Waste Management xxx (2014) xxx–xxx

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Waste Management

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Valorization of titanium metal wastes as tanning agent used in leatherindustry

http://dx.doi.org/10.1016/j.wasman.2013.12.0150956-053X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel./fax: +40 213235280.E-mail addresses: mariancrudu@yahoo.com (M. Crudu), viorica.deselnicu@

icpi.ro (V. Deselnicu), d_deselnicu@yahoo.com (D.C. Deselnicu), luminita.albu@gmail.com (L. Albu).

Please cite this article in press as: Crudu, M., et al. Valorization of titanium metal wastes as tanning agent used in leather industry. Waste Mana(2014), http://dx.doi.org/10.1016/j.wasman.2013.12.015

Marian Crudu a, Viorica Deselnicu a,⇑, Dana Corina Deselnicu b, Luminita Albu a

a The National Research & Development Institute for Textiles and Leather – Division Leather and Footwear Research Institute, 93 Ion Minulescu Str., Bucharest, Romaniab University Politehnica Bucharest, Splaiul Independentei Nr. 313, Sector 6, RO-060042 Bucharest, Romania

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 June 2013Accepted 18 December 2013Available online xxxx

Keywords:Titanium wasteTitanium tanning agentWet-white leather

The development of new tanning agents and new technologies in the leather sector is required to copewith the increasingly higher environmental pressure on the current tanning materials and processes suchas tanning with chromium salts. In this paper, the use of titanium wastes (cuttings) resulting from theprocess of obtaining highly pure titanium (ingots), for the synthesis of new tanning agent and tanningbovine hides with new tanning agent, as alternative to tanning with chromium salts are investigated.For this purpose, Ti waste and Ti-based tanning agent were characterized for metal content by induc-tively coupled plasma mass spectrometry (ICP-MS) and chemical analysis; the tanned leather (wet whiteleather) was characterized by Scanning Electron Microscope/Energy Dispersive Using X-ray (Analysis).SEM/EDX analysis for metal content; Differential scanning calorimetric (DSC), Micro-Hot-Table and stan-dard shrinkage temperature showing a hydrothermal stability (ranged from 75.3 to 77 �C) and chemicalanalysis showing the leather is tanned and can be processed through the subsequent mechanical opera-tions (splitting, shaving). On the other hand, an analysis of major minor trace substances from Ti-endwaste (especially vanadium content) in new tanning agent and wet white leather (not detected) andresidue stream was performed and showed that leachability of vanadium is acceptable. The resultsobtained show that new tanning agent obtained from Ti end waste can be used for tanning bovine hides,as eco-friendly alternative for chrome tanning.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction (III) content in leather digests or extracts, whereas an even stricter

Hitherto, the mineral tanning agents most frequently usedthroughout the world are salts of chromium (III) (ca. 85% of totalworld finished leather output), which remain unsurpassed in thequalities offered to leather; these, in turn, include high hydrother-mal, thermal and light stability and versatility with regard to thevariety of leather articles, which can be made from the intermedi-ate, chromium (III)-tanned leather, ‘‘wet-blue’’ (Covington, 2008).

In general, chromium (III) tanning agents uptake under typicaltechnological conditions is of the order of 60–80% of the offeredquantities (typical offer: 80–90 kg Cr-tanning salts/t of peltweight), with 3–7 kg Cr3+/t of raw hides/skins (2–7 g Cr(III)/Lt ofexhaust tanning liquor) discharged with the process effluent. Eventhough there is no legislation or norm that requires that chromium(III) should be absent from leathers, maximum allowable concen-trations have been stipulated for the total chromium or chromium

concurrent legislative requirement has been imposed for chro-mium (VI) absence (non-detectable) in most finished leathers. Inparticular, chromium (VI) and its salts are classified as known car-cinogens not used for tanning and normally absent from chromium(III) tanning salts. However, apart from its potential presence inpigments, colouring additives and fixatives, commercial chromiumtanned leathers can be tested positive for the presence of chro-mium (VI) in quantities exceeding the stipulated legal or norma-tive limits. De-facto chromium (VI) does not exist in finishedchrome-tanned leather, and apart from the frequently never toldtruth of test method inefficacy or non-appropriateness, intelligenttentative interpretations of the observed chromium (VI) formationagree that can be the product of oxidative conversion of chromium(III) under specific leather manufacturing or storage conditions e.g.high leather pH or use of specific fat liquoring agents. Along thesame lines, several eco-certification schemes stipulate limits inCr (III) content: (i) in aqueous extracts of leathers and leathersproducts with water, artificial sweat or in some cases in their di-gest and (ii) in the effluent after depuration (0.2–3 ppm) that areimpossible to match, if leathers continue to be tanned or/and retanned with chromium (III) tanning agents.

