HYDROPHOBISED CALCIUM CARBONATE PARTICLES

Abstract

The present invention relates to a process for the reduction of pitch in an aqueous medium generated in a papermaking or pulping process, comprising the following steps: a) providing an aqueous medium comprising pitch generated in a papermaking or pulping process; b) providing a ground calcium carbonate and/or a precipitated calcium carbonate; c) providing a hydrophobising agent selected from an aliphatic carboxylic acid having between 5 and 24 carbon atoms; d) contacting the ground calcium carbonate and/or the precipitated calcium carbonate of step b) with the hydrophobising agent of step c) for obtaining a hydrophobised ground calcium carbonate and/or a hydrophobised precipitated calcium carbonate; and e) contacting the aqueous medium provided in step a) with the hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate obtained in step d), to the use of a hydrophobised ground calcium carbonate and/or a hydrophobised ground calcium carbonate for reducing the amount of pitch in an aqueous medium as well as to a hydrophobised ground calcium carbonate and/or a hydrophobised ground calcium carbonate and a composite of hydrophobised ground calcium carbonate and/or hydrophobised ground calcium carbonate and pitch.

Claims

1. A hydrophobised ground calcium carbonate and/or a hydrophobised precipitated calcium carbonate, wherein between 10% and 19% of the specific surface area of the ground calcium carbonate and/or the precipitated calcium carbonate is covered by a coating consisting of an aliphatic carboxylic acid having between 5 and 24 carbon atoms and reaction products thereof.

2. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein between 10% and 19% of the specific surface area of the ground calcium carbonate and/or the precipitated calcium carbonate is covered by a coating consisting of stearic acid and reaction products thereof.

3. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein between 13% and 17% of the specific surface area of the ground calcium carbonate and/or the precipitated calcium carbonate is covered by a coating consisting of an aliphatic carboxylic acid having between 5 and 24 carbon atoms and reaction products thereof.

4. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein between 13% and 17% of the specific surface area of the ground calcium carbonate and/or the precipitated calcium carbonate is covered by a coating consisting of stearic acid and reaction products thereof.

5. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein ground calcium carbonate (GCC) is selected from marble, chalk, calcite, dolomite, limestone, and any mixture thereof and/or the precipitated calcium carbonate (PCC) is selected from one or more of the aragonitic, vateritic and calcitic mineralogical crystal forms.

6. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the ground calcium carbonate particles and/or the precipitated calcium carbonate particles have a weight median particle diameter d.sub.50 value of from 0.1 to 50 m, measured according to the sedimentation method.

7. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the ground calcium carbonate particles and/or the precipitated calcium carbonate particles have a weight median particle diameter d.sub.50 value of from 0.1 to 15 m, measured according to the sedimentation method.

8. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the ground calcium carbonate particles and/or the precipitated calcium carbonate particles have a weight median particle diameter d.sub.50 value of from 0.5 to 5 m, measured according to the sedimentation method.

9. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the ground calcium carbonate particles and/or the precipitated calcium carbonate particles have a specific surface area of from 0.5 m.sup.2/g to 25 m.sup.2/g, measured using nitrogen and the BET method.

10. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the ground calcium carbonate particles and/or the precipitated calcium carbonate particles have a specific surface area of from 0.5 m.sup.2/g to 11 m.sup.2/g, measured using nitrogen and the BET method.

11. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, wherein the hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate is in powder form or in the form of granules or in the form of slurry.

12. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, which is hydrophobised ground calcium carbonate.

