PROCESS FOR PREPARING A SULPHUR-CONTAINING SOIL IMPROVER

Abstract

A process for preparing an elemental sulphur-containing composition for use as a fertilizer and/or soil improver comprises wet milling elemental sulphur in a liquid to produce a micronized sulphur slurry for application to soil, and further comprises adding a preventive scavenging additive for fixating sulphur dioxide and hydrogen sulphide gases that are released downstream of the mill.

Claims

1. A process for preparing an elemental sulphur-containing composition for use as a fertilizer and/or soil improver, the process comprising wet milling elemental sulphur in a liquid to produce a micronized sulphur slurry for application to soil, wherein the process further comprises adding a preventive scavenging additive for fixating sulphur dioxide and hydrogen sulphide gases that are released by the slurry downstream of the mill, wherein the preventive scavenging additive is added prior to or during application of the slurry to the soil.

2. The process of claim 1, wherein the preventive scavenging additive includes one or more compounds selected from the following groups: (a) bases; and (b) complexing agents.

3. The process of claim 2, wherein the base is selected from caustic lime (calcium oxide), caustic potash (potassium hydroxide), caustic soda (sodium hydroxide), aqua ammonia (ammonium hydroxide), a carbamide, or an amine, or any combination thereof.

4. The process of claim 2, wherein the preventive scavenging additive base is added to the elemental sulphur in an amount to maintain the pH of the sulphur slurry within the range from pH 9 to 13.

5. The process of claim 2, wherein the complexing agent is selected from M.sup.II salts of transition metals, preferably a zinc and/or a copper salt.

6. The process according to claim 1, wherein the preventive scavenging additive is used in an amount up to and including 5 wt., based upon the total weight of the slurry.

7. The process of claim 1, wherein the preventive scavenging additive is added to the liquid and wet milled with the sulphur.

8. The process of claim 1, further comprising adding a lignosulphonate as a viscosity modifier in such an amount that the sulphur slurry comprises from 0.001 to 5.0 wt. % modifier, based on the total weight of the slurry.

9. The process of claim 1, further comprising adding a stabilizing agent selected from one or more of: xantham gum and agar; clays, such as bentonite clay, especially sodium bentonite clay, or attapulgite clays; and polymers such as polyethylene glycol; in such an amount that the sulphur slurry comprises from 0.1 to 5 wt. % of the agent based on the total weight of the slurry.

10. The process according to claim 1, wherein the elemental sulphur is added to the mill in an amount to produce a slurry comprising from 10 to 90 wt. % based upon the total weight of the slurry.

11. The process according to claim 1, wherein the liquid is water or is an aqueous solution or suspension.

12. A fertilizer composition incorporating a preventive scavenging additive obtained or obtainable by the process of claim 1.

13. (canceled)

14. (canceled)

15. A soil fertilizer comprising a micronized sulphur slurry obtained by wet milling elemental sulphur in a liquid, wherein the fertilizer further comprises a preventive scavenging additive for fixating sulphur dioxide and hydrogen sulphide gases in the slurry to avoid exposure of personnel to toxic levels of said gases during storage and handling of the slurry.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The invention is further illustrated by reference to the following drawing in which:

[0053] FIG. 1 shows a process block diagram of a process according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0054] FIG. 1 illustrates a process for preparing a sulphur slurry according to the present invention. In the process exemplified, separate feeds of the slurry components are provided, namely the aqueous solution (1), the elemental sulphur solid (2), the preventive scavenging additive (3), the viscosity modifier (4) and the thickening agent (5). Any of these components (1) to (5) can be fed separately to the wet milling device (6), prior to commencement of or during milling. Alternatively, some or all of the components (1) to (5) may be combined, such as by blending, prior to feeding to the milling device. Provision is also made to enable the components (3) to (5) to be fed to the micronized sulphur slurry once it has been transferred from the milling device (6) for storage.

[0055] Macro or micro nutrient (8) may optionally be fed at any stage, as shown by dashed lines, for example to the wet milling device or to the micronized slurry after discharge from the milling device for storage (9). Thereafter, the sulphur slurry may be conveyed (7) for application as a soil improver either directly to the soil or following dilution and application by irrigation.

[0056] It will be appreciated by the skilled person that various modifications, combinations, substitutions and alterations can be made to the process described above without deviating from the invention as described herein, or from the scope of the claims that follow. For example, the output from the mill may be directed to separate storage tanks so that the mill can be configured to give different slurry output in terms of particle size, particle grade, capacity or other mixing parameters. This affords a level of additional flexibility to the process that enables a plurality of separate and discrete product lines to be derived from a single common feedstream.

[0057] It will be appreciated that the process of the present invention further provides for combined arrangements in which the elemental sulphur is wet milled in dispersion mills that are arranged in series, in parallel; or in series and in parallel. In so doing, the level of control over resulting slurry product can be optimized.