gement

2 M. Crudu et al. / Waste Management xxx (2014) xxx–xxx

These practical and operational constraints have stimulatedresearch efforts to find an alternative to chromium (III) tanningGerman, 2010 for the production of Free-Of-Chrome (FOC) and insome cases also Metal-Free leathers, whilst retaining the often ex-pected by the consumer mineral character in leather articles, withsome profound examples of succeeding in replacing fully chrome-tanning lines in industrial upper leather production. Accordingly,Al (III), Zr (III) Hancock et al., 1980; Waldo et al., 1983, Ti (III andIV) Peng et al., 2007; Adiguzel Zengin et al., 2012; Mutlu et al., inpress, Fe –salts (Kleban), their mixed salts (Covington, 1988), andmost recently nano-silicates (Liu et al., 2010) and sodium waterglass (WASSERGLAS) were tested as effective partial or totalreplacement mineral tanning agents for the production of a revers-ibly or irreversibly – most recently – tanned new intermediatesemi-processed product and commodity: ‘‘wet-white’’ or ‘‘wet-sta-bilised’’ leather. Overall metal ion complexes have some affinity forprotein, however, the mechanism of their binding to collagen – iftaking place – is far from being resolved with several hypothesesand models often postulated and used, but seldom proven for thispurpose. Moreover, when applying the criteria of adequate reactiv-ity, colour, availability, cost and toxicity, and most recently Life Cy-cle Inventory Assessment (LCIA), nearly all of the commerciallyavailable agents were rendered redundant as viable options. Agood example is Aluminum salts that have long been associatedwith stabilising animal origin pelts and have the advantage ofbeing abundant and cheap. However, Aluminum is only looselybound and fixed to collagen, so that the reaction is readilyreversed, when the leather is wetted and found in acidic environ-ments; for this reason, this process is regarded as a pseudo-tan-nage and called tawing, rather than tanning. However, as shownby one of the co-authors in earlier studies (Covington et al.,1989) the effectiveness of a tanning molecule depends on its abilityto provide high molecular weight cross-linked moieties within thecollagen molecule and was possible to propose reactive Aluminumtanning agents preparations that match this requirement (Ioanni-dis et al., 1989) which, on the other hand, were never taken upby the Industry, due to emerging renewed toxicity considerations,but primarily as a result of the undoubtedly superior versatility,cost effectiveness and reliability of Cr (III)-tanning systems.

Within this framework of industrial needs high levels of excessCr(III)-tanning products remain a potential threat and hazard tothe environment or contribute significantly to the amount of recal-citrant pollutants. Consequently, there is mounting pressure ontanners to reduce levels of Cr(III)-tanning agents employed duringleather manufacture and their discharge with the outflow of tan-nery treatment plant.

Along these lines, new Ti (III)-based, Cr(III)-free, precursor tan-ning agents have been produced from metallurgic Industry endwaste, aiming at the development of new tailored sustainablewet-white tanning chemistry that enables for the first time thein situ generation of reactive Ti(IV)-tanning species, as a viablealternative to Cr(III), vegetable and syntan (pre)tanning agents.Hence, the principal axes of our synthetic approach, from productdesign phase to its industrial eventual application, have been:recovery and recycling of waste metals, simplicity and cost-effec-tiveness of the new tanning agent application, as well as closedloop processing, in order to protect the environment and improvethe quality of life. Major challenges to match in our efforts remaincommercial viability and consumer acceptability of the finishedleather article.

The new tanning agents, in fact, will act as a prelude towardsnew eco-friendly leather manufacture, in which no potentiallytoxic, noxious and harmful chemicals have been used and dis-charged – currently and according to the Environmental Reportsof the Tanning Sector 30–40% of chemicals used during leathermanufacture are characterized as potentially toxic or hazardous.

