Title of Invention

"A PROCESS FOR THE PREPARATION OF TILES/BRICKS USEFUL FOR BUILDING CONSTRUCTION"

Abstract

A process for the preparation of tiles/bricks useful for building construction which comprises : - (i) mixing tannery sludge to clays in an amount ranging from 5-25% wt. and 75-95% wt. and grinding them together to get a homogeneous mass. - ( i) shaping the resulting mixture to bricks/titles - (in) drying the resulting tiles/bricks 10 the desired moisture s- (iv) firing by heating the tiles/bricks and, - cooling to room temperature under reduced atmosphere at 9000-100°C to obtain tiles/bricks.

Full Text

The present invention relates to a process for the preparation of tiles/bricks useful for building construction. The tiles/bricks prepared by the process of the present invention are useful for building construction, Daneling on the walls, and also for decorative architecture in view of the black colour. Leather processing is one of the major industrial activity in India and many other countries of the world. Annual export realization for the leather sector at the moment is above 1.3 billion US$. There are about 1000 small scale and 75 medium scale tanneries in India. There are a variety of waste products coming out of the tannery which includes solution and solid forms. However, the solid wastes come to about 150,000 tonnes per year in India which is usually named as tannery sludge. The industry finds it very difficult to store them or to dispose them in bulk in any appropriate way. Another major factor which calls for concern in this industry is the use of chromium in tanning. Approximately 38,000 tonnes of basic chromium sulphate equivalent to 6500 tonnes of chromium is used by the industry in India every year. Assuming a reasonable estimate of 60% of chromium being absorbed in leather, about 2600 tonnes of chromium is emitted via waste water and tannery sludge every year. A typical Indian tannery sludge contains approxdimately 2-3% chromium and therefore the industry should be producing 125,000 tonnes of chrome bearing sludge every vear and most often this exceeds 6-7%. The Indian Pollution Control and Environmental Regulations demand that chrome content in industrial waste stream should be less than 0.2-3.0 ppm. The generally accepted environmental rules restrict the chrome content to be less than 50 ppm. Various options for effective disposal of the tannery sludge have been looked at earlier. The sludge can be filled in low lying areas after spreading on polyethylene sheets (land fill). Attempts to use sludge as fuel have also been made earlier, but the combustibility is poor. Further the nauseating smell of burning protein has restricted this attempt. Hence most of the attempts for the disposal of the sludge in bulk have met with less success. One of the earlier studies reported on the utilisation of tannery sludge is to use it as additive to clays for making bricks. An attempt in this direction by Italian researchers appears to have failed, due to the fact that the chromium in the fired bricks were easily leachable. A feasible way of fixing chromium and chromium containing mineral tailings is by incorporating in high temperature refractories where the temperatures are above 1400°C. The chromium reacts with silica and iron to form high temperature compounds and become immobilised. However, since tannery sludge contains considerable organics and other impurities such as calcium and sodium, such applications are not feasible. Further the high temperature ceramics which ought to be high density bodies, will end up in porous ones. In the attempt to understand the behaviour of the leachability of chromium in tannery sludge, a detailed information on the chromium chemistry becomes important. The common form of chromium in chrome sludge is expected to be chromic hydroxide in some polymerised form. The chromic hydroxide on thermal treatment gets converted to chrome' (III) sesquioxide and chrome (VI) trioxide. The former is leachable and the latter, unleachable. However, the high temperature form is always chrome (VI) in oxidising atmosphere. But on applying reducing atmosphere chrome (VI) gets reduced to Cr(III) and remains as Cr(III) upto about 400°C before getting reconverted to Cr(VI) in oxidising atmosphere. This principle has been used to convert Cr(III) to Cr(Vl) and back. The main objective of the present invention is to provide a process for the preparation of value added products such as tiles/bricks employing the waste sludge resulting from tanneries, and also to