[0058] The present invention will be further illustrated by the following Examples:

Examples 1 to 4

[0059] Exploratory tests were conducted in a Kady L-2000, model OC-30, high dispersion mill, to mill elemental sulphur (ES) pastilles. For the tests, the milling media was water. Various additives were tested as stabilizers. The additives tested were a 50% sodium hydroxide solution, calcium lignosulphonate solution, zinc oxide and xanthan gum. The sodium hydroxide, zinc oxide and calcium lignosulphonate additives were each added to the water milling medium prior to the addition of the ES pastilles. For all tests however, the xanthan gum solution was added to the milling vessel after completion of the milling time.

[0060] The raw materials required for each test were weighed using a mechanical balance. In the case of the xanthan gum, the gum was premixed with water to obtain a 20% solution.

[0061] Each test, consisting of 2.5 L batches, was conducted by filling the milling vessel with a predetermined amount of water. The VFD (Variable Frequency Drive) was turned on and the frequency (hertz) was increased to achieve a uniform flow pattern. Once the desired flow pattern was obtained, the manual addition of ES pastilles was started and wet milling was carried out.

[0062] The tables below contain the test details (Table 1) and the results (Tables 2 to 6).

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Component as a percentage based on total weight of slurry Calculated Elemental 50 50 50 50 Sulphur Content, % Calculated calcium 0.10 0.10 0.10 0.10 lignosulphonate Content (Dry Basis), % Calculated Xanthan Gum 0.25 0.25 0.25 0.25 Content, % Calculated Xanthan Gum 20 20 20 20 Solution, % Calculated Sodium — 0.10 — 0.10 Hydroxide Content (Dry Basis), % Calculated Zinc Oxide — — 0.05 0.05 Content, % Mill OC-30: Operating Conditions Milling Time, min 4 4 4 4 Energy Input, kWh/mt 56.2 53.7 39.9 50.8 ES

[0063] The contents of each test sample were then transferred quantitatively in four separated one gallon plastic buckets that were closed hermetically with a plastic lid fitted with a rubber stopper. This set-up enabled gas measurements to be performed on the gas cap of all the containers. H.sub.2S detection tests were conducted on the four samples. For H.sub.2S detection, a BUVECO Micro BUTOX 500 (MB), a BW Technologies by Honeywell (BW), and a Draeger X-am 5100 (DX) were used, and for SO.sub.2 a BUVECO Gas Alert Micro 5 multiple gas detector (M5) was used. Each test sample was shaken for 10 seconds, the stopper was removed and then the gas detector was placed on top of the opening for 10 seconds before a reading was made. On some occasions, a second meter was used to confirm findings.

TABLE-US-00002 TABLE 2 Results After 6 Days Example 1 Example 2 Example 3 Example 4 SO.sub.2 (M5) Not Not Not Not measured measured measured measured H.sub.2S (MB) 23-73 ppm 0 ppm 0 ppm 0 ppm

TABLE-US-00003 TABLE 3 Results After 9 Days Example 1 Example 2 Example 3  Example 4 SO.sub.2 (M5) Not Not Not Not measured measured measured measured H.sub.2S (MB) 70 ppm - 0 ppm 0 ppm 0 ppm Off limit

TABLE-US-00004 TABLE 4 Results After 13 Days Example 1 Example 2 Example 3 Example 4 SO.sub.2 (M5) 38 ppm/ 0 ppm 0 ppm 1 ppm Off limit H.sub.2S (MB) 70 ppm - 0 ppm 0 ppm 0 ppm Off limit H.sub.2S (DX) 138 ppm/ 0 ppm 0 ppm 1 ppm Off limit

TABLE-US-00005 TABLE 5 Results After 8 Weeks Example 1 Example 2 Example 3 Example 4 H.sub.2S (BW) 100 ppm/ 100 ppm/ 0 ppm 100 ppm/ Off limit Off limit Off limit

[0064] After these tests, 2.2 g of Zinc oxide were added to the slurry of Example 1, and an additional 7.7 g sodium hydroxide in solution form, were added to the slurries of Examples 2 and 4 respectively, the plastic buckets stirred, and allowed to sit for one hour. They were then tested and the results given in Table 6 below.

TABLE-US-00006 TABLE 6 Example 1 Example 2 Example 3 Example 4 H.sub.2S (BW) 100 ppm/ 0 ppm 0 ppm 0 ppm Off limit

[0065] The results show the significant action of the preventive scavenging additive to reduce toxic gases. It is believed that in respect of Example 3 the addition of the zinc oxide such that it was present during the wet milling phase meant that the powder became well dispersed through the slurry during milling and was able to fixate the toxic gases as they formed, or as they were released, during storage. In respect of Example 1 where zinc oxide has been added to an aged slurry, it is believed that the apparent lack of reduction of hydrogen sulphide is because dispersion was more difficult to achieve in the short time allowed, and it would take longer for a significant reduction effect to be achieved. Examples 2 and 4 show that addition of additives in solution form provides a significant effect to reduce the hydrogen sulphide gas, presumably through the increased short term dispersion possible through the slurry.