Title of Invention	"AN IMPROVED PROCESS FOR THE RECOVERY OF COMMON SALT FORM SALT CURED HIDES/SKINS FOR REDUCTION OF TOTAL DISSOLVED SOLIDS IN THE EFFLUENTS"
Abstract	This invention relates to an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent. A method is disclosed to treat salt cured hides/skins with saturated sodium chloride solution to ensure that the salt adhered to the skin settles down for subsequent separation as well as reuse. This ensures that the TDS of the leather processing effluent is significantly reduced. The process also provides a method to regenerate the contamination free saturated sodium chloride solution for subsequent use.

Title of Invention

"AN IMPROVED PROCESS FOR THE RECOVERY OF COMMON SALT FORM SALT CURED HIDES/SKINS FOR REDUCTION OF TOTAL DISSOLVED SOLIDS IN THE EFFLUENTS"

Abstract

This invention relates to an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent. A method is disclosed to treat salt cured hides/skins with saturated sodium chloride solution to ensure that the salt adhered to the skin settles down for subsequent separation as well as reuse. This ensures that the TDS of the leather processing effluent is significantly reduced. The process also provides a method to regenerate the contamination free saturated sodium chloride solution for subsequent use.

Full Text	Title of the Invention The present invention relates to an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent. Field of the Invention More particularly, the present invention provides a process to recover the common salt, used for curing raw hides/skins. The salt thus recovered in solid form reduces the Total Dissolved Solids (TDS) in the Tannery effluent to an extent of 50 - 60%, and provides an option for its reuse for similar applications. Thus the process has enormous potential application to ensure eco-benign approach for leather processing industry. Background of the Invention Hides and skins as they are obtained after flaying, referred as green or fresh hides/skins, contain water to the extent of about two-third of their weight. The presence of so much moisture in the green hides and their chemical constituents consisting mainly of proteins make them very liable to bacterial attack which decompose them. Curing is the treatment of raw hides and skins done to dehydrate the stock to avoid the risk of bacterial action and hence putrefaction to ensure temporary preservation. The raw hides and skins are currently salt cured in India. As reported by Sharphouse (Leather Technician Handbook, Leather producer association, London, XVI, Chapter 3, 8-19, 1971), curing using salt is done in three different ways 1. Brining: The hides are cleaned with water and are then hung in pits or run in large paddles using concentrated salt solution containing about 30 Ib salt to every 10 gallons of cold water. This ensures uniform salt penetration in 12 - 14 hours for heavy hides. The hides are then drained and piled, which may require further sprinkling of salt similar to that of wet salting process. 2. Wet salting: The cold, flayed hide or skin is spread out, flesh side up, on a concrete floor and well sprinkled with salt. A second hide is placed on the first one and also sprinkled with salt. The amount of salt used may vary for hides and skins. For skins 30 - 40% of salt is used and in case of hides nearly 15 - 20 % is used. This is repeated until stacks of 5 - 8 feet high are formed and the top hide is overlaid with salt. 3. Dry salting: The flayed skin or hide is salted by either, or both, of the above method and is then hung up to dry. Drying is carried out gradually and evenly. This reduces the weight and the cost of transport of the raw materials. But dry salted hide or skin obviously requires longer and careful soaking than wet salted hides. The salt cured hide or skin reaching the tannery contains less than its physiologic water content. It contains protein that are partially dried and coagulated. The cured stock has to be rehydrated prior to further processing for tanning. This is done during soaking, which is the initial step in leather processing where cured hides and skins are soaked in large amount of water. The main objective of soaking, as reported by Sarkar (Theory and Practice of Leather Manufacture, Chapter 5, 94-120, 1991,) are the following. 1. Cleaning the hides or skins (removing the dirt, blood and most of the salt used in curing). 2. Softening and swelling the fibres to bring the skins as far as possible back to the state of green hides, i.e., to rehydrate the fibres. 3. Dispersal and removal of interfibrillar proteins which otherwise cement the fibres together and prevent their thorough rehydration. Since salt is water soluble, the soaking operation results in a situation where the salt used for curing goes into solution, thereby increasing the TDS of the processed water. Thus the major limitation of the salt curing lies in the disposal of effluent containing large quantities of salt. As reported by Kanakaraj (Journal of American Leather Chemists Association, 95, 368-374, 2000), the electrolytes discharged in the form of chloride and sulphates form the largest component of tannery effluent contributing to TDS load and they are the most difficult to treat at the end of the pipe as the source of electrolytes is mainly from salt curing method currently followed and to some extent from pickling, which is another pretanning operation practised in tanneries. Chlorides being highly soluble and stable are not affected by effluent treatment and thus remain a burden to the environment. In the last decades, the evolution of the leather industry has been coupled with a growing awareness of the protection of the environment as a consequence of pollution caused due to the discharge of untreated effluents by tanneries into land and water bodies. In 1996 the Supreme Court of India ordered the closure of all tanneries that had not set up proper pollution control system. Public interest litigation cases had risen against tanneries, which culminated in court orders directing relocation or closure of tanneries that have not either erected Effluent Treatment Plants (ETPs) or connected to Common Effluent Treatment Plants (CETPs), as reported in http://www.york.ac.uk/depts/eeem/publish/edepdf/Confer-2000-79.pdf. Nearly 40,000 litres of effluent is being generated per tonne of leather processing, contributing to about 350 - 450 Kg of salt as TDS. As reported by Kanakaraj (Journal of American Leather Chemists Association, 95, 368-374, 2000), soaking contributes to 40% of TDS (salt) that is generated from the entire process of leather manufacture. The high amount of salt contained in the effluent when used for irrigation