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Sulphur Bentonite
Sulphur bentonite (also known as bentonite sulphur) is a mixture of elemental sulphur[i] and bentonite clay.[ii] Elemental sulphur is heated to its melting point and becomes a flowable product, referenced as molten sulphur. Dry bentonite clay is blended into the flowable sulphur. [iii]

The purpose of bentonite clay in the mixture is to allow the high “shrink-swell” properties of the bentonite clay to fracture the elemental sulphur into small particles. The smaller particles provide more surface area for bacteria (and in some cases fungi) to oxidize the elemental sulphur component and convert it to plant available sulphate.[iv]

Characteristics

 * 1) Physical/Chemical Properties
 * 2) Appearance: Greenish-tan pastilles. Particle Size: 280SGN
 * 3) pH: Not applicable
 * 4) Melting Point: 115 ºC (239 ºF) (SULFUR) (melting)
 * 5) Flash Point: 207 ºC (405 ºF) (closed cup) (SULFUR)
 * 6) Flammability (solid, gas): Flammable solid. (SULFUR)
 * 7) Upper/Lower Flammability or Explosive Limit
 * 8) 0.14% (SULFUR) (upper)
 * 9) 0.0035% (SULFUR) (lower)
 * 10) Solubility: Insoluble in water; Not available (in other liquids)
 * 11) Auto-ignition Temperature: 232 ºC (450 ºF) (SULFUR)
 * 12) Physical State: Solid
 * 13) Bulk Density: Approximately 68 lb/ft3
 * 14) Sulphur is an element and is not a molecule
 * 15) Chemical Structure as a solid: S8
 * 16) Agricultural Benefits
 * 17) Sulphur bentonite is commonly used in agriculture as a source of sulphur for plants. Sulphur bentonite can also be used as a soil amendment to adjust soil pH or in some cases to reduce soil sodium in sodic soils.[i]
 * 18) Micronutrients can also be added to the sulphur bentonite matrix to address nutrient deficiency problems.
 * 19) Sulphur must first be oxidized (converted) to a plant available sulphate form before it can be utilized by the plant.
 * 20) Elemental sulphur has a very limited movement in soil. Once it is converted to sulphate it can move with water through the soil profile.

Production History

 * 1) Manufacturing Process  The initial 1953 patent points out that sulphur and bentonite clay was fused together and ground to create a product (2 parts sulphur, 1 part bentonite clay) as a fungicide.[i]  Later patents for making solid pellets of a water-degrable solid suspension involve melting and mixing the mixture, forming drops and feeding them through a liquid nitrogen fertilizer solution for hardening (anneal) into pellets.[ii]  Today, the manufacturing process usually entails molten sulphur mixed with bentonite clay and the hot slurry pumped into a rotoformer. The rotoformer releases droplets of the mixture onto a stainless-steel cooling belt. Water is sprayed on the bottom of the belt to cool the product so it solidifies and can be packaged and stored/shipped.  Graphic - https://ipco.com/wp-content/uploads/2020/07/IPCO_principle-of-Rotoform-pastillation.gif
 * 2) Raw Materials
 * 3) Sulfur[iii]
 * 4) Bentonite[iv]
 * 5) Micronutrient[v]

Applications

 * 1) Fertilizer  Sulphur has some key functions in the plant. It is necessary for the formation of chlorophyll, responsible for 3 key amino acids that are the building blocks of protein, oil in the plant, activation of enzymes, Increase crop yield and quality. Sulphur is a secondary nutrient but has been referred to as the 4thprimary nutrient.[i] As a fertilizer, sulphur bentonite’s strength is that it may provide season-long, plant available sulphur through the growing season. Another strength is that sulphur bentonite allows for the building of deficient sulphur levels in the soil.  When plants are deficient in sulphur, it presents as yellowing and small growth in newest tissues. It is not a readily mobile nutrient in the plant.[ii]
 * 2) Soil Amendment  As a soil amendment, sulphur bentonite is used primarily in the area of changing soil pH. Soil pH of 6.5 is usually considered optimal for nutrient availability. Most nutrients are available in soils with pH levels of 6.5. Depending on the crop, a pH of 5.8-7.0 is considered favorable for plant growth and development.[iii] More information on the rate of application to change soil pH can be found in the Ohio State University Fact Sheet, Soil Acidification: How to Lower Soil pH AGF-507.[iv] It is critical to note that before pH levels can be modified, the free calcium in soil must first be neutralized.