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2. Materials and methods

2.1. Materials

Chemicals for synthesis of tanning agents: All chemicals usedwere of technical grade. Aluminum sulphate, Al2(SO4)3�18 H2O(15.3% Al2O3, 8.55% Al) (SR EN 878/2004); sodium citrate (STF116/2000); sodium tartrate (STF 34/1999); ammonium sulfate(STAS 450-1975); magnesium oxide (STAS 4995-1980); sulphuricacid (95–97% -STAS 97-1980).

Ti-end unrecyclable waste from the Ti-metallurgic industry with acomposition of min. 90% content of titanium.

Bovine pelts: For all tanning trials bovine pickled pelts of Roma-nian origin, with mean weights ranging from 20 to 25 kg were used(pH ca. 3.0).

2.2. Methods

Ti–Al tanning agent synthesis: For the solubilisation of Ti-endwaste in order to obtain tanning agents, an antacid reaction vesselequipped with jacket for temperature control, with a VELP SCIEN-TIFIC mechanical stirrer and gas outlet for gases resulting duringsynthesis was used. In-house design laboratory equipment withvacuum ILMVAC type was used for the filtration of titanium solu-tion resulted by dissolving wastes.

Tanning trials were undertaken using pickled bovine pelts and aDOSEMAT micro pilot DOSE MAT inox-drum. The tanning brinebath length varied from 200% to 400% on pickled weight and theinitial float pH = 3.1–3.2, before the adding of the tanning agent.The temperature of the tanning bath was about 25 �C and the drumrotational speed was 15 rpm. Ti- tanning agent was added with of-fers ranging from 2% to 10% w/pickled weight. The pH of the bathafter the addition of the tanning agent was pH = 2.2–2.3. The tan-ning bath had a characteristic purple colour and the section ofthe pelt was fully penetrated after 10–25 min (visual control). Basi-fication of the bath was initiated using 2–3% w/pickled weightMgO based products for this purpose. After 30–60 min – with heat-ing of float from 25-to-35 �C – 2–3% w/pickled weight cationicfatliquor was added and the drum run to reaction completion overa period of 1–6 h with the tanning bath fully de-coloured andpH = 3.4–3. Leathers are then retanned and finished in the tradi-tional manner (Crudu et al., 2011).

2.3. Characterization

Ti-end waste: Metals’ content was determined using inductivelycoupled plasma mass spectrometry device (ICP-MS).

Ti based tanning agent was analyzed as solution and as powderby chemical analysis and ICP-MS analysis.

Kinetic of tanning process was performed by varying the offer ofTi based tanning agent from 2%, 4%, 6%, 8% and 10% related atweight of pickled pelt and by measure metal oxides content of ini-tial and final tanning floats. The exhaustion index (Ie, %) was calcu-lated by formula:

Ie ¼ Ci � Cf

Ci� 100

where Ci is metal oxides content of the initial float, and Cf is metaloxides content of the final float.

Chemical analysis of leather tanned with Ti based tanning agent(so called wet-white leather because of light colour). After wetwhite leather was split in tree layers (grain, median and bottomsplit) was performed chemical analysis for determination of vola-tile meter, extractible, ash, metal oxides, total soluble, pH on eachlayer of leather.

tal wastes as tanning agent used in leather industry. Waste Management

(a) Titanium ingot (b) Cutting andshaping the ingots

(c) Unrecyclablecuttings

Fig. 1. Different type of titanium wastes.

Table 1Composition of the Ti wastes (ICP-MS analysis).

Metal (%) Ti Al V Other elements(Fe, Ni, Cr, C, N, O, etc.)

Sample 1 97.1 Traces Traces 2.9Sample 2 94.3 2.6 0.1 3.0Sample 3 88.30 6.7 4.0 1.0

M. Crudu et al. / Waste Management xxx (2014) xxx–xxx 3

Scanning Electron Microscope/Energy Dispersive Using X-ray(Analysis) (SEM–EDAX): The examination of wet white leather sam-ples tanned with the newly Ti based tanning agents was performedwith a scanning electronic microscope type TESLA. In ScanningElectron Microscopy, (SEM) an electron beam is scanned across a

Fig. 2. Synthesis pathway for obtaining

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sample’s surface. When the electrons strike the sample, a varietyof signals are generated, and it is the detection of specific signalswhich produces an image or a sample’s elemental composition.The three signals which provide the greatest amount of informa-tion in SEM are the secondary electrons, backscattered electrons,and X-rays. Secondary electrons are emitted from the atoms occu-pying the top surface and produce a readily interpretable image ofthe surface. The contrast in the image is determined by the samplemorphology. A high resolution image can be obtained because ofthe small diameter of the primary electron beam.