purpose after treatment will increase surface salinity through evaporation, reduces the fertility of soil resulting in the poor yield of crops. It is therefore of utmost importance to avoid this level of salt in the effluent to ensure eco-benign approach of leather processing. To minimize the level of salt in the tannery effluent, some tanneries practice solar evaporation where the soak liquor is segregated from the combined effluent stream. The liquor is settled, clarified, sand filtered and dried in solar evaporation pans, as is evident from http://www.tft.csiro.au/leather/cleantech.html. But this method requires larger area for its operation and is labour dependent. It also suffers problem with the disposal of the recovered salt. Tanneries located at Kanpur area practise a method called desalting. The objective of desalting is to remove the excess salt from the raw hides, reducing the Total Dissolve Solids in the effluent stream. Two efficient methods of desalting are: a) Manual desalting using wooden frame; b) Mechanical desalting using brush type desalting machine. A majority of tanneries carry out desalting without the use of mechanical devices. This leads to only partial removal of salt from the hide/skin. In only a handful of tanneries desalting is carried out with wooden frames or brush desalting. Efficient desalting can lead to 20-25% reduction of TDS and chloride in the combined effluent stream, as revealed in http://www.cuts-india.org/Leather Sector Study.doc (chapter III). Salt recovered in this process requires maximum efficiency and faces problem with disposal, as it cannot be reused for further application. There are several established technique like ion exchange, reverse osmosis, electro dialysis and distillation etc available to remove TDS (salt) in the effluent. As reported by Sahasranamam (Environment Management; A Study of Indian Leather Industry, Council for Leather Exports, Chennai, chapter 5, 39-47, 2003), these techniques are yet to be practiced in the tanneries in India. Similar situation is expected for tanneries elsewhere in the world probably because of the associated limitations like expensive membranes, complex system designs, which means high operating and maintenance costs. Objects of the Invention The main objective of the present investigation is to provide an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent, which obviates the limitations mentioned above. Another objective of the present invention is to reuse the recovered salt for curing as well as processing of raw hides/skins. Yet another objective of the present invention is to recycle the saturated brine solution after suitable treatment in pre-soaking operation. Summary of the Invention Accordingly, the present invention provides an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent, which comprises: i. treating one kg cured hides/skins with not less than 500% w/v of saturated sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking, removing cured hides/skins after a period of 30-60 minutes, separating the setded salt from salt solution by known method, ii. washing the salt, as obtained in step (i), with not less than 100% w/v of fresh saturated brine medium followed by drying the resulting salt by a known method to obtain salt in powder form, iii. treating the salt solution, as obtained after separation of salt in step (i), with not less than 0.5% w/w, of deodorising / decolorising compounds along with not less than 0.1% w/w, of alkali metal salt, selected from carbonate, bicarbonates or hydroxides for a period of not less than half an hour, followed by separation by known method and subsequent use of the resulting salt solution in step(i) followed by repetition of steps (ii) and (iii) to obtain salt in powder form. In an embodiment of the present invention, the known method of separation of salt may be selected from decantation, filtration, centrifugation. In another embodiment of the present invention, the known method of drying may be such as air-drying, vacuum drying, spin-drying. In yet another embodiment of the present invention, the compounds used for deodorization and decolouration may be selected from activated carbon, zeolites, silica gel, silica-alumina, aluminium sulphate, chlorinated copperas, sodium aluminite, either individually or in combination. In yet another embodiment of the present invention, alkali metal hydroxide used may be selected from sodium hydroxide, potassium hydroxide, either individually or in any combination. In still another embodiment of the present invention, carbonates/bicarbonates used may be selected from sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, either individually or in any combination. Brief description of the Invention The process of the present invention is described below in detail. The cured hides and skins are treated with not less than 500% w/v, of saturated sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking. Saturated solution of sodium chloride contains 35.7% of sodium chloride at 0°C and 39.1% of sodium chloride at 100°C. Solubility of sodium chloride remains in the above range at a temperature in the range of 0°C - 100°C. Saturated sodium chloride solution does not take up the salt coming out of cured hides and skins and therefore slowly trickles down and settles at the bottom of the tank. The salt that has settled to the bottom of the tank is recovered through known separation methods. The recovered salt is washed with multiple changes of not less than 100% w/v of fresh saturated sodium chloride solution to remove the organic and other suspended impurities. The recovered wet salt is then dried by known methods to remove the moisture. The saturated sodium chloride medium, which becomes contaminated during washing operation of cured hides and skins is regenerated by treating with not less than 0.5% w/w, of deodorising/decolourising compounds along with not less than 0.1% w/w, of alkali metal salt, selected from carbonate, bicarbonates or hydroxide for a period of not less than half an hour followed by separation by known method for further use. The inventive step of the present invention lies not only in the treatment of salted skins with saturated sodium chloride solution to ensure that the salt adhered to the skin settles down for subsequent separation as well as reuse, but also in the regeneration of the contamination free saturated sodium chloride solution for subsequent use, thereby providing a simple, economical and eco-benign option for addressing the problem of TDS, associated with the leather processing industry. The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention. Example 1 Eleven litres of saturated sodium chloride medium was prepared by dissolving 4.4 kg of common salt in 11 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 5.0 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of one hour, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 2.0 litres of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, it was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 178 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 25 grams of activated charcoal. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of sodium carbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration, which was reused for the next operation. Goatskin with 45% reduction of salt was then subjected to soaking for leather processing. Example 2 Twelve litres of saturated sodium chloride medium was prepared by dissolving 4.8 kg of common salt in 12 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 6 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 45 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 2 litres of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 207 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of aluminium sulphate. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of potassium carbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 50% reduction of salt was then subjected to soaking for leather processing. Example 3 Eleven litres of saturated sodium chloride medium was prepared by dissolving 4.4 kg of common salt in 11 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 8 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was centrifuged and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was spin dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 227 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of chlorinated copperas. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of sodium carbonate and potassium carbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 57% reduction of salt was then subjected to soaking for leather processing. Example 4 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 Litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of aluminium sulphate and chlorinated copperas. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of sodium carbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 5 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of zeolites. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of sodium bicarbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 6 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed With three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of silica gel. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of lithium carbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 7 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of zeolites and silica gel. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of sodium bicarbonate and lithium carbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 8 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of silica alumina. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of potassium bicarbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 9 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of sodium aluminite. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of lithium bicarbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 10 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was spin dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of silica alumina and sodium aluminite. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of potassium bicarbonate and lithium bicarbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Example 11 Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 Litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container. The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 12.5 grams of activated charcoal and 8 grams of silica gel. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of lithium carbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration. Goatskin with 62% reduction of salt was then subjected to soaking for leather processing. Advantages The main advantages of the present invention are the following i. Reduction of TDS in pre-soaking operation contributed by salt coming out of cure hides and skins during leather processing ii. Reduction in water consumption during soaking operation iii. Recovered salt can be used for curing and pickling iv. Medium can be recycled a number of times v. The chemicals employed for preparation and regeneration of the medium is cheap and is not hazardous to the environment, vi. The process is quick and time saving vii. Economical and cost effective method viii. No major equipment required We claim: 1. An improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent, which comprises: i. treating one kg cured hides/skins with not less than 500% w/v of saturated sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking, removing cured hides/skins after a period of 30-60 minutes, separating the settled salt from salt solution by known method, ii. washing the salt, as obtained in step (i), with not less than 100% w/v of fresh saturated brine medium followed by drying the resulting salt by known methods to obtain salt in powder form, iii. treating the salt solution, as obtained after separation of salt in step (i), with not less than 0.5% w/w, of deodorising/decolorising compounds along with not less than 0.1% w/w, of alkali metal salt, selected from carbonate, bicarbonates or hydroxides for a period of not less than half an hour, followed by separation by known method and subsequent use of the resulting salt solution in step(i) followed by repetition of steps (ii) and (iii) to obtain salt in powder form. 2. An improved process, as claimed in Claim 1, wherein the known method of separation of salt is selected from decantation, filtration, centrifugation. 3. An improved process, as claimed in Claims 1 and 2, wherein the known method of drying is such as air-drying, vacuum drying, spin-drying. 4. An improved process, as claimed in Claims 1 to 3, wherein the compound used for deodorization and decolouration is selected from activated carbon, zeolites, silica gel, silica- alumina, aluminium sulphate, chlorinated copperas, sodium aluminite, either individually or in any combination. 5. An improved process, as claimed in Claims 1 to 4, wherein alkali metal hydroxide used is selected from sodium hydroxide, potassium hydroxide, either individually or in any combination. 6. An improved process, as claimed in Claims 1 to 5, wherein carbonates/bicarbonates used are selected from sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, either individually or in any combination.

