an improved product-process for cleaner chrome tanning in leather processing

Journal of Cleaner Production 9 (2001) 483–491www.cleanerproduction.net

An improved product-process for cleaner chrome tanning in leatherprocessing

V. Suresh, M. Kanthimathi*, P. Thanikaivelan, J. Raghava Rao, B. Unni Nair*

Chemical Laboratory, Central Leather Research Institute, Adyar, Chennai 600 020, India

Received 29 August 2000; accepted 8 January 2001

Abstract

Severe restrictions imposed by the pollution control authorities on the disposal of chromium, total dissolved solids and chloridesin tannery effluents have forced the tanners to look for low-waste, high exhaust chrome tanning salts. An improved chrome syntanwith more than 90% uptake of chrome has been developed. The new product serves both as tanning and retanning agent and canbe applied directly to delimed pelts thus eliminating the conventional pickling stage in the leather processing. This modified processhelps to reduce the chemical oxygen demand (COD), total dissolved solids (TDS) and chlorides in the spent tan liquor by 51, 81and 99%, respectively. The product offers full, soft leathers having shrinkage temperature comparable to conventional chrometanned skins. Since the developed product is highly reactive, it saves time and reduces the water requirement when compared tothe conventional chrome tanning method. Thus the novel product/process developed not only has advantages in reducing pollutionloads but also seems to be techno-economically viable. 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Eco friendly; Total dissolved solids; Chemical oxygen demand; Chlorides; Chrome tanning; Exhaustion; Spent tan liquor

1. Introduction

Concern over environmental toxicology and demandfor safe disposal of industrial wastes are the topics ofcurrent interest [1,2]. The leather industry is associatedwith the generation of huge amounts of liquid wastes(30–35 l/kg of raw material processed) and thus disposalof these wastes becomes a serious problem [3]. It is welldocumented that technologies used for treatment ofwastes are not cost effective [4]. Therefore, there is afundamental need to go for improved product and pro-cess alternatives to combat the problem of voluminousdischarge. In general, cleaner chrome tanning practiceinvolves implementation of the following strategieseither individually or in combination.

� improvement of conventional tanning processeswhich helps to reduce the total dissolved solids andother toxic chemical outputs.

* Corresponding authors. Tel.:+91-44-491-1386; fax:+91-44-491-1589.

E-mail address: [email protected]

0959-6526/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved.PII: S0959-6526 (01)00007-5

� use of high exhaust tanning systems where the uptakeof the tanning agent is greater than 90% and

� use of environmentally friendly raw materials in thepreparation of synthetic tanning salts (syntans), ther-eby arresting the release of toxic chemicals in theeffluent after tanning.

In this communication, a reassessment of currentlyemployed chrome tanning methods and the preparationof a tanning agent capable of minimizing the environ-mental impact have been attempted. The more popularchrome tanning method has many advantages [5,6]. Butthe lack of adequate filling of the leathers demands theuse of retanning syntans [7]. Most of the commerciallyavailable syntans are derived from phenol-phenolic acidresins based on formaldehyde condensate, which pro-vides freedom of choice with respect to degree of cross-linking, molecular weight and particle size to impart full-ness. However, they undergo photo oxidation and leadto discoloration of the leathers [8,9]. There are mineralsyntans with chromium(III) and aluminium(III) as anintegral part of the syntan with improved uptake charac-teristics [9,10]. Even though these syntans resistdetannisation up to the neutralization pH of 5.5 to 6.0,

484 V. Suresh et al. / Journal of Cleaner Production 9 (2001) 483–491

the polymeric backbone, which forms the syntan moiety,is built up by using formaldehyde. Further, the methyl-ene bridge which forms the building blocks of the poly-meric back bone easily undergoes homolytic scissoringon exposure to sunlight resulting in highly reactive freeradicals as shown in Scheme 1. This species, by reson-ance gives rise to quinones, which are responsible forthe discoloration of the tanned leathers.

Moreover, when these condensates are used as tanningmaterial, there is a possibility of release of free formal-dehyde, which may pose occupational hazards [11].Most of the commercially available syntans based onformaldehyde condensates release free formaldehyderanging from 1500 to 15,000 ppm [12], which does notmeet the stipulated values of 5–10 ppm for free formal-dehyde [13]. Hence there is a need to use resinousmaterial containing multiple carboxylic acid groups inthe preparation of syntans. Such poly carboxylic acidpolymers are obtained without using formaldehyde andthey are expected to increase the fixation of mineral saltswith protein [14,15].

