CLIAMS:We claim
1. A process for the maximum recovery of silica from Kimberlite tailings wherein initially Kimberlite tailings is treated with 5 to15 % mineral acid like hydrochloric acid for 3-5 h at 95-100oC to remove acid soluble impurities as filtrate and silica enriched material as a solid, following which silica enriched solid is digested with 8 to 10 % alkali solution namely sodium hydroxide in a closed system at 95-190?C or in open system at boiling temperature for 3-4 h to prepare sodium silicate and separate the solid titanium from silica rich kimberlite of required properties useful for preparation titanium.
2. A process as claimed 1 wherein the kimberlite tailing used has the following chemical constituent 30-35% silica, 2-5% Al2O3, 5-8 % TiO2, 8-10% CaO, 20-24 % MgO, %-11% Fe2O3 and loss on ignition is in the rage of 13-15%.
3. The process as claimed in claim 1, where Kimberlite tailing generated during diamond mining is preferably used for acid treatment and further alkali treatment for preparing titanium rich quartz.
4. The process claimed in claims 1 & 2, wherein 15 % hydrochloric acid is preferably used for treating raw Kimberlite tailing in the temperature range 95-100?C with Kimberlite to acid ratio of 1:4 for the time duration of 3 to 5 h.
5. The process claimed in claims 1 & 3, wherein acid treated silica rich solid is digested with sodium hydroxide in the temperature range 95-105?C with solid to alkali ratio of 3 to 5 for the time duration of 2 to 6 h.
6. The process as claimed in 3, wherein quartz rich silica is digested (roasted) in! : 1 ratio of sulfuric acid for 3-4 hrs at 120 ?.
7. The process claimed in 6, where in the digested solid is diluted in distilled water.
8. The process as claimed 6 & 7, wherein diluted liquid is hydrolyzed with 10 % sodium hydroxide up to 10 pH complete precipitation under boiling condition.
9. The process claimed in 6 to 8, wherein the precipitated titanium hydroxide is washed with distilled water till chloride ion free.
10. The process claimed 6 to 9, where in the solid titanium hydroxide grounded and calcined at 800 to 900?.
,TagSPECI:The following specifications particularly describe the nature of the invention and the manner in which it is to be performed:

The present invention relates to a process for the preparation of Titanium dioxide from Kimberlite tailings and more particularly it is relates to the recovery of the titanium dioxide content of Kimberlite tailings in a manner that allows the preparation of titanium.

FIELD OF THE INVENTION

Kimberlite tailing is produced as a huge solid waste during diamond mining. In a country like India from its Panna diamond mines, typically around 100 tons of Kimberlite is generated per 10 carat of diamond mined. Around 8-9 million tons of Kimberlite is already accumulated during previous diamond mining in India. With an estimated life of 20 years for the Panna mines, huge quantity of Kimberlite waste is likely to be available in the country. Considering this problem on the global scale as countries like South Africa and Canada are also involved in diamond mining, the quantity of Kimberlite generated is of a serious concern. Therefore, it is pertinent to look for technical solutions to gainfully utilize Kimberlite accumulated during diamond mining. Typical chemical composition of Kimberlite is as follows:
SiO2 30 – 32%, Al2O3 2 – 5%, TiO2 5 – 8%, CaO 8 – 10%, MgO 20 – 24%, Fe2O3 5 – 11%, LOI 13 - 15%.

Kimberlite being rich in magnesia and silica, titanium, there is an opportunity to develop silica and magnesium based products from this material and also recovers the titanium. Therefore, efforts were made to prepare value-added products. The value addition of Kimberlite will not only make diamond mining more economical but will make it environment friendly process also.

In the process of invention, Kimberlite tailing is treated with mineral acid at about 100? to remove acid soluble matter and thereby Kimberlite enriched with silica is obtained. This acid treated kimberlite is digested with caustic soda at 100 to 190? in stainless steel container with continuous staring for desired time 3 to 5 hrs. The liquid sodium is separated by filtration and the solid titanium with quartz obtained. The solid titanium with quartz is heated at 400 to 450? and further treated (Roasted) with mineral acid in 1: 1 ratio for 3 to 4hrs. The treated solid is dissolved in water and silica is separated by filtration then titanium containing solution hydrolyzed by 10% sodium hydroxide under boiling condition with continuous staring thus titanium precipitate obtained. The titanium hydroxide solid is separated by filtration and filtered solid was washed with demeneralised water thoroughly till free from chloride ion. The product was dried and grounded then calcined at 800-850?. The product is confirmed by XRD, SEM and Chemical analysis.