Full Text

Title of the Invention
The present invention relates to an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent. Field of the Invention
More particularly, the present invention provides a process to recover the common salt, used for curing raw hides/skins. The salt thus recovered in solid form reduces the Total Dissolved Solids (TDS) in the Tannery effluent to an extent of 50 - 60%, and provides an option for its reuse for similar applications. Thus the process has enormous potential application to ensure eco-benign approach for leather processing industry. Background of the Invention
Hides and skins as they are obtained after flaying, referred as green or fresh hides/skins, contain water to the extent of about two-third of their weight. The presence of so much moisture in the green hides and their chemical constituents consisting mainly of proteins make them very liable to bacterial attack which decompose them. Curing is the treatment of raw hides and skins done to dehydrate the stock to avoid the risk of bacterial action and hence putrefaction to ensure temporary preservation. The raw hides and skins are currently salt cured in India. As reported by Sharphouse (Leather Technician Handbook, Leather producer association, London, XVI, Chapter 3, 8-19, 1971), curing using salt is done in three different ways
1. Brining: The hides are cleaned with water and are then hung in pits or run in large paddles using concentrated salt solution containing about 30 Ib salt to every 10 gallons of cold water. This ensures uniform salt penetration in 12 - 14 hours for heavy hides. The
hides are then drained and piled, which may require further sprinkling of salt similar to that of wet salting process.
2. Wet salting: The cold, flayed hide or skin is spread out, flesh side up, on a concrete
floor and well sprinkled with salt. A second hide is placed on the first one and also
sprinkled with salt. The amount of salt used may vary for hides and skins. For skins
30 - 40% of salt is used and in case of hides nearly 15 - 20 % is used. This is repeated
until stacks of 5 - 8 feet high are formed and the top hide is overlaid with salt.
3. Dry salting: The flayed skin or hide is salted by either, or both, of the above method
and is then hung up to dry. Drying is carried out gradually and evenly. This reduces the
weight and the cost of transport of the raw materials. But dry salted hide or skin
obviously requires longer and careful soaking than wet salted hides. The salt cured hide
or skin reaching the tannery contains less than its physiologic water content. It contains
protein that are partially dried and coagulated.
The cured stock has to be rehydrated prior to further processing for tanning. This is done during soaking, which is the initial step in leather processing where cured hides and skins are soaked in large amount of water. The main objective of soaking, as reported by Sarkar (Theory and Practice of Leather Manufacture, Chapter 5, 94-120, 1991,) are the following.
1. Cleaning the hides or skins (removing the dirt, blood and most of the salt used
in curing).
2. Softening and swelling the fibres to bring the skins as far as possible back to
the state of green hides, i.e., to rehydrate the fibres.
3. Dispersal and removal of interfibrillar proteins which otherwise cement the fibres together and prevent their thorough rehydration.
Since salt is water soluble, the soaking operation results in a situation where the salt used for curing goes into solution, thereby increasing the TDS of the processed water. Thus the major limitation of the salt curing lies in the disposal of effluent containing large quantities of salt. As reported by Kanakaraj (Journal of American Leather Chemists Association, 95, 368-374, 2000), the electrolytes discharged in the form of chloride and sulphates form the largest component of tannery effluent contributing to TDS load and they are the most difficult to treat at the end of the pipe as the source of electrolytes is mainly from salt curing method currently followed and to some extent from pickling, which is another pretanning operation practised in tanneries. Chlorides being highly soluble and stable are not affected by effluent treatment and thus remain a burden to the environment.
In the last decades, the evolution of the leather industry has been coupled with a growing awareness of the protection of the environment as a consequence of pollution caused due to the discharge of untreated effluents by tanneries into land and water bodies. In 1996 the Supreme Court of India ordered the closure of all tanneries that had not set up proper pollution control system. Public interest litigation cases had risen against tanneries, which culminated in court orders directing relocation or closure of tanneries that have not either erected Effluent Treatment Plants (ETPs) or connected to Common Effluent Treatment Plants (CETPs), as reported in http://www.york.ac.uk/depts/eeem/publish/edepdf/Confer-2000-79.pdf. Nearly 40,000 litres of effluent is being generated per tonne of leather processing, contributing to about
350 - 450 Kg of salt as TDS. As reported by Kanakaraj (Journal of American Leather Chemists Association, 95, 368-374, 2000), soaking contributes to 40% of TDS (salt) that is generated from the entire process of leather manufacture. The high amount of salt contained in the effluent when used for irrigation purpose after treatment will increase surface salinity through evaporation, reduces the fertility of soil resulting in the poor yield of crops.
It is therefore of utmost importance to avoid this level of salt in the effluent to ensure eco-benign approach of leather processing. To minimize the level of salt in the tannery effluent, some tanneries practice solar evaporation where the soak liquor is segregated from the combined effluent stream. The liquor is settled, clarified, sand filtered and dried in solar evaporation pans, as is evident from http://www.tft.csiro.au/leather/cleantech.html. But this method requires larger area for its operation and is labour dependent. It also suffers problem with the disposal of the recovered salt.
Tanneries located at Kanpur area practise a method called desalting. The objective of desalting is to remove the excess salt from the raw hides, reducing the Total Dissolve Solids in the effluent stream. Two efficient methods of desalting are: a) Manual desalting using wooden frame; b) Mechanical desalting using brush type desalting machine. A majority of tanneries carry out desalting without the use of mechanical devices. This leads to only partial removal of salt from the hide/skin. In only a handful of tanneries desalting is carried out with wooden frames or brush desalting. Efficient desalting can lead to 20-25% reduction of TDS and chloride in the combined effluent stream, as revealed in http://www.cuts-india.org/Leather Sector Study.doc (chapter III). Salt recovered in this
process requires maximum efficiency and faces problem with disposal, as it cannot be
reused for further application.
There are several established technique like ion exchange, reverse osmosis, electro dialysis and distillation etc available to remove TDS (salt) in the effluent. As reported by Sahasranamam (Environment Management; A Study of Indian Leather Industry, Council for Leather Exports, Chennai, chapter 5, 39-47, 2003), these techniques are yet to be practiced in the tanneries in India. Similar situation is expected for tanneries elsewhere in the world probably because of the associated limitations like expensive membranes, complex system designs, which means high operating and maintenance costs.
Objects of the Invention
The main objective of the present investigation is to provide an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent, which obviates the limitations mentioned above.
Another objective of the present invention is to reuse the recovered salt for curing as well as processing of raw hides/skins.
Yet another objective of the present invention is to recycle the saturated brine solution after suitable treatment in pre-soaking operation.
Summary of the Invention
Accordingly, the present invention provides an improved process for the recovery of common salt from salt cured raw hides/skins for reduction of total dissolved solids in the effluent, which comprises:

i. treating one kg cured hides/skins with not less than 500% w/v of saturated
sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking, removing cured hides/skins after a period of 30-60 minutes, separating the setded salt from salt solution by known method, ii. washing the salt, as obtained in step (i), with not less than 100% w/v of fresh saturated brine medium followed by drying the resulting salt by a known method to obtain salt in powder form, iii. treating the salt solution, as obtained after separation of salt in step (i), with not less than 0.5% w/w, of deodorising / decolorising compounds along with not less than 0.1% w/w, of alkali metal salt, selected from carbonate, bicarbonates or hydroxides for a period of not less than half an hour, followed by separation by known method and subsequent use of the resulting salt solution in step(i) followed by repetition of steps (ii) and (iii) to obtain salt in powder form. In an embodiment of the present invention, the known method of separation of salt may be selected from decantation, filtration, centrifugation.
In another embodiment of the present invention, the known method of drying may be such as air-drying, vacuum drying, spin-drying.
In yet another embodiment of the present invention, the compounds used for deodorization and decolouration may be selected from activated carbon, zeolites, silica gel, silica-alumina, aluminium sulphate, chlorinated copperas, sodium aluminite, either individually or in combination.
In yet another embodiment of the present invention, alkali metal hydroxide used may be selected from sodium hydroxide, potassium hydroxide, either individually or in any combination.
In still another embodiment of the present invention, carbonates/bicarbonates used may be selected from sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, either individually or in any combination. Brief description of the Invention
The process of the present invention is described below in detail.
The cured hides and skins are treated with not less than 500% w/v, of saturated sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking. Saturated solution of sodium chloride contains 35.7% of sodium chloride at 0°C and 39.1% of sodium chloride at 100°C. Solubility of sodium chloride remains in the above range at a temperature in the range of 0°C - 100°C. Saturated sodium chloride solution does not take up the salt coming out of cured hides and skins and therefore slowly trickles down and settles at the bottom of the tank. The salt that has settled to the bottom of the tank is recovered through known separation methods. The recovered salt is washed with multiple changes of not less than 100% w/v of fresh saturated sodium chloride solution to remove the organic and other suspended impurities. The recovered wet salt is then dried by known methods to remove the moisture. The saturated sodium chloride medium, which becomes contaminated during washing operation of cured hides and skins is regenerated by treating with not less than 0.5% w/w, of deodorising/decolourising compounds along with not less than 0.1% w/w, of alkali metal
salt, selected from carbonate, bicarbonates or hydroxide for a period of not less than half an hour followed by separation by known method for further use.
The inventive step of the present invention lies not only in the treatment of salted skins with saturated sodium chloride solution to ensure that the salt adhered to the skin settles down for subsequent separation as well as reuse, but also in the regeneration of the contamination free saturated sodium chloride solution for subsequent use, thereby providing a simple, economical and eco-benign option for addressing the problem of TDS, associated with the leather processing industry.
The following examples are given by way of illustration only and therefore should not be construed to limit the scope of the present invention.
Example 1
Eleven litres of saturated sodium chloride medium was prepared by dissolving 4.4 kg of common salt in 11 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 5.0 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of one hour, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 2.0 litres of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, it was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 178 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 25 grams of activated charcoal. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of sodium carbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration, which was reused for the next operation.
Goatskin with 45% reduction of salt was then subjected to soaking for leather processing.
Example 2
Twelve litres of saturated sodium chloride medium was prepared by dissolving 4.8 kg of common salt in 12 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 6 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 45 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 2 litres of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 207 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of aluminium sulphate. Dissolved impurities of calcium and magnesium salts were eliminated by
treatment with 16 grams each of potassium carbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 50% reduction of salt was then subjected to soaking for leather processing.
Example 3
Eleven litres of saturated sodium chloride medium was prepared by dissolving 4.4 kg of common salt in 11 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 8 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was centrifuged and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was spin dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 227 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of chlorinated copperas. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of sodium carbonate and potassium carbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium
hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 57% reduction of salt was then subjected to soaking for leather processing.
Example 4
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 Litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of aluminium sulphate and chlorinated copperas. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of sodium carbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 5
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every
15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with
salt settled at the bottom. The solution was filtered and wet salt was collected in a
container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride
solution to remove colloidal and suspended organic and inorganic (calcium and
magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient
temperature to remove the moisture. The amount of dried powdered salt collected was
found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of zeolites. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with
16 grams each of sodium bicarbonate and sodium hydroxide as insoluble calcium
carbonate and magnesium hydroxide. Purified saturated medium solution was obtained
through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 6
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every
15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with
salt settled at the bottom. The solution was filtered and wet salt was collected in a
container. The salt was washed With three changes of 1 litre of saturated Sodium Chloride
solution to remove colloidal and suspended organic and inorganic (calcium and
magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient
temperature to remove the moisture. The amount of dried powdered salt collected was
found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of silica gel. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with
16 grams each of lithium carbonate and potassium hydroxide as insoluble calcium
carbonate and magnesium hydroxide. Purified saturated medium solution was obtained
through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 7
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was
collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of zeolites and silica gel. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of sodium bicarbonate and lithium carbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 8
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every
15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of silica alumina. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of potassium bicarbonate and sodium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 9
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was filtered and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride
solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was vacuum dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 16 grams of sodium aluminite. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of lithium bicarbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 10
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was spin dried at an ambient
temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 8 grams each of silica alumina and sodium aluminite. Dissolved impurities of calcium salts were eliminated by treatment with 8 grams each of potassium bicarbonate and lithium bicarbonate as insoluble calcium carbonate. Magnesium salts were eliminated by treatment with 8 grams each of sodium hydroxide and potassium hydroxide as magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Example 11
Thirteen litres of saturated sodium chloride medium was prepared by dissolving 5.2 kg of common salt in 13 litres of water. One salted goatskin weighing 1 kg was collected from slaughterhouse and taken in a vat. 10 Litres of saturated Sodium Chloride solution was added to the vat. The skin was subjected to manual shaking every 15 minutes in the vat. After a period of 30 minutes, the skin was taken out of the vat with salt settled at the bottom. The solution was decanted and wet salt was collected in a container. The salt was washed with three changes of 1 litre of saturated Sodium Chloride solution to remove colloidal and suspended organic and inorganic (calcium and magnesium) impurities. Finally, the recovered wet salt was air dried at an ambient temperature to remove the moisture. The amount of dried powdered salt collected was found to be 250 grams. It was stored in plastic container.
The saturated sodium chloride solution, which got contaminated during washing operation of salt cured goatskin, was reclaimed by treatment with 12.5 grams of activated charcoal and 8 grams of silica gel. Dissolved impurities of calcium and magnesium salts were eliminated by treatment with 16 grams each of lithium carbonate and potassium hydroxide as insoluble calcium carbonate and magnesium hydroxide. Purified saturated medium solution was obtained through the process of filtration.
Goatskin with 62% reduction of salt was then subjected to soaking for leather processing.
Advantages
The main advantages of the present invention are the following
i. Reduction of TDS in pre-soaking operation contributed by salt coming out of
cure hides and skins during leather processing ii. Reduction in water consumption during soaking operation
iii. Recovered salt can be used for curing and pickling
iv. Medium can be recycled a number of times
v. The chemicals employed for preparation and regeneration of the medium is
cheap and is not hazardous to the environment,
vi. The process is quick and time saving
vii. Economical and cost effective method
viii. No major equipment required