Biological Process

 * 1) Bacterial breakdown  http://canola.okstate.edu/cropproduction/fertility/sulfuroxidation.pdf  The most important bacteria responsible for the conversion of elemental sulphur to sulphate is Acidthiobacillus sp.[v] Conversion speed is a function of size of the sulphur particle, temperature, moisture, aeriation of soil, and number of microbes that will convert the elemental sulphur.[vi] When elemental sulphur has been added to the soil, typically the numbers of microbes capable of converting the elemental sulphur increase. Just as plants thrive in a fertile soil, so do the microbes that can convert elemental sulphur.
 * 2) Season-long  Plants utilize sulphur that is in the sulphate form and are unable to directly utilize elemental sulphur. As the microbes convert the elemental sulphur, they provide a continuous source of sulphate to the plant during the growing season. When soil temperature falls below 65oF ( 18oC) the bacteria are less active and sulphur to sulphate conversion decreases.[vii]

Precautions

 * 1) Inhalation Precautions  Repeated or long-term exposure may cause respiratory problems due to the silica, quartz in the bentonite clay. Always follow safe handling practices outlined in the product’s GHS Safety Data Sheet.
 * 2) Ignition Precautions  Like most dusts, sulphur will burn in a confined space, possibly creating an explosion. Follow safe handling practices outlined in the product’s GHS Safety Data Sheet. Refer to National Fire Protection Association (NFPA) 655, Standard for Prevention of Sulfur Fires and Explosions.[viii]

See also...

 * 1) Links to related pages
 * 2) Tiger-Sul Company Page
 * 3) Sulfur Page
 * 4) Bentonite Page
 * 5) References
 * 6) Further Reading
 * 7) External Links

[i] The Sulfur Institute. https://www.sulphurinstitute.org/about-sulphur/sulphur-the-fourth-major-plant-nutrient/

[ii] Plant Nutrients. Mobile. https://en.wikipedia.org/wiki/Plant_nutrition#Mobile

[iii] Competency Area 5: Soil pH and liming. (2010) Northeast Region Certified Crop Adviser Study Resources. Cornell University. https://nrcca.cals.cornell.edu/nutrient/CA5/CA0539.php

[iv] Mullen, R., E. Lentz and M. Watson. (2016) Soil Acidification: How to Lower Soil pH (AGF-507) Ohio State University. https://ohioline.osu.edu/factsheet/agf-507

[v] Acidithiobacillus. https://en.wikipedia.org/wiki/Acidithiobacillus

[vi] Sulfate -vs- Elemental Sulfur Part II: Characteristics Of S Oxidation To SO4. Canola, Oklahoma State University. http://canola.okstate.edu/cropproduction/fertility/sulfuroxidation.pdf

[vii] Acidithiobacillus thiooxidans. https://en.wikipedia.org/wiki/Acidithiobacillus_thiooxidans

[viii] NFPA 655, Standard for Prevention of Sulfur Fires and Explosions. (2017) https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=655 [i] United States Patent Office, 2,664, 379. Bentonite Sulfur. Russo, V.J. and J.F. Les Veaux. Patented Dec. 29, 1953. https://patentimages.storage.googleapis.com/82/de/5e/abae3ee8775fcc/US2664379.pdf

[ii] United States Patent Office, 4,133,669. Process for pelletizing a sulphur-bentonite clay mixture and the product formed thereby. https://patents.justia.com/patent/4133669

[iii] Sulfur. https://en.wikipedia.org/wiki/Sulfur

[iv] Bentonite. https://en.wikipedia.org/wiki/Bentonite

[v] Micronutrient. https://en.wikipedia.org/wiki/Micronutrient [i] Sodic soils. https://en.wikipedia.org/wiki/Soil_salinity [DCA1]Reference Sulfur Wiki page. [i] Sulfur. https://en.wikipedia.org/wiki/Sulfur

[ii] Bentonite. https://en.wikipedia.org/wiki/Bentonite

[iii] Process for pelletizing a sulphur-bentonite clay mixture and the product formed thereby. Eagle Picher Industries, Inc., https://patents.google.com/patent/US4133669A/en

[iv] Surface area of particles of different sizes. https://en.wikipedia.org/wiki/Surface_area#/media/File:Surface_area.svg