Hydrothermal stability measurements of leathers: Wet-white(tanned with Ti–Al tanning agent) and control leathers (tannedwith chromium tanning agent) were analyzed using three differentmethods:

the new Ti based tanning agents.

tal wastes as tanning agent used in leather industry. Waste Management

Table 2Chemical analysis of the Ti based tanning agent.

Characteristics Solution Powder

Aspect Violet solution Grey powderDensity (g/cm3) 1.45Total metal oxides (g/dm3) 102.62Total metal oxides (%) – 15.2pH (1:10) 2.47 2.01pH 1.85 –

Table 3Elemental analysis of Ti based tanning agent (in powder) (ICP-MS analysis).

Element %

Ti 74.7Al 24.9V 0.13Mg 0.33Fe 0.03Zr 0.23Cr, Cd, Pb, Hg, Ni, As Undetectable

Table 4Kinetic of tanning process and exhaustion of the tanning bath.

Nr. crt Offer, % Tibased tanningagent

Initial phase Final phase Exhaustion ofthe tanningbath, Ie (%)

pH % MeO pH % MeO

1 2 1.45 6.09 3.70 4.21 30.872 4 1.42 9.71 3.85 6.30 35.113 6 1.40 10.25 3.91 5.83 43.124 8 1.37 11.23 3.93 5.34 52.445 10 1.34 11.90 3.95 5.21 56.21

Fig. 3. Wet-white leather split and shaved.

Table 5Chemical analyses of wet white leather.

No. Characteristics Wet white layer Test method

Grainlayer

Medianlayer

Bottomlayer

1 Volatile matters (%) 53.10 51.10 51.02 SR EN ISO 4684: 20062 Extractible (%) 2.58 1.57 1.35 SR EN ISO 4048-20093 Ash (%) 17.36 14.73 13.91 SR EN ISO 4047: 20024 Metal oxides (%) 8.16 9.25 8.32 ICPI method5 pH of water extract 3.89 4.01 4.00 SR EN ISO 4045-20086 Total soluble (%) 20.59 16.25 17.32 SR EN ISO 4098-2006

4 M. Crudu et al. / Waste Management xxx (2014) xxx–xxx

(i) by Differential scanning calorimeter (204 F1 PHONIX-NET-ZSCH) (DSC): to determine the curves of heat of enthalpychange as a function of the temperature a Perkin–ElmerDSC 7 calorimeter was used. Each sample was weighed(3–6 mg) and placed in an Aluminum crucible. Thermaleffects were measured against a similar empty crucible inthe calorimeter at room temperature while nitrogen waspurged, and heated in the temperature range 50–260 �C.

(ii) Shrinkage temperature measurements were recorded withinthe range 22–100 �C at a heating rate of 2�/min using theMicro-Hot-Table technique with a CALORIS Micro HotTable coupled with a LEICA Stereomicroscope. This is annondestructive method which analyze only few fibers.

(iii) Standard shrinkage temperature measurements were under-taken using a standard GIULANNI apparatus according to SREN ISO 5397:1996.

Analysis of sewage waste water resulted from wet-whiteleather processing according with SR EN ISO 11885, SR EN ISO11886.

Leaching test for sewage sludge (1:10 leaching test) resulted fromPilot Station from leather processing (chrome and wet-whiteleather) was performed according to the method EN 12457/2-2003: arsenic, barium, cadmium, total chromium, copper, mercury,molybdenum, nickel, lead, antimony, selenium, zinc, chloride, fluo-ride, sulphates, Dissolved Organic Carbon (DOC), Total dissolvedsolids (TDS) EN 12457/2-2003.

