USE OF UREA AS AN ANTIMICROBIAL ADDITIVE IN AN AQUEOUS SUSPENSION

Abstract

Use of urea as an antimicrobial additive in an aqueous suspension, comprising from 5 to 85 wt.-%, based on the total weight of the suspension, of at least one calcium carbonate-comprising material and having a pH of between 7.0 and 14, a process for preserving an aqueous suspension against microbial growth, an aqueous preparation obtainable by the inventive process as well as the use of the aqueous preparation in agriculture.

Claims

1. Use of urea as an antimicrobial additive in an aqueous suspension, comprising from 5 to 85 wt.-%, based on the total weight of the suspension, of at least one calcium carbonate-comprising material and having a pH of between 7.0 and 14, wherein the antimicrobial additive is present in the suspension in an amount of at least 1.2 wt.-%, based on the total weight of the aqueous suspension and wherein the weight ratio of urea:water in the aqueous suspension is from 1:100 to 50:100.

2. Use according to claim 1, wherein the antimicrobial additive is added as a water based solution to the aqueous suspension comprising the calcium carbonate-comprising material, preferably in the form of a water based solution comprising from 20 to 75 wt.-%, more preferably from 30 to 72 wt.-%, even more preferably from 40 to 65 wt.-% and most preferably from 50 to 60 wt.-% of urea, based on the total weight of the water based solution.

3. Use according to claim 1, wherein the antimicrobial additive is added as a dry material to the aqueous suspension comprising the calcium carbonate-comprising material.

4. Use according to claim 1, wherein the antimicrobial additive is added to the suspension in an amount of 1.2 to 20 wt.-%, preferably in an amount of 1.5 to 15 wt.-%, more preferably in an amount of 2.0 to 10 wt.-%, and most preferably in an amount of 2.5 to 8.5 wt.-%, based on the total weight of the suspension.

5. Use according to claim 1, wherein the calcium carbonate-comprising material comprises at least 50 wt.-%, preferably at least 80 wt.-%, and more preferably at least 97 wt.-% of calcium carbonate relative to the total dry weight of said calcium carbonate-comprising material.

6. Use according to claim 1, wherein the aqueous suspension comprises from 10 to 84 wt.-%, preferably from 30 to 83 wt.-%, more preferably from 50 to 82 wt.-%, even more preferably from 60 to 80 wt.-% and most preferably from 68 to 78 wt.-%, based on the total weight of the suspension, of at least one calcium carbonate-comprising material.

7. Use according to claim 1, wherein the calcium carbonate-comprising material is selected from the group consisting of ground calcium carbonate, preferably marble, limestone, dolomite and/or chalk, precipitated calcium carbonate, preferably vaterite, calcite and/or aragonite and surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donor treatment and/or is supplied from an external source and mixtures thereof, more preferably the at least one calcium carbonate-comprising material is ground calcium carbonate.

8. Use according to claim 1, wherein the antimicrobial agent prevents or reduces the occurrence of at least one strain of bacteria and/or at least one strain of yeast and/or at least one strain of mould when present in the aqueous suspension.