The conventional chrome tanning method is associa-ted with large release of chromium content in the effluent[16]. There are reports about special types of mineralsyntans and salts, where total replacement of chromiumhas been considered [17,18]. But all these salts havebeen applied on skins/hides treated with sodium chloride(to prevent swelling) and sulphuric acid (pickling) at apH of 2.5–4.0. The various processes involved in leathermaking are given in Fig. 1. It is well documented thatthe objective of pickling is to bring the entire matrix touniform chemical and physical conditions and also toprevent the rapid combination of the skin substrate withchromium compound. This results in the release of large

Scheme 1. Process of homolytic scissoring of Bis(4-hydroxy phenyl) methane in the presence of light.

quantities of chlorides in the effluent [19] (30 g/kg ofskin processed). One of the major pollutants from tan-nery wastewater has been identified as sodium chloride[20], which emanates largely from the soaking, picklingand chrome tanning practices employed in leather pro-cessing. The composition of waste pickle and chrometanning solutions is given in Table 1 [3]. It is evidentthat COD and TDS contributions from these two oper-ations are significant. This is due to the use of hugequantities of sodium chloride in pickling and poorexhaustion behaviour of chrome tanning salt. Hence,there is a need to eliminate or integrate the pickling-chrome tanning processes so as to reduce the pollutionload. A new strategy has been designed to retain chrometannage with all its established advantages by applyinga novel high exhaust chrome syntan directly to delimedpelts without a pickling process. The mechanism for theeffectiveness of no-pickle tannage is based on providinga wider pH range for the complex-substrate interactionand allowing the intrinsic acidity of the chrome tanningreagent to reduce the pH to conventional levels. Thisnovel technique does not require basification (treatmentwith a mild alkali such as sodium bicarbonate) or mask-ing agents (sodium formate, sodium acetate) for the com-pletion of chrome tanning. This approach not only dem-onstrates a possibility of improved conventional chrometanning but also seeks advantages in avoiding pollutantsand environmental acceptability. In the present study, wereport the features of a newly developed formaldehyde-free chrome syntan, the mechanism of the pickle-lesstanning process, physico-chemical properties of thetanned leathers and environmental benefits.

485V. Suresh et al. / Journal of Cleaner Production 9 (2001) 483–491

Fig. 1. Process flow sheet for conventional leather processing.

Table 1Characteristics of the liquid wastes from conventional pickling andchrome tanning processes [3]a

Parameters Pickling Chrome tanning

Volume of effluent 1 1.5(l/kg of skinsprocessed)pH 2.0–3.0 3.0–4.0BOD 400–700 350–800COD 1000–3000 1000–2500Total solids 35000–70,000 30,000–60,000Total dissolved 34,000–67,000 29,000–57,500solidsChlorides 20,000–30,000 15,000–25,000Total chromium as nil 2000–5000Cr

a All values are in ppm except pH.

2. Experimental methods

2.1. Preparation of novel chrome syntan

A typical process involves sulphonation of aromatichydrocarbon, complexation of chromium(III) salts withmulti-functional polymeric matrix without using formal-dehyde. A combination of organic tricarboxylic anddicarboxylic acids was introduced during complexationto prevent the metal ion from hydrolysis at high pH con-ditions. This is followed by neutralization of the reactionmass, filtration and drying. The sample for tanning stud-ies was collected from a typical bench-scale preparationin 2–3 kg level. The product was developed, stan-dardized and tested for tanning trials in three tanneries.The process know-how for the production of above syn-tan is patented [21].

For chemical analysis of the product, the reagentsused were of analytical grade without further purifi-cation. For tannery trials, commercial grade materialswere employed and the trials were conducted at both theCentral Leather Research Institute (CLRI) and at com-mercial tanneries.

2.2. Specification of new chrome syntan

The product was analyzed for chromium content usingstandard spectrophotometric technique, after oxidation tochromate [22]. The amount of chromium is expressed as%Cr2O3. The moisture, total solubles and sulphates wereestimated by known methods [23] and the pH of a 10%solution of the product was determined by conventionalmethod [24] using a digital pH meter with glass elec-trode.

