Aqueous suspension of inorganic particulate material

Abstract

An aqueous suspension comprising an inorganic particulate material and dimethylethanolamine, use of dimethylethanolamine to prevent pH decrease or reduce the rate of pH decrease of an aqueous suspension comprising an inorganic particulate material over time, use of dimethylethanolamine as an anti-microbial additive in an aqueous suspension comprising an inorganic particulate material, and a method of preparing an aqueous suspension comprising inorganic particulate material.

Claims

1. A method comprising: forming an aqueous suspension comprising an amount of 2-(Dimethylamino)ethanol (DMEA) and one of an alkaline earth metal carbonate, wollastonite, talc, or clay present in the aqueous suspension in an amount ranging from about 66% to about 82%, wherein the pH of the aqueous suspension is maintained in a pH range from about 9.5 to about 10.5 for an amount of time ranging from 1 day to 6 weeks.

2. The method of claim 1, wherein the alkaline earth metal carbonate is calcium carbonate.

3. The method of claim 1, wherein the aqueous suspension has an initial viscosity ranging from about 100 to about 500 mPa.Math.s.

4. The method of claim 1, wherein the aqueous suspension is devoid of biocide.

5. The method of claim 1, wherein the aqueous suspension further comprises an additive which increases the pH of the aqueous suspension.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain embodiments of the invention will now be described, by way of example only and without limitation with reference to the following Figures and Examples, in which:

(2) FIG. 1 shows the change in pH ( pH) of the calcium carbonate slurry samples prepared in Example 1 over time.

(3) FIG. 2 shows the change in pH of calcium carbonate slurry samples as aliquots of 2-amino-2-methyl-1-propanol (AMP) or DMEA are added to the sample as described in Example 2.

(4) FIG. 3 shows the effect of increasing amounts of glutaraldehyde, both alone and in combination with 600 ppm of DMEA, on total viable count of the calcium carbonate slurry samples prepared in Example 3, after 0 days.

(5) FIG. 4 shows the effect of increasing amounts of benzisothiazolinone and methylisothiazolinone, both alone and in combination with DMEA, on total viable count of the calcium carbonate slurry samples prepared in Example 4, after 1 day.

(6) FIG. 5 shows the effect of increasing amounts of DMEA on total viable count of the calcium carbonate slurry samples prepared in Example 5, after 0 days.

(7) FIG. 6 shows the effect of increasing amounts of DMEA on total viable count of the calcium carbonate slurry samples prepared in Example 5, after 7 days.

EXAMPLES

Example 1

(8) 1 kg samples of a calcium carbonate slurry having 78 wt % solids and 60% of particles less than 2 m in size (measured using a micrometrics sedigraph) were adjusted to pH at room temperature using 2-amino-2-methyl-1-propanol (AMP) or dimethylethanolamine (DMEA). The control sample was adjusted to pH 10 using dilute sodium hydroxide solution. The solids content of the samples was adjusted using deionised water.

(9) The pH of each slurry was lowered to pH 8 by aspirating the sample with carbon dioxide (CO.sub.2) enriched air (2%) using a flow rate of 5 mL/min. When pH 8 had been reached, aspiration of the sample was stopped.

(10) Recovery of the sample pH was then monitored and recorded over subsequent days using the Mettler Toledo FE20 pH meter as described above in the detailed description. The results are shown in Table 1 and FIG. 1.

(11) TABLE-US-00001 TABLE 1 pH of pH of Day pH of sample sample measurement Control comprising comprising taken sample pH AMP pH DMEA pH 0 9.20 9.50 10.00 0.5 8.00 0.0 8.00 0.00 8.00 0.00 1 8.09 0.1 8.16 0.13 8.22 0.22 2 8.16 0.2 8.26 0.23 8.28 0.28 3 8.17 0.2 8.35 0.35 4 8.43 0.43 9 8.52 0.52 11 8.55 0.55 16 8.30 0.3 8.46 0.43 8.58 0.58 20 8.31 0.4 8.50 0.47 8.60 0.60 23 8.31 0.4 8.52 0.49 8.64 0.64 24 8.31 0.4 8.58 0.55 8.65 0.65 27 8.27 0.3 8.61 0.58 8.70 0.70 28 8.27 0.3 8.66 0.66 8.79 0.79

(12) It was surprisingly found that the pH of the sample comprising DMEA increased to 8.8, whereas the pH of the control sample increased to 8.3. The pH of the sample comprising DMEA increased more rapidly and to a higher level than both the sample comprising AMP and the control sample.

(13) In practice, the absorbed atmospheric carbon dioxide would not reduce the pH so dramatically and in such a rapid manner. As such, the addition of DMEA to an aqueous suspension would be more effective in maintaining slurry pH for a given period of time.

Example 2

(14) 50 mg/kg aliquots of either AMP or DMEA were sequentially added to 250 g calcium carbonate slurry samples having 78 wt % solids and 60% of particles less than 2 m in size (measured using a micrometrics sedigraph). In this context, 50 mg/kg means that 50 mg of AMP or DMEA was added per kg of dry inorganic particulate material in the aqueous suspension. The pH of the samples was measured after stirring immediately after each 50 mg/kg addition. The results are shown in Table 2 and FIG. 2.

(15) TABLE-US-00002 TABLE 2 Samples Total mg/kg of comprising AMP Samples comprising DMEA chemical added pH of sample pH pH of sample pH 0 9.01 8.94 50 9.28 0.27 9.19 0.25 100 9.49 0.21 9.36 0.17 150 9.64 0.15 9.49 0.13 200 9.78 0.14 9.60 0.11 250 9.92 0.14 9.67 0.07 300 10.01 0.09 9.74 0.07 350 10.08 0.07 9.80 0.06 400 10.15 0.07 9.85 0.05 450 10.22 0.07 9.90 0.05 500 10.27 0.05 9.95 0.05 550 10.32 0.05 9.99 0.04 600 10.37 0.05 10.01 0.02

(16) The results show that a similar pH increase was seen with both AMP and DMEA.

Example 3

(17) Samples of a contaminated calcium carbonate slurry having 78 wt % solids and 60% of particles less than 2 m in size (measured using a micrometrics sedigraph) comprising various amounts of the biocide glutaraldehyde, and DMEA were prepared. The total viable count (cfu/ml) of each sample was measured after 0, 1 and 7 days by the method described above in the detailed description. The results are shown in Table 3 and FIG. 3.

(18) TABLE-US-00003 TABLE 3 Total Viable Count (cfu/ml) of Chemical samples as 10.sup.x Addition (ppm) (0 days (1 day (7 days Glutar- after after after Sample aldehyde DMEA preparation) preparation) preparation) 1 0 0 6 6 6 2 0 600 5 4 0.1 3 50 0 3 0.1 0.1 4 50 600 0.1 0.1 0.1 5 100 0 0.1 0.1 0.1 6 100 600 0.1 0.1 0.1 7 400 0 0.1 0.1 0.1 8 400 600 0.1 0.1 0.1

(19) It was surprisingly found that samples comprising DMEA in combination with a 50 ppm dose of glutaraldehyde have a lower total viable count after 0 days in comparison with a sample comprising a 50 ppm dose of glutaraldehyde but no DMEA. The use of DMEA in combination with a 50, 100 or 400 ppm dose of glutaraldehyde is at least as effective in reducing total viable count after 1 and 7 days as using glutaraldehyde alone.

Example 4

(20) Samples of a contaminated calcium carbonate slurry having 78 wt % solids and 60% of particles less than 2 m in size (measured using a micrometrics sedigraph) comprising various amounts of DMEA and the biocides benzisothiazolinone (BIT) and methylisothiazolinone (MIT) were prepared. The total viable count (cfu/ml) of each sample was measured after 0, 1 and 7 days by the method described above in the detailed description. The results are shown in Table 4 and FIG. 4.

(21) TABLE-US-00004 TABLE 4 Total Viable Count (cfu/ml) of samples as 10.sup.x Chemical (0 days (1 day (7 days Addition (ppm) after after after Sample BIT/MIT DMEA preparation) preparation) preparation) 1 0 0 6 6 6 2 0 600 5 4 0.1 3 81 0 5 5 4 4 81 600 5 0.1 0.1 5 162 0 5 5 4 6 162 600 5 0.1 0.1 7 650 0 5 4 0 8 650 600 4 0.1 0.1

(22) It was surprisingly found that samples comprising DMEA in combination with a 81, 162 or 650 ppm dose of BIT/MIT had a lower total viable count after 1 day and 7 days than samples comprising BIT/MIT but no DMEA.

Example 5

(23) Samples of a contaminated calcium carbonate slurry having 78 wt % solids and 60% of particles less than 2 m in size (measured using a micrometrics sedigraph) comprising various amounts of DMEA were prepared. The total viable count (cfu/ml) of each sample was measured after 0, 1 and 7 days by the method described above in the detailed description. The results are shown in Table 5 and FIGS. 5 and 6.

(24) TABLE-US-00005 TABLE 5 Total Viable Count (cfu/ml) of sample as 10.sup.x DMEA (ppm) in (0 days after (1 day after (7 days after sample preparation) preparation) preparation) 0 6 6 6 400 5 4 0.1 500 5 4 0.1 600 5 4 0.1

(25) It was surprisingly found that samples comprising 400, 500 and 600 ppm doses of DMEA alone (without any additional biocide) slightly reduced the level of microbes in the samples after 0 days, and further reduced the level of microbes in the samples after 1 day and 7 days in comparison with samples comprising no DMEA.

(26) It was thus surprisingly shown that DMEA can be used as an anti-microbial additive in an aqueous suspension comprising inorganic particulate material, when used either alone or in combination with a biocide. DMEA can be used in a lower dose than other biocides to achieve the same microbe level (for example total viable count).

(27) The foregoing broadly describes certain embodiments of the present invention without limitation. Variations and modifications as will be readily apparent to those skilled in the art are intended to be within the scope of the present invention as defined in and by the appended claims.