IL114199A - Process for the manufacture of pure silica from rock containing it - Google Patents

Description

AN IMPROVED PROCESS FOR THE MANUFACTURE OF PURE SILICA FROM ROCK CONTAINING IT nn i N ' Don y7on n ' i7 D ηί7'7· ο ~ιι^''7 IDIWD η·7ηη THE APPLICANTS: : jvaumn Rotem Amfert Negev Ltd. D"y.l ΖΠ] 01DDN DJin P.O.Box 435 435 .1.11 Dimona 86103 86103 Π3Ι0Ί THE INVENTORS: : D ' K ' 3ΡΡΪΊ 1. Alexander IOSEF ηθΙ ' "1TDDD7N .1 5/2 Hakanayim St. 5/2 D'NDfm mm Arad 80700 80700 Tiy 2. David BASHIRI 'TBI ΤΠ.2 23/1 Hatzvi St. 23/1 Ίϋη aim Beer-Sheva 2W--|N2 ffoe present invention relates to a process for the manufacture of pure precipitated silica from rocks. More particularly, the invention relates to an improved process for the manufacture of pure precipitated silica from rocks containing non-crystalline silica, such as: porcel 1 ani te , diatomite and amorphic quartz.

This is a patent of addition to our Parent Application Number 104,584.

] BACKGROUND OF THE INVENTION ■ The known process for the manufacture of pure precipitated silica from rocks, is based on the use of an aqueous solution of silica, such as obtained from the product obtained by fusion of sodium carbonate with quartz at high temperatures, the molar ratio between the Si02 to Na20 (ratio known under the term modul ) being above 3, generally being in the range of 3.2 to 3.5.

Porcel lanite is a sedimentary rock, which is encountered in many places in the world and also in Israel. A typical analysis of the Israeli rock is as follows: Si02 : 69% CO2 : 7%, and Na20 : 0.45%.

Pure amorphous silica, also known as precipitated silica or active silica, is a valuable material useful for many purposes , such as: fillers, extenders, adsorbents, supports, dentrifices, etc. There are many patents which describe various approaches for obtaining active silica from alkali metal silicates and a mineral acid, such as hydrochloric acid, or sulfuric acid. A typical example is the U.S. Patent Number 3,993,497 which claims the manufacture of precipitated silica by the treatment of a solution of sodium silicate with sulfuric acid in the presence of aluminum ions.

According to the East German Patent Number 293,097, powdered amorphous silica is obtained by reacting a solution of alkali metal silicate with an acidic substance, in the presence of a mixture of cationic and non-ionic surfactant which is added before an electrolyte concentration of 0.3N is reached.

In our previous Israeli Patent Application Number 104,584 a process was described for the manufacture of pure amorphous silica from rocks containing nop-crystal 1 i ne silica, which involves the dissolution of said rock in an alkaline solution comprising sodium hydroxide and sodium carbonate. The sodium silicate solution obtained is treated with sodium bicarbonate, at a weight ratio of Si02 to Na20 in the range of between 0.5 to 3.0, the sodium carbonate solution being transformed into crystalline sodium bicarbonate and recycled to the process after a salting out reaction with sodium chloride. As pointed out, the above range is quite critical in order to obtain an efficient dissolution of silica and to avoid undesi red reactions. The process was found to be quite useful, producing a valuable product in many cases. However, when the respective rocks, contain appreciable amounts of calcium carbonate, such as encountered in several places, including Israel, it is necessary to increase the ratio CaC03 to a20 in order to achieve the desired modul (ratio Si02 to a20) . But in this case, the respective by-products obtained, calcium hydroxide and sodium carbonate, cause a decrease in the yield of the product obtained in the dissolution. This decrease in the yield is a consequence of the reaction between calcium hydroxide and sodium silicate which precipitates out calcium silicate according to the following reaction : Ca(OH)2 + NaSi03 = CaSiOa + 2NaOH 114,199/2 Also, this decrease is due to an increase in the concentration of sodium carbonate, as a result of the following side equilibrium reaction: CaC03 + 2NaOH Na2C03 + Ca(OH)2 It is an object of the present invention to provide an improved process for the manufacture of pure precipitated silica from non-crystalline rocks. It is another object of the present invention to provide an improved process for the manufacture of pure precipitated silica from non-crystalline rocks containing calcium carbonate. It is yet another object of the present invention, to provide an improved process for the manufacture of pure precipitated silica from non-crystalline rocks of a very high quality and at relatively low production costs.

BRIEF DESCRIPTION OF THE INVENTION The invention relates to an improved process for the manufacture of pure precipitated silica from non-crystalline rocks containing calcium carbonate, in the range of between 10-15% (expressed as CaO) which comprises the steps of: (a) removal of the calcium carbonate from the respective rock; (b) dissolution of the treated rock in an alkaline solution comprising sodium hydroxide and sodium carbonate obtaining a solution of sodium silicate, the molar ratio between Si02 and Na20 being up to 4, (c ) precipitation of pure amorphous silica by adding sodium bicarbonate into said sodium silicate thus co-producing sodium carbonate, and (d) the resulted sodium carbonate solution being transformed into crystalline sodium bicarbonate by carbonization with gaseous carbon dioxide followed by a salting out reaction with sodium chloride, the sodium carbonate being recycled to the process. A most preferred method to remove the calcium carbonate in step (a) is to treat said rock with a dilute solution of hydrochloric acid.

DETAILED DESCRIPTION OF THE INVENTION.

