| Chrome Recovery and Recycling in the Leather Industry | Greece | 1988 - 1990 | Full scale |
TANNING AND DRESSING OF LEATHER # 11
Background
The project was carried out with the aim of enabling the Germanakos SA tannery located near Athens in Greece, to comply with discharge standards for trivalent chromium (Cr3+). This is used in tanning which is a chemical process that converts putrescible hides and skins into a stable material. Vegetable, mineral and other tanning agents may also be used - either separately or in combination - to produce leather with different qualities and properties. However Cr3+, is the major agent used since it produces a modern, thin, light leather suitable for shoe uppers, clothing and upholstery. However recent limits for discharge to the environment have limited Cr3+ discharge to levels as low as 2mg/liter in wastewater.
The Germanakos SA tannery was founded in 1978. Today it produces good quality upper leather from cattle hides, processing 2200 tons per year and with an annual turnover of US$ 8.4m and a staff of 65.
The Greek and Dutch governments have a framework of bilateral collaboration in the field of environmental protection. One result of this has been that a clean technology developed at The Toegepast Natuurwetenschappelijk Onderzoek (TNO), a Netherlands organization for applied scientific research has been applied in a full-scale co-operative R & D project between the two countries. The full-scale project was carried out by the Institute of Environmental and Energy Technology, Netherlands from 1988 to 1990 with support of the European Union.
Cleaner Production Principle
Recovery, Reuse and Recycle
Cleaner Production Application
The technology developed involves the recovery of Cr3+ from the spent tannery liquors and its reuse.
Tanning of hides is carried out with basic chromium sulfate, Cr(OH)SO4, at a pH of 3.5-4.0. After tanning, the solution is discharged by gravity to a collection pit. The liquor is sieved during this transfer to remove particles and fibers that have come from the hides. The liquor is then pumped to the treatment tank and a calculated quantity of magnesium oxide is added with stirring until the pH reaches at least 8. The stirrer is switched off and the chromium precipitates as a compact sludge of Cr(OH)3. After settling, the clear liquid is decanted off. The remaining sludge is dissolved by adding a calculated quantity of concentrated sulfuric acid (H2SO4) until a pH of 2.5 is reached. The liquor now contains Cr(OH)SO4 and is pumped back to a storage tank for reuse.
In conventional chrome tanning processes 20-40% of the used chrome is discharged into wastewater. In the new process, 95-98% of the waste Cr3+ can be recycled.
Environmental and Economic Benefits
The project benefits include,
| More consistent product quality. |
| Much reduced chromium content of effluent waters. |
For the Germanakos tannery, which has a chrome recycling capacity of 12m3/day, the approximate costs were as follows:
| Savings | 73,750 US$/year |
| Operating cost | 30,200 US$/year |
| Total net savings | 43,550 US$/year |
| Capital Investment | 40,000 US$ |
The payback period was 11 months.
Constraints
This technology is expected to be economical only for chrome recovery plants processing more than 1.7m3/day.
Contacts
Review Status
This case study was originally published in the UNEP IE document, "Cleaner Production Worldwide". In the process of preparing the document the case study underwent a technical review. Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.