achieve efficient chrome management. Another object of the present invention is to provide a process for the preparation of tiles/bricks employing the tannery waste sludge by incorporating the sludge in building ceramic materials. The present invention is based on the finding that the incorporation of the tannery sludge to clays and shaping the resulting mixture to bricks/tiles, drying the resulting bricks/tiles to the desired moisture and firing by heating the tiles/bricks and cooling to room temperature under reducing atmosphere results in bricks/tiles which are useful as building materials. Accordingly, the present invention provides a process for the preparation of tiles bricks useful for building construction which comprises . (i) mixing tannery sludge to clays in an amount ranging from 5-25% wt and 75-95% wt and grinding them together to get a homogeneous mass, (ii) shaping the resulting mixture to bricks/tiles, ( iii) drying the resulting tiles/bricks to the desired moisture. ( iv) firing by heating the tiles/bricks and, (v) cooling to room temperature under reduced atmosphere at 9000-1000 C to obtain tiles/bricks. Then amount of the clay and the tannery sludge may preferably range from 75-95%, and 5.25% respectively. The clay employed for the mixing may be selected from paddy fields, backwaters or secondary clay deposits having particle size 5-03 um and high plasticity along with mouldability and brick red fired colour. Generally the clays now in the and brick manufacture can be used for this process also. The drying mav be effected either by sunlight in the open or in a temperature controlled heating oven. The moisture content of the resultant bricks/tiles may range from 20% to 30% depending on the conditions of the extrusion mixture. The firing may preferably be effected by oxidative firing by using coal, oil or wood as fuel. The cooling may be effected by employing oxidative tiring and reductive cooling (OFRC) by passing reducing gases so as to reduce Cr(Vl) present in the sludge to Cr(III) and thenfixing chromium as non leachable component. The reductants such as a mixture of kerosene/water can be employed. Other possibilities are mixture of alcohols/water and coal gas/steam or any hydrocarbon/steam mixtures. The size of the bricks/tiles may be of standard size such as 22cm x 11cm x 9cm or also 20cm x 10cm x 10cm, and 50mm x 50mm x 50mm. The invention is illustrated by the following examples which should not be construed to limit the scope of the present invention. Example I 160 gm of red burning clay (tile clay) was powdered and mixed well with 16 gms of powdered tannery sludge in a laboratory mixer for 10 hrs. This mixture was pressed to tiles of size 50mm x 50mm x 10mm at a pressure of 100 MPa, dried in the electric oven at 105°C, fired at 900°C. The tile was cooled after switching off the furnace. The leachability of chromium was found out by analysis. The clay had 60% silica, 15% alumina and 2.5% iron oxide are the tannery sludge had 40% loss on ignition. Example II 85 gms of the red burning clay containing 65% silica, 8% iron oxide and 18% aluminium oxide was mixed with 15 gm of powdered tannery sludge containing 30% loss on ignition, 2.5% silica and 2% fibres and pressed to tiles of 50mm x 50mm x 10mm size, fired at 900°C for two hrs. The leachability of chromium was found out. Air was allowed to flow in the furnace during firing and cooling. Example III 360 gm of the brick clay powder was mixed with 36 gm of the tannery sludge powder intimately with water content of 12%. The powder mixture was pressed to tiles of size 50mm x 50mm x 1.0 mm and fired at 950°C with a soaking period of 2 hrs. During rooling, which was at the average rate of 5°C per minute, under a flow of CO2 gas. Example IV 750 gm of dry clay powder having an alumina content of about 16.5% and silica content 67.8% were taken and mixed with ground tannery sludge containing loss on ignition of 60% (150 g) intimately using a mixer with moisture in the range 10-12%. The mixture was pressed to blocks of size 50mm x 50mm x 50mm at a pressure of 100 MPa. These blocks were fired in an electrically heated furnace at a heating rate of 10°C per minute upto 950°C. The cooling was low at a rate of 2°C per minute upto 500°C and then at faster rates. During cooling, nitrogen gas was allowed to flow through the tube till the temperature reached 300°C. The ieachability of the chromium (VI) form was estimated and result is presented in Table 1. Example V 150 gm of the tile/brick clay (red burning clay* used for bricks) having