CZ289531B6 - Process for preparing aqueous solutions of lithium silicates - Google Patents

Abstract

The invented process for preparing aqueous solutions of lithium silicates is characterized in that alkalis are removed from the sodium water glass on a cation exchange resin within He+ cycle and the obtained acid solution of silicon dioxide is thickened, after addition of a stabilizing alkali, to 20 to 50 percent by weight of SiOi2 and after thickening it is brought into reaction with a solution of lithium hydroxide at a temperature ranging from 20 to 60 degC.

Description

Technical field

The invention relates to the production of aqueous lithium silicate solutions from sodium water glasses, silica and lithium hydroxide.

BACKGROUND OF THE INVENTION

Lithium silicates are mainly produced by reacting amorphous silica with lithium hydroxide. According to patent SU 1498709, liquid lithium water glass is produced by dispensing silicic acid with a content of 15 to 80% by weight. SiO ₂ at a rate of 5 to 20 kg / h into the preheated lithium hydroxide solution. The process according to patent J 59-069417 starts from a silica gel which is mixed at 40 ° C with lithium hydroxide and stirred for 1 hour and then left to stand at 40 ° C for 16 hours. This is followed by heating to 80 ° C and aging at 95 ° C for 12 hours. After cooling and filtration, liquid lithium silicate is obtained. In patent J 54-020480, lithium silicate is obtained from sodium or potassium silicates, which, by contact with an ion exchange resin, is converted to silica with a concentration of 1 to 7% SiO ₂ and reacted with powdered or liquid lithium hydroxide. A similar procedure is described in patent J 50-030658. The silicic acid obtained by contact with the ion exchange resin is reacted with lithium hydroxide under pressure at 90 ° C. A method is also known in which lithium silicate is obtained by reacting silicon powder of 20-80 µm particle size with an aqueous lithium hydroxide solution at a temperature of 65-85 ° C. Czechoslovakian Certificate No. 262074 describes a process for the production of potassium pure water glasses from sodium water glass, which, after dilution, was dealkalized by passing it through a cation exchange resin in H form and the resulting acidic silica solution was thickened to 20 to 50%. SiO ₂ wt. Pure potassium water glass was obtained from the concentrated silica solution by treatment with potassium hydroxide. The reaction with potassium hydroxide proceeded easily at room and elevated temperatures. Similarly, pure sodium water glass could be produced by mixing the thickened silica solution with sodium hydroxide to form a gel which, upon heating, immediately dissolved into pure sodium water glass. Such a reaction has hitherto not been possible with lithium hydroxide, which upon mixing with the concentrated silica solution immediately turned into a gel, and the gel-like form remained even after heating to a higher temperature in an attempt to accelerate the reaction.

SUMMARY OF THE INVENTION

These disadvantages have been overcome by the present invention. It has now been found that the reaction of lithium hydroxide with a concentrated silica solution produced in a similar manner as described in U.S. Pat. Certificate No. 262 074 is possible. If the gel formed is mixed for a long time at 20 to 60 ° C, or preferably at 40 to 60 ° C, the gel will gradually dissolve into lithium silicate. At temperatures below 40 ° C the dissolution is disproportionately long and incomplete, and a portion of the silica can always remain undissolved, especially with lithium silicates with a mole. At temperatures below 20 ° C, dissolution virtually stops and does not take place. When heated to a temperature higher than 60 ° C, the gel does not dissolve at all and, in addition, the dissolved lithium silicate passed back to the gel.

The present invention utilizes a process for preparing a concentrated silica according to the process disclosed in U.S. Pat. No. 262,074. This procedure consists in diluting the soda water to a concentration of 2 to 6% by weight with distilled water. and subjected to dealkalization by passing through a cation exchange column in an H ⁺ cycle. In this way, an acid sol of a silica solution having a pH of 2 to 5 is prepared. To a portion of the acidic silica solution a stabilizing additive or sodium hydroxide solution is added to bring the pH

Adjusted to a value of 9 to 12, and then concentration is started. It is carried out by evaporating the water under heat supply and the evaporated water is replaced by an acidic silica solution. The concentration is terminated by achieving a silica concentration of 20 to 50 wt.

SUMMARY OF THE INVENTION The present invention relates to a process for the production of lithium silicates, characterized in that a concentrated solution of 20-50 wt. Allow the silica to react with an aqueous solution of hydroxide in such a proportion that to 1 mol of lithium oxide contained in the lithium hydroxide used add 3 to 25 mol of silica contained in the concentrated silica solution and stir at 20 to 60 ° C after reaction. until completely dissolved.

The lithium silicates of the present invention can be prepared with a molar ratio of SiO 2: L 12 O = 3: 1 to 25: 1. They are useful as binders for corrosion protective coatings. In contrast to sodium and potassium silicates, lithium silicate solutions, when dried, form poorly water-soluble films which can be cured even at lower temperatures. Particularly, in the case of coupling 15 with powdered zinc, a curing process involves the reaction of the metal zinc with the silicate ions, thereby forming a complex of zinc silicates. The zinc powder may be replaced with lead or zinc oxide powder and the like.

Examples

Example 1

Sodium liquid water glass weighing 1185 g and having a composition of 27% by weight. % SiO2, 8.16 wt. Na2O,

64.84 wt. H2O was diluted with 6257 g of distilled water. 7442 g of diluted water glass of 4.3 wt. % SiO2 and 1.3 wt. Na2O. The entire amount of diluted waterglass was subjected to dealkalization on a cation-exchange column packed with an Ostion KS vlT cation exchange column. Dealkalization yielded 7265 g of silica acid containing 4% 30 wt. SiO 2 and pH 2.7. The remaining 177 g of diluted waterglass were losses due to the operation of the ion exchanger. To 960 g of silica acid sol was added 30 g of sodium water glass to give 990 g of a basic solution having a pH of 10.4. The stock solution was heated to 102 ° C in a glass flask equipped with a glass condenser. The evaporated water was condensed in a water-cooled condenser and the decreasing volume of liquid was continuously replaced by an acidic solution of silica. A total of 1000 g of a concentrated solution was obtained which contained 29.95 wt. SiO ₂ . 717.9 g of the concentrated SiO2 solution was removed and cooled to 50 ° C. 59.8 g of lithium hydroxide was dissolved in 222.3 g of water, the solution was heated to 50 ° C, and concentrated solution of lithium hydroxide was metered into the lithium hydroxide solution with vigorous stirring and stirred at 40-60 ° C until complete dissolution. 1000 g of a clear low-viscosity solution with low opalescence were obtained.

Analysis of the obtained lithium silicates:

silicon dioxide content lithium oxide content

PH specific weight viscosity mol. SiO2 / Li2O ratio

22.80 wt.

2.29 wt.

11.37

1207.00 kg / m ³

4.32 mPas

4.94

-2GB 289531 B6

Example 2

A concentrated S1O2 solution was prepared as in Example 1. In 296.9 g of water, 42.7 g of lithium hydroxide was dissolved at 40-60 ° C, and 660.3 g of the concentrated S1O2 solution was added with vigorous stirring. Then stirred at 40-60 ° C for 8 hours until complete dissolution. 1000 g of clear solution with low opalescence was prepared.

Analysis of the obtained lithium silicate:

content SiO ₂ content L12O specific weight viscosity mol. ratio S1O2 / Li2O

21.25 wt.

1.78 wt. 1183 kg / m ³

4.00 mPas

5.93

Claims (1)

PATENT CLAIMS Process for the manufacture of aqueous solutions of lithium silicates, characterized in that the sodium water glass is diluted with distilled or deionized water to a concentration of 2 to 6% by weight. of silica and subjected to dealkalization by passing through a cation exchange column in an IT cycle to prepare an acidic silica solution having a pH of 2 to 5, to a portion of the acid solution is added a sodium water glass stabilizer or sodium hydroxide solution to adjust the pH to a value of 9 to 12, followed by concentration by evaporation of the water under heat supply, the evaporation water being replaced by an acidic silica solution, the concentration being terminated to a silica concentration of 20 to 50% by weight, then the concentrated solution is left at 20 to 60 ° C, react with an aqueous solution of lithium hydroxide in a ratio such that 3 to 25 moles of silica contained in the concentrated solution are added per mole of lithium oxide contained in the lithium hydroxide solution and stirred at 20 to 60 ° C for the reaction. 60 ° C until complete dissolution to give ro % of a solution containing 10 to 26 wt. % silica and 0.2 to 4.3 wt. lithium oxide.