ADSORBING AND/OR REDUCTION OF THE AMOUNT OF ORGANIC MATERIALS IN AN AQUEOUS MEDIUM BY USING COLLOIDAL PRECIPITATED CALCIUM CARBONATE

Abstract

The present invention relates to the use of a colloidal precipitated calcium carbonate (cPCC) for adsorbing and/or reducing the amount of at least one organic material in an aqueous medium.

Claims

1. A method for adsorbing and/or reducing the amount of at least one organic material in an aqueous medium comprising contacting the aqueous medium with a colloidal precipitated calcium carbonate (cPCC) to adsorb and/or reduce the amount of at least one organic material in an aqueous medium, wherein the cPCC has a specific surface area of at least 5.0 m.sup.2/g, measured using nitrogen and the BET method.

2. The method according to claim 1, wherein the cPCC has a specific surface area from 5.0 m.sup.2/g to 200.0 m.sup.2/g, preferably from 10.0 m.sup.2/g to 100.0 m.sup.2/g and most preferably from 15.0 m.sup.2/g to 50.0 m.sup.2/g, measured using nitrogen and the BET method.

3. The method according to claim 1, wherein the cPCC comprises aggregates having a weight median particle diameter d.sub.50 value from 0.1 to 50.0 m, preferably from 0.2 to 25.0 m, more preferably from 0.3 to 10.0 m and most preferably from 0.4 to 5.0 m, measured according to the sedimentation method.

4. The method according to claim 3, wherein the cPCC aggregates consist of single crystals having a weight median particle diameter d.sub.50 value from 0.01 to 5.0 m, preferably from 0.02 to 2.5 m, more preferably from 0.03 to 1.0 m and most preferably from 0.04 to 0.5 m, measured according to the sedimentation method.

5. The method according to claim 1, wherein the cPCC is in powder form or in form of an aqueous suspension comprising the cPCC and having a pH of 6.0, measured at 20 C. (1 C.).

6. The method according to claim 1, wherein the cPCC is a) surface-treated with at least one aliphatic carboxylic acid having a total amount of carbon atoms from C4 to C24, preferably stearic acid, and/or b) stabilized with one or more dispersants, preferably one or more cationic and/or anionic dispersants.

7. The method according to claim 1, wherein the cPCC is used in combination with at least one further adsorbing material selected from the group comprising talc, kaolin, calcined kaolin, natural calcium carbonate selected from marble, chalk, calcite, limestone and dolomite, non-colloidal PCC, gypsum, silicate-containing minerals, hydroxide-containing minerals, calcium sulfoaluminates, plastic particles, organic pigments, surface-reacted calcium carbonate, hydrophobised GCC, hydrophobised PCC and mixtures thereof, preferably talc, surface-reacted calcium carbonate, hydrophobised GCC, hydrophobised PCC and mixtures thereof.

8. The method use according to claim 7, wherein the amount of the at least one further adsorbing material is 25.0 wt.-%, preferably 10.0 wt.-%, more preferably 5.0 wt.-% and most preferably 2.0 wt.-%, based on the total dry weight of cPCC and the at least one further adsorbing material.

9. The method according to claim 1, wherein the aqueous medium comprising at least one organic material is generated in a papermaking or pulping process, preferably the aqueous medium is selected from bleached and unbleached pulp such as mechanical pulp, ground pulp, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), kraft pulp, sulfate pulp, recycled pulp and mixtures thereof.

10. The method according to claim 1, wherein the at least one organic material in the aqueous medium is at least one dissolved and/or colloidal material generated in a papermaking or pulping or paper recycling process.

11. The method according to claim 10, wherein the at least one dissolved and/or colloidal material is/are a) originated from wood and/or wood resins, preferably selected from the group comprising polysaccharides, such as hemicelluloses, lignin, starch and pectins, resin acids, fats, fatty acids, fatty alcohols, terpenes, terpenoids, polyisoprenes, sterols, steryl esters, waxes and mixtures thereof, and/or b) originated from paper coatings, coating binders, printing inks, de-inking chemicals, hot melts and/or adhesives.

12. The method according to claim 1, wherein the cPCC is added to the aqueous medium in an amount from 0.05 to 90.0 wt.-%, preferably from 0.1 to 50.0 wt.-%, more preferably from 0.25 to 25.0 wt.-%, even more preferably from 0.5 to 10.0 wt.-% and most preferably from 0.5 to 5.0 wt.-%, based on the total weight of oven dry (100 C.) fibers in the aqueous medium.