13. The hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1, which is hydrophobised precipitated calcium carbonate.

14. A composite comprising the hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate according to claim 1 and pitch.

15. A composite comprising hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate and adsorbed pitch, that is obtained by a process comprising the following steps: a) providing an aqueous medium comprising pitch from paper pulp, wherein the pitch is natural resin from the paper pulp, wherein the paper pulp is selected from the group consisting of mechanical pulp, ground wood, TMP (thermo mechanical pulp), chemithermomechanical pulp (CTMP), chemical pulp, and kraft or sulphate pulp, and wherein the pulp is not recycled pulp; b) contacting the aqueous medium provided in step a) with calcium carbonate consisting of a partially hydrophobised ground calcium carbonate and/or partially hydrophobised precipitated calcium carbonate so that the calcium carbonate adsorbs pitch in the aqueous medium to form a composite comprising the hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate and adsorbed pitch, wherein the aqueous medium is contacted with 0.05 to 20 wt.-% of the partially hydrophobised ground calcium carbonate and/or the partially hydrophobised precipitated calcium carbonate, based on the total weight of the aqueous medium, wherein the adsorbed pitch is natural resin from the paper pulp, and wherein the partially hydrophobised ground calcium carbonate and/or a partially hydrophobised precipitated calcium carbonate is ground calcium carbonate and/or precipitated calcium carbonate that has been mixed with a hydrophobising agent selected from the group consisting of one or more aliphatic carboxylic acids having between 5 and 24 carbon atoms at a temperature of at least 50 C. such that the hydrophobising agent is in a liquid or molten state and less than 20% of the specific surface area of the ground calcium carbonate and/or the precipitated calcium carbonate is covered by a coating consisting of the hydrophobising agent and reaction products thereof; and c) separating the composite comprising the hydrophobised ground calcium carbonate and/or the hydrophobised precipitated calcium carbonate and adsorbed pitch from the aqueous medium.

Description

DESCRIPTION OF THE FIGURES

[0155] FIG. 1: illustrates the normalised turbidity after the mineral treatment of the TMP filtrate. 100% corresponds to 349 NTU.

[0156] FIG. 2: illustrates the normalised chemical oxygen demand (COD) after the mineral treatment of the TMP filtrate. 100% corresponds to 3 644 mg O.sup.2 /dm.sup.3.

[0157] FIG. 3: illustrates the thermo gravimetric analysis of the mineral after the adsorption. The weight fraction lost was recorded between 200 and 1 000 C. and is corrected with the weight loss of the corresponding mineral powder.

[0158] FIG. 4: illustrates the normalised chemical oxygen demand (COD) values, gravimetry and turbidity of a TMP filtrate after an adsorption experiment with the mineral powders against the surface coverage of the mineral powders with stearic acid.

[0159] FIG. 5: illustrates the thermo gravimetric analysis of the mineral phase after the adsorption experiments against the surface coverage of the mineral powders with stearic acid. The weight loss of the starting mineral powders (prior the addition to the TMP filtrate) is subtracted (net loss).

[0160] FIG. 6: illustrates the hydrophobicity of the tested mineral powders with their range of stearic acid coverage X.sub.SA including also the high surface area (HSA) talc sample. The larger the area on the right side of the line the greater the hydrophobicity. The shaded area reflects the situation for talc.

[0161] FIG. 7: illustrates the adsorption isotherm based on turbidity data for untreated OMC-1, treated (15% surface coverage) ground calcium carbonate (GCC) and HSA-talc.

[0162] FIG. 8: illustrates the petroleum ether extractives content of the TMP filtrate 4 prior and post adsorption. The extractives are split into the groups: fatty acids, resin acids, lignans, sterols, sterylesters, triglycerides and an unknown fraction.

[0163] FIG. 9: illustrates the relative composition of the extractives groups in the TMP filtrate prior and post adsorption.

[0164] FIG. 10: illustrates the carbohydrate, acid soluble and acid insoluble content in the TMP filtrates prior and post adsorption.

EXAMPLES

[0165] A. Materials and Methods

[0166] 1. Pitch Containing Pulp

[0167] Four separate trials are provided using unbleached TMP that consisted of 70% spruce, the rest being composed of fir and a small part of pine. These TMP samples were collected in a paper mill in Switzerland. The mill uses 100% fresh water in their TMP plant. The fresh wet pulp was taken from the accept of the screen at a temperature of 90 C. before the bleaching step. The TMP was left overnight to cool down to room temperature (rt). The TMP was filtered through a filter of 2 m pore size (filter paper, circular 602 EH). The filtrate was checked under a light microscope (Olympus AX-70) for the absence of fibres and fibrils. The adsorption experiments were performed immediately after filtration. The pH of the filtrates was usually between 6.0 and 7.0. It was adjusted with 0.1 M sodium hydroxide to pH 7.0-7.5.

