Development and Application of Cleaner Production in Rural Tanneries

Abstract Sudanese rural tanning is an inherited craft. The methods and the indigenous materials employed by the rural tanners have remained unchanged for a long time. This is due to poverty, illiteracy, poor communications and lack of access to modern scientific technologies of leather production. As a result, the leathers produced by rural tanners are hard, crusty, liable to crack, tear. Moreover, the process period is long. The objective of the study is to investigate the possibilities of adoption of modern tanning methods to rural tanning with appropriate modifications (1) to speed up the process, (2) take out some of the hard manual work, (3) improve the quality of the produced leathers, (4) increase the production of the rural tanneries and (5) direct rural tanners toward cleaner production. For this purpose, a hand-operated drum was designed to carry out all wet processes through soaking to retanning. Modern tanning materials were introduced in all processes. Little amounts of chromium were used as a pre-tanning agent. The optimum amount of chromium was found to be 3% (based on the fleshed weight) which gave acceptable shrinkage temperature and good physical properties. After developing the tanning recipe and selecting the optimum chrome powder to be applied by rural tanneries, recycling of spent liquors was carried out to (1) minimize the environmental impact and to (2) reduce the production cost. Considerable savings on chemicals and water were obtained. Rural tanneries play a vital role in national economy and they have to be improved. Rural tanneries can create employment opportunities for a large number of people if attention has been paid for revamp and modification.

Table of Contents

Dedication…………………………………………………………………………………………..I

Acknowledgements………………………………………………………………………………..II

Abstract (English)………………………………………………………………………………...III

Abstract (Arabic)…………………………………………………………………………………IV

Table of contents…………………………………………………………………………………..V

List of Tables……………………………………………………………………………………..IX

List of Figures…………………………………………………………………………….X

1 Introduction…………………………………………………………………………………...1

1.1 Leather…………………………………………………………………………..............1

1.2 Tanning………………………………………………………………………………….2

1.3 Modern tanning method…………………………………................................................3

1.4 Sudan leather industry………………………………………………………...................4

1.5 The study problem………………………………………………………........................5

1.6 The importance of the study…………………………………………………………….5

1.7 General objectives……………………………………………………………………….5

1.8 Specific objectives……………………………………………………………................6

1.9 About the study………………………………………………………………………….6

2 Literature review……………………………………………………………………...............7

2.1 Raw materials……………………………………………………………………………7

2.1.1 Structure of hides and skins.................……………………………………………7

2.1.2 Chemical constituents of hides/skins ....................................................................9

2.1.3 Types of raw materials......................................................................................... 9

2.1.4 Quality of hides and skins .................................................................................. 10

2.1.5 Curing of hides and skins................................................................................... 10

2.2 Pre- tanning operations………………………………………………………………...11

2.2.1 Soaking.............................................................................................................. 11

2.2.2 Unhairing and liming ......................................................................................... 12

2.2.3 Mechanical operations after liming..................................................................... 12

2.2.4 Deliming............................................................................................................ 13

2.2.5 Bating................................................................................................................ 13

2.2.6 Pickling ............................................................................................................. 14

VI

2.2.7 Degreasing......................................................................................................... 16

2.3 Tanning operations……………………………………………………………………..17

2.3.1 Chrome tanning ................................................................................................. 18

2.3.2 Basification........................................................................................................ 23

2.3.3 Vegetable tanning .............................................................................................. 24

2.3.4 Alternatives to chromium................................................................................... 30

2.3.5 Combination tannage ......................................................................................... 31

2.4 Post- tanning Operations……………………………………………………………….35

2.4.1 Neutralization .................................................................................................... 37

2.4.2 Leather Dyeing .................................................................................................. 38

2.4.3 Fatliquoring and oiling....................................................................................... 43

2.4.4 Drying ............................................................................................................... 48

2.5 Finishing operations……………………………………………………………………48

2.5.1 Mechanical Finishing operations........................................................................ 49

2.5.2 Finishing materials............................................................................................. 49

2.5.3 Pigment finishing............................................................................................... 50

2.6 Cleaner production in leather industry…………………………………………………50

2.6.1 Cleaner technology in soaking............................................................................ 51

2.6.2 Clean technology in liming and unhairing .......................................................... 52

2.6.3 Clean technology in deliming and bating............................................................ 52

2.6.4 Pickling and chrome tanning .............................................................................. 53

2.6.5 Vegetable tanning .............................................................................................. 54

