第17 卷第4 期 皮 革 科 学 与 工 程 Vol117 ,No14
2007 年8 月L EATHER SCIENCE AND ENGINEERING Aug1 2007
Artical ID :1004 - 7964 (2007) 04 - 0003 - 06
Received Date :2007205221
3 P. Mokrejs :Corresponding author. Phone N°: + 420 57 603 1230 ;Fax N°: + 420 57 603 1563 ;e2mail :mokrejs @f t . utb. c2
Recycling Technology for Waste Tanning Liquors
P. Mok rejs1 3
, D. J anacova2 ,M. Mladek1 , K. Kolomaz nik2 , F. L angmaier1 ,V . V asek2
(1. Tomas B ata University , Faculty of Technology , Department of Protein and Leather , nam.
TGM 275 , 762 72 Zlin, The Czech Republic ;2. Tomas B ata University , Faculty of
A p plied Inf ormatics , Institute of Processing Cont rol and A p plied Computer Science ,
N ad S t ranemi 4511 , 760 05 Zlin, The Czech Republic)
Abstract :Tannery belongs to typical indust rial branches which during t he technological process
p roduce considerable quantities of liquid and solid wastes cont ributing to polluting t he environ2
ment . The presented work describes dechromation of waste tanning liquor utilising chrome sludge
p roduced t hrough enzymatic hydrolysis of chrome2tanned leat her wastes. The principle of dechro2
mation consist s in sorption of chrome f rom waste liquor af ter tanning to chrome sludge. Recy2
cling technology is characterised by an almost 99 % efficiency , simplicity and low investment re2
quirement s.
Key words :solid waste ;liquid waste ;chrome sludge ;waste tanning liquor ;chrome recovery
CLC number :X 794 Document code :A
鞣制废液的循环技术
摘 要:制革属于典型的工业分支,制革工业中会产生大量的污染环境的废液和废固。该论文利用铬鞣革废物的
酶法水解用铬污泥除去鞣制废液中的铬。除去铬的原理是鞣后的铬污泥从废液中吸收铬。该循环技术回收率可
达99 % ,操作简单、成本低廉。
关键词:固体废弃物;液体废弃物;铬污泥;鞣制废液;铬回收
1 INTRODUCTION
The tanning indust ry p rocesses wastes of the
meat indust ry , raw hides , and t ransforms t hem
t hrough chemical , chemico2p hysical and mechani2
cal processes into leather s. During t he technologi2
cal process , solid and liquid wastes arise which ,
particularly as a consequence of t he cont rover sial
chrome t hey contain , burden the environment .
Processing one met ric ton of raw hide produces ap2
prox. 200 kg finished leat her . About 30 , 000 kg
wastewaters arise through processing and more
t han 70 % chrome passes into liquid and solid
wastes [1 ] .
In classic tanning , approx. 40 % chrome (t he
starting charge of 15 - 17 kg Cr / t ) remains in
leat her , 26 % - 30 % chrome passes into solid
wastes and 30 % - 34 % chrome remains in liquid
wastes. In t he tanning of hides using technological
procedures ensuring high removal of chrome com2
pounds by white hide , 54 % - 57 % chrome remains
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net
in leat her , 31 % - 38 % chrome passes into solid
wastes and 5 % - 15 % remains in liquid wastes [2 ] .
For modifying t he tanning process , organic acids ,
e. g. are used , which cont ribute to improving the
removal of chrome ions.
1. 1 Liquid waste
Manufacture of chrome2tanned leat hers pro2
duces 115 - 2 times quantities of wastewater s t han
manufact ure of vegetable2tanned leat her s [3 ] . Los2
ses of chrome compounds in waste tanning liquor s
may be prevented in several ways. The simplest
approach is the direct recycling method consisting
in re2using exhausted liquor in t he tanning process.