[0168] A pH titration of the electrophoretic mobility was made in order to quantify the colloidal stability of the wood resin droplets. This was done on a Malvern Zetasizer NS using 0.1 M hydrochloric acid and 0.1 M sodium hydroxide solutions. In addition the total electrochemical charge was determined by titrating the TMP filtrate with 0.0025 M poly-DADMAC [poly-(allyldimethyl-ammonium chloride) using a streaming current detector (SCD) from Mtek (PDC-03). In addition the ion content was quantified by ion chromatography on a Dionex DX 120 Ion-chromatograph.

[0169] After adjustment of the pH the TMP filtrate was distributed into glass bottles each containing 200 cm.sup.3 of the TMP filtrate. The desired amount and type of mineral was added either as a powder or dispersed in water. In most cases the mineral dosage was 10 g/dm.sup.3 and in the case of the isotherm the mineral dosage was varied between 2.5 and 50.0 g/dm.sup.3. For all samples in a trial row the same amount of water was added (usually 18 cm.sup.3). The bottles were equipped with a magnetic stirring bar, closed with an air-tight lid and stirred on a magnetic stirrer for 2 hours. After this time the magnetic stirring bar was removed and the experimental mixtures centrifuged (Jouan C 312 by IG Instruments) for 15 minutes at 2 600 g. Two phases were collected; an upper liquid phase and a lower sediment mineral-containing phase. Centrifugation of the untreated TMP filtrate did not show any sediment. However, sedimentation of the pure mineral dispersions showed in some cases air bubbles with entrapped mineral particles.

[0170] The upper liquid phase was analysed for turbidity by means of a NOVASINA 155 model NTM-S turbidity probe. The particle size was measured by photon correlation spectroscopy on a Malvern Zetasizer NS without any further treatment or dilution. Chemical oxygen demand (COD) was measured using a Lange CSB LCK 014, covering a range 1 000-10 000 mg/dm.sup.3 with a LASA 1/Plus cuvette. 100 cm.sup.3 of the liquid phase was dried in an aluminium beaker at 90 C. for 12 hours and the residue weighed to provide a result for the gravimetric residue.

[0171] The properties of the four TMP samples are summarized in the following Table 1. The presented ranges are based on the standard deviation of three independent experiments.

TABLE-US-00001 TABLE 1 TMP filtrate 1 TMP filtrate 2 TMP filtrate 3 TMP filtrate 4 Turbidity [NTU].sup.[1] 349 1 358 1 393 8 497 Chemical Oxygen 3 644 21 3 944 27 3 140 49 4 350 40 demand [mg/dm.sup.3] Gravimetry [g/dm.sup.3] 3.11 0.0005 3.43 0.005 2.84 0.014 3.57 Electrochemical 2.3 1.3 1.1 0.3 charge (SCD) [Eq/g] pH 7.0 7.0 7.0 7.2 Conductivity 926 1 500 1 140 1 200 [S/cm] Na.sup.+ [mM] 9.5 12.9 9.1 9.2 K.sup.+ [mM] 1.1 1.1 1.0 1.2 Ca.sup.2+ [mM] 1.4 0.9 0.8 1.4 Mg.sup.2+ [mM] 0.2 0.2 0.2 0.3 Cl.sup. [mM] n.a. 0.7 0.5 0.7 SO.sub.4.sup.2 [mM] n.a. 0.4 0.4 0.4 .sup.[1]NTU = Nephelometric turbidity uni

[0172] In one trial set up the upper liquid phase was also analysed for the wood extractives content and the carbohydrate content. The wood extractives content was determined by extraction of the TMP filtrate with petroleum (Saltsman et al., 1959, Estimation of tall oil in sulphate black liquor, Tappi, 42(11), 873). The GC-FID analysis for the group determination in the wood extractives was performed according to the method of rsa and Holmbom (rsa et al., 1994, A convenient method for the determination of wood extractives in papermaking process waters and effluents; J. Pulp. Pap. Sci., 20(12), 361). The samples were hydrolysed with sulphuric acid at 121 C. in an autoclave according to SCAN-CM 71:09. The solubilised monosaccharides were quantified using an ion chromatograph coupled to a pulsed amperometric detector (IC-PAD). The acid insoluble residue was determined gravimetrically and the acid soluble residue (lignin) was measured with UV spectrophotometry at 205 nm and quantified using an absorption coefficient of 110 dm.sup.3/(gcm).