On Sewage sludge resulted from Pilot Station from leatherprocessing (chrome and wet-white leather) a Leaching test (1:10leaching test) was performed according to the method EN 12457/2-2003: arsenic, barium, cadmium, total chromium, copper,

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mercury, molybdenum, nickel, lead, antimony, selenium, zinc,chloride, fluoride, sulphates, Dissolved Organic Carbon (DOC), Totaldissolved solids (TDS) EN 12457/2-2003 and the test for maximumallowable concentrations of heavy metals in sludge intended for agri-cultural use (mg/kg dry matter) according to Order 344/2004.

3. Results and discussion

3.1. Characterization of Ti waste

The main classification criterion for Ti wastes was their contam-inant level (Buzatu and Moldovan, 1994). The highest contaminantlevel in titanium wastes and titanium alloys is in cuttings resultingfrom the mechanical processing of ingots and cast articles (Fig. 1).

The composition in metals of the titanium wastes (filings) differas function of the production of different titanium product (pure Tiingots or titanium alloys) as is presented in Table 1. Titanium is themain component, but the Ti waste contain Aluminum, Vanadiumand other elements in small quantities or traces. For our studies,as raw materials for the synthesis of the new Ti based tanningagents, were selected Ti waste with higher content of titaniumand low content of Vanadium and other metals (sample 1 and 2).All elements were investigated for their presence in new tanningagent, wet-white leather and the residue stream (sewage wastewater and sludge) obtained in wet-white leather manufactureprocess.

3.2. Synthesis of Ti based tanning agent

In the reaction vessel, 24% industrial water and 15% aluminumsulphate are added, the mixture is stirred for 30 min at 30 �C, then11.3% sulphuric acid of 95% and 4.5% Ti waste were added in smallportions while stirring intermittently and heated to 90 �C for

tal wastes as tanning agent used in leather industry. Waste Management

Element Wt% At% CK 11.75 18.45 OK 48.75 57.47 NaK 07.64 06.27 MgK 02.72 02.11 AlK 02.61 01.83 SK 17.70 10.41 TiK 08.25 03.25 VK 00.58 00.21 Matrix Correction ZAF

Fig. 4. SEM-EDAX mapping of wet white leather 1 (grain).

Element Wt% At% CK 14.77 22.48 OK 49.03 56.04 NaK 07.21 05.73 MgK 02.64 01.99 AlK 02.44 01.65 SK 15.90 09.07 TiK 07.30 02.79 VK 00.71 00.25 Matrix Correction ZAF

Fig. 5. SEM-EDAX mapping of wet white leather 1 (bottom split).

M. Crudu et al. / Waste Management xxx (2014) xxx–xxx 5

180 min until complete dissolution of metal wastes. 17% sodiumcitrate previously dissolved in 26% water is then added and stirringcontinues at a temperature of 90 �C for 360 min, the mixture isthen cooled at 30 �C and 2.3% magnesium oxide is added understirring for 360 min until a final pH of the solution 1.8–2.0 wasreached. The tanning solution is then filtered and concentrated.Tanning solution can be dehydrated by freeze drying or atomiza-tion, resulting in a light grey coloured powder (Crudu et al., 2011).

The schematic outline of the synthesis pathway designed isshown in Fig. 2 (Crudu et al., 2008, 2009).

3.3. Characterization of new Ti based tanning agent

New Ti based tanning agent was characterized as solution bychemical analysis and in powder form by chemical analysis andby elemental analysis (Tables 2 and 3).

This investigation show a content of 15.2% metal oxides fromwhich titanium is major element (74.7%) followed by Aluminum24.9%. Mg (0.33%) and Vanadium (0.13%) represent minor compo-nents of new tannin agent.

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3.4. Characterization of the tanning process

Table 4 show kinetic of tanning process and exhaustion of thetanning bath was performed by varying the offer of Ti based tan-ning agent from 2%, 4%, 6%, 8% and 10% related at weight of pickledpelt and by measure metal oxides content of initial and final tan-ning floats. The figures show an increased absorption of tanningagent by pelt with increasing of offer of it. The best exhaustion ofthe tanning bath was 56.21% with on offer of 10% tanning agent.

3.5. Wet-white leathers characterization

Full thickness semi-processed tanned leathers resulting fromapplication of the new Ti based tanning agents as described hereis white, with a smooth grain full and supple, as shown with thephotographic image in Fig. 3.