The main shortcoming of t his method is a negative
effect of salt s and other contaminating substances
on quality of finished leather . Af ter being recycled
several times , wastewater has to be discharged into
sewage [4 ] . Anot her potential met hod is indirect
recycling , in which chrome is obtained f rom ex2
hausted sludge t hrough precipitation using a suit2
able alkaline agent , e. g. sodium hydroxide , sodi2
um carbonate , sodium hydrogen carbonate , mag2
nesium oxide , calcium sulp hate , calcium hydroxide
[5 ] . A f urt her met hod consist s in employing elabo2
rate techniques , e. g. elect ro2dialysis , membrane
separation , ion exchangers , wit h which chrome
may be separated f rom ot her salt s contained in ex2
hausted sludge. Chrome thus obtained is character2
ised by much higher p urity than that obtained
t hrough indirect recycling. Disadvantages are a
high cost and limited po ssibilities of applying t hese
demanding technologies in tanning factories [ 4 ] .
Unutilised chrome in liquid wastes , apart
f rom significant economic losses for tanneries , al so
poses great hazard for t he environment and for
man. The most stable and most important oxida2
tion state is Cr ( III) . Compounds of Cr (VI) occur
in t he form of chromates and dichromates and ex2
hibit quite st rong oxidative properties [6 ] .
Chrome is found in liquid tanning wastes in it s
t rivalent form , there exist s , however , potential
danger of it s oxidising to hexavalent compounds ,
particularly when t reating groundwater s to drink2
ing waters. Hexavalent compounds , when com2
bined wit h calcium or magnesium ions , are st rong2
ly carcinogenic[7 , 8 ] .
An extensive research exploring negative
effect s of tanning wastewaters f rom local tanneries
on t he adjacent ecosystem was conducted in Indi2
a[9 ] . Highest level s of chrome contained in soil
were found in t he vicinity of tanneries , at approx.
60 g/ kg. Highest chrome accumulation was ob2
served in cauliflower stalks (72 mg/ kg) in locali2
ties near tanneries. In st udies investigating Cr ac2
cumulation in fish organs it was found t hat most
chrome accumulates in t he liver (approx. 22 mg/
kg) and least in muscles (approx. 1 mg/ kg) . The
po ssible t ransfer of hazardous Cr doses into t he
food chain and consequently to human beings is
t hus quite obvious.
112 Sol id waste
Tannery processing al so produces a considera2
ble quantity of solid chrome2tanned wastes which
present a significant problem due to t heir chrome
content . The problem of solid wastes has been
solved so far by land filling which , of course , be2
side ever increasing land filling co st s al so brings
t he danger of chrome escaping into t he ecosystem.
Due to t heir containing a sizeable proportion of
protein material , solid tanned wastes started to be
processed. Enzymatic hydrolysis has being em2
ployed to considerable extent in latest year s , wit h
it s particular advantages being mild reaction condi2
tions and economic cost2effectiveness [10 , 11 ] . The
main product of enzymatic hydrolysis is collagen
hydrolysate , whose application possibilities are
broad , e. g. as feed additive , nit rogenous fertili2
ser , raw material for preparing adhesives , corro2
sion inhibitor s , etc. The remaining waste product
af ter enzymatic hydrolysis (chrome sludge) has not
yet found lucrative application. It s employment ,
due to chrome content , has not been much adopted
for preparing combined tanning bat hs.
Subject of the presented work is potential use
4 皮革科学与工程 第17 卷
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net
of t he waste product af ter enzymatic hydrolysis of
chrome2tanned solid wastes (chrome sludge) for i2
solating chrome compounds f rom waste tanning
liquor s.
2 MATERIALS AND METHODS
Solid was determined according to ISO 4684
[12 ] , ash according to ISO 4047 : 1998[13 ] , nit rogen
according to ISO 5397 : 1984 [14 ] , Cr2 O3 according
to ISO 5398 [ 15 ] , Cr according to ISO 9174 : 1998
[16 ] and Mg according to ASTM D511203 [ 17 ] .