reasonable plasticity was mixed with 20 gm of the tannery sludge, ground in semi dry condition (20% moisture) and plastically moulded to blocks of size 50mm x 50mm x 25mm, dried in oven at 95°C for 24 hrs, fired at 1000°C. The cooling was done at 5°C/minute under constant flow of vapour of a mixture of alcohol and water in the ratio (2% alcohol/98% water) . The Diock after firing and cooling was black in colour and was very well sintered with strength above 120 Kg/cm . The chromium (VI) leachable form was less than 5 mg/kg (Table I). Example VI About 150 gm of clay as mentioned in example IV was mixed with 15gm of powdered and dried tannery sludge uniformly and dry pressed in a die at 200 MPa pressure to block of 50mm x 50mm x 20mm. A dozen of the similar blocks were made and were fired at 900°C and cooled under a reducing atmosphere. This reducing atmosphere was made by passing a mixture of 10% kerosene and 90% water through a hot tube outside the furnace, the open end of the tube being introduced inside the furnace. All possible outlets of the furnace were closed to avoid any leakage of the vapours to outside or entry of air from outside to inside of the furnace. Majority of the blocks were strong and black in colour, a few being under transition from dark grey to black. The chromium leachability was determined and were below 10 mg/kg (Table I). Example VII Another experiment was conducted with a bulk clay powder, average particle size lower than 0.5 microns and iron content 4.5-5%, and alumina 20.05% and silica 52% and iron oxide, 5.8%, high plastic material. A batch of 10 blocks of size 50mm x 50mm x 50mm were made by extrusion after homogenising the mixture containing 16-20% moisture. Such blocks were dried for 36 hrs at 95°C, fired in an electric kiln with a soaking of 5-6 hrs. The cooling was done at a very slow rate under flowing reducing gases produced from a mixture of 2 % kerosene and water from a preheater. The cooling from 950°C to 800°C was done at 2°C/min. and then later, at 5°C/min. But the cooling was continued under reducing atmosphere till the temperature reached to 200°C. The leachability of Cr(VI) in this case from the fired blocks were in the range less than 20 mg/kg and the colour was varying between grey and black. Example VIII About 3000 kg/of red burning clay containing about 10% of moisture and having silica 65.5%, alumina 16.7% and iron oxide 3.25% as major contituents was mixed with 300 Kg of powdered tannery sludge intimately in a pan mill for reaching to a homogeneous mass. The net water content was about 15%. This mass was extruded in a pug mill and was wire cut to bricks of size 20cm x 10cm x 10cm and dired in air at 30°C for two days followed by drying in oven to moisture content as low as 3-4% such blocks were fired in a kiln having facility for closed firing. The initial firing was done in oxidising atmosphere at about 900°C with a soaking at the high temperature for 2-3 hrs. The cooling was done in presence of flowing reducing gas mixture containing carbon dioxide and steam generated from a mixture of kerosene and water, kerosene content varying from 10% to 2% during cooling. A cooling rate of 2 - 5 ° C per minute was maintained till the temperature reached 200°C. The furnace was cooled by natural air to room temperature and the bricks were taken out. More than 800 of the bricks were fully black in colour with chromium leacha-bility levels less than 5 mg/kg. However, a few bricks were grey to red at the door side of the kiln which had leachability ranging from 50-100 mg/kg. This has happened due to reoxidation during cooling. Example IX 3 blocks of size 50mm x 50mm x 50mm were made by pressing a mixture of 15% tannery sludge (containing 1.8% chromium) and clay. These blocks were fired in an electric furnace at 900°C and cooled in a reducing atmosphere containing vapours of kerosene and water. The leachable Cr (VI) was estimated. Example X About 1 Kg of the red burning clay was powdered and mixed with tannery sludge (containing 3.5% chromium) having a total organic matter to the extent of 75%, 150 gms and further ground to a homogeneous mass. This was pressed to blocks of 50mm x 50mm x 50mm, dried and fired in the range 850-950°C with a soaking at the peak temperature for 2 hrs. The cooling was done under flowing reducing gases containing vapours of kerosene and water. The Ieachable chromium was estimated. Example XI About 650 gms of clay powder and 100 gms of tannery sludge was mixed intimately and moulded to blocks of size 50mm x 40mm x 50mm. The