BACKGROUN OF THE INVENTION

Titanium dioxide is produced either in the anatase or rutile crystal form. Most titanium dioxide in the anatase form is produced as a white powder; whereas various rutile grades are often off-white and can even exhibit a slight color, depending on the physical form, which affects light reflectance. Titanium dioxide may be coated with small amounts of alumina and silica to improve technological properties. Commercial titanium dioxide pigment is produced by either the sulfate process or the chloride process. The principal raw materials for manufacturing titanium dioxide include ilmenite (FeO/TiO2), naturally occurring rutile, or titanium slag. Both anatase and rutile forms of titanium dioxide can be produced by the sulfate process, whereas the chloride process yields the rutile form.

Titanium dioxide can be prepared at a high level of purity. Specifications for food use currently contain a minimum purity assay of 99.0%. Titanium dioxide is the most widely used white pigment in products such as paints, coatings, plastics, paper, inks, fibres, and food and cosmetics because of its brightness and high refractive index (> 2.4), which determines the degree of opacity that a material confers to the host matrix. When combined with other colors, soft pastel shades can be achieved. The high refractive index, surpassed by few other materials, allows titanium dioxide to be used at relatively low levels to achieve its technical effect.

Titanium dioxide or Titanium (IV) oxide (TiO2, Formula Weight 79.88).Natural titanium dioxide exists in nature in one of three crystalline forms, the two most important of which are anatase and rutile , the third
being brookite . Although these minerals are essentially pure titanium dioxide, they do not appear white, because of the presence of impurities, such as iron, chromium, or vanadium, which darken them. Rutile is the thermodynamically stable form of titanium dioxide; The overall process of manufacture is to take an impure TiO2 feedstock and to convert this into the pure white TiO2 pigment. In essence the process sounds very simple but to achieve this it is necessary to chemically convert the impure TiO2 into another chemical, separate out the impurities then to convert back to pure TiO2 — in effect a chemical purification.

There are two commercial processes used to achieve this, the so called ‘chloride’ and ‘sulphate’
process routes.

The chloride process route.

The overall chemistry of this process can be represented as:-
TiO2 + C + 2Cl2 _ TiCl4 + CO +CO2
TiCl4 +O2 _ TiO2 + 2Cl2
The chlorine released when the titanium dioxide is reformed is recycled back to the beginning of the process such that the only chlorine consumed is that which reacts with impurities.

The sulphate process route

The overall chemistry of the process can be represented as:-
FeTiO3 + 2H2SO4 _ TiOSO4 + FeSO4 + H2O
TiOSO4 + H2O _ TiO2n.H2O + H2SO4
TiO2n.H2O _ TiO2 = n.H2O
The sulphate process is more complicated in terms of the number of unit operations involved.
The feedstock is first digested in strong sulphuric acid which converts the titanium components into titanyl sulphate and the iron into sulphates. Where the feedstock used is ilmenite based, a reduction step is required in which iron is added to convert any ferric iron to the ferrous form to aid separation later in the process. This is followed by a clarification step to remove any undigested material from the liquor. For an ilmenite process crystallization typically follows which separates out co-product ferrous sulphate heptahydrate (copperas), though it is also possible to extract copperas later in the process. Copperas is sold for a range of applications including water treatment, agriculture and use in cement. The liquor passes forward to a hydrolysis stage in which the oxysulphate is reacted with water to produce a hydrated titanium dioxide product and releases sulphuric acid. The hydrated TiO2 passes forward to a rotary kiln where it is calcined to produce the anhydrous titanium dioxide product. Further processing (finishing), is then analogous to the chloride process involving chemical surface treatments (coating), milling and drying operations.