Chrome sludge is a waste product of enzymatic
hydrolysis of chrome2tanned solid waste and it s
composition is given in Tab. 1. Typical composi2
tion of chrome2tanned solid waste is given in Tab.
2.
Tab11 Composition of chrome sludge1)
表1 铬污泥成份
Parameter Value
TS/ % 1614
Ash/ % 3410
N / % 114
Cr2O3 / % 1215
MgO / % 1115
1) based on total solids
Tab12 Composition of chrome2tanned solid waste1)
表2 铬鞣革固体废弃物成份
Parameter Value
TS/ % 6911
Ash/ % 1019
N/ % 2011
Cr2O3 / % 415
1) based on total solids
Tab13 Composition of waste tanning liquor
表3 鞣制废液成份
Parameter Value
TS/ % 718
Ash/ %1) 8713
N/ %1) 018
Cr/ (mg/ kg) 1 ,769
Mg/ (mg/ kg) 693
p H 412
colour blue2green
1) based on total solids
Waste tanning liquor was obtained f rom tan2
ning of cowhides and it s composition is presented
in Tab. 3.
The experimental part was divided into two
part s. The fir st part contained five selected mass
ratio s of chrome sludge ∶ waste liquor and three
various dechromation times , see Table 4. Practical
dechromation was performed under laboratory con2
ditions by stirring chrome sludge with waste tan2
ning liquor at room temperat ure in accordance wit h
t he scheme shown in Fig. 1. Af ter dechromation ,
t he heterogeneous mixt ure was cent rif uged. A part
of supernatant was analysed for Cr content . The
investigated object in view was quantity of residual
chrome in waste tanning liquor af ter dechromation.
The second part of test s followed up result s of
waste liquor dechromation efficiency in t he first ex2
perimental part . The mass ratio of chrome sludge
∶waste liquor producing greatest dechromation ef2
ficiency was selected and a series of test s per2
formed to t he p urpo se of st udying dechromation re2
action kinetics.
Fig1 1 Scheme of dechromation of waste tanning liquor
图1 鞣制废液的脱铬流程
3 RESULTS
Test s and dechromation result s at various
mass ratios of chrome sludge ∶waste liquor and va2
rious dechromation times are shown in Tab14.
Tab15 t hen shows dechromation result s at mass ra2
tio of chrome sludge ∶waste liquor = 1 ∶1 and va2
rious dechromation times. Each test was performed
t hreefold and arit hmetic mean calculated , standard
deviation ranged wit hin ±5 %.
第4 期 P. Mokrejs ,et al :Recycling Technology for Waste Tanning Liquors 5
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net
Tab14 Dechromation results of waste tanning liquor at mass ratios of Cr sludge/ waste liq. and dechromation times
表4 铬污泥与废液不同质量比以及不同脱铬时间条件下鞣制废液的脱铬结果
Test
No.
Batch( g)
sludge :liquor
t
/ min
In2process
pH
Cr liq. /
( mg/ kg)
Eff iciency
/ %
1 7114 ∶50 30 6134 - 7108 807 5414
2 90 190 8912
3 180 116 9315
4 20183 ∶50 30 6195 - 7148 146 9117
5 90 58 9617
6 180 33 9811
7 35171 ∶50 30 7121 - 7168 53 9710
8 90 33 9811
9 180 36 9810
10 50 ∶50 30 7130 - 7190 24 9817
11 90 23 9817
12 180 17 9910
13 70 ∶50 30 7148 - 8102 41 9717
14 90 32 9812
15 180 79 9516
1) Starting content of chrome in waste tanning liquor = 1769 mg/ kg
Tab1 5 Dechromation results of waste tanning liquor and
times1)
表5 铬污泥与废液质量比为1 ∶1 不同脱铬时间条件下鞣
制废液的脱铬结果
Test
No.
t
/ min
In process
pH
Cr liq.