3. Characterization of the product

3.1. Potentiometric titration [24]

The pH titration curve for the developed chrome syn-tan was obtained as follows: 25 ml of 10% (w/v) solutionof the syntan was titrated against 0.25 M sodium hydrox-ide solution. The sodium hydroxide solution was addedin 0.5 ml portions with thorough mixing using a mag-netic stirrer. The pH of the solution was recorded aftereach addition of the base solution. A plot of pH vs vol-ume of NaOH consumed was drawn. The mid point ofthe tangent drawn along the log phase of the plot wastaken as the point of precipitation.

3.2. Ion exchange studies on the product

In order to establish the chemical nature of thedeveloped product, a 5% aqueous solution of the syntanwas prepared and aged for one hour at a pH of 3.0. A5 ml aliquot of this stock solution was loaded on aDowex 50W-X4, cation exchange (H+ form) column (1.2cm dia., 10 cm length). The column was repeatedlywashed with double distilled water. The unabsorbed,non-cationic portions of the syntan as well as its wash-ings were collected together. A 5 ml aliquot of the abovenon-cationic eluate was loaded on an anion exchangecolumn, Dowex 1-X8 (Cl- form). The unabsorbed por-tion was collected by washing the column using water.The unabsorbed portion remaining after passing through


both anion and cation exchange columns was consideredas non-ionic. The chrome content in the stock solution,non-cationic and non-ionic fractions were determinedindependently. From these values, the percentages ofcationic, anionic and non-ionic species were calculated.

3.3. Tanning trials

Delimed goatskins were tanned with the developedchrome syntan (E) as follows: (all percentages are basedon fleshed weight of the limed goat skins). A float lesstanning method was employed using syntan equivalentto 1.5% Cr2O3 (given in three instalments at 10 minintervals). The pelts were mixed for 30 min in a drum,flooded with 100% water and further run for 2 h. ThepH of the tanning solution was found to be 4.0–4.2.Hence, the process does not require basification step asfollowed in conventional chrome tanning. This isbecause the tanning agent being offered on delimed peltsat a pH of 7.0–8.0 and the acidity of the productreadjusts the pH of the tanned leather as well as the sol-ution to a pH 4.0–4.2. The shrinkage temperature of thechrome tanned leathers was measured using a TheisShrinkage Tester [25]. The spent tan liquor was collectedand analyzed for chromium content, COD, TDS andchloride contents by conventional analytical methods[23,26].

A control trial (C) was performed in parallel by usinga commercial basic chromium sulphate (BCS) salt(specifications [27] are given in Table 2). Delimed goat-skins were pickled conventionally to a pH 2.8–3.0 andtanned using commercial BCS at an offer equivalent to1.5% Cr2O3 as described above. The pH of the solutionafter flooding followed by running for 30 min was 3.0.The skins were basified to a pH 4.0 using sodium bicar-bonate (1.2% in 10% water, given in three instalments at10 min intervals followed by 2 h running). The shrinkagetemperature of the leathers were measured as mentionedabove. The spent tan liquor was collected and analysedas described above.

The wet blue leathers (leathers from chromium basedtanning in wet condition) made in this study were sub-jected to post tanning operations employing fatliquorsand dyes without using synthetic tanning agent and con-verted into upper leathers. A techno-economic viability

Table 2Characteristics of the developed chrome syntan and commercial BCS

Parameter Chrome syntan BCS [27]

% Cr2O3% 18.8±1 24.0±1Moisture 5±0.5 10±0.5Total sulphates as Na2SO4 45±2 30±5% Total solubles 95±2 97±3pH of 10% solution 3.4±0.2 3.0±0.2

assessment has been made by comparing the reductionin the cost of leather production, water and time require-ment, power consumption, effluent treatment cost andlabour cost when conventional pickling-chrome tanningmethodology was replaced with an integrated chrometanning method developed in this study.

3.4. Analysis of strength characteristics

Samples of standard dimensions for various physicaltests were obtained as per IULTCS method [28]. Theleather specimens were conditioned at 80±4 F for a per-iod of 48 h. The physical properties such as tensilestrength, % elongation at break, bursting strength andtear strength were then investigated [29].