13. The method according to claim 1, wherein the at least one organic material in the aqueous medium is at least one endocrine disrupting compound (EDC), preferably the at least one EDC is selected from the group comprising endogenous hormones such as 17[beta]-estradiol (E2), estrone (E1), estriol (E3), testosterone or dihydro testosterone; phyto and myco hormones such as [beta]-sitosterol, genistein, daidzein or zeraleon; drugs such as 17[alpha]-ethinylestradiol (EE2), mestranol (ME), diethylstilbestrol (DES), and industrial chemicals such as 4-nonyl phenol (NP), A-tert-octyl phenol (OP), bisphenol A (BPA), tributyltin (TBT), methylmercury, phthalates, PAK or PCB.

14. The method according to claim 1, wherein after the addition of the cPCC a) the turbidity of the aqueous medium is reduced compared to the turbidity of an aqueous medium without the use of the cPCC, and/or b) the chemical oxygen demand (COD) of the aqueous medium is reduced compared to the COD of an aqueous medium without the use of the cPCC, and/or c) the electrochemical charge (SCD) of the aqueous medium is increased compared to the electrochemical charge of an aqueous medium without the use of the cPCC.

15. The method according to claim 1, wherein the aqueous medium, after the addition of the cPCC in an amount of at least 10 g/L aqueous medium, has a) a turbidity being at least 20%, preferably at least 40.0%, more preferably at least 50.0%, even more preferably at least 75.0% and most preferably at least 90.0% below the initial turbidity, i.e. the turbidity (NTU) of the aqueous medium before the addition of the cPCC, and/or b) a chemical oxygen demand (COD) being at least 1.0%, preferably at least 5.0%, more preferably at least 10.0%, even more preferably at least 15.0%, still more preferably at least 20.0% and most preferably at least 50.0% below the initial COD, i.e. the COD (mg/L) of the aqueous medium before the addition of the cPCC, and/or c) an electrochemical charge (SCD) being at least 5%, preferably at least 15.0%, more preferably at least 20.0%, even more preferably at least 25.0% and most preferably at least 50.0% above the initial electrochemical charge, i.e. the electrochemical charge (Eq/g) of the aqueous medium before the addition of the cPCC.

Description

EXAMPLES

Measurement Methods

[0154] BET Specific Surface Area of a Material (m.sup.2/g)

[0155] BET specific surface area values were determined using nitrogen and the BET method according to ISO 9277.

Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Grain Diameter (d.sub.50) of Particulate Material

[0156] Weight median grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph 5100.

[0157] 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% by weight of Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and ultrasonic.

Suspension pH Measurement

[0158] The pH of a suspension was measured at 23 C. using a Mettler Toledo Seven Easy pH meter equipped with the corresponding Mettler Toledo pH expansion unit and a Mettler Toledo InLab 730 Expert Pro pH electrode.

[0159] A three point calibration (according to the segment method) of the instrument is first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20 C. (from Aldrich).

[0160] The reported pH values are the endpoint values detected by the instrument (the endpoint is when the measured signal differs by less than 0.1 mV from the average over the last 6 seconds).

Conductivity (mS/cm)

[0161] The conductivity was measured at 25 C. by using Mettler Toledo Seven Multi instrumentation equipped with the corresponding Mettler Toledo conductivity expansion unit and a Mettler Toledo InLab 730 conductivity probe, directly following stirring the aqueous medium at 1 500 rpm using a pendraulik tooth disc stirrer.

[0162] The instrument is first calibrated in the relevant conductivity range using commercially available conductivity calibration solutions from Mettler Toledo. The influence of temperature on conductivity is automatically corrected by the linear correction mode.

[0163] Measured conductivities are reported for the reference temperature of 20 C. The reported conductivity values are the endpoint values detected by the instrument (the endpoint is when the measured conductivity differs by less than 0.4% from the average over the last 6 seconds).

Weight Solids (% by Weight) of a Material in Suspension

[0164] The weight of solids is determined by dividing the weight of the solid material by the total weight of the aqueous suspension.

[0165] The weight of the solid material is determined by weighing the solid material obtained by evaporating the aqueous phase of suspension and drying the obtained material to a constant weight

Gravimetric Analysis of a Suspension (Mg/Dm.SUP.3.)

