MXPA98007418A - Composition of calcium tolerant carbonate raised and uses for the mi - Google Patents

Abstract

An alcid tolerant calcium carbonate characterized in that it comprises a mixture of calcium carbonate with at least about 0.1%, based on the dry weight of calcium carbonate, of sodium aluminum, together with at least about 0.1%, based on the dry weight of calcium carbonate, of one or more weak acids

Description

COMPOSITION OF CALCIUM CARBONATE TOLERANT TO ACID AND USES FOR THE SAME DESCRIPTION OF THE INVENTION This invention relates generally to calcium carbonate for use in the manufacture of paper, and related industries, and more particularly to calcium carbonate having properties tolerant to acid. Titanium dioxide and calcined clay have traditionally been used as filling materials in the preparation of neutral to weakly acidic paper in order to improve the optical properties, especially the gloss, of the resulting product. These materials, however, especially titanium dioxide, have the disadvantage of being very expensive, resulting in high production costs and non-competitive paper product in price. Calcium carbonate, particularly calcium carbonate particularly precipitated, has been used as a filler in the manufacture of wood-free alkaline paper. Such use results in a paper with improved optical properties, particularly high gloss and opacity, without the expense incurred in the use of titanium oxide fillers, resulting in a much less expensive product. The calcium carboan, however, can not be used generally as a filler in acidic paper made of proportions of mechanical pulp since they decompose in an acidic environment. Already that the mechanical pulp sheets and press paper are prepared in the acid range, there is a great need to develop a calcium carbonate composition which is acid stable and resistant to decomposition at low pH, so that it can be used as filling material in the manufacture of such paper, such as agerrin paper, where the use of an alkaline filler has a negative impact on the final properties of the paper. Paper made from mechanical pulps has traditionally been produced under acidic papermaking conditions due to the "alkaline dimming of the fiber" that occurs as soon as the pH increases. This means that there is a reduction in the brightness of the paper (brightness reversal) when the acid to alkaline pH is increased in systems containing wood. Alkaline darkening will occur to some degree in any of the wood pulps with significant lignin content. The degree of darkening will depend on the particular pulps, pH and quality of the water. In general, the fillers of ground calcium carbonate and precipitated calcium carbonate dampen extremely well in the range of 7.5-8.2. The acid-resistant calcium carbonate compositions thus provide a means for reducing the degree of alkaline dimming of the fiber and reversion of the gloss due to its ability to keep the pH stabilized.

U.S. Patent 5,043,017 describes and claims a calcium carbonate stable in acid resistant to degradation in a slightly acidic environment which comprises a mixture of a calcium chelating agent or a conjugate base, and a weak acid, in such a way that the calcium carbonate is coated by, and is in equilibrium with, the calcium-binding agent or conjugate base and the weak acid. Preferred calcium carbonate compositions contain sodium hexametaphosphate and phosphoric acid. Sodium aluminate has been used in papermaking, primarily as a replacement for, or in addition to, alum, which is used to fix the sizing. It has been indicated that sodium aluminate is not an economical pH control chemical since only a small portion of the alkalinity is available as a free caustic, see, Thomas, "Sodium Aluminate in Paper Manufacture" 1979 Retention and Drainage Seminar Notes , published by the Technical Association of the Pulp and Paper Industry Ine, Atlanta Ga. It is an object of the present invention to provide an acid-tolerant calcium carbonate composition especially suitable for use in papermaking applications. It is a further object of the present invention to provide a process for the preparation of the calcium carbonate compositions mentioned above.

Still a further object of the present invention is to provide a paper having improved optical qualities prepared using the calcium carbonate compositions of the present invention. The present invention relates to an improved form of calcium carbonate which is acid tolerant to allow its use as a filling agent in the manufacture of neutral to weakly acidic paper, and a process to produce this calcium carbonate tolerant to acid. More particularly, this invention relates to an acid-tolerant calcium carbonate composition comprising a mixture of calcium carbonate with at least about 0.1 percent, based on the dry weight of calcium sarbonate, of a sodium aluminate, together with at least about 0.1 percent, based on the dry weight of the calcium carbonate, of one or more weak acids. It has been surprisingly found that the inclusion of sodium aluminate together with a quantity of a weak acid sufficient to neutralize the composition confers a higher degree of acid resistance to the calcium carbonate composition in the presence of fiber suspension, and a higher pH stability than calcium carbonate compositions stabilized in acid. In an optional embodiment, the weak acid may consist of a mixture of phosphoric acid together with an organic, polymeric acid.

BRIEF DESCRIPTION OF THE INVENTION Figure 1 is a graph comparing the gloss of pads made with various amounts of untreated calcium carbonate compositions (designated as non-PCC) with the gloss of pads made with various amounts of a sodium carbonate composition. Acid tolerant precipitate / sodium aluminate / phosphoric acid (designated as ECCI-ATPCC). Figure 2 is a graph comparing the pH of the pads made with various quantities of untreated calsium carbonate compositions (designated as non-PCC) with the pH of pads made with various amounts of an acid-tolerant precipitated sodium carbonate composition / sodium aluminate / phosphoric acid (designated ECCX-ATPCC). Figure 3 is a graph comparing the various amounts of phosphoric acid needed to "buffer" the system at the desired pH (6.5 or 7.0). Figure 4 is a graph comparing the gloss of pads produced using various amounts of untreated calcium carbonate compositions (designated as non-PCC) pads produced with various amounts of an acid-fast precipitated sodium carbonate / sodium aluminate composition. phosphoric acid (designated as ECCI-ATPCC).

Figure 5 is a graph comparing the gloss of pads produced using various amounts of untreated calcium carbonate compositions (designated as non-PCC) pads produced using various amounts of an acid-fast precipitated sodium carbonate / sodium aluminate composition. phosphoric acid (designated as ECCI-ATPCC). Figure 6 is a graph comparing the brightness of sheets formed using various amounts of untreated calcium carbonate composites (designated corao * not PCC) with sheets formed using various amounts of an acid-tolerant precipitated sodium carbonate composition. sodium aluminate / phosphoric acid (designated as ECCI-ATPCC). Figure 7 is a graph comparing pulp TAPPI brightness: press paper formed using various amounts of untreated calcium carbonate compositions (designated as non-PCC) are sheets formed using various amounts of a composition of precipitated sodium sarbonate-tolerant precipitate. acid / sodium aluminate / phosphoric acid (designated ECC1-ATPCC). Figure 8 is a graph comparing the gloss of paper formed using various amounts of different forms of untreated calcium carbonate compositions (designated as Sc-PCC [scalenehedral calcium carbonate], ph-PCC [rhombic preslipped calsium carbonate]) with formed paper using various amounts of different forms of an acid-tolerant calcium carbonate composition (designated as AT-Sc-PCC [precipitated calcium carbonate scalenic acid-tolerant aluminate / sodium aluminate / phosphoric acid somatization] or AT-Rh-PCC [ Acid-tolerant rhombic precipitated calcium carbonate / sodium aluminate / phosphoric acid composition]). Figure 9 is a graph comparing the gloss of paper formed using various amounts of untreated calcium carbonate compositions (designated as non-Rh-PCC) with paper formed using various sanctities of an acid-tolerant rhombic calcium carbonate composition. (designated as ECCI Rh-ATPCC). Figure 10 is a graph comparing the pH during maturation of an acid tolerant calcium sarbonate composition containing 1% sodium aluminate, 2% phosphoresis acid and 1% acid polyacrylate, with a calcium carbonate composition. Acid-tolerant milled calcium containing 1% sodium aluminate, 4% phosphoric acid and 1% acid polyacrylate, and an acid-tolerant calsium rpolida carbonate composition containing 1% sodium aluminate, 6% phosphoric acid. % and 1% poliasrilate in a period of 180 hours. Figure 11 is a graph comparing the pH during maturation of a calcium carbonate deposition Scalenohedric acid-tolerant precipitate that has 0.5% sodium aluminate, 4% phosphoresis, and 1% polimaleiso, with an acid-tolerant scalenic acid precipitated calcium carbonate composition containing 0.5% sodium aluminate, acid 6% phosphoric and 1% polymaleic acid. The improved form of calcium carbonate prepared by the present invention is acid tolerant to allow its use as a filler in the manufacture of neutral to weakly acidic paper. While not wishing to be bound by any particular theory as to the operability of the present invention, it is believed that the acid resistance conferred to the calcium carbonate compositions of the present invention is a result of the inactivation of the surface of calcium carbonate. by the addition of sodium aluminate and the weak acid. In the present research, the acid-tolerant calcium carbonate compositions are carried by the inclusion in the calcium carbonate composition of at least about 0.1 percent, based on the dry weight of calcium carbonate, of aluminate of sodium together with one or more weak acids in an amount which is at least about 0.1 percent, based on the dry weight of the calcium carbonate. In an optional embodiment, the weak acid may consist of a mixture of weak acids whereby at minus one of the components is derived from an organic, polymeric acid. Another view is not to join any particular theory, it is believed that the ability of the acid-stabilized calcium carbonate of the present invention to resist dissociation in an acidic environment is due to the reaction of the calcium carbonate surface with the aluminate. of podium.

This mechanism of inactivation of the surface is different from the absorption or reaction of sodium h-exametaphosphate of the prior art on the surface of the carbonate > of calcium, and the resulting damping action. The sodium aluminate used in the present invention is typically an aluminate compound containing the id Al * 3 in a hydroxy or oxoid complex. Typical forms of sodium aluminate are expressed as NaA102 or Na2Al204. The sanctity of sodium aluminate is at least 0. 1 percent based on the dry weight of the calcium carbonate, and preferably it is about 0.5 to about 1.0 percent by weight, based on the dry weight of the calcium carbonate. The amount of the weak base used is at least 0.1 percent, based on the dry weight of the calcium carbonate, and is preferably about 1 to about 6 percent, based on the dry weight of the calcium carbonate. calsium carbonate. The weak acid used in the compositions of the present invention is preferably a weak acid selected from the group consisting of phosphoric acid, metaphosphoric acid, hexametaphosphoric acid, ethylenediaminetetraacetic acid (EDTA), citric acid, sulfurous acid, boric acid, acetic acid, and mixtures thereof. As indicated above, the weak acid may be a mixture of weak acids together with highly adisiopal organelles, polimeris, such as acidic polyacrylate, polystyrene acid and polycarboxylic acid, and mixtures thereof. The organic polymeric acid is typically an organic polymer having a weight average molecular weight, Mw, in the range of 750-1,000,000, which consists of regularly repeating units or chemically similar units, joined by primary covalent eplaces. The total sanctity of the weak acid used is at least 0.1 percent, based on the dry weight of calcium carbonate, and is preferably about 1 to about 8 percent, based on the dry weight of calcium carbonate. Typically, 2-4% phosphoric acid is used in combination with 1-6% of the organic, polymeric acid. Preferred combinations for use in the present invention include sodium aluminate / phosphoric acid; sodium aluminate / acid phosphoric / acid polyacrylate; Y sodium aluminate / phosphoric acid / polymaleic acid. Where the weak acid is a mixture, preferred combinations include 1% sodium aluminate / 6% phosphoric acid / 1% acid polyacrylate; and 0.5% sodium aluminate / 6% phosphoric acid / combinations of 1% polymaleic acid. The sodium carbonate used is preferably finely divided and can be either precipitated calcium carbonate (PCC) or natural ground gypsum (GCC). The process for producing this acid-tolerant calcium carbonate involves first adjusting the pH of the calcium carbonate to about 11 or 12, and then adding at least about 0.1 percent, based on the dry weight of the calcium carbonate, of the aluminate in the calcium carbonate. sodium. Then, at least about 0.1 percent, based on the dry weight of the calcium carbonate, of one or more weak acids is added to this resulting mixture. Finally, the resulting mixture is mixed for a sufficiently long period of time to ensure uniform mixing of the ingredients. Calcium carbonate can be "used in the process" described above either as a dry powder or an aqueous suspension with up to about 60 percent solids content.The sodium aluminate can be used in the present process either as a Dry solid or as aqueous solutions When calcium carbonate is used as a powder dry, it is preferable to use an aqueous solution of sodium aluminate in order to facilitate homogeneous mixing. Where a suspension of the calcium sarbonate is used, the solid form of the sodium aluminate is readily dissolved therein such that an aqueous solution is unnecessary.

The weak acid (or acids) can be used in the preparation process in either a pure concentrate form or as aqueous solutions. The composition of the present invention can be used to improve the optical properties of neutral to weakly acidic paper by its addition to paper during standard manufacturing processes. Typically, the calcium carbonate composition of the present invention is added to a primary paper supply which are necessary to make the acidic paper to thereby form a supply of secondary paper. The sanctity of the calcium carbonate solution that is added to the paper supply is dependent on the particular characteristics of the particular provision, and the desired degree of gloss desired in the finished product. Representative amounts of the deposition for typical paper supplies are in the range of about 1 to about 15% by weight of the weight of the finished product. More preferably, the sodium carbonate compositions are used in the range of about 5 to about 10% by weight of the finished product.

The invention will be further illustrated by the following Examples, which are considered illustrative of the invention, and not limited to the precise embodiments shown. EXAMPLE 1 Calcium carbonate for provisions containing wood To demonstrate the usefulness of the compositions of the present invention in the use of paper such as mechanical pulp sheets and press paper, made in the acid pH range, the following are made Experiments with supplies of wood-containing paper suals usually experience alkaline dimming and decomposition of salsium carbonate at acidic pH. Experimental I. Brightness in Cojincillos Acid-tolerant precipitated calcium carbonate (ATPCC) composition 1% sodium aluminate is added to a carbonate suspension. This resulting suspension containing the sodium aluminate is mixed at 250 rpm for 1 hour. At the end of the mixing, 4% phosphoric acid is added. The suspension is stirred for 1 minute and matured without agitation for an additional 3 hours. Formation of the pad 1. Variable pH The pulp suspension is adjusted (consistency of the 0. 5%) at the desired pH with phosphoric acid or sodium hydroxide. The used supply of a mechanical pulp mill in the South is obtained. The salivary sarbonate is added to the pulp suspension and mixed gently (200 rpm) for 30 minutes. After this, stir at 950 rpm for 30 seconds. The suspension is filtered on a Bushner filter equipped with a Whatman 41 filter paper. The cushions are bent and dried in the drum dryer. The brightness of each cushion is measured by Teledyne Misro S-5. 2. Constant pH The pH of the pulp (consistency = 0.5%) is adjusted to 7.0 or 6.5 with sodium hydroxide or diluted phosphorous acid. The provision is the same as that used in the previous experiments. After adjusting the pH, a known amount of calcium carbonate is added to the previously described provision. The pH is maintained constant by periodic additions of 5% phosphoric acid to the suspension. The suspension is slowly mixed and the pH is kept constant for 1 hour. The weight of the phosphoric acid used to keep the pH constant at the end of each experiment is recorded. After this the suspension is mixed at high speed of 950 rpm for 30 seconds. A cushion for brightness is formed by emptying the suspension through a Buchner funnel equipped with a Whatman 42 filter without ash. The pads are pressed twice and dried in a drum dryer (two steps). Again, measure the brightness with a Teledyne Micro S-5. II. M / K Sheet Maker M / K Sheet Maker Parameters A 9000 M / K Series Computer Sheet is used to fabricate the sheets. The sheet former consists of forming and preseeding / drying sections, a white water and chemical re-circulation system, and a supply feed system. The supply consists of deinked press paper de-inked from a Southern factory. The weight of the base sheet remains constant. Oshenta percent of the white paper is made for the manufacture of the sheets. The pH of the white water is kept constant at 6.5. This is done by adding phosphoric acid to the white water holding tank. The calcium carbonate / lysium aluminate composition at 1% / 4% phosphoresis is prepared as described in part 1 of this example. III. Herty base test A test is carried out on Pilot Paper Machine No. 1. This machine is a 36-inch lowdrill fourdrinier sondesional machine. This provision is obtained by re-forming press paper from a press factory in Western Canada. The base weights of the final leaf produced is around 45 gsm. The speed is 175 fpm. The retention aid consists of a dual polymer system. The addition rate is 0.2 to 0.3 tf / Ton of Eclipse 1200 and Stylus 100. Running parameters of the paper machine The running parameters of the paper machine are given in Table I below. A solution of 5% phosphoric acid in the white water is added in tray of the paper machine to control the pH of the upper compartment.

TABLE I HEFTY PROOF ON PRESS PAPER 13-14-15 OF NOVEMBER 1995.

Table I continues Physical properties of calcium carbonates The physical properties of calcium carbonates are given in Table 2 below. Table II Physical properties of fillers Calcium carbonate / sodium liluminate / phosphoric acid composition is prepared as described in part I of this example.

IV Syracuse Test (State University of New York College of Environmental Science &Forest Engineering) Acid-Tolerant Calcium Carbonate Composition Acid-tolerant calcium carbonate is prepared as described in Sections I. Run parameters Se re-forms pulp paper from the West of Canada in pulp maker Barrasuda. The pH is immediately adjusted to 5.0 with concentrated sulfuric acid. After transferring the supply to the high consistency storage tanks, the pH is again adjusted to 5.0 with sulfuric acid filtered. From the high consistency tanks, the pulp is diluted to a low consistency in the feed tank that is located before the fan pump. The pH is adjusted to the desired upper compartment pH by adding 0.5% phosphoric acid to the top of the fan pump. The phosphoric flux is recorded for each pH and filter level. The calcium carbonate is added to the union "T" between the fan pump and the upper compartment.The pH is measured on a belt in the upper compartment.The gramage of the paper produced is maintained around 45 gsm. of 45. Results and conclusions I. Glitter in pH pads not adjusted In the first investigation, the initial pH is 6.0 or 7.0; but it is allowed to change. The results are given, for samples of acid-tolerant PCC and not treated in Figure 1.