3.5.1. Chemical analysis of leather tanned with Ti based tanning agentIn order to characterize the new wet-white leather and prove

the tanning potential of tanning potential of the newly synthesized

tal wastes as tanning agent used in leather industry. Waste Management

Fig. 6. SEM-EDAX mapping of wet white leather 2 (grain). Fig. 7. SEM-EDAX mapping of wet white leather 2 (split).

6 M. Crudu et al. / Waste Management xxx (2014) xxx–xxx

compounds, chemical analyses has been carried out on the split,median and grain layers of the product leathers and the results ob-tained are shown in Table 5. Analytical values obtained for all lay-ers tested have led to the conclusion that the penetration of thenew tanning agents was not only complete but also uniform, assur-ing sufficient stabilization of the wet-white for further mechanicalor other chemical processing.

3.5.2. Scanning Electron Microscope/Energy Dispersive Using X-ray(Analysis) (SEM–EDAX)

The evaluation new tanning agents’, and in particular topo-graphic distribution – mapping – of the metal species, was ob-tained by means of SEM–EDAX analyses. Regarding topograficdistribution of metals Two wet white leather (1 and 2) were ana-lyzed and different results regarding content of metals in theleather structure have been obtained. (Figs. 4–7). As first observa-tion it can see quite uniform distribution of metals between grainand split layers like show also chemical analysis (Table 5). Leather1 contains more Titanium and Aluminum than Leather 2; Leather 1also contain small quantity of Vanadium, 0.58 in grain layer and0.71 in split layer, but Leather 2 do not contain Vanadium. Thiscould depend on leather structure which is not a homogenousmaterial; physical–chemical properties differ from leather toleather. Much tests and more measurements have to be made inthis direction because the content of metal in leather and its uni-form distribution through thickness give information about tan-ning process.

3.5.3. Hydrothermal stability measurements of leathersShrinkage temperature gives information about stabilization of

leather structure in order to be able to be processed through thesubsequent mechanical operations of splitting, as well as shaving.

(i) The thermal behavior of the new wet white leather wasobtained by using DSC analysis. A typical example of thethermographs recorded for samples taken from the

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wet-white leathers tanned with the new Ti based tanningagent is shown in Fig. 8.

The endothermic transitions recorded for the new wet whiteleathers consists of at least three (3) peaks, indicative of consecu-tive denaturation processes. The first transition is recorded fortemperatures within the range 50 �C and 125 �C. A second set ofpeaks is registered for temperature values between 130� and250 �C, strongly linked to the processing history of the material(in particular the degree of tanning); the denaturation processoccurring can be tentatively explained by the crystalline-amor-phous two-phase model of collagenic materials. According to thismodel the super-coiled triple-a helix is partially crystalline andembedded in an amorphous matrix. Consequently, the minimumof endotherm II is associated with uncoiling/melting of the crystal-line region. In turn, the tanning process by inducing the formationof synthetic crosslinks, can result in increased stiffness of the ma-trix, and, thus, is responsible for the observed shift of the meltingprocess to higher temperature values. Monitoring the tempera-tures at which process II occurs may, therefore, reveals the degreeand effectiveness of tanning, where as for leathers tanned withCr(III)-salts the second peak is not visible as it overlaps with thepyrolytic transition. Hence, DSC thermographs, as those recordedfor wet-white leathers and shown in Fig. 8 are specific to eachmaterial and can be used as material-specific and unique ‘‘finger-prints’’ (Budrugeac et al., 2004).

(ii) Hydrothermal stability of the wet white leathers wasobtained with measurements undertaken using the Micro-Hot Table device, with average Ts = 76.1 �C, as shown inFig. 9.

(iii) Finally, the standard method which is usually used forshrinkage temperature (Ts) measurement of leather wasused for wet white leather. The Ts obtained by this methodwas 77 for grain and 75 for split wet white leather. Table 6

tal wastes as tanning agent used in leather industry. Waste Management

Fig. 8. DSC thermograph for wet-white leather.

Tin A1 B1 C B2 A2 Tfin

°C

27.5 69.7 72.7 76.1 79.1 80.0 83.4

Fig. 9. Determination of shrinkage temperature of wet white leather by MHT method.

Table 6Shrinkage temperature of wet-white leather (grain and split).