tannery sludge contained very high chromium levels of above 6.5%. The sludge-clay blocks were fired at 900°C and cooled in a mixture of vapours rich in kerosene and steam (10% kerosene) upto 200°C. The black blocks thus obtained were tested for leachable chromium content. All the results of the leachability tests on the examples where the firing was done at varying conditions are provided in Table I and II. Table I Residual leachable chromium (VI) from the fired sludge-clay mixtures from the different experiments Example Leachable Chromium (VI) mg/kg Example I 350 - 500 Example II 1400 - 1600 Example III L300 - 1450 Example IV 800 - 1000 Example V Example VI Example VII Example VIII Table. II Residual leachable chromium (VI) from fired sludge-clay mixtures containing varying chromium contents Initial Chromium Leachable Chromium Example content (%) content Example IX 1.8 Example X 3.5 Example XI >6.0 The inference from the above table is that irrespective of the initial chrome content, the OFRC process can effectively control the chromium leachability and thus find an effective method of environment friendly disposal. The advantages of the present process: (1) The process can utilize bulk (>15%) of the tannery sludge from the leather industry. No existing processess can utilise so effectively the pollution creating sludge. {2) Complete conversion of Cr(VI) to Cr(III) non leachable form can be achieved. It becomes very difficult to convert Cr(VI) to Cr(III) at usual processing conditions. While heating the bricks in oxidising atmosphere is a must to impart strength to the bricks, Cr(III) also automatically gets converted to Cr(VI) which always leaches out into the streams or environment. A reduction during cooling is the only solution to this problem. Usually the clays are available in nearby tanneries and hence transportation of tannery sludge would not pose any problem. Usually tannery sludge contains 10-15% water which is actually used in the preparation of the sludge-clay mixtures. Hence predrying of the sludge is not required, thus saving considerably on energy. The tannery sludge contains more than 60% of organic volatiles which decompose during heating. This provides energy in the form of heat, thus tannery sludge acts as an internal fuel. This has been found true in the present finding that more than 15% fuel is saved in the firing of sludge clay bricks compared to ordinary clay bricks under similar experimental conditions. These bricks are about 20% lighter and hence save energy in transportation since more number of bricks can be transported with same fuel requirements compared to ordinary clay bricks. This finding has sufficient implication in technology related to clay building materials since the addition of tannery sludge results in upto 15% saving in clay (top soil) and hence contributes to environmental protection of fertile top soil in agricultural lands. (8) Usually tannery sludge is a relatively difficult material to reduce to size by grinding. The sludge-clay mixture can be homogenised by grinding in a pan mill because the silica in clay acts as a grinding medium. We claim : 1 A process for the preparation of tiles/bricks useful for building construction which comprises : (i) mixing tannery sludge to clays in an amount ranging from 5-25% wt and 75-95% wt and grinding them together to get a homogeneous mass, (ii) shaping the resulting mixture to bricks/tiles, (iii) drying the resulting tiles/bricks to the desired moisture, (iv) firing by heating the tiles/bricks and,. (v) cooling to room temperature under reduced atmosphere to obtain tiles/bricks. 2. A process as claimed in claim 1 wherein the clay employed is selected from paddy field, backwaters or secondary clay reserves usually employed in making building bricks/tiles. 3. A process as claimed in claims 1-2 wherein the moisture content of the resultant bricks/tiles produced range from 20-30%. 4. A process as claimed in claims 1-3 wherein the firing preferably be effected by oxidative firing by fuels such as wood, coal or oil. 5. A process for the preparation of tiles/bricks useful for building construction substantially as herein described with reference to the examples.

Documents:

892-del-1995-abstract.pdf

892-del-1995-claims.pdf

892-del-1995-correspondence-others.pdf

892-del-1995-correspondence-po.pdf

892-del-1995-description (complete).pdf

892-del-1995-form-1.pdf

892-del-1995-form-2.pdf

892-del-1995-form-4.pdf

892-del-1995-form-9.pdf

892-del-1995-others-documents.pdf

892-del-1995-petition-others.pdf