[0173] The lower sedimented mineral-containing phase was analysed by thermo gravimetric analysis (TGA) on the Mettler Toledo TGA/STDA 851e. The samples were heated from 20 to 1 000 C. with a heating rate of 20 C./min. The weight loss was recorded between 200 and 1 000 C.

[0174] 2. Minerals

[0175] Various mineral powders were tested in this study. On one hand two Finnish talc grades were used as references. One is commercially available talc, Finntalc P05 from Mondo Minerals and the other talc grade is derived from Finntalc P05 with subsequent comminution and delamination to generate fineness, high aspect ratio and enhanced specific surface area. The Finntalc P05 will be labelled as LSA (low surface area) talc and the delaminated quality will be labelled as high surface area (HSA-talc) talc. The specific surface areas and particle sizes of the various mineral powders are reported in the following Table 2.

TABLE-US-00002 TABLE 2 Specific surface d.sub.50/m Electrophoretic area (Sedigraph mobility/ Name Abbrev. Type [m.sup.2/g] 5120) 10.sup.8 m.sup.2/(Vs) Finntalc P05 LSA- Talc 8.7 2.4 3.4 talc Delaminated HSA- Talc 45.0 0.8 3.9 Finntalc P05 talc Omyacarb OMC- Calcium 1.3 n.a. n.a. 10 10 carbonate Omyacarb 1 OMC-1 Calcium 3.9 1.5 1.7 carbonate Comminuted HSA- Calcium 10.2 0.6 n.a. Omyacarb 1 GCC carbonate

[0176] The specific surface area, particle size (d.sub.50) and electrophoretic mobility are determined in a 0.01 M NaCl solution as medium for the suspension of the investigated minerals.

[0177] On the other hand various ground calcium carbonate grades were tested. One is commercially available as Omyacarb 10 (OMC-10), another as Omyacarb 1 (OMC-1) and a third quality was produced from OMC-1 by chemical free grinding to obtain a high surface area ground calcium carbonate (HSA-GCC) compared to OMC-1 and OMC-10, which both are low surface area ground calcium carbonates. The ground calcium carbonate samples were supplied by Omya and origin from Avenza, Italy.

[0178] The specific surface area was measured by nitrogen adsorption on a Micromeritics Tristar based on the BET adsorption model according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Buchner funnel, rinsed with deionised water and dried overnight at 90 to 100 C. in an oven. Subsequently the dry cake is ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130 C. until a constant weight is reached.

[0179] The weight median equivalent spherical hydrodynamic particle diameter (d.sub.50) was measured under sedimentation with a Micromeritics Sedigraph 5120. The sedimentation method is an analysis of sedimentation behaviour in a gravimetric field. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonic.

[0180] 3. Stearic acid treatment

[0181] The stearic acid was a high purity grade from Sigma Aldrich. The GCC powder was filled into the MTI mixer (Type M3/1.5) which was heated to 80 C. The powder was stirred for a period of 2.5 min at 3 000 rpm. The stearic acid was added to the pre-heated powder. The amount of stearic acid was calculated according to Eq 1 as defined above to derive a product with a defined coverage factor. The blend was again mixed for 2.5 min at 3 000 rpm. The mixer was opened, the powder manually mixed to ensure even distribution in the mixer and closed again for another 2.5 minutes mixing time at 3000 rpm. During the whole procedure the temperature of the mixer was kept at 80 C.

[0182] For the calculation of the surface coverage Eq 2 was used in which m.sub.SA is the mass of stearic acid (SA) that has to be added to treat 1 g of calcite with a surface coverage fraction by stearic acid X.sub.SA. This is calculated with the specific surface area of the mineral .sub.m obtained via nitrogen adsorption, the molecular weight of stearic acid Mw.sub.SA, the Avogadro constant N.sub.A and the surface area that is covered by one stearic acid molecule A.sub.SA which is 0.26 nm.sup.2.