3.5. Scanning electron microscopic analysis

In order to study the effect of the chrome syntan onthe fibre bundles, samples measuring 5×2 mm were cutwith fresh stainless steel blades from the wet blueleather, dehydrated slowly as per standard procedures[30] and subjected to SEM analysis. The leathers weremounted on aluminium stubs and then coated with goldusing a Polaron SC500 sputter coater. The stubs werethen introduced into the specimen chamber of LeicaCambridge Stereoscan 440 Scanning Electron Micro-scope. The micrographs for the grain surface and crosssection were obtained by operating the SEM at an acce-lerating voltage of 20 kV and at magnifications of 100×,1000× and 500×, respectively.

3.6. Composite liquor analysis

Composite liquor was made by mixing pickling andchrome tanning solutions in the case of conventionalchrome tanning (C). In the case of experimental (E)chrome tanning, spent chrome liquor alone was collectedand considered as composite liquor. The compositeliquors from these two processes were analysed forchemical oxygen demand, chlorides and total dissolvedsolids as per the standard procedures [23,26]. From this,emission loads were calculated by multiplying theCOD/TS/Cl- values (mg/lit) with volume of compositeeffluent (lit) per ton of raw skins processed.

4. Results and discussion

4.1. About the product

The specifications of the developed chrome syntan aswell as normal BCS are given in Table 2. The syntan isgreen in colour and freely soluble in water. From thetable it is obvious that the Cr2O3 content in the syntanis comparable to those of commercial chrome syntans


Fig. 2. Potentiometric titration curve of the chrome syntan.

(13–15%). Although many chrome syntans are commer-cially available, the speciality of this newly developedproduct is that the polymeric matrix does not containformaldehyde, exhibits high exhaustibility character-istics, gives fullness to tanned leathers when used as aself tanning agent. The most significant feature about thetanning salt is its effectiveness in no-pickle tannage byproviding a wider pH range for the complex-substrateinteractions. The potentiometric titration curve of theproduct is depicted in Fig. 2. From the figure, it isobserved that the precipitation of the product starts at apH of 5.5–6.0. Thus the incorporation of multifunctionalpolymeric matrix along with suitable choice of ligandsincreases the pH of precipitation to higher values. Eventhough the product was offered to delimed pelts directlyat a pH of 7–8, there is no observable turbidity in thefinal spent tan liquor thus showing its high pH stabilitytowards hydrolysis.

4.2. Ion exchange studies

Table 3 shows the charge distribution of the developedsyntan estimated by ion exchange chromatographic tech-nique. The distribution of commercial basic chromiumsulphate is also given for comparison [31]. When com-pared to normal BCS, the neutral charged species in theformaldehyde-free syntan is less (�1%) and cationicspecies is more. Thus, we have a convincing and com-pelling evidence of the new product with low non-ionicand anionic species with higher charged cationic com-

Table 3Chemical nature of commercial BCS and developed chrome syntana

Complex BCS Chrome syntan

Anionic 10±0.5% 9±0.5%Non-ionic 5±0.2% 1±0.05%Cationic 80±1% 90±1%

a Based on a 5% solution after ageing for 1 h.

plex to improve the exhaustion of chromium to greaterthan 90%. Thus, our claim for improved uptake of chro-mium is due to the reduced percentage of zero-chargedcomplexes and the introduction of polymeric agent toproduce a more reactive tanning agent which in turnreduces the tanning time when compared to conventionalchrome tanning.

4.3. Integrated chrome tanning vs commercial pickle-chrome tanning

4.3.1. Tanning and spent tan liquor studiesThe percentage chrome uptake and the shrinkage tem-

perature values are given in Table 4. A comparison wasmade with a commercial basic chromium sulphate (BCS)salt on equivalent Cr2O3 offer basis. Although it is verydifficult to establish the chemical identity of the syntanmoiety retained after binding with protein, it is obviousfrom the uptake data that there is no hydrolysis of themetal ion. This indicates that the poly functional poly-meric ligand along with suitable masking agents helpsthe metal ion to exhibit a high degree of complexation.The conventional chrome tanning using BCS as tanningsalt shows an uptake of 65% as Cr2O3 [32] whereas thedeveloped product gives an uptake of 92% exhibiting ashrinkage temperature of 119°C, which is similar to thatof conventional chrome tanned leathers. The spentchrome liquor was analyzed for chrome content, totaldissolved solids (TDS), chemical oxygen demand (COD)and chloride contents. The values are presented in Table4. A comparison was made with the spent liquor col-lected from normal chrome tanning process. From thespent liquor analysis, it is evident that the developed pro-duct exhibits high exhaustion of chrome when comparedto normal BCS tanned spent liquor. The total dissolvedsolids in conventional chrome tanned liquor is twice thatof the tan liquor from pickle less tanning process usingthe developed product. Similarly the chloride content inthe former spent liquor is more than 20 times when com-pared to the latter. However, the COD content is more inthe later confirming the presence of aromatic component,which forms the major ingredient of syntan moiety.