9. Use according to claim 8, wherein (i) the at least one strain of bacteria is selected from the group comprising Methylobacterium sp., Salmonella sp., Escherichia sp. such as Escherichia coli, Shigella sp., Enterobacter sp., Pseudomonas sp. such as Pseudomonas mendocina, Pseudomonas stutzeri, Pseudomonas aeruginosa, and/or Pseudomonas putida, Burkholderia sp. such as Burkholderia cepacia, Bdellovibrio sp., Agrobacterium sp., Alcaligenes sp. such as Alcaligenes faecalis, Flavobacterium sp., Ochrobactrum sp. such as Ochrobactrum tritici, Kocuria sp. such as Kocuria rhizophila, Rhizobium sp. such as Rhizobium radiobacter, Sphingobacterium sp., Sphingomonas sp., Aeromonas sp., Chromobacterium sp., Vibrio sp., Hyphomicrobium sp., Leptothrix sp., Micrococcus sp., Staphylococcus sp. such as Staphylococcus aureus, Agromyces sp., Acidovorax sp., Comamonas sp. such as Comomonas aquatic, Brevundimonas sp. such as Brevundimonas intermedia and Brevundimonas diminiuta, Spingobium sp. such as Spingobium yanoikuyae, Thauera sp. such as Thauera mechernichensis, Caldimonas sp., Hdrogenophaga sp., Teipidomonas sp., and mixtures thereof, and mixtures thereof, and/or (ii) the at least one strain of yeast is selected from the group comprising Saccharomycotina, Taphrinomycotina, Schizosaccharomycetes, Basidiomycota, Agaricomycotina, Tremellomycetes, Pucciniomycotina, Microbotryomycetes, Candida sp. such as Candida albicans, Candida tropicalis, Candida stellatoidea, Candida glabrata, Candida krusei, Candida guilliermondii, Candida viswanathii, Candida lusitaniae and mixtures thereof, Yarrowia sp. such as Yarrowia lipolytica, Cryptococcus sp. such as Cryptococcus gattii and Cryptococcus neofarmans, Zygosaccharomyces sp., Rhodotorula sp. such as Rhodotorula mucilaginosa, Saccharomyces sp. such as Saccharomyces cerevisiae, Pichia sp. such as Pichia membranifaciens and mixtures thereof, and/or (iii) the at least one strain of mould is selected from the group comprising of Acremonium sp., Alternaria sp., Aspergillus sp., Cladosporium sp., Fusarium sp., Mucor sp., Penicillium sp., Rhizopus sp., Stachybotrys sp., Trichoderma sp., Dematiaceae sp., Phoma sp., Eurotium sp., Scopulariopsis sp., Aureobasidium sp., Monilia sp., Botrytis sp., Stemphylium sp., Chaetomium sp., Mycelia sp., Neurospora sp., Ulocladium sp., Paecilomyces sp., Wallemia sp., Curvularia sp., and mixtures thereof.

10. Use according to claim 1, wherein the pH of the aqueous suspension is between 7.5 and 12, preferably between 8.2 and 10.0 and most preferably between 8.5 and 9.5.

11. Use according to claim 1, wherein no further antimicrobial additives apart from urea are added to the aqueous suspension.

12. Use according to claim 1, wherein the weight ratio of urea:water in the aqueous suspension is from 5:100 to 40:100 and preferably from 9:100 to 30:100.

13. Process for preserving an aqueous suspension against microbial growth, the process comprising the steps of: a) providing at least one calcium carbonate-comprising material, b) providing urea as antimicrobial additive, c) contacting the at least one calcium carbonate-comprising material of step a) with the at least one antimicrobial additive of step b) to provide an aqueous suspension, wherein the aqueous suspension comprises from from 5 to 85 wt.-%, based on the total weight of the suspension, of at least one calcium carbonate-comprising material and has a pH of between 7.0 and 14, and wherein the aqueous suspension comprises the antimicrobial additive in an amount of at least 1.2 wt.-% based on the total weight of the suspension and wherein the weight ratio of urea:water in the aqueous suspension is from 1:100 to 50:100.

14. Process according to claim 13, wherein the calcium carbonate-comprising material is selected from the group consisting of ground calcium carbonate, preferably marble, limestone, dolomite and/or chalk, precipitated calcium carbonate, preferably vaterite, calcite and/or aragonite and surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors in an aqueous medium, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donor treatment and/or is supplied from an external source and mixtures thereof, more preferably the at least one calcium carbonate-comprising material is surface-reacted calcium carbonate.

15. Aqueous preparation obtainable by the process of claim 13.

16. Use of the aqueous preparation according to claim 15 in agriculture as a plant booster and/or a mineral fertilizer for stimulation of a photosynthetic process in plants, stimulation of plant growth, reinforcement of resistance to plant diseases, improvement of nutrient absorption and plant nutrition.

Description

EXAMPLES

1. Measurement Methods

[0271] In the following, measurement methods implemented in the examples are described.

[0272] BET Specific Surface Area of a Material

[0273] Throughout the present document, the specific surface area (in m.sup.2/g) of a material is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m.sup.2) of the mineral filler is then obtained by multiplication of the specific surface area and the mass (in g) of the mineral filler prior to treatment.