Sulfate process (Kirk-Othmer, 1997; Kirk-Othmer, 2006; DeMerlis, 2005) both anatase and rutile grades of titanium dioxide can be produced by the sulfate process, depending on particular processing conditions. briefly, ilmenite or ilmenite and titanium slag is digested with sulfuric acid and the product is diluted with water or dilute acid. Most of the titanium dioxide from the ore is solubilized as a titanium oxo-sulfate and iron is present in its +II oxidation state. The resulting liquor is clarified by sedimentation to remove insoluble
residues such as silica. Iron is removed by crystallization as its sulfate salt (FeSO4•7H2O), followed by filtration. To produce the anatase form of the titanium dioxide, a small portion of the clarified liquor is neutralized with alkali to produce anatase microcrystals. These microcrystals are then introduced into the mother liquor, which is then hydrolysed under carefully controlled conditions to produce crystals of anatase. These are subsequently filtered, washed, calcined, and micronized. During calcination, the final temperature reaches about 800-850o.

The generated flow diagram for the above process of TiO2 is present in fig. no 1

DISCLOSURE OF THE INVENTION

The main object of the present invention is to use Kimberlite tailings as a source of Titanium for the preparation of sodium silicate.
Another object of the present invention is to prepare Titanium employing an energy efficient process which obviates the drawbacks as detailed above.
Yet another object of the present invention is to provide a process for enabling maximum recovery of all constituent as a value added product from Kimberlite tailings generated during diamond mining.
Yet another object of the present invention is to provide a process for preparing titanium dioxide suitable for utilization of reject of silica rich kimberlite, which will generated after recovery of Magnesium oxide, sodium silicate, Precipitated silica, zeolite-A, from kimberlite.
Yet another object of the present invention is to provide a process wherein Kimberlite tailings are containing Titanium dioxide in a solid solution of quartz.

SUMMARY OF THE INVENTION

A known weight of Kimberlite tailing is added to 18% wt./Vol. of hydrochloric acid previously taken in a glass round bottom flask, keeping solid to liquid ratio 1:4 with continuous stirring at boiling temperature under refluxing conditions. After refluxing for 3 to 5 hours, the slurry is filtered and wet cake is washed with tap water till free from acid. For the preparation of sodium silicate, acid treated Kimberlite tailing thus obtained was digested with 8 to 10 weight percent NaOH solution keeping solid to liquid ratio as 1:4. The required quantity of sodium hydroxide is dissolved in requisite volume of water previously taken in a stainless steel reactor. To this alkali solution, required weight of acid treated Kimberlite was added slowly under stirring in order to prepare homogenous slurry. Reaction temperature was achieved by electrically heated oil bath to the reactor. After attaining the temperature, the digestion was continued for a specific time under constant stirring. After completion of the reaction, slurry was filtered and residue was washed with tap water to recover silica and alkali. Residue is containing titanium in solid solution of quartz, further solid waste reacting it with sulfuric acid followed by heat treatment at 400? -450? which is subsequently dissolved the treated solid in water and neutralized with alkali to precipitate titanium. The product is useful for paint, metal etc.

Description of the invention

Accordingly, the present invention provides a process for the utilization of tailing of silica rich kimberlite which will be generated from after removal of all constituent which is present in kimberlite.
The Raw Kimberlite typically contains about 32-35% silica. In order to recover silica and to convert this silica into value added product, it is essential to increase the silica content of the Kimberlite tailings by means of its up gradation. Enrichment of silica in the Kimberlite is necessary for its effective use as source of silica to produce sodium silicate and the residue is containing 70% Titanium and 30% silica. Kimberlite tailing was treated with hydrochloric acid at boiling temperature under refluxing conditions and continuous stirring to remove the acid soluble impurities. The silica content in the acid treated Kimberlite tailing increases up to 72-78%. Kimberlite tailing enriched in silica is used for the preparation of storage stable sodium silicate and residue of sodium silicate solid is used for preparation of titanium dioxide.

