Title of Invention

"A PROCESS FOR THE RECOVERY OF TITANIUM OXIDE FROM ALUM SLUDGE"

Abstract

This process described the recovery of the useful constituents from alum sludge and reducing the pollution load. Metal values like TiO2, AI2O3, Fe2O3 are extracted from it in a techno-economically feasible way. Selective enrichment of alum sludge with respect to TiO2 which constitutes 15-20% of the waste, by eliminating AI2O3, Fe2O3, SiO2 and organic matters from it, has been developed by the process.

Full Text

This invention relates to process for the recovery of titanium oxide from alum sludge. Alum sludge is a waste material from the alum producing plants in which high grade bauxite is treated with concentrated sulphuric acid. As a result of this reaction aluminium goes into solution as aluminium sulphate with traces of other impurities. The residue left behind after filtration is known as alum sludge. It primarily contains Al203(30-48%), TiO2(15-20%), Fe203(6-10%), Si02(3-13%) and some amount of organic matter. Owing to the widespread application of alum in purifying drinking water, leather tanning, dyeing, sizing of paper and pharmaceutical industries, small scale alum industries are coming up all over the country. These plants generate substantial amount of sludge, equivalent to the amount of alum produced. This waste (alum sludge) contains some amount of free sulphuric acid and so is hazardous to the environment upon disposal without treatment. So this problem calls for an urgent redressal. Titanium oxide pigments are usually prepared from titania or enriched titania present in other ores by acid dissolution and precipitation in powder form. Due to higher cost of the raw materials and non-availablity from indigenous sources, these are imported at a high cost. Alum sludge, a by-product of bauxite processing plants for production of alum, is a cheap and easily available raw material which can be treated through a process as envisaged in the present invention to produce pigment grade titanium oxide. This process aims at recovery of the useful constituents from alum sludge and reducing the pollution load. Metal values like Ti02, Al203, Fe2O3 are extracted from it in a techno-economically feasible way. Selective enrichment of alum sludge with respect to TiO2, which constitutes 15-20% of the waste, by eliminating AI2O3, Fe2O3, SiO2 and organic matters from it has been developed by the process. The other object of this invention is to prevent pollution caused by the disposal of highly toxic waste produced from small scale alum plants usually located in populated localities. The process of this invention involves the following steps: In the first step, alum sludge is fused with Na2CO3 and subsequently leached with water to extract the aluminium part into the solution. The second step involves reduction of the ferric ion in the residue to ferrous state by using Na2S, to facilitate better leaching of iron when treated with concentrated HCI. Finally in the third step, the residue, devoid of iron and aluminium, is roasted at 800°C and then treated with H2SO4 and HF to eliminate silica. The mixture of acids dissolve the residue, which subsequently is treated with concentrated ammonia to precipitate out titanium hydroxide. The precipitate is ultimately roasted at 800°C to obtain a predominantly titanium dioxide (90-93%) bearing end-product suitable for use as a pigment. Accordingly the present invention provides, a process for the recovery of titanium oxide from alum sludge which comprises fusing alum sludge with Na2CO3 at 750°-800°C, at a ratio 1: 5, then leaching with water, separating the residue by conventional methods such as herein described, and treating with reducing agent selected from SO2, SnCI2 and Na2S preferably Na2S, followed by leaching with 4 to 6N HCI for 2 hours, separating and roasting the residue at 700°-800°C and treating with concentrated H2SO4 and HF till fully dissolves and SO3 fumes evolve, adding NH3 to precipitate titanium hydroxide and roasting at 750°-800°C for 3 hours to get titanium oxide. The reducing agent used is selected from SnCl2, SO2 in presence of mineral acids and Na2S. A few drops of H2S04 are added to the residue before addition of HF in excess to remove silica. The following examples are given to illustrate the process of invention. However, this should not limit the scope of the invention. Example-1: 100gm of finely ground(150µ) alum sludge containing Si02, Ti02, Fe203, AI203 and organic matter is fused with 500gm Na2CO3 at 800°C, in a titanium lined container for 2 hours. The fused mass is extracted with water and filtered through a sintered crucible. The filtrate contains 22.44gm (94.89%) Al203 and 1.44gm (10.80%) Si02. The residue is leached with 90gm of Na2S in requisite amount of water for 3 hours till all the Fe3+ ions present are reduced to Fe+2 state. The resultant mixture is centrifuged and the residue is subsequently leached with 100ml of 4N HCI for 2 hours. The filtrate at this stage analyse 10.12gm (98.06%) Fe20s, 1.174gm (4.96%) Al20s and 5.5gm (27.22%) Ti02. The residue is then roasted at 700°C and is subsequently treated with a few drops of concentrated H2S04 followed by 5-7ml of HF, with heating, till all the silica present decomposes and white SO3 fumes evolve. The resultant solution is transferred to a beaker and titanium is precipitated using concentrated NH3. The precipitate is filtered and roasted at 800°C for 3 hours. The product weighs 15.47gm and contains 14.46gm of 93.47% pure TiO2 with other impurities (primarily Fe203 and AI2O3). Example-2: 100gm of alum sludge containing Si02,Ti02, Fe203, AI203 and organic matter is fused with Na2C03 and is extracted with water. The water extract contains 43.98gm (93.22%) AI203 and 0.15gm (9.4%) Si02- Then the residue is treated with more than stoichiometric amount of Na2S(85gm) in required amount of water to reduce the iron content. The mixture is separated by centrifugation and the residue is treated with 125ml of 4N HCI. The leach liquor contains 7.01gm Fe203 (97.72%) , 5.3gm Ti02 (26.15%) and 2.78gm AI2O3 (5.91%). The resulting residue is roasted at 700°C and treated with 3-4 drops of concentrated H2S04 followed by 4-6ml of HF, till complete decomposition of silica and SO3 fume evolves. The solution is then treated with concentrated NH3 to precipitate the titanium as hydroxide which is finally roasted at 800°C to give an end product rich in titanium dioxide. This product weighs 15.53gm and contains 14.81gm of 95.33% pure TiO2- Advantages: The process has the following advantages as compared to the conventional or reported processes: 1. The process makes use of alum sludge to produce pigment grade titanium oxide, an useful product and prevents pollution due to disposal of highly acidic/ toxic sludge into the environment. 2. Alum sludge is the only indigenous and cheap raw material for titanium recovery as compared to titaniferrous magentites and other ores/minerals and so most of the country's requirements are met through imports. 3. The raw material is already decomposed at high temperature in presence of a strong mineral acid during alum production and so cost of processing a complex raw material is saved. We Claim: 1. A process for the recovery of titanium oxide from alum sludge which comprises fusing alum sludge with Na2CO3 at 750°-800°C, at a ratio 1 : 5, leaching with water, separating the residue by conventional methods such as herein described, and treating with reducing agent selected from SO2, SnCI2 and Na2S preferably Na2S, followed by leaching with 4 to 6N HCI for 2 hours, separating and roasting the residue at 700°-800°C and treating with concentrated H2SO4 and HF till fully dissolves and SO3 fumes evolve, adding NH3 to precipitate titanium hydroxide and roasting at 750°-800°C for 3 hours to get titanium oxide. 2. A process for the recovery of titanium oxide from alum sludge substantially as herein described.

Documents:

542-del-1999-abstract.pdf

542-del-1999-claims.pdf

542-del-1999-correspondence-others.pdf

542-del-1999-correspondence-po.pdf

542-del-1999-description (complete).pdf

542-del-1999-form-1.pdf

542-del-1999-form-19.pdf

542-del-1999-form-2.pdf