Table 4Analytical data on spent chrome liquor and shrinkage temperaturebased on developed chrome syntan and commercial BCS

Parameter BCS Chrome syntan

% Chrome uptake 65±3 90±2TDS (ppm) 56,000 28,036COD (ppm) 1500 2120Chloride (ppm) 20,000 715Chrome content as Cr 3300 216(ppm)Shrinkage temperature 120±2 118±2(°C)


Thus, the data provide compelling evidence for the mini-mization of metal content and TDS in the tan liquor ther-eby helping the safe disposal of tannery effluent.

4.4. Scanning electron microscopic analysis

Scanning electron photomicrographs showing thegrain surface of the leathers tanned with BCS andchrome syntan at a magnification of 100 are shown inFig. 3(a,b), respectively. The grain surface of the leathertanned using commercial BCS [Fig. 3(a)] seems to beflat without any wrinkles compared to the leather tannedwith the chrome syntan [Fig. 3(b)]. This could be dueto the rapid reaction of the chrome syntan with the grainsurface as against a mild and gradual fixation of chro-mium in commercial chrome tanning. Both the samplesexhibit a clear grain surface, which indicates that thereis no physical deposition of chromium. Higher magnifi-cation (×1000) scanning electron microphotographs [Fig.4(a,b)] confirm the above observation, where the hairfollicles look clean without any foreign materials in bothcases. Scanning electron photomicrographs showing thecross section of the leathers tanned with BCS and

Fig. 3. (a) Scanning electron micrographs showing the grain surface(×100 magnification) of the chrome tanned leather; (a) tanned withcommercial BCS; (b) tanned with chrome syntan.

Fig. 4. (a) Scanning electron micrographs showing the grain surface(× 1000 magnification) of the chrome tanned leather; (a) tanned withcommercial BCS; (b) tanned with chrome syntan.

chrome syntan at a magnification of 500 are depicted inFig. 5(a,b), respectively. The fibre bundles seem to beless dispersed (separation of fibres) in the BCS tannedsample compared to a chrome syntan tanned sample.This explains the empty nature of the conventionalchrome tanned leather. Since the chrome syntan tannedsample exhibits slightly dispersed (opened up) fibrestructure, it would, in principle, exhibit an increased full-ness and softness in the final leather.

4.5. Leather characteristics

Performance of the leathers made in this study wasassessed by evaluating strength characteristics. Thephysical testing data for the leathers tanned with BCSand chrome syntan is given in Table 5. All the strengthcharacteristics are improved for the chrome syntantanned leathers compared to BCS tanned leathers. Thiscould be due to the presence of the resinous polymer inthe syntan formulation, which aids the sliding of fibres.

4.6. Environmental benefits

Composite liquor was prepared by mixing spentliquors from pickling and chrome tanning processes. Itshould be noted that the experimental chrome tanningmethod does not have a pickling process and hence spent


Fig. 5. (a) Scanning electron micrographs showing the cross section(×500 magnification) of the chrome tanned leather; (a) tanned withcommercial BCS; (b) tanned with chrome syntan.

Table 5Physical properties of leathers tanned with BCS and chrome syntan

Parameter BCS Chrome syntan

Tensile strength (kg/cm2) 300±12 335±10% Elongation at break 57±6 78±4Tear strength (kg/cm) 67±3 86±5Bursting strength (load in 26±3 45±4kg)

chrome liquor alone was considered as composite. Theliquors were analysed for COD, TDS, chlorides and thevalues are presented in Table 6. Analysis of the impactof these parameters on the environment requires calcu-

Table 6Composite liquor analysis for conventional and experimental chrome tanninga

Process COD (ppm) TDS (ppm) Cl� (ppm) Volume of Emission load (kg/ton of raw skins processed)effluent (lit/ tonof raw skins)

COD TDS Cl�

C 1700 57,600 24,000 2500 4.3 144 60E 1413 18,660 477 1500 2.1 28 0.72

a Composite liquors were collected including pickling and chrome tanning for control (C) and without pickling for experimental (E).

