylindrical containers which are similar toindustrial washing machines, where the hides/skins aretreated with water, normally added with chemical productsor enzymes which favour washing and unhairing thehides/skins. The hides/skins are then treated with machinerythat eliminate the subcutaneous tissue (fleshing) andin some cases are cut lengthwise, obtaining two or morelayers (splitting) before passing on to the next processingoperations. At this point, the cycle continues again insidethe drums where the hides/skins are washed to removethe residues of the chemical products used in the limingand to achieve optimum tanning conditions.14
The quantities of water consumed during thebeamhouse operations are proportional to theweight of the hides/skins treated. The water dischargedis laden with dissolved substances whichinfluence the quality of the water; the beamhouseoperations mainly influence the parameters ofthe water discharges, for example: the chemicaloxygen demand (COD), suspended solids, chlorides,sulphides and organic Nitrogen. The water istreated (possibly differentiated for some baths)to reduce the pollutants to values which do notrepresent risks to the environment. The hair canbe recovered in special grids to be subsequentlyreused as felt. Some innovative technologies enablethe hair to be removed with enzymes and torecycle the unhairing baths, with a decrease in thewater consumption and pollutant emissions. Thefleshing operation produces fleshings that mustbe treated like a solid residue in the same way asthe waste produced by trimming. All the varioustypes of waste products are collected separatelyin the tannery to enable the waste products concernedto be transferred to the correct destination.The fleshings, the hair and the trimmings aretransferred for re-use with various destinations inthe industrial sector and in the agricultural andlivestock sectors.tanningThe hides/skins are subjected to the actual tanning phaseafter having been subjected to the treatments designedto eliminate the excess substances, change the pH valuesand prepare the collagen fibres. Tanning is performed byusing substances which fix themselves irreversibly to thehide/skin fibres and prevent decomposition, rendering thefibres stable and long-lasting, without changing their naturalproperties. Various types of tanning exist and theirrespective phases are very different depending on theprocesses and the product’s intended use: mineral tanning(mainly performed using chrome salts), vegetable tanningand organic and mixed tanning. The most widespreadtanning is chrome tanning performed in tanning drumswith the tanning product in a bath that has an acid pH.The vegetable tanning system used most frequently forsole leather foresees immersing the hides/skins in a seriesof successive pits containing solutions of tannin extractsat increasing concentrations. The process time can evencorrespond to 30 days. The production of sole leather inItaly uses mainly a mixture of chestnut, mimosa and quebrachotannins. Vegetable tanning is characterised by adiffusion process from a solution (tanning bath) to the solidphase (hides/skins) that is maintained until a balanceis reached and that treats the hide/skin’s entire thickness.The treatment is performed in pits with the hides/skinsflowing counter current: when the hides/skins enter the15
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Page 4: INTRODUCTIONThe Italian tanning ind
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figure 1 - Innovation by typefigure
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U NCUNIC TANNINGIntroductiono caThe
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THE TANNERIES® Adelaide S.p.A.Bass
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72Via Brisa, 3 -20123 Milano - Tel.
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Via Brisa, 3 -20123 Milano - Tel. 0
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