No. Shrinkage temperature (�C) Layer

Grain Split

1 Shrinkage temperature(standard method SR EN ISO 3380-2003)

77 75

2 Shrinkage temperature (MHT method) 76.1 73.93 Shrinkage temperature (DSC method) 75.3 (Full leather)

M. Crudu et al. / Waste Management xxx (2014) xxx–xxx 7

summarize the shrinkage temperature values determinedfor new wet white leather by the 3 different method whichranged from 73.9 to 77 �C. This shrinkage temperature canassure successfully processing of wet white leather throughthe subsequent mechanical operations as demonstratedwith the photographic image of Fig. 3.

3.6. Analysis of sewage waste water

Analysis of sewage waste water resulted from wet-whiteleather processing was performed. The results obtained are pre-sented in Table 7 and all values were in the limits of maximum

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allowable value according Order nr. 161/2006 – The Regulationson the classification of surface water quality to determine the eco-logical status of water bodies.

3.7. Analysis of sludge

Analysis of sludge resulted after pretreatment of waste waterfrom wet-white leather processing was performed. The results ob-tained are presented in Table 8 and all values were in the limits ofmaximum allowable value technical regulations on environmentalprotection and especially the soil when using sewage sludge inagriculture (Order 344/2004 in accord with 86/278/CEE Directive/1986). In Table 9 the sludge was analyzed for 1:10 leaching test.Vanadium was under detection limit.

In Table 10 a synoptic analysis of important elements enteringin the composition of new Ti based tanning agent is presented.Vanadium, which could be a problem from environmental pointof view, was found in Ti waste max. 4%, in new tanning agent0.13%, in wet white leather 0.71%, but in sewage waste waterand sludge was under detection limit. Vanadium content in Tibased tanning agent can be reduced by a better selection of Tiwaste with low content of Vanadium.

tal wastes as tanning agent used in leather industry. Waste Management

Table 7Waste water analysis and maximum allowable value according Order nr. 161/2006 – the regulations on the classification of surface water quality to determine the ecologicalstatus of water bodies.

No Test Unit Results Maximum allowable value Method

1 Lead lg/l <1 1.7 SR EN ISO 11885-092 Cadmium lg/l <0.011 0 SR EN ISO 15586-043 Chromium total lg/l <0.5 2.5 SR EN ISO 11885-094 Copper lg/l 1.3 1.3 SR EN ISO 15586-045 Zinc lg/l 36 5000 SR EN ISO 11885-096 Nickel lg/l 1.9 2.1 SR EN ISO 11885-097 Anthracene lg/l <0.005 0.063 SR EN ISO 17993-048 Benz (a) anthracene lg/l <0.005 0.0 SR EN ISO 17993-049 Benzo (b) fluoranthene lg/l <0.005 0.03 (sum) SR EN ISO 17993-04

Benzo (k) fluoranthene10 Temperature �C 18.4 40 –11 pH pH unit 7.10 6.5-8.5 SR EN ISO 10523-1212 Suspended meters mg/l 139 350 SR EN 872-0513 Chemical oxygen demand (COD) mgO2/l 96.0 500 SR ISO 6060-9614 Biochemical oxygen demand (BOD) mg O2/l 35.4 300 SR EN 899/1-200315 Synthetic detergents mg/l 25 SR EN 903-03

– anionic 1.16 SR ISO 7875/2-96– nonionic 0.74

16 Extractible in organic solvents mg/l <20 30 SR 7587-96

Table 8Sewage sludge analysis and technical regulations on environmental protection and especially the soil when using sewage sludge in agriculture (Order 344/2004).

No Test Unit Results Maximum allowable concentrationsfor heavy metals (Order 344/2004)

Method

1 pH pH unit 7.53 – SR EN 12176/20002 Moisture % 63.65 – SR EN 12880/20023 Volatile matters % 25.8 – SR EN 12879-024 Mineral substances % 74.2 – SR EN 12879-025 Total nitrogen % d.m. 1.13 – SR EN 13342-026 Total phosphorus mg/kg d.m. 99,681 – SR EN 14672/20067 Calcium mg/kg d.m. 274,981 – STAS 12834/19908 Magnesium mg/kg d.m. 1310 – STAS 12833/19909 Potassium mg/kg d.m. 349 – STAS 12678/1988

10 Cadmium mg/kg d.m. 0.46 10 SR EN ISO 11885-0911 Copper mg/kg d.m. 147 500 SR EN ISO 11885-0912 Nickel mg/kg d.m. 715 100 SR EN ISO 11885-0913 Lead mg/kg d.m. 3.60 300 SR EN ISO 11885-0914 Zinc mg/kg d.m. 601 2000 SR EN ISO 11885-0915 Mercury mg/kg d.m. 0.79 5 SR EN ISO 12846-1216 Total chromium mg/kg d.m. 469 500 SR EN ISO 11885-0917 Cobalt mg/kg d.m. 5.36 50 SR EN ISO 11885-0918 Arsenic mg/kg d.m. <0.01 10 SR EN ISO 11885-09

Table 9Sewage sludge analysis – 1:10 leaching test.

No Test Unit Sewage sludge MethodL/S =10 l/kg

1 Arsenic mg/kg d.m. (dry matter) <0.01 SR EN ISO 11885-092 Barium mg/kg d.m. 0.13 SR EN ISO 11885-093 Cadmium mg/kg d.m. <0.01 SR EN ISO 11885-094 Chromium total mg/kg d.m. 0.39 SR EN ISO 11885-095 Copper mg/kg d.m. 0.19 SR EN ISO 11885-096 Mercury mg/kg d.m. <0.01 SR EN ISO 12846/127 Molybdenum mg/kg d.m. 0.04 SR EN ISO 11885-098 Nickel mg/kg d.m. 0.21 SR EN ISO 11885-099 Lead mg/kg d.m. <0.05 SR EN ISO 11885-0910 Antimony mg/kg d.m. <0.1 SR EN ISO 11885-0911 Selenium mg/kg d.m. <0.05 SR EN ISO 11885-0912 Zinc mg/kg d.m. 0.97 SR EN ISO 11885-0913 Vanadium mg/kg d.m. <5 ECOIND (in house)14 Chloride mg/kg d.m. 347.9 SR ISO 9297-0115 Fluoride mg/kg d.m. 0.48 SR ISO 10359/1-0116 Sulphates mg/kg d.m. 376.6 EPA 427C17 Dissolved organic carbon (DOC) mg/kg d.m. 265.26 SR EN 1484-0618 Total dissolved solids (TDS) mg/kg d.m. 2220 STAS 9187-84

8 M. Crudu et al. / Waste Management xxx (2014) xxx–xxx

Please cite this article in press as: Crudu, M., et al. Valorization of titanium metal wastes as tanning agent used in leather industry. Waste Management(2014), http://dx.doi.org/10.1016/j.wasman.2013.12.015

Table 10Synoptic analysis of important elements entering in the composition of new Ti based tanning agent.

No Element Ti waste (%) Ti based tanning agent(in powder) (%)

Wet whiteleather (%)

Sewage wastewater (mg/l)

Sewage sludge

1 Titanium 88–97 74.7 2.32–8.25 – <100a

2 Aluminium Traces – 6.7 24.9 1.21–2.61 <2.5 g/l <100a

3 Vanadium Traces – 4.0 0.13 0–0.71 <1.2 lg/l Not detected

a Not included in Order 344/2004: technical regulations on environmental protection and especially the soil when using sewage sludge in agriculture.

M. Crudu et al. / Waste Management xxx (2014) xxx–xxx 9

4. Conclusions

The paper presents a way for valorization of titanium wasteswhich cannot be recycled in metallurgical industry, by transferringthem into raw material for obtaining a new Ti based tanning agentwith application in leather manufacture.

Total or partial replacement of chromium salts in the tanningprocess with cheap to produce and easy to apply in bovine leathermanufacture is possible and require minimum process rationaliza-tion or modification.

Data obtained for main important elements entering in thecomposition of new Ti based tanning agent, composition of wetwhite leather, quality of sewage waste water and sludge encouragethe authors to continue the researches in the direction of improv-ing the methods of Ti waste selection and processing to make themmore eco-efficient.

Acknowledgements

This work has been financed by the European Fund for RegionalDevelopment and the Romanian Government in the framework ofSectoral Operational Programme POS CCE-AXIS 2 Operation 2.1.2.,contract nr. 242/20.09.2010 under the project INNOVA-LEATHER:‘‘Innovative technologies for leather sector increasing technologi-cal competitiveness by RDI, quality of life and environmentalprotection’’.

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