lation of emission load. Emission loads were calculatedby multiplying COD/TDS/Cl- values (mg/l) with volumeof composite effluent (l) per ton of raw skins processed.The values are given in Table 6. It is evident that theCOD, TDS and Cl- loads are reduced by 51, 81 and 99%,respectively for the integrated chrome tanning (E)method compared to conventional chrome tanning (C).The reduction in TDS and chloride loads helps in achiev-ing cleaner chrome tanning. Especially the reduction ofchlorides by 99% is a significant achievement in avoid-ing pollution due to chlorides. As the ground wateraround many of the tannery sites is saline in nature, thisintegrated chrome tanning approach would help inattaining palatable water. The adoption of the pickle-lesstanning method could bring a phenomenal change in thetanning industry by making it environmentally sus-tainable in the context of cleaner production.

4.7. Techno-economic feasibility

Any development of a new product/process requirescommercial feasibility apart from achieving the requiredquality in order to capture the market. The product usedin this study costs one and half times that of commercialBCS. However, the developed integrated chrome tanningmethod eliminates two important processes namely pic-kling and basification. The consumption of chemicals,water, time and power for the control and experimentalchrome tanning processes is given in Table 7. It is appar-ent that there is a significant reduction in the consump-

Table 7Consumption of chemicals, water, time and power for the control (C)and experimental (E) chrome tanning (processing capacity: 1000 kgof pelts)

Process Chemicals Water (l) Time (min) Power(kg) (kWh)

C 182a 2500 375 188E 80b 1500 180 90% Reduction 56 40 52 52

a Includes sodium chloride, sulphuric acid, basic chromium sulphateand sodium bicarbonate.

b Includes chrome syntan.


tion of chemicals, water, power and time. This couldreduce the cost of leather production for the integratedchrome tanning to some extent. The application of thisproduct on thick bovine hides (5–10 mm) needs longerduration for complete penetration of the chrome syntan.This can be avoided by splitting the thick bovine hidesto uniform thickness before tanning. One of the mainbenefits of using this chrome syntan is substantialreduction in the input of synthetic tanning agents duringpost tanning operations. This reduction may offset theincreased cost of the developed product. It has beenobserved that the consumption of the total amount ofsynthetic tanning agents during post tanning of commer-cial chrome tanned leathers is nearly equivalent to theamount of the developed chrome syntan offered duringintegrated chrome tanning. Moreover, the cost of thepost tanning syntans is 1.3 times that of the developedchrome syntan. Hence, there will be a net reduction inthe total cost of leather production apart from reductionin effluent treatment cost. However, commercial levelstudies are necessary in order to establish a reliableassessment.

5. Conclusion

The ecological concerns have become a key issue inthe present global industrial activities. Although leatherprocessing has emerged from the by-product of the meatindustry, it has turned out to be an independent activitydue to the intrinsic nature of the leather for its end uses.However, the discharge of waste streams with severalpollutants has raised a social threat to the leather sector.In the present scenario, integrated cleaner leather pro-cessing towards a greener environment is the currenttheme for sustainable leather industry. Especially, pic-kling-chrome tanning processes which release enormousamounts of chlorides, sulphates and chromium. To cir-cumvent this, an integrated chrome tanning approachwithout pickling using a novel chrome syntan hasbeen developed.

The studies on the characterisation of the developedproduct revealed that the product has higher stabilitytowards hydrolysis as well as higher reactivity with theskin matrix. The tanning studies show that the elimin-ation of the pickling process does not affect the proper-ties of the final leathers. This is further substantiatedthrough the scanning electron microscopic studies. Thechrome uptake for the developed product is above 90%,thus the integrated product cum process reduces theamount of chromium in the wastewater by 94% com-pared to the conventional chrome tanning. The strengthproperties seem to be better than the conventionalchrome tanned leather. The developed integratedapproach enables environmental benefits through thereduction of the COD, TDS and chlorides loads by 51,

81 and 99%, respectively compared to commercialchrome tanning practices. This investigation leads to animproved process/product development for cleanerchrome tanning which is technically viable.

Acknowledgements

The authors thank Dr T. Ramasami, Director, CentralLeather Research Institute for his constant encourage-ment and suggestions in the development of this process.The authors are also thankful to Mr R. Sundaram andDr K.J. Sreeram for their timely help.

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an improved product-process for cleaner chrome tanning in leather processing

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