[00001]$\begin{array}{cc}{m}_{\mathrm{SA}}=\frac{{}_M.Math.{\mathrm{Me}}_{\mathrm{SA}}.Math.X_{\mathrm{SA}}}{A_{\mathrm{SA}}.Math.N_A}& \left[2\right]\end{array}$

[0183] 4. Semi-Quantitative Wetting Test

[0184] Mixtures of water and ethanol were prepared in volume ratios of 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90 and 0:100. 50 cm.sup.3 of each of these mixtures were placed in a 100 cm.sup.3 beaker. About 0.5-1.0 g of the powder in question was carefully put on top of the liquid. The wetting behaviour was quantified by the time needed for the powder to be wetted according to the following judgment:

[0185] 0.fwdarw. immediate wetting of the powder (sinks within 30 seconds)

[0186] 0.25.fwdarw. within 5 minutes all of the powder is wetted

[0187] 0.5.fwdarw. after 5 minutes more than 50% of the powder is wetted

[0188] 0.75.fwdarw. after 5 minutes less than 25% of the powder is wetted

[0189] 1.fwdarw. the powder is not wetted within 5 minutes

[0190] B. Results

[0191] 1. Surface Coverage with Stearic Acid and Pitch Adsorption Ability

[0192] For the determination of the degree of surface coverage with stearic acid and its pitch adsorption ability, several samples, namely OMC-10, OMC-1 and HSA-GCC, were treated with 30% and 60% stearic acid (based on surface area) and were studied to screen the influence of the degree of stearic acid treatment and the surface area. For comparison reasons, untreated ground calcium carbonate and LSA talc were also tested.

[0193] The TMP filtrate used was sample 1 (sampled in November 2009) which was analyzed as described above in Table 1. The electrophoretic mobility of the particles in the TMP filtrate 1 was found to be 0.510.sup.8 m.sup.2/(Vs). The EM remained constant within the relevant pH range of 7-8.

[0194] It has been found that ground calcium carbonate products with 60% of the surface covered with stearic acid could not be wetted by the TMP filtrate, leading to foam and undefined phases after centrifugation. Thus, no results were obtained for these products. Even with the 30% surface treated samples wetting was a problem. Interestingly, the wetting improved during the experiments, suggesting thus the adsorption of surface active compounds from the TMP filtrate.

[0195] The turbidity of the TMP filtrate was clearly reduced as a result of mineral addition (cf. FIG. 1). An increased specific surface area (SSA) further improved the removal efficiency for colloidal material. In the case of the 30% surface covered ground calcium carbonate the turbidity was reduced down to 77% of the original 349 NTU with the OMC-10, down to 41% with the OMC-1 and down to 21% with the HSA-GCC. The treatment with stearic acid increased the efficiency of colloidal pitch adsorption. Both, the surface treated and the surface untreated ground calcium carbonate products reduced the turbidity even more efficiently than the LSA talc, which gave only a reduction of 50%. The observed efficiency can, however, also be caused by an agglomeration process of wood resin droplets. The particle size prior and post adsorption in the liquid phase did slightly decrease.

[0196] Because the size analysis in the liquid phase did not include agglomerates that settled during centrifugation it is also important to consider other analyses like COD (cf. FIG. 2) or TGA (cf. FIG. 3). The COD analysis showed a slightly different trend. On the other hand the values for the OMC-10 as well as both the fatty acid treated HSA-GCC and the untreated HSA-GCC did not show significantly different values. The only difference was observed for the OMC-1 for which, oppositely to turbidity, the untreated ground calcium carbonate was seen to be more efficient. A possible explanation for these contrary observations may be that different species are adsorbed onto treated and untreated ground calcium carbonate powders. In the case of the treated ground calcium carbonate powders, the adsorbable compounds contribute rather to turbidity and are thus of colloidal nature and in the case of the untreated ground calcium carbonate powder the adsorbable species is rather of dissolved nature, contributing preferentially to COD rather than to turbidity. Also the talc powder shows very much the same efficiency as the ground calcium carbonate powders. The analysis of the mineral phase after the adsorption experiment confirmed again the turbidity analysis. The adsorbed amount on the mineral surface increased with the specific surface area. Partially hydrophobised ground calcium carbonate adsorbed slightly more material than native ground calcium carbonate, i.e. not hydrophobised and not surface treated ground calcium carbonate. Both, hydrophobised and native ground calcium carbonate adsorbed more material than talc.