The invention is based on the finding that the prior removal of the calcium carbonate present in the rock, before its dissolution in the alkaline solution, avoids the detrimental effect caused by the by-products obtained during said dissolution. One may also conceive to carry out this treatment by physical methods, such as elutriation or classification. However, the chemical methods, such as acidulation by a mineral acid or bubbling a stream of carbon dioxide to generate calcium bicarbonate being preferred. The acidulation with dilute solutions of hydrochloric acid seems to be the most preferred, particularly when such solutions are available at site.

The acidulation with hydrochloric acid may be carried out with dilute solutions containing up to 300 g/1 HC1 and preferably in the range of between 100g/l to 200 g/1 at room temperature. The amount of acid which is added should be according to the respective stoichiometric amount based on the carbon dioxide present, a slight excess being preferred. After filtering the resulted slurry, the treated porcellanite was washed with water to a pH of about 4. It was found that by this method the silica content in the resulted product was between 92% to 94% (on dry basis).

In the following Table 1, section A, there are summarized a number of experiments carried out according to the present invention, the original rock being acidulated with an aqueous solution of 100 g/1 hydrochloric acid, using an excess of about 10% above the stoichiometrical ly required. Sction B, in the Table show the comparative results without removal the calcium carbonate by the prior treatment.

TABLE 1 : Resul ts on precipitated silica produced with a prior acidulation (A) and without this treatment (B) .

Section A (with a prior acidulation).

Feed Ratio odul in the % efficiency of % a2C03 in the Si02:Na20 product dissollution mixture* 2.0 1.87 93.5 2.3 2.5 2.07 82.8 1.9 3.0 2.33 77.7 0.9 3.5 2.63 75.1 1.7 4.0 2.89 72.3 2.5 4.5 3.10 66.7 1.6 Section B (without a prior acidulation) 71 85.5 5.5 94 77.6 6.1 23 74.4 6.6 51 71.7 6.3 63 65.8 7.6 26 50.2 6.7 * mixture of sodium hydroxide and sodium carbonate The attached three Figures also illustrate in a graphic manner the following main parameters for the above two types of porcel lani te : A obtained by a prior acidulation and B obtained without the prior acidulation.

The experiments were carried out under the same conditions which were as follows: - Temperature during the experiments: 120°C (1.8 Atm) .

- The starting sodium carbonate content in the mixture sodium carbonate to sodium hydroxide were between 1.6-2.3.

- The amount of porcellanite used was calculated according to the ratio Si02:NaOH (between 2 to 4.5).

- Dissolution period: 30 minutes.

- The concentration of NaOH: 120 g/1 , and - The Si02 in the feed: 94% with acidulation, and 69% without acidulation.

Figure 1 : The modul in the product as a function of the ratios in the feed.

Figure 2: The efficiency as a function of the ratios in the feed .

Figure 3: The sodium carbonate content in the mixture Na2C03/NaOH as a function of the ratios in the feed .

The invention will be hereafter illustrated by the following Example, being understood that this Example is presented only for a better understanding of the invention, without limiting the scope of the patent. A person skilled in the art after reading the present specification will be in a position to insert slight modifications, but without being outside the attached Claims which cover the invention.

EXAMPLE 1.

Into an open reactor of 10 1 provided with a mixer, an amount of 4926 ml of a solution of hydrochloric acid (10% by weight) was introduced. An amount of 1866 g of dried porcel-lanite containing 65% Si02 and a size particles of - 6 mesh was added in small portions.

At the end of the reaction (after about 40 minutes) the liquid phase was separated by decantation and the solids were washed with an amount of 2500 ml of tap water on a laboratory Buchner filter, thus removing substantially the chloride present in the cake. After drying at a temperature of 105°C, an amount of 1241 g of porcelianite was obtained, containing 94% Si02 and humidity 2.2% (i.e 1213 g of dried porcel 1 ani te) .

Into a closed reactor of 5 1 , provided with a mixer, the above dried porcelianite and 2984 g of a solution of sodium hydroxide (120 g/1 ) were introduced.

The reactor with the above reagents was thoroughly mixed and heated to about 120°C for about 30 minutes. After cooling, the slurry was filtered on a Buchner filter, obtaining 2750 g of solution of sodium silicate having the following composi tion: Dissolution modul : 3.1 Na∑0 : 6.36% Si02 : 19.1% Na2C03 : 1.6%

Claims (7)

- 11 - 114,199/2

1. C L A I M S :- 1. An improved process for the manufacture of pure amorphous silica from non-crystalline rocks containing calcium, in the range of between 10-15% (expressed as CaO) which comprises the steps of: (a) removal of the calcium carbonate from the respective rock; (b) dissolution of the treated rock in an alkaline solution comprising sodium hydroxide and sodium carbonate obtaining a solution of sodium silicate, the molar ratio between Si02 and Na20 being up to 4; (c ) precipitation of pure amorphous silica by adding sodium bicarbonate into said sodium silicate thus co-producing sodium carbonate; and (d) the resulted sodium carbonate solution being transformed into crystalline sodium bicarbonate by carbonization with gaseous carbon dioxide, followed by a salting out reaction with sodium chloride.

2. The improved process according to Claim 1 , wherein the removal of the calcium carbonate in step (a) is carried out by treating the rock with a dilute solution of hydrochloric acid.

3. The improved process according to Claims 1 or 2, wherein the concentration of the hydrochloric acid is in the range of between 100 to 300 g/1.

4. The improved process according to Claims 2 or 3, wherein a slight excess of hydrochloric acid over the stoichiometrically required, is used.

5. The improved process according to Claim 4, wherein said excess is about 10%.

6. The improved process according to Claims 2 to 5, wherein after the acidulation, the treated rock is washed with water until reaching a pH of about 4.

7. An improved process for the manufacture of pure amorphous silica from non-crystalline rocks, substantially as described in the specification and claimed in any one of Claims 1 to 6. For the Applicants, Simon Lavie Patent Attorney