[0274] Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Diameter (d.sub.50) of a Particulate Material

[0275] Weight median grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation process, i.e. an analysis of sedimentation behaviour in a gravitational field. The measurement was made with a Sedigraph™ 5100 of Micromeritics Instrument Corporation.

[0276] The volume-based median particle diameter of the surface-reacted calcium carbonate was determined by using a Malvern Mastersizer 2000.

[0277] 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 are dispersed using a high speed stirrer and supersonics.

[0278] Solids Content

[0279] The solids content (also known as “dry weight”) was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120° C., automatic switch off 3, standard drying, 5 to 20 g of product.

[0280] pH Measurement

[0281] The pH of a suspension is measured at 25° C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab® Expert Pro pH electrode. 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). 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 s).

[0282] Brookfield-Viscosity

[0283] The Brookfield viscosity is measured by a Brookfield DV-III Ultra viscometer at 20° C.±3° C. at 100 rpm using an LV-3 spindle and is specified in mPa.Math.s. Once the spindle has been inserted into the sample, the measurement is started with a constant rotating speed of 100 rpm. The reported Brookfield viscosity values are the values displayed 60 seconds after the start of the measurement.

[0284] Total Viable Bacterial Counts

[0285] All quoted bacterial counts (Total viable counts (TVC) values), unless otherwise indicated, are given in cfu/ml and determined after at least 2 days following plate-out and incubation at 30° C. and in accordance with the counting method described in “Bestimmung von aerobe mesophilen Keimen”, Schweizerisches Lebensmittelbuch, chapter 56, section 7.01, edition of 1985, revised version of 1988.

[0286] Unless otherwise stated, per tryptic soy agar plate (TSA, prepared using BD 236950) 0.1 ml of a solution or suspension is plated. Counts from 10000 cfu/ml to 99999 cfu/ml are reported as >1E4 cfu/ml. Counts from 100000 cfu/ml to 999999 cfu/ml are reported as >1E5 cfu/ml. Counts above 1000000 cfu/ml are reported as >1E6 cfu/ml.

[0287] To identify the bacteria present in concentrated urea solutions (>25% w/w urea), 3 ml urea solution is diluted in sterile 12 ml 0.9% (w/w) NaCl solution. The mixture is then centrifuged (10 min at 400 g) and the supernatant is removed until 0.1 ml supernatant remains with the pellet. The pellet is resuspended in the remaining supernatant and the TVC is determined of 0.1 ml as described above. The bacterial counts are given as cfu/3 ml.

2. Examples

[0288] Preparation of Calcium Carbonate-Comprising Material Suspensions

[0289] An aqueous slurry of calcium carbonate-comprising material (Italian marble; d.sub.50=10 μm; 21%<2 μm, calcium carbonate content≥97.5 wt.-%) is prepared at 75 wt.-% solid content, based on the total weight of the slurry. The slurry is wet ground at 95° C. using 0.6 wt.-% in respect to dry solids material of a sodium/calcium neutralized polyacrylate grinding agent (Mw 6000) in a 2001 vertical ball mill to the following final particle size distribution.

[0290] H60 refers to slurries with the characteristics of particle size distribution of d.sub.50=1.4-1.6 μm; 58.8-61.5 wt.-%<2 μm; 37-40.3 wt.-%<1 μm, 8.2-12.4 wt.-%<0.2 μm, a Brookfield viscosity of 100-150 mPa.Math.s, a pH of 8.5-9.0 and solid contents of ≥75 wt.-%, based on the total weight of the slurry.

[0291] H90 refers to slurries with the characteristics of particle size distribution of d.sub.50=0.67 μm; 89.9 wt.-%<2 μm; 63.3 wt.-%<1 μm, 21.2 wt.-%<0.2 μm, a Brookfield viscosity of 100-150 mPa.Math.s, a pH of 8.5-9.0 and solid contents of ≥75 wt.-%, based on the total weight of the slurry.

[0292] Sterile slurries of H60 and H90 are prepared by autoclaving under steam pressure 1 kg slurry aliquots in containments of 21 for 15 minutes at 121° C.