[0197] Furthermore, it has been found that the treatment with ground calcium carbonate clearly increased the pH from 7.0 to 7.8. Also the conductivity increased from 926 S/cm to 980 S/cm. Very crucial in paper mill water circuits is the calcium ion concentration. Calcium ions can be one of the main contributors to pitch agglomeration. The concentration increased from 1.45 mM to 1.90 mM. The addition of talc had no effect on the calcium ion concentration.

[0198] Accordingly, the treatment of the ground calcium carbonate surface with stearic acid is beneficial for pitch adsorption but too much surface treatment with stearic acid can cause wetting problems.

[0199] 2. The Degree of Surface Coverage with Stearic Acid

[0200] It was tried to optimise the amount of stearic acid surface treatment between 0 and 30% surface coverage X.sub.SA. OMC-1 was used for this optimisation. Again the TMP filtrate 1 was used. The electrophoretic mobility (EM) of the particles in the original TMP filtrate was 0.810.sup.8m.sup.2/(Vs) and no dramatic change of the EM was observed within the relevant pH range (7-8) for this study.

[0201] Already during the trial it was observed that with a higher surface coverage with stearic acid the immersion of the powder into the TMP filtrate was harder and consequently a foamy layer formed. This undefined phase clearly affected the turbidity measurement (cf. FIG. 4). An optimum in turbidity reduction was obtained at 15% surface coverage. From COD and gravimetry measurements one could not distinguish between the different degrees of treatment. The thermo gravimetry measurement (cf. FIG. 5) also showed the optimum dosage to be about 15%. Finally, the semi-quantitative hydrophobicity test (cf. FIG. 6) showed that the sample with about 15% surface coverage had a comparable hydrophobicity to that of talc.

[0202] 3. Adsorption Isotherm

[0203] For further studies the OMC-1 product, with a specific surface area of 3.9 m.sup.2/g and a surface coverage with stearic acid of about 15%, was used.

[0204] In order to quantify the effect of the stearic acid treatment adsorption isotherms were recorded for an untreated OMC-1 and an OMC-1 with about 15% surface coverage by stearic acid. As a comparison the high surface area talc (HSA talc) was also included. The isotherm was recorded at 24 C. For this work, the TMP filtrate 3 was used providing an electrophoretic mobility of the particles of 0.810.sup.8 m.sup.2/(Vs). Within the relevant pH range of 7-8 the EM changed only slightly. The analyses of the TMP filtrate prior to the adsorption experiments are shown in Table 1 above.

[0205] An adsorption isotherm presents the loading on the mineral phase in equilibrium (.sup.turb) versus the equilibrium concentration in the liquid phase (c.sub.eq.sup.turb), as determined by turbidity, i.e. in this case turbidity was the parameter that contained the information about the equilibrium concentration of colloids. The loading of turbidity causing species on the mineral was calculated with the following Eq 3, by subtracting the equilibrium concentration in the liquid phase (c.sub.eq.sup.turb) from the initial turbidity prior to adsorption (c.sub.o.sup.turb).

[00002]$\begin{array}{cc}{}_{\mathrm{eq}}^{\mathrm{turb}}=\frac{c_0^{\mathrm{turb}}-c_{\mathrm{eq}}^{\mathrm{turb}}}{m_M}& \left[3\right]\end{array}$

[0206] The Langmuir adsorption isotherm is given by Eq 4 below. is the loading of adsorbate on the adsorbent (mineral) in equilibrium. c.sub.eq is the bulk concentration of the adsorbate in equilibrium. The Langmuir constant (K.sub.L) indicated that the untreated ground calcium carbonate powder has a higher affinity (0.025 (NTU).sup.1) for the colloidal material than the partially hydrophobised (0.013 (NTU).sup.1) (cf. Table 3). The HSA-talc grade had the lowest affinity (0.007 (NTU).sup.1) with the lowest K.sub.L. The maximum loading (F.sub.max) increases from the untreated (25 NTU/g) to the treated (37 NTU/g) OMC-1 as can be gathered from the following Table 3 and FIG. 7.