The increase in brightness for all samples is similar.

This can be explained by observing the pH sambios. For all samples, the pH increase is shown in the graph in Figure 2. The amount depends on the treatment and concentration of the CCP. The brightness versus pH curve for mechanical pulp is a surva "S". typical are the equivalent point around pH 7. At the pH of 7.5, the brightness decreases to a constant level; therefore, since all the samples change to pH higher than 8, the alkaline dimming is observed in all the samples. It is concluded therefore that it is necessary to adjust the pH of the system in such a way that the pH does not sampie. Constant pH 1. Acid composition The use of various amounts of phosphoric acid is shown to "dampen" the system at the desired pH £ 6.5 or 7. 0) in the graph of Figure 3. At the pH of 7.0, the amount of phosphoric acid consumed is about half the sanity of the acid used to reach pH 6.5. The acid-fast precipitated calcium carbonate composition (AT-PCC) consumes less phosphoric acid than untreated PCC. 2. Brightness Several conclusions can be reached by analyzing the graphs shown in Figures 4 and 5. a. Phosphoric acid imparts a degree of tolerance to acid to calcium carbonate. The provisions that fit with phosphoresis have a higher brightness and surva intercepts the brightness targets. b. It takes approximately 4% of the escalenohedric calcium carbonate not treated in a non-phosphoric acid system to reach the original brightness target. II. Forming of the Leaf M / K The results, shown by the graph of the Figure 6, obtained are the M / K Sheet trainer validate the previous conclusions. Samples containing the calcium carbonate tolerant to acid / sodium aluminate / phosphoric acid composition give a superior gloss. III. Herty base test The results are plotted on the graph shown in Figure 7. The performance of acid-fast precipitated calcium carbonate / sodium aluminate / phosphoric acid composition exceeds the samples are untreated calcium sarbonate. The brightness results obtained in this test are similar to the experiments of cushions for brightness. The brightness curves for these two samples are parallel to each other and require approximately 4% untreated precipitated calsium carbonate to reach the original white brightness again. IV. Syracuse test (State University of New York School of Environmental Science and Forest Engineering) At the pH of 7.0, the data shown by the graph in Figure 8 and the graph in Figure 9 clearly show two trends. Acid-tolerant calcium carbonates show higher brightness than untreated salting sarbonates. The compositions of rhombic calcium carbonate show some advantages; however, these disadvantages can be attributed to the provision of the provision. At the pH of 6.5, rhombic salbonate salbonate samples outperform untreated rhombic samples.

Ground calcium carbonate compositions The suspension of acid-tolerated ground calcium carbonate can be obtained by the addition of sodium aluminate, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylate acid. Initially, 1% sodium alummate is added, in based on the dry weight of calcium carbonate, in a suspension of 20% solids of ground calcium carbonate. The inisial pH of the calcium carbonate suspension is 8.01. after mixing, 2-6% phosphoric acid and 1% acid polyacrylate are added, based on the dry weight of calcium carbonate. The pH is measured for each sample after 167 hours of maturation, as graphically shown in Figure 10. The initial pH of the suspension treated with 1% sodium aluminate / 1% acid polyacrylate / 4% phosphoric acid is measured. % and it is found to be 5.12. After 167 hours of maturation, the pH is measured again and found to be 5.83. EXAMPLE 3 Presented sodium carbonate essalenohydrous compositions An acid-tolerant scalenohedral hydrated calcium carbonate can be obtained by the addition of sodium aluminate, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polymaleic acid. - Initially, 0.5% sodium aluminate is added, based on the dry weight of calcium carbonate, in a suspension of solids at 19.7% of salsio sarbonate precipitated escalenohedron. The inisial pH of the calcium carbonate suspension is 8.83. After mixing, 4-6% phosphoric acid and 1% polymaleic acid are added, based on the dry weight of the calcium sarbonate. The pH is measured for each sample after 27 hours of maturation, as shown graphically in Figure 11. The initial pH of the suspension treated with 0.5% sodium aluminate / 1% polymaleic acid / 4% phosphoric acid is measured. % and it is found to be 5.76. after 27 hours of ripening, the pH is measured again and found to be 6.69. EXAMPLE 4 Compositions of Ground Calcium Carbonate A suspension of acid-tolerant ground calcium carbonate can be obtained by the addition of sodium aluminate, followed by the addition of a weak acid such as phosphorous acid and a polymeric acid such as acidic polyacrylate. Initially, 3% sodium aluminate, based on the dry weight of calcium carbonate, is added in a slurry of 20% solids of ground salsium sarbonate. The inisial pH of the calcium sarbonate suspension is 8.01. After mixing, 6% phosphoric acid and 1% acid polyacrylate are added, based on the dry weight of the salsium sarbonate. The pH of the suspension is measured and found to be 6.29. After 65 hours of maturation, the pH is measured again and found to be 6.74. EXAMPLE 5 Compositions of Ground Calcium Carbonate A carbonate suspension can be obtained from ground calcium acid tolerant by the addition of sodium aluminate, followed by the addition of a weak acid such as phosphoric acid and a polymeric acid such as polyacrylate acid. Inicially, 1% sodium aluminate is added, based on the weight of calcium carbonate, in a suspension of 20% solids of ground calcium carbonate. The initial pH of the calcium carbonate suspension is 8.01. After mixing, 1% phosphoric acid and 6% acid polyacrylate are added, based on the dry weight of the salted carbonate. The pH of the suspension is measured and found to be 6.02. After 64 hours of maturation, the pH is measured again and it is found that it is 6.59.

Claims (17)

1. CLAIMS 1. An acid-tolerant calcium carbonate characterized in that it comprises a mixture of salsium crbonate with at least about 0.1 percent, based on the dry weight of calcium carbonate, of sodium aluminate, together with at least about 0.1 per cent. cent, based on the dry weight of the carbonate of caclio, of one or more weak acids.
2. 2. The acid-tolerant calcium carbonate according to claim 1, characterized in that the weak acid of the group consisting of the phospho-serous acid is selessioned, and the mixtures are a weak solid-semistructured solid of the group consisting of acid polyacrylate, polymaleic acid, acid polycarboxylic, and msalas of them.
3. 3. Acid-tolerant calcium carbonate according to claim 1, characterized in that the weak acid is phosphoric acid.
4. 4. Acid-tolerant calcium carbonate according to claim 1, characterized in that the weak acid is a mixture of phosphoric acid and acid polyacrylate.
5. 5. The acid-tolerant calsium carbonate according to claim 1, characterized in that the weak acid is a mixture of phosphoric acid, polymaleic acid.
6. 6. The acid-tolerant calcium sarbonate according to claim 1, characterized in that the weak acid is a mixture of phosphorous acid and polycarboxylic acid. The acid-tolerant calcium sarbonate according to claim 1, characterized in that the sodium aluminate is present in an amount of about 1 to about 6 percent, based on the dry weight of the carbonate of salsium. 8. The acid tolerant salting sarbonate according to claim 1, characterized in that the total amount of the weak acid is present at a sanity of about 1 to about 8 percent, based on the dry weight of the calcium carbonate. 9. A process for the preparation of an acid-tolerant calcium sarbonate characterized in that it comprises: a) adjusting the pH of a calcium carbonate suspension to about -1-1 or 1-2-; b) adding to it, with mixing, at least about 0.1 percent, based on the dry weight of calcium carbonate, sodium alummate; c) adding to the mixture of b, with mezslado, an amount of a weak acid sufficient to bring the pH of the resulting mixture to approximately
7. 7. or less . 10. The process according to claim 8, characterized in that the weak acid is selected from the group consisting of phosphoric acid, and mixtures with a weak polymeric acid selected from the group consisting of acid polyacrylate, polymaleic acid, polycarboxylic acid, and mixtures thereof. the same. 11. The conformity process is the sarasterized claim 8 because the weak acid is phosphoric acid. 12. The process of compliance with the redirect 8 sarasterized because the weak acid is a mixture of acid phosphoric and acid polyacrylate. 13. The process according to claim 8, characterized in that the weak acid is a mixture of phosphoric acid, polymalene acid. 14. The process according to claim 8 characterized in that the weak acid is a mixture of phosphoric acid and polycarboxylic acid. 15. The process according to claim 8, characterized in that the sodium aluminate is present in an amount of about 1 to about 6 percent, based on the dry weight of the calcium carbonate. 16. The process according to claim 8 characterized in that the weak acid is present in an amount of about 1 to about 8 percent, based on the dry weight of calcium carbonate. 17. A method for improving the optical properties of neutral to weakly acidic paper by the addition of the sonformity submission is claim 1.