[0293] Preparation of Preserved Calcium Carbonate-Comprising Material Suspensions

[0294] Calcium carbonate-comprising material slurries containing urea are prepared by combining the above slurries (H60 or H90) either with dry urea (Sigma-Aldrich 15604) or concentrated urea solutions (≥50 wt.-%) and/or water.

[0295] The urea solutions are either prepared using dry urea and deionized water or using industrial grade 50 wt.-% urea solution, based on the total weight of the urea solution as supplied by Vendor (Yara Canda Inc.).

[0296] The resulting urea contents, water contents and calcium carbonate contents are calculated from the measured amounts of water, urea and/or slurries combined using the measured solid content of the calcium carbonate slurry. For calculations the solid content of the slurries is considered to consist of 100% calcium carbonate.

[0297] Preparation of Inoculum

[0298] Non-sterile slurries (H60 or H90) contain contamination with environmental bacteria at a TVC>100000 cfu/ml. The contamination originates spontaneously and a bacterial burden of at least>100000 cfu/ml is confirmed prior use as inoculum by TVC. The following bacterial species are known to occur, as identified by 16S RNA sequencing or MALDI-TOF-MS analysis: Rhizobium radiobacter, Brevundimonas intermedia, Brevundimonas diminiuta, Sphingomonas sp., Pseudomonas stutzeri, Pseudomonas sp., Comomonas aquatic.

[0299] For the preparation of inoculum with a single bacterial species (for example Escherichia coli (DSMZ 46295) or Pseudomonas putida), bacteria are spread onto Tryptic soy broth agar (BD, 236950) by dilution streaking followed by incubation at 30° C. for at least 24 h until colonies appear. Overnight cultures are generated by inoculation of 3 ml Tryptic soy broth (Fluka 22092) with a single colony followed incubation with agitation at rotations per minute (rpm) at 30° C. for 24 h.

Example 1

[0300] 50 g sterile slurry H90 with a solid content of 75 wt.-%, based on the total weight of the H90 slurry is supplemented with different concentrations of dry urea. The samples are then stored for 3 days at 30° C. After the storage, the samples are inoculated with 1 ml non-sterile calcium carbonate slurry (H90), incubated for 3 days at 30° C. and the TVC is determined. Samples are further inoculated with 1 ml non-sterile calcium carbonate slurry (H90). Up to three inoculations are performed.

TABLE-US-00001 TABLE 1 Preservation efficacy of slurries with different urea contents. calcium TVC cfu/ml TVC cfu/ml TVC cfu/ml urea carbonate water 1.sup.st 2.sup.nd 3.sup.rd content.sup.1 content.sup.1 content.sup.1 Inoculation Inoculation Inoculation    0% 75% 25% >1E6 >1E6 >1E6 0.025% 75% 25% >1E6 >1E6 >1E6  0.05% 75% 25% >1E6 >1E6 >1E6 0.075% 75% 25% >1E6 >1E6 >1E6 .sup.1Calculated per total slurry as w/w.

[0301] As can be seen from table 1 urea is not able to preserve calcium carbonate slurries from bacterial growth at low urea concentrations.

Example 2

[0302] 50 g sterile slurry H60 with a solid content of 76.5 wt.-%, based on the total weight of the H60 slurry is supplemented with different amounts of 61 wt.-% urea solution or water. The samples are then inoculated with 1 ml non-sterile calcium carbonate slurry (H60), 1 ml non-sterile calcium carbonate slurry (H90), 0.02 ml overnight culture of Escherichia coli (DSMZ 46295) and 0.02 ml overnight culture of Pseudomonas putida. The control samples are not inoculated. Samples are incubated at 30° C. and the TVC and pH are determined at various time points (0 day, 1 day, 4, days, 8 days, 9 days and/or 13 days).

TABLE-US-00002 TABLE 2 Preservation efficacy of slurries with different urea contents. Detection limit 100 cfu/ml. calcium TVC TVC TVC TVC TVC Urea carbonate Water cfu/ml cfu/ml cfu/ml cfu/ml cfu/ml pH content.sup.1 content.sup.1 content.sup.1 Inoculum Day 0 Day 1 Day 4 Day 8 Day 13 Day 8   0% 73.6% 26.4% none <100 <100 <100 <100 >1E5 9.06 2.75% 73.1% 24.15% none nd <100 <100 <100 <100 9.16  7.6% 67.1% 25.3% none nd <100 <100 <100 <100 9.25   0% 73.6% 26.4% E. coli >1E5 >1E5 >1E5 >1E5 >1E5 nd 2.75% 73.1% 24.15% E. coli nd <100 <100  500 <100 nd  7.6% 67.1% 25.3% E. coli nd <100 <100 <100  100 nd   0% 73.6% 26.4% P. putida >1E5 >1E5 >1E5 >1E5 >1E5 nd 2.75% 73.1% 24.15% P. putida nd <100 <100  100 <100 nd  7.6% 67.1% 25.3% P. putida nd <100 <100 <100 <100 nd   0% 73.6% 26.4% H60 >1E5 >1E5 >1E5 >1E5 >1E5 nd 2.75% 73.1% 24.15% H60 nd 4′400.sup.  <100 <100 <100 nd  7.6% 67.1% 25.3% H60 nd <100 <100 <100 <100 nd   0% 73.6% 26.4% H90 >1E5 >1E5 >1E5 >1E5 >1E5 nd 2.75% 73.1% 24.15% H90 nd <100 <100 <100 <100 nd  7.6% 67.1% 25.3% H90 nd <100 <100 <100 <100 nd .sup.1Calculated per total slurry as w/w; nd: not determined

TABLE-US-00003 TABLE 3 Preservation efficacy of slurries with different urea contents. Detection limit 100 cfu/ml. calcium TVC TVC TVC TVC Urea carbonate Water cfu/ml cfu/ml cfu/ml cfu/ml pH content.sup.1 content.sup.1 content.sup.1 Inoculum Day 0 Day 1 Day 4 Day 9 Day 4   0% 76.5% 23.5% none <100 <100 <100 >1E5 8.94 0.65% 75.7% 23.65% none nd <100 <100 nd 9.06 1.28% 74.9% 23.82% none nd <100 <100 nd 9.05 2.75% 73.1% 24.15% none nd <100 <100 <100 9.11   0% 76.5% 23.5% E. coli >1E5 >1E5 >1E5 >1E5 nd 0.65% 75.7% 23.65% E. coli nd >1E5 >1E5 nd nd 1.28% 74.9% 23.82% E. coli nd <100 <100 nd nd 2.75% 73.1% 24.15% E. coli nd <100 <100 <100 nd   0% 76.5% 23.5% P. putida >1E5 >1E5 >1E5 >1E5 nd 0.65% 75.7% 23.65% P. putida nd >1E5 >1E5 nd nd 2.75% 73.1% 24.15% P. putida nd <100 <100 <100 nd   0% 76.5% 23.5% H60 >1E5 >1E5 >1E5 >1E5 nd 0.65% 75.7% 23.65% H60 nd >1E5 >1E5 nd nd 2.75% 73.1% 24.15% H60 nd 3′500.sup.   100 <100 nd   0% 76.5% 23.5% H90 >1E4 >1E5 >1E5 >1E5 nd 0.65% 75.7% 23.65% H90 nd >1E5 >1E5 nd nd 2.75% 73.1% 24.15% H90 nd <100 <100 <100 nd .sup.1Calculated per total Slurry as w/w. nd: not determined

[0303] As can be seen from tables 2 and 3 urea is able to preserve calcium carbonate slurries from bacterial growth over at least 13 days when present at high urea concentrations.

Example 3

[0304] 50 g sterile calcium carbonate slurry (H60) with a solid content of 77.3 wt.-%, based on the total weight of the H60 slurry is supplemented with industrial grade 50% (w/w) urea solution (Yara Canda Inc.) or water to different final concentrations. The industrial grade contained natural resident (i.e. bacteria in a non-growing state) bacteria. The bacterial of the industrial urea burden is 5 cfu/3 ml as determined by TVC. The species are identified by characterizing the grown colonies from the TVC by 16 S RNA sequencing, known to the person skilled in the art.

[0305] The species identified are Sporosarcina koreensis, (Gram positive, urease positive, spore forming), Paenibacillus sp., (Gram positive, urease positive, spore forming) and Halobacillus trueperi (Gram positive, urease negative, spore forming).

[0306] The samples are further artificially inoculated with 1 ml non-sterile calcium carbonate slurry (H60), 1 ml non-sterile calcium carbonate slurry (H90), 0.02 ml overnight culture of Escherichia coli (DSMZ 46295) and 0.02 ml overnight culture Pseudomonas putida. The control sample are not inoculated. Samples are incubated at 30° C. and the TVC and pH are determined at various time points (0 day, 1 day, 4, days, 8 days, 11 days and 15 days).

TABLE-US-00004 TABLE 4 Preservation efficacy of slurries with different urea contents using industrial grade urea, containing urease positive bacteria. Detection limit 100 cfu/ml. calcium TVC TVC TVC TVC TVC TVC Urea carbonate Water cfu/ml cfu/ml cfu/ml cfu/ml cfu/ml cfu/ml pH content.sup.1 content.sup.1 content.sup.1 Inoculum Day 0 Day 1 Day 4 Day 8 Day 11 Day 13 Day 16 .sup. 0% 73% .sup. 27% none <100 <100 <100 <100 <100 <100 8.97 5.5% 69% 25.5% none nd <100 <100  100 <100 <100 9.02 .sup. 0% 73% .sup. 27% E. coli >1E5 >1E5 >1E5 >1E5 >1E5 >1E5 8.52 5.5% 69% 25.5% E. coli nd <100 <100 <100 <100 <100 9.02 .sup. 0% 73% .sup. 27% P. putida >1E5 >1E5 >1E5 >1E5 >1E5 >1E5 8.5 5.5% 69% 25.5% P. putida nd <100 <100 <100 <100 <100 9.04 .sup. 0% 73% .sup. 27% H60 >1E5 >1E5 >1E5 >1E5 >1E5 >1E5 8.09 5.5% 69% 25.5% H60 nd 1′800.sup.  <100 <100 <100 <100 9.00 .sup. 0% 73% .sup. 27% H90 >1E5 >1E5 >1E5 >1E5 >1E5 >1E5 8.11 5.5% 69% 25.5% H90 nd >1E4  300 <100 <100 <100 8.97 .sup.1Calculated per total Slurry as w/w. nd: not determined

Example 4

[0307] 50 g sterile calcium carbonate slurry (H60) with a solid content of 78.3 wt.-%, based on the total weight of the H60 slurry are supplemented with 61% (w/w) urea solution to different final concentrations. The samples are inoculated with 1 ml non-sterile calcium carbonate slurry (H60). Samples are incubated at 30° C. and TVC and pH are determined at various time points (0 day, 1 day, 4, days, 11 days).

TABLE-US-00005 TABLE 5 Preservation efficacy of slurries with different Urea contents. Detection limit 100 cfu/ml. calcium TVC TVC TVC TVC Urea carbonate Water cfu/ml cfu/ml cfu/ml cfu/ml pH content.sup.1 content.sup.1 content.sup.1 Inoculum Day 0 Day 1 Day 4 Day 11 Day 11 0.00% 75.80% 24.20% H60 >1E5 >1E5 >1E5 >1E5 8.55 0.40% 75.61% 23.99% H60 nd >1E5 >1E5 >1E5 9.05 1.10% 75.48% 23.42% H60 nd >1E5 >1E5 >1E5 9.25 2.80% 75.21% 21.98% H60 nd >1E4 600 <100 9.10 .sup.1Calculated per total Slurry as w/w. nd: not determined

Example 5

[0308] 1 kg calcium carbonate slurry (H60) with a solid content of 75 wt.-%, based on the total weight of the H60 slurry is stirred at approximately 500 rotations per minute (rpm) and 27.5 g dry urea is added slowly during agitation, leading to 2.68 wt.-% urea and 73 wt.-% calcium carbonate, based on the total weight of the obtained slurry. The blend is further mixed for 30 minutes at slow speed (<500 rpm).

[0309] The addition of dry urea does not give any negative impact on the product. No clumps were formed, and the viscosity does not increase. The product remains stable for 7 days at room temperature and 40° C.