[00003]$\begin{array}{cc}=\frac{c_{\mathrm{eq}}.Math.K_L.Math.{}_{\max }}{1+c_{\mathrm{eq}}.Math.K_L}& \left[4\right]\end{array}$

TABLE-US-00003 TABLE 3 95% Confidence Mineral Parameter limits Untreated K.sub.L [(NTU).sup.1] 0.025 0.019 0.032 .sub.max [NTU/g] 24.9 23.0 26.0 Treated K.sub.L [(NTU).sup.1] 0.013 0.009 0.018 .sub.max [NTU/g] 37.1 32.9 41.4 HSA talc K.sub.L [(NTU).sup.1] 0.007 0.003 0.011 .sub.max [NTU/g] 212.4 127.0 252.2

[0207] The adsorption isotherm parameters are based on a non-linear least squares (NLLS) fit to the Langmuir equation (Eq 4) performed by TableCurve 2D.

[0208] The differences between the fitted parameters K.sub.L and .sub.max are significant. As a result of the high specific surface area of the HSA talc (45 m.sup.2/g) the maximum loading of colloidal particles on the talc (212 NTU/g) was proportionally higher, in relation to the specific surface area of the OMC-1, having only about 4 m.sup.2/g.

[0209] 4. Chemical Analysis

[0210] For the chemical analysis and agglomeration tests, TMP filtrate 4 was collected which had an electrophoretic mobility of the particles at the original pH of 7.2 of 0.610.sup.8 m.sup.2/(Vs). Again, the EM was stable in the relevant pH range of 7-8. The properties of the TMP filtrate 4 are listed in Table 1 above.

[0211] In order to cover the relevant regions of the adsorption isotherms, different amounts of mineral were added to the TMP filtrate. In the case of the HSA-talc a talc dosage of 0.4 g/dm.sup.3 was provided to represent the region where the dissolved and colloidal substances are in excess and a talc dosage of 4 g/dm.sup.3 to represent the region where the talc surface is available in excess. Because the specific surface area of the ground calcium carbonate powders is much lower (cf. Table 2 above) the mineral addition was increased to 8 and 40 g/dm.sup.3.

[0212] The petroleum ether extractives content of the TMP filtrate 4 was 142 mg/dm.sup.3 as outlined in the following Table 4 and FIG. 8. Table 4 further summarizes the carbohydrate content, acid soluble (lignin) content and acid insoluble content of the TMP filtrate 4 as further described below.

TABLE-US-00004 TABLE 4 Type Amount/mg/dm.sup.3 Extractives Fatty Acids 9.1 Resin Acids 32 Lignans 3.5 Sterols 2.9 Sterylesters 26 Triglycerides 63 Unknown 5.1 Total: 142 Carbohydrates 1 052 Acid soluble (Lignin) 527 Acid insoluble 403 Total: 1 982

[0213] The petroleum ether extractives content of the TMP filtrate 4 is around 4% of the total material in the TMP filtrate. The main constituents of the extractives were triglycerides (44%, triacylglycerides) followed by resin acids (23%) and sterylesters (18%). Free fatty acids (6%), lignans (2%) and sterols (2%) were rather a minor fraction. The remaining 5% is of unknown origin. As can be gathered from FIG. 5, the addition of 0.4 g/dm.sup.3 HSA-talc reduced the extractives content to 120 mg/dm.sup.3 and the addition of 4 g/dm.sup.3 resulted in an extractives content of 32 mg/dm.sup.3. The ratio of the extractives groups was in both cases not affected (cf. FIG. 9). The dosage of 8 g/dm.sup.3 OMC-1 reduced the extractives content to 107 mg/dm.sup.3 and 40 g/dm.sup.3 to 28 mg/dm.sup.3, respectively. The ratio of the extractives groups was not affected for the low mineral dosage but was strongly affected for the high mineral dosage. A similar picture was observed for the hydrophobised OMC-1 (OMC-1 Treated). The lower mineral dosage led to a residual amount of extractives of 73 mg/dm.sup.3 and the higher mineral dosage to 23 mg/dm.sup.3, respectively.

