US2339594A - Bleaching clay - Google Patents

Description

Fli- 8309 unlluw w Patented Jan. 18, 1944 cause mil" minim.

\JUul Ul E BLEACHING CLAY Ira Williams, Burger, Tex., assignor toS'godaCorporation, Huber, Ga., a corporation of New Jersey No Drawing. Application MarchZll, 1941,. Serial No. 384,288

12 Claims.

This invention relates to thebleachingoi clay and particularly to a. method. of bleaching clay whereby the brightness of the clay is improved.

It is common practice to treat clays, especially those which are to be employed in the manufacture of. paper, in a manner. which will improve their color. Since the color of clay is usually due to the presence of oxides of iron. in an insoluble form, these treatments usually have, been directed-toward reducing the-oXides-of iron to-sol uble ferrous compounds which could be brought intosolution and thus removed from the clay. Various compounds of hydrosulfurous acidhave been employed for this purpose, such as, for example, the sodium, zinc and calcium hydrosulfites. These hydrosulfites usually have been added directly to the clay in' the form of a slip or, in some cases, have been formed in situ in the clay slip by the interaction of'a metallic powder,

suchas' Zinc'dust', with sulfurous acid or its salts. Frequently, strong non-oxidizing mineral acids have been added in order to assist the solution of the reduced iron compounds.

In the preparation ofclay, particularly for use in the manufacture of paper and for usein'coating compositions, it is usual. to employ both a degritting and a bleaching operation. A typical example of such a process comprises suspending clay in Water to produce a clay slip containing from about to about of clay and treating such clay slip with a peptizing agent, such as sodium pyrophosphatezor ammonia, in ordertogreatly reduce the viscosity of the slip. The coarse material, consisting largely of sand, mica and clay particles, is'permitted'to settle and the Hydrosulfurcus acid and its compounds-are relatively unstable and rapidly decompose in solution, particularly at elevated. temperatures andespecially in the presence of strong mineral acids. hydrosulfurous acid, such. as sodium hydrosulfite. not attempted to employ the hyclrosulfuro-us compoundsfor the bleaching ofclay at elevated temperatures, as it was expected that the hydrosulfurous compounds would: largely decompose undersuch-conditions whereby large propor tionsof. the hydrosulfurous compound would be wasted; and-poorer. results would be obtained;

This is particularly true of the salts of' Accordingly, those skilled in the art have- It is'an object of my invention to providev an improved method for bleaching argilaceous materials. Another object is to provide a method of bleaching clay in a greatly reduced time. A further object is to provide a method of bleaching clay in a reduced length of time and, at the same time, increasing the effectiveness of the bleaching materials and securing an improvement in the color ofclay beyond that usually employed with such bleaching materials. Other objects are to advance theart. Still other objects will, appear hereinafter.

The above-and other objects may be accom plished in. accordance with my invention which comprises bleaching clay slips by means of Water soluble hydrosulfurous compounds at tempera-. tures between 50 C. and 100 C;, either with or without an added strong. non-oxidizing mineral acid. I have, found that, in spite of the reducedstability of the hydrosulfurous' compounds at such elevated temperatures, by employing such compounds at such temperatures, I am able to greatly reduce the time required for bleaching the clay and, at thesametime, obtain anincreased degree of bleach and a clay of increased brightness. Whilev materially improved results are-obtained by employing temperatures between 50 and 100- 0;, I'have found that the best results are obtained at temperatures of from about C. to about C. and I, therefore, prefer the latter temperatures.

By the terma hydrosulfurous compound, I mean to include hydrosulfurous acid, salts of hydrosulfurous acid and the correspondingsulfoxylates. By the terms an alkali metal hydrosulfurous compound and a zinc hydrosulfurous compound,' I' mean the alkali metal and zinc salts; respectively, of hydrosulfurous acid and the sulfoxylates. Of the hydrosulfurous compounds, which maybe employed in accordance with my invention, it will generally be preferred to employ the metal salts, and particularly the Zinc, alkali metal and alkaline earth metal salts. By the term sulfoxylate, I mean the compounds formed by the reaction of aldehydes with metal" salts ofhydrosulfurous acid. Of'these, the formaldehyde sulfoxylates, obtained from formaldehyde and salts of hydrosulfurous acid, will be preferred. Thespecific compounds, which I particularlyprefer to employ in accordancewith my invention are, sodium hydrosulfite, zinc hydroe sulfite, calcium hydrosulfite and the correspond.- ing-salts of formaldehyde sulfoxylate, particularly sodium formaldehyde sulfoxylate.

The amount of hydrosulfurous compound, which will be employed in accordance with my invention, will vary largely with the particular clay, particularly its color, and with the amount of bleaching desired; Generally, from about 0.05 to' about 0.252% of hydrosulf urous compound based on the clay will be satisfactory for most clays and most purposes. This amounts to from about 1 to about 5 pounds of hydrosulfurous compound per ton of clay. Larger amounts of hydrosulfurous compound may be employed, if desired, but are generally unnecessary and uneconomical. I preferably employ from about 0.1 to about 0.2% of hydrosulfurous compound based on the clay.

It is possible, at the elevated temperatures employed in accordance with my invention, to bleach clay in the absence of added strong mineral acid. However, under such circumstances, the bleaching is less satisfactory than in the presence of acid and the color is more likely to reappear on drying the clay. The reason for this is that acid assists in causin solution of the iron and hence results in a more complete removal of the iron compounds from the clay. Acidic materials, which may be employed with the hydrosulfurous compounds in the process of my invention, are the strong non-oxidizing mineral acids, such as sulfuric acid, hydrochloric acid, phosphoric acid. sulfurous acid and the like and acidifying com pounds of such acids which release such acids in solution to produce acidic solutions. When a strong mineral acid is employed with the hydrosulfurous compounds of my process, such acid may be added to the clay slip prior to the addition of the hydrosulfurous compound, with the hydrosulfurous compound, or even after the bleaching has been completed but prior to separation of the clayfrom theslip as by filtration.

The hydrosulfurous compounds may be added to the clay slip in dry form. However, it will generally be preferred to add such compounds in the form of aqueous solutions thereof. In some cases, it will be preferred to form the hydrosulfurous compounds in situ in the aqueous clay suspension as by treatin the Clay slip with sulfur dioxide, sodium bisulfite and the like and with a metal powder, such as zinc dust. When the hydrosulfurous compound is formed in situ, it will generally be preferred to have a strong mineral acid present so as to facilitate the production of the hydrosulfurous compound.

In order to illustrate my invention more clearly, the preferred modes of carrying the same into effect and the advantageous results to be obtained thereby, the fOllOWing examples are given:

Example 1 A 35% aqueous suspension of degritted Georgia Kaolin was treated with three pounds of sodium hydrosulfite and four pounds of sulfuric acid per ton of clay. Portions were bleached at different temperatures for sufiicient time to produce the maximum bleaching efiect. The clay was then recovered, dried and the brightness determined. The brightness of the unbleached clay, when washed with sulfuric acid alone, was 82.31. The following are the results obtained with the bleached samples:

Temperature of bleach, C. Time of bleach Brightness -The improvement of 0.9 point in brightness, between the sample bleached at 32 and that lok ached at 80, is readily apparent to the unaided eye and constitutes an important increase in brightness.

Example 2 A 35% aqueous suspension of degritted clay was acidified with 5 pounds of aluminum sulfate per ton of clay and was then treated with zinc hydrosulfite at the rate of 2.5 pounds per ton. When bleached for 2 /2 hours at 30 C., a brightness of 81.50 was obtained. When bleached for 20 minutes at C., a brightness of 82.22 was obtained.

Example 3 A 40% aqueous suspension of degritted clay was treated with 3.75 pounds of sulfuric acid and 0.66 pound of zinc powder per ton of clay. One portion was treated with an aqueous solution of sulfur dioxide equivalent to one pound per ton of clay. After bleaching for 2 hours at 30 0., the brightness was 83.13. The second portion was heated to 80 C. and sulfur dioxide, equivalent to one pound per ton of clay, was introduced slowly and with stirring into the bottom of the clay slip. Some of the sulfur dioxide escaped due to the decreased solubility at the elevated temperature. The slip was bleached for 20 minutes and the clay recovered by filtration. The brightness was 83.96.

Example 4 A clay slip was treated with two pounds of zinc powder and 5.5 pounds of sodium bisulfite per ton of clay and divided into two portions. One portion was acidified with ten pounds of sulfuric acid per ton of clay and bleached for /2 hour at 25 C. The brightness was 83.98. The second portion was heated in a closed container to 80 C. and acidified with ten pounds of sulfuric acid per ton of clay. After 20 minutes, the brightness was 84.20.

Example 5 A clay slip, containing 42 percent of degritted kaolin, was prepared and portions were treated with 2.5 pounds of sodium formaldehyde sulfoxylate and five pounds of acidifying ingredient per ton of clay. The portions were bleached under various conditions of time and temperature and the brightness determined. The results are shown in the following table:

Temper- Time of Acidifymg ingredient ature of bleach in Brightness bleach, C. minutes Sulfuric acid 25 120 82.88 Do 60 30 83. 52 80 20 83. 58 20 83. 12 25 150 82. 81 80 15 83. 80 80 35 83. 70 95 60 83. 34 25 150 81. 70 8O 20 83. 52 30 82. 54 80 2O 83. 58

The above examples are given for illustrative purposes only and my invention is not to be limited to the specific embodimens disclosed therein. It will be readily apparent to those skilled in the art that many variations and modifications may be made therein, particularly in the specific agents employed and their proportions. The concentration of clay in the slip may be varied within wide limits and the bleaching process may be carried out without subjecting the clay to a degritting step. Ac-

iiilit'maalaiMom CATION F TEXTILES & HBE-RS, 2,339,594 3 1 1 0 cordingly, I intend to claim my invention broad= ly as in the appended claims.

From the above description, and particularly the examples given therein, it will be apparent that, while others have considered it impracticable to employ hydrosulfurous compounds for the bleaching "6T clay at the elevated temperatures employed by me, I have been able, by the use of such higher temperatures, to greatly reduce the time required for bleaching the clay and, at the same time, have been able to obtain a more efficient bleaching action and clay of a brightness greatly superior to that which it was possible to obtain by the processes heretofore employed. These results were unobvious and could not have been predicted.

I claim:

1. The process which comprises bleaching a clay slip under acidic conditions by means of a water-soluble hydrosuliurous compound at tem peratures between 50 C. and 100 C. and in a proportion of from about 0.05% to about 0.25% based on the clay.

2. The process which comprises bleaching a clay slip under acidic conditions by means of an alkali metal hydrosulfurous compound at temperatures between 50 C. and 100 C. and in a proportion of from about 0.05% to about 0.25% based on the clay.

3. The process which comprises bleaching a clay slip under acidic conditions by means of a water-soluble metal salt of hydrosulfurous acid at temperatures between 50 C. and 100 C. and in a proportion of from about 0.05% to about 0.25% based on the clay.

4. The process which comprises bleaching a clay slip under acidic conditions by means of a zinc hydrosulfurous compound at temperatures between 50 C. and 100 C. and in a proportion of from about 0.05% to about 0.25% based on the clay.

5. The process which comprises bleaching a clay slip under acidic conditions by means of an'alkali metal hydrosulfite at temperatures of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2% based on the clay.

6. The process which comprises bleaching a clay slip underacidic conditions by means of g, sodium hydrosulfite at temperatures of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2% based on the clay.

7. The process which comprises bleaching a clay slip under acidic conditions by means of a water-soluble metal salt of a sulfoxylate at temperatures of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2% based on the clay.

8. The process which comprises bleaching a clay slip under acidic conditions by means of an alkali metal salt of a sulfoxylate at temperatures of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2% so based on the clay.

9. The process which comprises bleaching a clay slip under acidic conditions by means of an alkali metal salt of formaldehyde sulfoxylate at temperatures of from about 65 C. to about 33, 85 C. and in a proportion of from about 0.1%

to about 0.2% based on the clay.

10. The process which comprises bleaching a clay slip under acidic conditions by means of the sodium salt of a sulfoxylate at temperatures so of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2%

based on the clay.

11. The process which comprises bleaching a clay slip under acidic conditions by means of sodium formaldehyde sulfoxylate at temperatures of from about 65 C. to about 85 C. and in a proportion of from about 0.1% to about 0.2% based on the clay.

12. The process which comprises bleaching a 40 clay slip under acidic conditions by means of zinc hydrosulfite at temperatures of from about C. to about C. and in a proportion of from about 0.1% to about 0.2% based on the clay.

IRA WILLIAMS.