[0166] For a gravimetric analysis, a 100 cm.sup.3 sample of aqueous medium was placed into a pre-weighed aluminium beaker and dried in an oven (90 C., 24 h) to get a total amount of non-volatile residue in the aqueous medium, i.e. any organic and inorganic material.

Suspension Turbidity Analysis (NTU)

[0167] 45 cm.sup.3 samples were used to analyse turbidity caused by colloidal substances by means of a NOVASINA 155 Model NTM-S turbidity probe. The measurement was carried out on the aqueous liquid phase of the samples obtained by separating the solid substances from the liquid phase, e.g. by filtration. This instrument transmits light in the near infrared spectrum through an optical fibre probe where the emerging beam is scattered by small particles in suspension. Light scattered back at 180 is collected by parallel optical fibres in the probe and focused onto a photo-diode. The resulting signal is amplified and displayed directly in Nephelometric Turbidity Units (NTU), defined as the intensity of light at a specified wavelength scattered, attenuated or absorbed by suspended particles, at a method-specified angle from the path of the incident light, compared to a synthetic chemically prepared standard. Interference from ambient light is eliminated by the adoption of a modulated transmission signal, removing the need for light-tight sample handling systems.

Chemical Oxygen Demand (COD, mg O.sub.2/dm.sup.3)

[0168] 2 cm.sup.3 samples were used to make chemical oxygen demand (COD) analyses, which give a value for the total organic content in the aqueous medium. The measurement was carried out on the aqueous liquid phase of the samples obtained by separating the solid substances from the liquid phase, e.g. by filtration. The COD analysis expresses the quantity of oxygen necessary for the oxidation of organic materials into CO.sub.2 and was measured using a Lange CSB LCK 014, range 1 000-10 000 mg dm.sup.3 with a LASA 1/plus cuvette.

Streaming Current Detector Equivalency (SCD, Eq/g)

[0169] SCD titration measures the total electrochemical charge of the dissolved and colloidal substances in suspension and was evaluated by using Mtek PDC-03 instrumentation.

Materials

TMP Sample

[0170] The TMP sample consisting of 70 wt.-%, based on the total weight of oven dry (100 C.) fibers in the sample, of spruce, the rest being composed of fir and a small part of pine, was collected from a Swiss paper mill directly after the screen and prior to the bleaching step. The TMP sample was collected at a temperature of 95 C. It had a consistency of 2.3% and a pH of 6.5. The sample was cooled overnight to room temperature (rt) and filtered through a 2 m filter to remove all fines and fibers. Light microscopic evaluation after filtration did not reveal the presence of any fibers. The TMP filtrate had a pH of 7.0, conductivity of 1.27 mS/cm and a turbidity of 490 NTU. The electrolyte concentration and composition is shown in Table 1.

TABLE-US-00001 TABLE 1 electrolyte concentration and composition of the TMP sample TMP filtrate Na.sup.+/mM 12.74 0.04 K.sup.+/mM 1.81 0.13 Ca.sup.2+/mM 1.97 0.07 Mg.sup.2+/mM 0.37 0.00 Cl.sup./mM 1.02 0.11 NO.sup.2/mM <0.02 Br.sup./mM 0.03 0.01 NO.sup.3/mM <0.02 PO.sub.4.sup.3/mM 0.13 0.02 SO.sub.4.sup.2/mM 0.38 0.06 SCD/Eq/g 1.55 0.05

[0171] The TMP filtrate was titrated versus pH and turbidity and electrophoretic mobility were recorded. The pH was first adjusted to a pH of 11 with 0.1 M NaOH solution and subsequently titrated with 0.1 M HCl solution to 2.7. It can be seen that the turbidity increased with decreasing pH (FIG. 1). The effect becomes less pronounced at alkaline pH. This is mainly related to the dissolution of resin and fatty acids. The electrophoretic mobility (EM) of the particles in the TMP filtrate (FIG. 2) was stable in the relevant pH region of 7-9. It is, however, important to note that below pH 4 the electrophoretic mobility substantially increased towards 0 (pzc) indicating a lower stability of the particles as a result of protonation of the acid anions of the resins and fatty acids forming protonised charge carriers. The point of zero charge (pzc) is around 2. Above a pH 10 the EM strongly decreased, pointing towards complete saponification of the triglycerides as well as of the resin and fatty acids.