We claim:
1. An improved process for the recovery of common salt from salt cured raw hides/skins
for reduction of total dissolved solids in the effluent, which comprises:
i. treating one kg cured hides/skins with not less than 500% w/v of saturated
sodium chloride solution for not less than 10 minutes, preferably with intermittent shaking, removing cured hides/skins after a period of 30-60 minutes, separating the settled salt from salt solution by known method,
ii. washing the salt, as obtained in step (i), with not less than 100% w/v of fresh
saturated brine medium followed by drying the resulting salt by known methods to obtain salt in powder form,
iii. treating the salt solution, as obtained after separation of salt in step (i), with
not less than 0.5% w/w, of deodorising/decolorising compounds along with not less than 0.1% w/w, of alkali metal salt, selected from carbonate, bicarbonates or hydroxides for a period of not less than half an hour, followed by separation by known method and subsequent use of the resulting salt solution in step(i) followed by repetition of steps (ii) and (iii) to obtain salt in powder form.
2. An improved process, as claimed in Claim 1, wherein the known method of separation of salt is selected from decantation, filtration, centrifugation.
3. An improved process, as claimed in Claims 1 and 2, wherein the known method of drying is such as air-drying, vacuum drying, spin-drying.
4. An improved process, as claimed in Claims 1 to 3, wherein the compound used for deodorization and decolouration is selected from activated carbon, zeolites, silica gel, silica-
alumina, aluminium sulphate, chlorinated copperas, sodium aluminite, either individually or in any combination.
5. An improved process, as claimed in Claims 1 to 4, wherein alkali metal hydroxide used
is selected from sodium hydroxide, potassium hydroxide, either individually or in any
combination.
6. An improved process, as claimed in Claims 1 to 5, wherein carbonates/bicarbonates used are selected from sodium carbonate, sodium bicarbonate, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, either individually or in any combination.