2.7 Planning a rural tannery………………………………………………………………..55

2.7.1 Site .................................................................................................................... 55

2.7.2 Size.................................................................................................................... 55

2.7.3 Basic sections .................................................................................................... 56

2.7.4 Machinery.......................................................................................................... 58

2.7.5 Drums................................................................................................................ 58

2.7.6 Paddles .............................................................................................................. 61

2.8 Sudanese rural tanning…………………………………………………………………62

2.8.1 Raw materials (types and quality)....................................................................... 62

2.8.2 Soaking.............................................................................................................. 63

2.8.3 Liming and unhairing......................................................................................... 65

VII

2.8.4 Bating................................................................................................................ 66

2.8.5 Fleshing............................................................................................................. 67

2.8.6 Tanning ............................................................................................................. 67

2.8.7 Oiling ................................................................................................................ 69

2.8.8 Drying and staking............................................................................................. 70

2.8.9 Uses of tanned leathers....................................................................................... 71

2.8.10 Services ............................................................................................................. 71

2.8.11 Hazards and safety equipments........................................................................... 72

2.8.12 Training............................................................................................................. 72

2.8.13 Acceptance for new techniques .......................................................................... 72

2.8.14 Problems facing rural tanners............................................................................. 73

3 Materials and Methods……………………………………………………………................74

3.1 Raw materials…………………………………………………………………………..74

3.2 Tools, instruments, machines and apparatuses………………………………………...74

3.3 Chemicals………………………………………………………………………………75

3.3.1 Chemical used for tanning operations................................................................. 75

3.3.2 Reagents used for chemical analysis of crust leathers ......................................... 75

3.3.3 Chemicals used for analysis of spent liquors....................................................... 75

3.4 Design of a hand – operated drum……………………………………………………..76

3.5 Developing an optimum recipe to be used for rural tanneries…………………………77

3.6 Physical testing of leathers……………………………………………………………..79

3.6.1 Sample preparation ............................................................................................ 79

3.6.2 Conditioning...................................................................................................... 80

3.6.3 Measurement of thickness.................................................................................. 80

3.6.4 Measurement of tensile strength and percentage ................................................. 80

3.6.5 Measurement of tearing load .............................................................................. 82

3.6.6 Measurement of distension and load at grain crack............................................. 83

3.6.7 Measurement of shrinkage temperature .............................................................. 83

3.7 Chemical analysis of leathers…………………………………………………………..84

3.7.1 Sampling ........................................................................................................... 84

3.7.2 Determination of moisture content in leather ...................................................... 84

3.7.3 Determination of oils and fats............................................................................. 84

3.7.4 Determination of water soluble matter................................................................ 85

VIII

3.7.5 Determination of insoluble ash........................................................................... 85

3.7.6 Determination of chromium in leather................................................................ 86

3.7.7 Determination of total ash .................................................................................. 87

3.8 Recycling operations…………………………………………………………...............87

3.8.1 Estimation of sodium sulphide in used lime liquor.............................................. 88

3.8.2 Analysis of used lime liquor............................................................................... 88

3.8.3 Analysis of pickle liquor (NaCl – HCl system)................................................... 89

3.8.4 Determination of chromium in used liquor ......................................................... 90

3.8.5 Tannin analysis.................................................................................................. 91

4 Results and discussion………………………………………………………………………94

4.1 Developing an optimum recipe to be used for rural tanneries…………………………94

4.1.1 Effect of chrome offer on chromic oxide content in leather................................. 94

4.1.2 Effect of chromic oxide content in leather on shrinkage temperature................... 95

4.1.3 Effect of chromic oxide content on physical properties of crust leathers.............. 96

4.1.4 Chemical analysis of crust leathers..................................................................... 97

4.1.5 Recommended recipe......................................................................................... 98

4.2 Recycling of spent liquors……………………………………………………..............98

4.2.1 Recycling of soaking liquors.............................................................................. 98

4.2.2 Recycling of unhairing and liming liquors.......................................................... 99

4.2.3 Recycling of deliming liquors .......................................................................... 100

4.2.4 Recycling of pickle – chrome liquors ............................................................... 100

4.2.5 Recycling of retanning liquors.......................................................................... 101

4.2.6 Physical and chemical characteristics of recycled leathers ................................ 102

4.2.7 Summary of recycling operations..................................................................... 103

5 Conclusion and recommendations…………………………………………………………104

5.1 Conclusion……………………………………………………………………………104

5.2 Recommendations…………………………………………………………………….104