[0214] In addition also the water-soluble part of the TMP filtrate was analysed. This analysis is split into three fractions: i) carbohydrates, ii) acid soluble (lignins) and iii) acid insoluble (wood resin, salts etc.). In this respect it is utilized that only the lignin in the acid soluble fraction has its absorption maximum at 280 nm in UV-spectroscopy. Hence, by measuring the UV spectrum one can determine the soluble lignin contained in the acid soluble fraction. The original TMP filtrate 4 contains 1 052 mg/dm.sup.3 carbohydrates, 527 mg/dm.sup.3 acid soluble (lignin) and 403 mg/dm.sup.3 acid insoluble materials (cf. FIG. 10, Table 4). The carbohydrates content during the talc treatment was reduced only slightly (1 034 mg/dm.sup.3) for the low talc dosage but a large reduction in the carbohydrates content was observed for the high talc dosage (696 mg/dm.sup.3). The untreated OMC-1 adsorbed only a very minor fraction of the carbohydrates. 1 024 mg/dm.sup.3 for the low dosage and 952 mg/dm.sup.3 for the high OMC-1 dosage, respectively, were measured. Also the hydrophobised OMC-1 adsorbed a very minor amount. For both mineral dosages the carbohydrate content was around 980 mg/dm.sup.3. In the case of the acid soluble (lignin) fraction the reduction after the mineral treatment was <3%, except for the HSA-talc with 4 g/dm.sup.3. In this case the remaining lignin content was 396 mg/dm.sup.3. The acid insoluble fraction, finally, varied proportionally to the extractives reduction.

[0215] The pH of the samples increased as a result of the alkaline nature of the mineral powders. The pH for the lower mineral dosages was between 7.3 and 7.6 and for the higher dosages between 7.7 and 7.8.

[0216] The calculated ratios between dissolved and colloidal material in the TMP filtrate 4 prior and post adsorption are given in the following Table 5.

TABLE-US-00005 TABLE 5 Dissolved/Colloidal ratio HSA talc 0.4 g/dm.sup.3 1.3 HSA talc 4 g/dm.sup.3 4.4 OMC-1 8 g/dm.sup.3 1.0 OMC-1 40 g/dm.sup.3 1.1 OMC1 Treated 8 g/dm.sup.3 1.4 OMC1 Treated 40 g/dm.sup.3 0.8

[0217] The ratios of the amount of extractives and the amount of carbohydrates plus acid soluble lignin are calculated similar to Eq 2. It can be seen in Table 5 that in the case of high talc dosage (excess of talc surface) the ratio of dissolved to colloidal substances is clearly shifted towards the dissolved fraction (4.4). A possible explanation could be that the pitch droplets adsorb together with their stabilising carbohydrate layer (low mineral dosage), thus, resulting in a constant ratio. After having removed most of the colloidal fraction (high mineral dosage) the talc adsorbs also dissolved materials like carbohydrates, lignins and dissolved wood resin constituents (resin acids, etc), whereas the ground calcium carbonate does not adsorb material from the dissolved fraction. Also the adsorption isotherms for the colloidal substances in the form of the Langmuir constant K.sub.L showed these different adsorption preferences. Talc showed the lowest affinity for the colloidal fraction and the untreated GCC the highest affinity. Interestingly, the affinity of the hydrophobised GCC was in between.

[0218] Another observation is that, at high ground calcium carbonate dosages, a substantial amount of resin acids was found in the aqueous phase. A possible explanation could be that the resin acids were dissolved during the adsorption experiment. It is well known that about 20-30 mg/dm.sup.3 are dissolved in the pH range of 7 to 8. The pH after the adsorption experiments was measured as being 7.8 for the high mineral dosages. Because the pH before the extraction procedure is acidified, the resin acids will become insoluble again and will be measured as a part of the extractives.

[0219] Thus, the effective reduction of colloidal material, i.e. pitch, from the sample is favored by the hydrophobised ground calcium carbonate, whereas the pick-up of dissolved carbohydrates fractions is favored by talc.

[0220] Consequently, an especially hydrophobised ground calcium carbonate has been shown to adsorb readily pitch species in the paper making environment. Typical pitch control talc appears to have insufficient surface area to cope with all the probable constituents contained in a pulp. Hydrophobised ground calcium carbonate and/or hydrophobised precipitated calcium carbonate or combinations thereof with talc provide possibilities for synergistic water system treatments as for TMP wood pitch.