/ ( mg/ kg)
Eff iciency
/ %
1 4 7120 - 7133 438 7512
2 8 7127 - 7145 351 8012
3 12 7151 - 7189 299 8311
4 16 7176 - 7194 230 8710
5 20 7180 - 7191 206 8814
6 24 7181 - 7194 200 8817
7 28 7181 - 7196 139 9211
8 32 7182 - 7199 43 9716
9 36 7188 - 8103 32 9812
10 40 7190 - 8104 19 9819
11 60 7186 - 8106 28 9814
12 80 7187 - 8107 22 9818
13 100 7180 - 8111 35 9810
1) Starting content of chrome in waste tanning liquor =
1769 mg/ kg ;mass ratio of chrome sludge ∶waste liquor = 1
∶1
Figure 2 shows column plot s representing re2
sidual chrome content in waste tanning liquor af ter
t he dechromation procedure at various chrome
sludge ∶waste liquor ratios and various dechroma2
tion times. With a mass ratio of 1 ∶7 af ter 30 min
dechromation , a drop of chrome in liquor exceeding
50 % was found , af ter 180 min the dechromation
efficiency was greatest . Wit h a ratio of 1 ∶214 ,
t he tendency of chrome content in liquor to de2
crease wit h time was at it s greatest , residual
chrome content in liquor coming down to 3314 ppm
which represent s dechromation efficiency exceeding
98 %. Wit h a ratio of 1 ∶114 t he tendency of
chrome decrease is similar , when t he greatest drop
of chrome content in liquor was already recorded
af ter 90 min of dechromation ( to 3312 mg/ kg) .
Wit h a ratio of 1 ∶1 , lowest level s of residual
chrome in liquor were already at tained in 30 min of
dechromation app rox. 24 mg/ kg , representing al2
most 99 % dechromation efficiency. A f urt her in2
crease in dechromation times produced but negli2
gibly decreased chrome content in liquor . Wit h a
ratio of 114 ∶1 , t he greatest drop of chrome con2
tent in liquor was recorded af ter 90 min dechroma2
tion. Fig13 shows dechromation kinetics of waste
tanning liquor at mass ratio of chrome sludge ∶
waste liquor = 1 ∶1 and various dechromation
times. From result s it is obvious t hat af ter 40 min
6 皮革科学与工程 第17 卷
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net
dechromation chrome content in waste tanning liq2
uor decreased to approx. 20 mg/ kg , which com2
pared wit h starting content of chrome in waste tan2
ning liquor ( 1769 mg/ kg) signifies almost 99 %
chrome removal efficiency. Further increases in
dechromation time did not show in markedly in2
creased chrome removal efficiency , and values of
residual chrome content in slurry fluct uated be2
tween 20 and 35 mg/ kg.
4 DISCUSSION
During past decades , a t ransfer occurred of a
notable part of tanning plant s f rom economically
advanced west European count ries to developing
count ries and to count ries of t he Asian continent .
In latest year s , however , t he environmental load
produced by t hese plant s became unsustainable and
intensive negotiations on resolving t he mat ter got
under way. When rest ructuring existing and con2
st ructing new tanning plant s , issues coming partic2
ularly under consideration are solid and liquid
wastes containing chrome. Contamination of
groundwater s wit h liquid wastes containing chrome
is obvious. Release of chrome f rom solid wastes
第4 期 P. Mokrejs ,et al :Recycling Technology for Waste Tanning Liquors 7
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net
can proceed particularly t hrough elution by rain
with great hazard of groundwater contamination.
The danger of Cr ( III) oxidising to Cr (VI) was al2
ready mentioned in t he fir st part of this cont ribu2
tion.
Test result s showed t he solid waste product ,
chrome sludge , may be successf ully employed to i2
solate chrome f rom waste tanning liquors , and t hat
with an efficiency of app rox. 99 %. The advanta2
ges of recycling technology may primarily comprise
simplicity and low demand for investment cost s ,
which make it ideally applicable when recycling
waste tanning liquor s especially in tanning plant s
in t he developing world.
Utilisation of chrome2enriched sludge remains
an open issue. A feasible alternative is it s combus2
tion and separation of chrome , which may be used ,
e. g. in pigment manufacture. A particular compli2
cation is presented by accompanying magnesium ,
which is undesirable for t hese applications. Isola2
ting magnesium f rom chrome sludge will be subject
of a following research. Employment of chrome2
enriched sludge for p reparing f resh tanning baths
al so remains an open issue.
5 CONCLUSION
Recycling technology developed for removing
chrome f rom waste tanning liquors wit h application
of waste chrome sludge achieves almost 99 % effi2
ciency. Dechromed waste liquor represent s a mini2
mal load on t he environment . Chrome2enriched
sludge , following isolation of ot her accompanying
element s (especially magnesium and calcium) com2
plicating it s f urther processing , could serve to pre2
pare pigment s. Result s of experimental measure2
ment s and an elaborated mat hematical model of re2
cycling technology will serve to propose an algo2
rit hm of enclosed dechromation cycle cont rol which
will be t he subject of pilot2plant test s.
Acknowledgements : The aut hors would like to
t hank to The Minist ry of Education of The Czech
Rep ublic for financial support to t his work execu2
ted under MSM Grant No : 7088352102.
References :
[1 ] Process technology for recovery and recycling of chromi2
um f rom leather waste and sludge , BLC , EV5VO542
(1994 1996) .
[2 ] Ludvik J . Chrome balance in leather processing [ J ] .
UNIDO , US/ RAS/ 92/ 120/ 11 - 51 (2000) .
[3 ] Mladek M ,et al . Leather indust ry waste t reatment [M] .
State Technical Literature Publishing , Prague ( 1971) :
261 - 265.
[4 ] Rajamani S. A system for recovery and reuse of chromi2
um f rom spent tanning liquor using magnesium oxide and
sulphuric acid[J ] . UNIDO (2003) .
[ 5 ] Covington A D , Sykes R L , Barlow J R , et al. A practi2
cal chrome recovery system using magnesium oxide[J ] . J
Soc Leather Technol Chem ,1985 , (69) :166 - 174.
[6 ]Cotton F , Wilkinson G. Advanced Inorganic Chemist ry
( A Comprehensive Text ) [ M ] . Academia , Prague
(1973) . 788 - 803.
[7 ] Hartford W H. Proceedings Chromium Symposium [J ] .
Indust rial Health , Foundation , Pitt sburg (1989) .
[8 ]Vijayalakshm R . A Study of the interaction of Cr ( III)
complexes and their selective binding with B2DNA. A
molecular modelling approach[J ] . J Biom St ruc Dynam ,
2002 (19) :1063 - 1072.
[9 ] Chattopadhyay B. The environmental impact of waste
chromium of tannery agglomerates in the east Calcutta
wetland ecosystem[J ] . J Soc Leather Technol Chem ,2000
(84) :94 - 100.
[ 10 ] Cabeza L F. Isolation of protein product s f rom chromi2
um2containing leather waste using two consecutive en2
zymes and purification of final chromium product : Pilot
plant studies [ J ] . J Soc Leather Technol Chem , 1999
(83) :14 - 19.
[11 ] Langmaier F. Product s of enzymatic decomposition of
chrome2tanned leather waste [J ] . J Soc Leather Technol
Chem , 1999 (83) :187 - 195.
[12 ] ISO 4684 , Determination of volatile matter.
[ 13 ] ISO 4047 : 1998 , Determination of sulphated total ash
and sulphated water insoluble ash.
[14 ] ISO 5397 : 1984 , Determination of nit rogen and hide
substance.
[15 ] ISO 5398 , Determination of chromic oxide.
[16 ] ISO 9174 :1998 , Water quality 2 Determination of chro2
mium 2 Atomic absorption spect romet ric methods.
[17 ]ASTM D511 - 03 , Standard test methods for calcium
and magnesium in water.
8 皮革科学与工程 第17 卷
© 1994-2008 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net

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