Analysis of Titanium Oxide

Weigh about 0.2 gm of sample, fuse with KHSO4 (5-7 gm) in a 100 ml DURAN make conical flask. Dissolve in 15 ml of conc.H2SO4. Cool the solution & transfer it to a 500 ml conical flask. To this add 150 ml water & 30 ml of HCL. Fit it with a two-hole rubber cork. Through one hole insert a delivery tube whose other end immediately is dipped in to a saturated solution of sodium bi carbonate. Through the second hole fit a glass rod, whose other end is wrapped with pure aluminum sheet (about 2 gm), which is immersed in the solution. Boil this solution on hot plate, till the reduction is complete and the solution turns violet. Cool the solution along with the delivery tube dipped in saturated solution of sodium bi carbonate. After cooling remove the cork and add 2 ml of 24% NH4CNS (indicator) and titrate with standard ferric ammonium sulphate till the color changes to blood red.

EXPRESSION OF THE RESULT:

Factor = Weight of standard Ti O2 (0.2gram) X54.69 % in standard Ti O2

27.5 ml of titrant X 100

= 0.003977

48.5 ml of titrant X 0.003977 X 100
% of Ti 02 = ______________________________
0.2 gram Weight of the sample

= 96.45

Example 1

200g of Kimberlite tailing was treated with 20% hydrochloric acid at 95-100°C under continuous stirring keeping solid to liquid ratio 1:4 for 5 hrs. Then the slurry was filtered and washed with tap water till wet cake becomes acid free. After completion of washing, it was dried in oven at 110°C and dried silica rich kimberlite solid (90g) is used for sodium silicate preparation. For the preparation of sodium silicate, 285.8 gram of alkali was dissolved in 3588 ml of water was taken in to stainless steel container. To this, 90 g of acid treated silica rich Kimberlite was added under continuous stirring. Then the reactor was heated for 5 h at 105°C. After completion of reaction, slurry was filtered under vacuum and solid was dried at110°C and dry solid (40g) is taken for Titanium preparation.

40g of dried solid was treated in a muffle furnace at 450°C for 2h. Then the solid was again treated with 1: 1 conc. sulfuric acid in a platinum disc with manual stirring with the help of a glass rod at 100? for 4 hrs up to complete solid dryness. This solid was dissolved in distilled water and filtered with vacuum pump to separate silica. The titanium containing solution was neutralized by 10% sodium hydroxide under boiling condition with continuous stirring up to 10pH, white precipitate was filtered and dried at 110?. The dried solid was calcined at 800? for 1h. Recovery of TiO2 was found to be 94.25%. Analysis of titanium dioxide is given below

TiO2 = 94.25%
LOI = 5.75%

Example 2

5.0 Kg of Kimberlite tailing was treated with 20% hydrochloric acid at 95-100°C under continuous stirring keeping solid to liquid ratio 1:4 for 5 h. Then the slurry was filtered and washed with tap water till wet cake becomes acid free. After completion of washing, it was dried in oven at 110°C and dried silica rich kimberlite solid (2.3Kg) is used for sodium silicate preparation. For the preparation of sodium silicate, 730.0 gram of alkali was dissolved in 9100 ml of water and taken in to stainless steel container. To this, 2.3Kg of acid treated Kimberlite was added under continuous stirring. Then the reactor was closed and heated for 5 h at 105°C. After completion of reaction, slurry was filtered under vacuum and solid was dried at110°C and dry solid (800g) is taken for Titanium preparation.

800g of dried solid was treated in a muffle furnace at 450°C for 2h. Then the solid was again treated with 1: 1 conc. sulfuric acid in a platinum disc with manual stirring with the help of a glass rod at 100? for 4 hrs up to complete solid dryness. This solid was dissolved in distilled water and filtered with vacuum pump to separate silica. The titanium containing solution was neutralized by 10% of sodium hydroxide under boiling condition with continuous stirring up to 10pH, white precipitate was filtered and dried at 110?, and the dried solid was calcined at 800? for 1h. Recovery of TiO2 was found to be 96.45%. Analysis of titanium dioxide is given below

TiO2 = 96.45%
LOI = 3.55%

X-Ray diffraction pattern showed that product obtained is TiO2. X-ray diffraction of the product is shown in FIG.1. SEM of the product showed cubic crystal structure of TiO2 with round corner and edge having particle size of less than 0.5micro meter, the SEM of the product TiO2 is shown in FIG 2. The product quality is international quality, further the process is the utilization of kimberlite a solid waste generated from diamond mining