Adsorbing Materials

[0172] A scalenohedral PCC, a colloidal PCC and talc (Finntalc P05 of Mondo Minerals, Netherlands) were tested as adsorbing materials. Their properties are listed in Table 2.

TABLE-US-00002 TABLE 2 Properties of the adsorbing materials sPCC cPCC Talc Sedigraph <2 m/% 82 89 41 <1 m/% 31 55 d.sub.50/m 1.36 0.92 Mastersizer <2 m/% 35 34 8 <1 m/% 9 7 2 d.sub.50/m 2.58 2.51 6.30 Specific surface area/m.sup.2/g 10 24 8 Electrophoretic mobility in 0.1M 0.2 0.9 3.8 NaCl/10.sup.8 m.sup.2/Vs TGA Loss (200-1 000 C.)/% 44.0 43.7 5.4

TMP/Adsorbing Material Sample Preparation

[0173] After the above described filtration, the TMP filtrate was placed in plastic bottles and the corresponding adsorbing material was dosed in chemical free slurry form. The adsorbing material dosages were chosen to be between 1 and 50 g/L TMP filtrate. The added water from the adsorbing material slurries was leveled by additional water for the low mineral containing samples in order to have the same dilution throughout the trial series. The bottles were well mixed by shaking and then agitated for 2 hours with closed lid. Afterwards, the suspensions were centrifuged with 2580 rpm. The solid and liquid phases were separated and the upper liquid phase was analyzed for turbidity, COD, gravimetry, pH, conductivity, SCD and ions (Ca.sup.2+, Mg.sup.2+, Cl.sup., SO.sub.4.sup.2).

Results

[0174] As can be gathered from FIG. 3, talc had the lowest impact on pH. The pH increased from 7 to 7.7. The pH increased strongly for cPCC and sPCC. CPCC showed the strongest increase up to 8.7.

[0175] In contrast thereto, the cPCC showed a rather low increase of conductivity (FIG. 4), which is comparable to the conductivity measured for talc. SPCC showed the strongest increase in conductivity of the three minerals.

[0176] Furthermore, it is to be noted that the calcium and magnesium ion concentrations were mostly affected by the corresponding adsorbing material treatment. In particular, the calcium concentration dropped with increasing adsorbing material dosage, while the magnesium concentration increased with increasing adsorbing material dosage.

[0177] As can be gathered from FIG. 5, the cPCC was the most efficient adsorbing material for reducing the anionic charge of the TMP filtrate.

[0178] All three adsorbing materials clearly reduced the turbidity of the TMP filtrate (FIG. 6). However, the strongest reduction in turbidity was measured for the cPCC. Talc showed for low dosages a medium reduction. A talc addition of more than 20 g/L aqueous medium did not further reduce the turbidity. Initially, the sPCC showed the weakest turbidity reduction but exceeded the talc above a dosage of 20 g/L aqueous medium. The turbidity analysis for the cPCC showed a great potential in collecting colloidal and therefore extractable material from the TMP filtrate. Similarly, the analysis of the chemical oxygen demand (FIG. 7) showed the high potential of the cPCC as an efficient adsorbing material for wood resin constituents. It can be further noted that talc performed nearly as good as the cPCC in the COD analysis. This can be attributed to the high affinity of talc to the dissolved fraction in particular hemicelluloses and lignin. A plot of COD versus turbidity (FIG. 8) illustrated that well. The steepness of the linear region indicated the ratio of colloidal to dissolved material that was adsorbed. Below a certain turbidity level the data for cPCC deviated from the linear behavior indicating a change in the ratio of dissolved versus colloidal material towards the dissolved fraction.

[0179] The quantification of the gravimetric residue (FIG. 9) confirmed the data obtained for the turbidity analysis. In particular, it can be gathered that cPCC reduced the gravimetric residue most efficiently. This is followed by talc again reaching a value where the reduction was stopped (>20 g/L aqueous medium).

[0180] Thus, it can be concluded that all adsorbing materials tested in the present application act to adsorb dissolved and colloidal substances from a TMP filtrate and thus are effective in reducing the amount of organic materials in the TMP filtrate. However, cPCC was surprisingly found to be the most efficient adsorbing material as can be gathered from the turbidity, COD and gravimetric analysis.