Documents:

2421-DEL-2004-Abstract-(07-03-2012).pdf

2421-del-2004-abstract.pdf

2421-DEL-2004-Claims-(07-03-2012).pdf

2421-del-2004-claims.pdf

2421-DEL-2004-Correspondence Others-(07-03-2012).pdf

2421-del-2004-correspondence-others.pdf

2421-DEL-2004-Description (Complete)-(07-03-2012).pdf

2421-del-2004-description (complete).pdf

2421-DEL-2004-Form-1-(07-03-2012).pdf

2421-del-2004-form-1.pdf

2421-del-2004-form-18.pdf

2421-del-2004-form-2.pdf

2421-DEL-2004-Form-3-(07-03-2012).pdf

2421-del-2004-form-3.pdf

2421-del-2004-form-5.pdf

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Patent Number

251934

Indian Patent Application Number

2421/DEL/2004

PG Journal Number

16/2012

Publication Date

20-Apr-2012

Grant Date

18-Apr-2012

Date of Filing

02-Dec-2004

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	PRAVEEN KUMAR SEHGAL	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA.
2	PREETHI VASUDEVAN	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA.
3	NARASIMAHAN KANNAN CHANDRABABU	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA.
4	RAMAKRISHNAN RAMESH	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA.

PCT International Classification Number

C22B 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA