Technologies for Reduction of Chrome Discharge:
Chromium Tanning salt is used today in more than 85% tanning operations. The Trivalent form is generally used. Chrome wastes are of great concern.
The conventional chemicals and processes used in tanning have a low utilization potential for chromium uptake with hardly 40 -70% of the applied salt being taken up by the leather. This results in the balance finding its way to effluents and creating environmental problems. As per an estimate for 1998, 45000 tonnes of basic chrome sulphate were used out of which 18000 tonnes were released in the waste water streams. It is, however, now possible to increase the uptake of chromium to nearly 98-99%. More than 500 plants have been installed in the India for recovery and recycle of Chromium salts. Cleaner chrome tanning methods based on high exhaustion principles have been evolved. Closed pickle tan loop method gives a saving of about Rs. 2000 per tonne of leather produced. Chromium recovery can be achieved either by a direct recycling of the spent liquor by adding make up quantities. Salts and other impurities tend to accumulate and may have an adverse effect on quality of leather. Recovery of Chromium by alkaline precipitation and consequent dissolution in Sulphuric acid and a reuse of the resultant solution is an efficient methodology. The highly reactive alkalis may give a voluminous sludge . Lime may also give Calcium Sulphate which makes the reuse of chromium difficult. Using MgO as alkali is considered more appropriate for small as well as large tanneries because of ease of operation and low investment costs.
Use of Chromium free tanning has also been advocated as a clean technology option. Synthetic organic tanning agents alone or in a combination with metallic cations can be considered as a substitute for chromium. Vegetable tanning has also got a high pollution potential because of the low biodegradability. Recovery of vegetable tanning floats has been used by ultrafiltration in many European countries and the recovered tannins can be used in the tanning process. Vegetable and aluminum tanning can also produce chrome free leather.
Within the options of clean technology during post tanning operations, absence of chromium during retanning and not using polluting dyestuffs, benzidene dyes and halogenated oils in fat liquors are strongly advocated.
The finishing processes should ideally work on water based finishes. Pigments should not contain heavy metals.
Water Management:
With up to 40 tonnes of water being used to process 1 tonne of hide, there is a need to conserve water. This can be achieved by reduction through low float processing, batch type washing instead of rinsing and combining processes and may give a reduction of about 30% in the water consumption. The recycle of soaking, liming,unhairing, pickling and chrome tanning liquors can also reduce the overall water consumption by 20 -40%. Treated effluents can be also used through membrane filters to further reduce the water consumption.
we are interested to plan Leather Tanning business, we need to know more details of this project, machinery and also we want to know cost of production for this project to run, please email me the details.
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